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SSLC Chemistry Chapter 7 Notes Questions and Answers Pdf Some Compounds of Industrial Importance
SCERT Class 10 Chemistry Chapter 7 Some Compounds of Industrial Importance Notes Pdf
SSLC Chemistry Chapter 7 Questions and Answers – Let Us Assess
Question 1.
Chemical formula of certain salts are given below.
| KCl,(NH4)2SO4, AlCl3, CH3COONa |
Choose the correct ones from the given statements related to them and write it down.
(i) KCl does not undergo hydrolysis.
(ii) (NH4)2SO4 is an acidic salt.
(iii) AlCl3 is a basic salt.
(iv) CH3COONa is used to increase the basicity of an aqueous solution.
Answer:
Here the correct statements are (i), (ii) and (iv)
(i) KCl does not undergo hydrolysis.
(ii) (NH4)2SO4 is an acidic salt.
(iv) CH3COONa is used to increase the basicity of an aqueous solution.
Question 2.
A flow chart of the industrial production of hydrochloric acid is given below.
What is A and B?
Answer:
A – HCl oven or HCl Burner
B – Deionised water
Question 3.
A word web indicating the uses of a compound is given. Complete it by adding A, B, C and D.
A – Sodium Hydroxide
B – Used for the production of rayon
C – Used in the preparation of soaps and detergents
D – Used to produce paper.
Question 4.
Explain with chemical equations of the chemical reactions that take place in the left and right chambers of the membrane cell during the chlor-alkali process.
(Hint: Type of reaction, chemical equation, the gas liberated, compound formed)
Answer:
Left Chamber (Anode)
The left chamber contains the anode, which is the positive electrode.
- Type of Reaction: Oxidation
- Chemical Equation: 2Cl–(aq) → Cl2(g) + 2e–
- Gas Liberated: Chlorine gas (Cl2)
At the anode, negatively charged chloride ions (Cl–) are attracted to the positive electrode. They lose electrons (oxidation) and form neutral chlorine atoms, which then combine to form chlorine gas.
Right Chamber (Cathode)
The right chamber contains the cathode, which is the negative electrode.
- Type of Reaction: Reduction
- Chemical Equation: 2H2O(l) + 2e– H2(g) + 2OH–(aq)
- Gas Liberated: Hydrogen gas (H2)
- Compound Formed: Sodium hydroxide (NaOH)
At the cathode, positively charged sodium ions (Na+) and hydrogen ions (from the dissociation of water) are attracted. However, hydrogen ions are more easily reduced. They gain electrons (reduction) and form hydrogen gas. As hydrogen ions are consumed, the water equilibrium shifts to produce more of them, leaving behind hydroxide ions (OH–). These hydroxide ions then combine with the sodium ions (Na+) that have passed through the membrane to form a solution of sodium hydroxide (NaOH).
Question 5.
The basicity of phosphoric acid (H3PO4) is 3.
(i) Write the ionisation equations of phosphoric acid.
(ii) Write the possible salts that can be formed when phosphoric acid reacts with sodium hydroxide.
Answer:
(ii) Phosphoric acid can donate one, two, or three protons; it can react with sodium hydroxide (NaOH) to form three different types of salts
- Monosodium Dihydrogen Phosphate (NaH2PO4): This salt forms when only one proton is replaced by a sodium ion.
H3PO4 +NaOH → NaH2PO4 + H2O - Disodium phosphate (Na2 HPO4): This salt forms when one molecule of phosphoric acid reacts with two molecules of sodium hydroxide.
H3PO4 + 2NaOH → Na2HPO4 + 2H2O - Trisodium phosphate (Na3PO4): This salt forms when one molecule of phosphoric acid reacts with three molecules of sodium hydroxide.
H3PO + 3NaOH → Na3PO4 + 3H2O
Question 6.
Explain the effect of pressure on the following reversible reactions.
(i) H2(g) + I2(g) \(\text { ⇌ }\) 2HI(g)
(ii) N2(g) + 3H2(g) \(\text { ⇌ }\) 2NH3(g)
Answer:
(i) Here in this reaction, the total number of reactant molecules is equal to the total number of product molecules. In a reversible reaction, if there is no change in the number of molecules and products, pressure will have no effect on the chemical equilibrium.
(ii) According to Le Chatelier principle, when the pressure of a system at equilibrium is increased, the system will try to attain equilibrium by reducing the pressure. This is achieved by increasing the reaction in the direction where the number of moles of molecules decreases. So in this reaction, as the pressure increases the rat? of forward reaction increases. Thus more amount of product is produced.
Question 7.
2NO(g) + O2(g) \(\text { ⇌ }\) 2NO2(g) + heat
Complete the table given below by indicating the possible measures to increase the amount of N02 in this chemical reaction.
Answer:
| Temperature | Decrease |
| Pressure | Increase |
| Amount of oxygen | Increase |
| Amount of NO | Increase |
Question 8.
Haber process is an exothermic process. What changes can be done in the system to increase the amount of the product?
Answer:
Based on Le Chatelier’s Principle, here are the changes that would increase the yield of ammonia:
- Increase Pressure: Increasing the total pressure of the system will shift the equilibrium to the side with fewer moles of gas. Since the product side has fewer moles (2 moles vs. 4 moles), increasing the pressure will increase the amount of NH3 produced.
- Decrease Temperature: Since the forward reaction is exothermic, decreasing the temperature will shift the equilibrium to the right to produce more heat, thus increasing the amount of NH3 produced.
- Increase Reactant Concentration: Adding more nitrogen (N2) or hydrogen (H2) to the system will shift the equilibrium to the right to consume the added reactants, thereby increasing the amount of NH3 produced.
- Remove Product: Continuously removing the product, ammonia (NH3), from the system will also shift the equilibrium to the right to replace the removed product, which increases the overall yield.
Question 9.
Complete the table.
Answer:
| Chemical name of the compound present in fertilizer | Calcium nitrate | Ammonium sulphate | Calcium phosphate | Potassium sulphate |
| Primary nutrient in the fertilizer | Nitrogen | Nitrogen | Phosphorous | Potassium |
| Secondary nutrient in the fertilizer | Calcium | Sulphur | Calcium | Sulphur |
Question 10.
Examine the following statements related to Contact process. Write which among A, B, C or D is correct.
(i) Contact process is the process used for the industrial production of sulphuric acid.
(ii) In Contact process, the reaction between SO2 and O2 is endothermic.
(iii) Increasing the pressure will produce more SO3.
(iv) Increasing the amount of oxygen will decrease the amount of the product.
(v) Increasing or decreasing the amount of SO2 does not change the amount of SO3
(vi) V2O5 is used as a catalyst.
(vii) Here, the catalyst does not affect the chemical equilibrium.
A. (i), (ii), (iv) and (vi) are right and (iii), (v)’and (vii) are wrong.
B. (i), (iii), (vi) and (vii) are right and (ii), (iv) and (v) are wrong.
C. (i), (ii), (iii) and (iv) are right and (v), (vi) and (vii) are wrong.
D. (i), (iii) and (vi) are right and (ii), (iv), (v) and (vii) are wrong.
Answer:
B. (i), (iii), (vi) and (vii) are right and (ii), (iv) and (v) are wrong.
Question 11.
(i) Which substance is used as the drying agent in the laboratory preparation of ammonia?
(ii) Can concentrated sulphuric acid be used as a drying agent in this process? Write the chemical equation that occurs if it is used.
Answer:
(i) Quick lime (CaO)
(ii) Concentrated sulphuric acid is not used as a drying agent in the preparation of ammonia because ammonia is basic and can react with concentrated Sulphuric acid, and then it will form ammonium sulphate.
NH3 + H2SO4 → (NH4)2SO4
Question 12.
Certain fertilizers are given.
| Urea, sodium nitrate, ammonium phosphate, potassium chloride |
Complete the table.
Answer:
| Function in plants | Fertilizers that can be used |
| To accelerate plant growth
To increase productivity To boost immunity of plants |
Urea, Sodium nitrate
Ammonium Phosphate Potassium chloride |
Chemistry Class 10 Chapter 7 Notes Kerala Syllabus Metals
Question 1.
What are the elements essential for the growth of plants?
Answer:
Plants require several essential elements for proper growth. These are:
| Macronutrients (needed in large amounts) | Micronutrients (needed in small amounts) |
| Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), Sulphur (S). |
Iron (Fe), Zinc (Zn), Copper (Cu), Boron (B), Molybdenum (Mo), Chlorine (Cl). |
These elements are essential for photosynthesis, protein formation, growth, and overall crop yield.
On the basis of examining the presence of acids, bases and salts in the soil, necessary remedial measures are taken before cultivation. This helps agricultural crops to grow well and give maximum yield.
Question 2.
a) Observe the colour and odour of the ammonia gas produced and tick (✓) the correct one in the table given below.
b) Moist blue and red litmus papers are shown above the watch glass. Which litmus paper shows a change in colour? [Blue litmus paper / Red litmus paper]
Answer:
The red litmus paper changes colour.
c) What property of the gas is indicated by the change in colour of the litmus paper?
[Acidic nature / Basic nature]
Answer:
Basic
Question 3.
Complete the chemical equation of the reaction that occurred in the watch glass.
Answer:
2NH4 Cl + Ca(OH)2 → 2NH3 + CaCl2 + 2H2 O
LABORATORY PREPARATION OF AMMONIA
When ammonia is passed through quick lime (CaO) in the drying tower, the moisture contained in it is removed.
Question 4.
In the figure, the jar used for collecting ammonia is kept inverted. Write the reason for this, relating it to the density of ammonia.
Answer:
The gas jar is inverted because ammonia is lighter than air.
Let us carry out an experiment using ammonia gas. Collect ammonia in a round-bottomed flask. Arrange the apparatus as shown in the figure below. Dip the jet tube in the beaker containing water mixed with phenolphthalein. Using a syringe, inject a few drops of water into the flask containing ammonia.
a) What do you observe?
Answer:
A fountain-like effect is seen when water rushes into the flask.
The solution turns pink.
b) What can be inferred about the solubility of ammonia in water? Why does water rush into the flask?
Answer:
Ammonia is highly soluble in water.
c) Why does the water entering the flask change its colour?
Answer:
Ammonia gas dissolves rapidly in water, reducing the pressure inside the flask.
The higher outside pressure pushes water into the flask, creating the fountain effect.
d) Why does the water entering the flask change its colour?
Answer:
Because the water contains phenolphthalein indicator, which turns pink in an alkaline solution.
Ammonia dissolves in water to form ammonium hydroxide (NH4OH), which is alkaline.
NH3 + H2O → NH4OH
e) Which property of ammonia is responsible for this change in colour?
Answer:
The basic nature of ammonia.
Question 5.
Ammonium hydroxide is the product obtained when ammonia dissolves in water. Find its chemical formula by completing the chemical equation given below.
Answer:
NH3 + H2O → NH4OH
Question 6.
Let us do an experiment showing the chemical reaction between ammonia and hydrogen chloride in a glass tube, as shown in the picture.
Place a cotton dipped in HCl at one end and another piece of cotton dipped in ammonia solution at the other end of the glass tube, such that these are well inside the glass tube. Close both ends of the glass tube using a cork. Observe the changes inside the glass tube.
a) Did you observe the thick white fumes formed?
Answer:
Yes, It is due to the formation of ammonium chloride-by the combination of HCl gas and NH3 gas, which sticks on the walls of the glass tube.
When the glass tube is heated, the ammonium chloride decomposes.
b) Write the chemical equation of the formation of ammonium chloride.
Answer:
HCl (g) + NH3(g) → NH4Cl(S)
c) What are the reactants in this reaction?
Answer:
Hydrogen chloride (HCl)
Ammonia (NH3)
d) What is the product?
Answer:
Ammonium chloride (NH4Cl)
e) Write the chemical equation of the decomposition of ammonium chloride.
Answer:
NH4Cl (S) → NH3 (g) + HCl (g)
| A reaction in which reactants are converted to products is called a forward reaction. A reaction in which products are converted to reactants is called a backward reaction. |
Let us write these chemical equations together.
NH3 + HCl \(\text { ⇌ }\) NH4Cl
The “ \(\text { ⇌ }\) ” sign indicates that the reaction takes place in both directions.
Question 7.
Examine the reversible reactions given in the following table and complete it.
Answer:
Question 8.
A graph related to the rate of reaction is given below. Analyse the graph and answer the questions given.
a) Only the reactants are present at the beginning of the reaction. Then, in which direction does the reaction progress?
[Forward reaction / backward reaction]
Answer:
Forward reaction
b) What happens to the rate of the forward reaction as time proceeds?
Answer:
The rate of the forward reaction decreases
c) What change occurs in the concentration of the product, as the chemical reaction proceeds?
Answer:
The concentration of the product (NH3) increases.
d) What happens to the rate of the backward reaction?
Answer:
The rate of the backward reaction increases.
e) Identify the point at which the rates of forward and backward reactions become equal?
Answer:
Point A is the intersection of the two rate curves. At this point, the rate of the forward reaction equals the rate of the backward reaction. This state is known as chemical equilibrium.
Question 9.
Analyse the effect of a change in concentration in the above equilibrium system and complete the table given below.
Answer:
| Action | Change in concentration | Change in rate |
| More hydrogen is added. | Increases the concentration of the reactant. | Rate of forward reaction increases. |
| More NH3 is added | Increases the concentration of product. | Rate of backward reaction increases. |
| Ammonia is removed | Concentration of product decreases. | Rate of forward reaction increases. |
| More nitrogen is added. | Concentration of reactant increases. | Rate of forward reaction increases. |
| Nitrogen is removed | Concentration of reactant decreases. | Rate of forward reaction decreases. |
| Hydrogen is removed. | Concentration of reactant decreases. | Rate of backward reaction increases. |
| According to Le Chatelier principle, if the concentration of reactants is increased in a system at equilibrium, the rate of forward reaction increases. If the concentration of product is increased, the rate of backward reaction increases. |
Question 10.
Examine the chemical equation of the formation of ammonia.
N2(g) + 3H2(g) \(\text { ⇌ }\) 2NH3(g)
a) In which state do the reactants and products exist?
Gaseous state / Liquid state / Solid state
Answer:
Gaseous state
b) Which physical state is influenced by pressure?
Answer:
Gaseous state
| How many moles of reactant molecules are present? | 4 moles |
| How many moles of product molecules are present | 2 moles |
| Change that takes place in forward reaction. | 4 moles of reactant molecules react to form 2 moles of product molecules. |
| Changes that take place in a backward reaction. | 2 moles of product molecules decompose to form 4 moles of reactant molecules. |
| Change in volume in forward reaction | Volume decreases |
| Change in volume in backward reaction | Volume increases |
Question 11.
At fixed volume, what happens to the pressure of a gaseous system if the number of molecules is increased?
Answer:
Increases
| According to Le Chatelier principle, when the pressure of a system at equilibrium is increased, the system will try to attain equilibrium by reducing the pressure. This is achieved by increasing the reaction in the direction where the number of moles of molecules decreases. |
Question 12.
Identify the influence of pressure in the production of ammonia and complete the table.
Answer:
N2(g) + 3H2(g) \(\text { ⇌ }\) 2NH3(g)
| Number of molecules (at the beginning of the chemical reaction) | Action | Change in rate of chemical reaction. |
| Total number of reactant molecules more. | Increase the pressure. | Rate of forward reaction increases. |
| Rate of backward reaction decreases. | ||
| Total number of product molecules less. | Reduce the pressure | Rate of forward reaction decreases. |
| Rate of backward reaction increases. |
Question 13.
Examine the following chemical equation.
H2(g) + I2(g) \(\text { ⇌ }\) 2HI(g)
a) What is the total number of reactant molecules?
Answer:
2
b) What is the total number of product molecules?
Answer:
2
c) What is the relation between the total number of reactant molecules and the total number of product molecules?
Answer:
The total number of reactant molecules is equal to the total number of product molecules
d) Does pressure influence this reaction?
Answer:
No. Pressure changes only shift the equilibrium if there is a change in the total number of gaseous moles between the reactant and product sides.
| In a reversible reaction, if there is no change in the number of molecules of reactants and products in gaseous state, pressure will have no effect on the chemical equilibrium. |
Question 14.
Here, which is the endothermic reaction?
Forward reaction / Backward reaction
Answer:
Backward reaction
On increasing the temperature, the system tries to reduce it by increasing the rate of the endothermic reaction. As a result, the rate of backward reaction increases. So, the temperature has to be reduced in order to increase the rate of the forward reaction. But at low temperature, the number of molecules having threshold energy will be less. Therefore, the rates of forward and backward reactions get significantly reduced, and hence the system will take more time to attain equilibrium. So, in the manufacture of ammonia, 450°C is taken as the optimum temperature.
In a system at equilibrium, increase in temperature will increase the rate of endothermic reaction.
Decrease in temperature will increase the rate of exothermic reaction.
Question 15.
What happens to the rate of reaction of a system at equilibrium when a catalyst is added?
Answer:
The catalyst increases the overall reaction rate but does not change the position of the equilibrium. It only helps the system reach the equilibrium state faster.
Question 16.
What is the catalyst used in the manufacture of ammonia?
Answer:
The primary catalyst used in the Haber process is Sponge iron (Fe).
Question 17.
The manufacture of ammonia is a reversible reaction. Which conditions are favourable to obtain more product? Record them in your science diary.
Answer:
The conditions favourable for maximising the yield of ammonia (shifting the equilibrium to the right) are determined by Le Chatelier’s Principle.
N2(g) + 3H2(g) \(\text { ⇌ }\) 2NH3(g)
| Condition | Favourable Choice | Reason (Le Chatelier’s Principle) |
| Temperature | Low Temperature | The forward reaction is exothermic. Lowering the temperature shifts the equilibrium to the right to produce heat, favouring the product. |
| Pressure | High Pressure | There are 4 moles of gas on the reactant side (1N2 + 3H2) and 2 moles of gas on the product side ( 2NH3). Increasing the pressure shifts the equilibrium to the side with fewer moles of gas to reduce the pressure, favouring the product. |
| Concentration | High Concentration of- Reactants (N2 and H2) | Increasing the reactant concentration forces the system to shift forward, consuming excess reactants. |
| Catalyst | Catalyst (e.g., Iron) | A catalyst does not change the equilibrium position, but it helps to attain equilibrium faster. |
Question 18.
Complete the chemical equation given below to find out the product formed when sulphur trioxide dissolves in water.
Answer:
SO3 + H2O → H2SO4
Dissolving sulphur trioxide in water gives sulphuric acid. Yet, Sulphur trioxide not dissolved directly in water in the industrial production of sulphuric acid. Since the dissolution of SO3 in water is an exothermic process, the sulphuric acid initially formed turns into fog like particles (smog) which will hinder further dissolution.
Question 19.
The flow chart of industrial production of sulphuric acid is given. Identify (a) and (b) in this and write it down.
Answer:
Physical properties of sulphuric acid
- Colourless
- Viscosity is higher than that of water.
- Denser than water.
- Dissolves in water.
Solubility
Question 20.
Take 5 ml water in a test tube and slowly add a few drops of concentrated sulphuric acid to it. Touch the bottom of the test tube. What do you feel?
Answer:
The test tube gets hot.
Question 21.
Is the reaction exothermic or endothermic?
Answer:
Exothermic
While diluting sulphuric acid, the acid has to be added to water in very small quantities by stirring. If dilution is done by adding water to acid, the chance of splashing out of the acid leading to an accident is very high.
Chemical properties of sulphuric acid
Dehydrating property
Question 22.
Take a little sugar in a watch glass and add a few drops of concentrated sulphuric acid. Observe the changes. Analyse the chemical equation of this experiment.
a) What is the black substance that remains?
Answer:
Carbon
b) What is the ratio of the number of atoms of hydrogen and oxygen in a molecule of sugar?
Answer:
H: O = 22: 11 = 2 : 1
c) What is the role.of sulphuric acid in the chemical reaction?
Answer:
Sulphuric acid absorbs the elements hydrogen and oxygen from sugar in the same ratio as in water.
| Dehydration is the process of absorbing chemically combined water, or hydrogen and oxygen in the same ratio as in water from substances. Concentrated sulphuric acid is a strong dehydrating agent. |
Question 23.
Perform the following activities, which demonstrate the dehydrating properties of sulphuric acid, and record your observations.
Answer:
| Activity | Observations |
| Add a little con. sulphuric acid to glucose taken in a beaker. | Glucose turns black |
| Add con. sulphuric acid drop by drop to blue copper sulphate taken in a watch glass. | CuSO4 loses its colour. |
Drying property
Drying agents are substances capable of absorbing the moisture present in a substance.
Concentrated sulphuric acid is used as a drying agent in the preparation of CO2, SO2 and HCl.
Question 24.
Concentrated H2SO4 is not used as a drying agent in the preparation of NH3. Why?
Answer:
Concentrated sulphuric acid is not used as a drying agent in the preparation of ammonia because ammonia is basic and can react with concentrated Sulphuric acid, and then it will form ammonium sulphate.
Reaction with salts
Concentrated sulphuric acid reacts with chlorides to form hydrogen chloride and with nitrates to form nitric acid. Chemical equations of these reactions are given.
NaCl + H2SO4 → NaHSO4 + HCl
KNO3 + H2SO4 → KHSO4 + HNO3
Concentrated sulphuric acid can displace acids from their salts.
This method is employed in the preparation of hydrochloric acid, nitric acid, etc
Oxidising Nature
Question 25.
Analyse the following chemical equation.
C + 2H2SO4 → CO2 + 2SO2 + 2H2O
a) What is the oxidation state of elemental carbon?
Answer:
Zero (0)
b) What is the oxidation state of carbon in carbon dioxide?
Answer:
+4
c) What happened to carbon in this reaction?
Oxidised/Reduced
Answer:
Oxidised (0 changes to +4. Oxidation number increases)
Question 26.
Have a look at the chemical equation of the reaction between concentrated sulphuric acid and copper.
Cu + 2H2SO4 → CuSO4 + SO2 + 2H2O
Here, what change has occurred to. copper? Examine by writing the oxidation state.
Oxidised/Reduced
Answer:
Oxidised (Oxidation number changes from 0 to +2).
Concentrated sulphuric acid reacts with metal as well as non metals and oxidise them. Concentrated sulphuric acid is a good oxidising agent.
Question 27.
Complete the following table by writing the equation of ionisation.
Answer:
| Acid | Equation of ionisation |
| HNO3 | HNO3 → H+ + NO3– |
| HCl | HCl → H+ + Cl– |
| HBr | HBr → H+ + Br– |
| HF | HF → H+ + F– |
Question 28.
How many hydrogen ions are liberated when each of the acid in the table ionises?
Answer:
One
| The basicity of an acid is the number of hydrogen ions that the molecule of the acid can donate. If basicity is 1, the acid is called monobasic acid. |
Question 29.
Examine the equation of ionisation of sulphuric acid.
a) How many hydrogen ions are liberated when a molecule of sulphuric acid is ionised?
Answer:
Two
b) If so, what is the basicity of sulphuric acid?
Answer:
Two
| If the basicity of. an acid is 2, it is called dibasic acid. |
Question 30.
Complete the following table by writing the equation of ionisation
Answer:
| Acid | Equation of ionisation |
| H2C2O4(HOOC – COOH) | H2C2O4 → 2H+ + C2O42- |
| H2CO3 | H2CO3 → 2H+ + CO32- |
Question 31.
Complete the equation of ionisation of phosphoric acid.
H3PO4 → ……………… + PO43-
Answer:
H3PO4 → 3H+ + PO43-
Question 32.
What will be the basicity of H3PO4? ……………………
Answer:
Three (3)
| If the basicity of an acid is 3, it is called tribasic acid. |
Alkalies are bases that dissolve in water.
Question 33.
Write the chemical formula of sodium hydroxide.
Answer:
The equation of the reaction that takes place when sodium hydroxide dissolves in water.
NaOH → Na+ + OH–
Question 34.
Complete the given table
Answer:
| Chemical name of alkali | Chemical formula | Equation of ionisation in water |
| Sodium hydroxide | NaOH | NaOH → Na+ + OH– |
| Calcium hydroxide | Ca(OH)2 | Ca(OH)2 → Ca2+ + 2OH– |
| Ammonium hydroxide | NH4OH | NH4OH → NH4+ + OH– |
Question 35.
What is the common ion liberated when alkalies dissolve in water?
Answer:
OH–(Hydroxide ion)
Alkalies are substances which increase the concentration of hydroxide ions in aqueous solutions.
Arrhenius stated that when acids and bases dissolve in water, they dissociate into ions. According to Arrhenius theory, acids are substances which liberate H+ ions and bases are substances which liberate OH– ions in aqueous solutions.
Question 36.
What are the ions formed when sodium chloride dissolves in water?
Answer:
Na+ and Cl– ions (Positively charged sodium ion and negatively charged Chloride ion)
Question 37.
Which ion undergoes oxidation at the anode?
Answer:
Chloride ion
Question 38.
Complete the oxidation equation.
2Cl– → ………………… + …………………….
Answer:
2Cl– → Cl2 + 2e–
Question 39.
Which gas is liberated in the left chamber?
Answer:
Chlorine gas
Na+ ions in the left chamber move to the right chamber through the membrane.
Water molecules undergo reduction at the cathode in the right chamber.
Question 40.
Complete the reduction equation.
2H2O + 2e– → …………….. + 2OH–
Answer:
2H2O + 2e– → H2 + 2OH–
Question 41.
Which gas is liberated here?
Answer:
Hydrogen gas'(H2)
Sodium hydroxide is formed in the right chamber by the combination of Na+ions and ions.
Na+ + OH– → NaOH
In this process, hydrogen and chlorine are also formed in addition to sodium hydroxide. Sodium hydroxide is also known as caustic soda.
Uses of sodium hydroxide
- For the preparation of soaps and detergents.
- For the purification of bauxite in the manufacture of aluminium.
- To produce paper.
- For the production of rayon.
- To manufacture medicines like aspirin.
Question 42.
Which is the salt formed when sodium hydroxide reacts with hydrochloric acid?
Answer:
HCl + NaOH → NaCl + H2O.
The salt formed is Sodium Chloride.
Question 43.
After dissolving sodium chloride in water, use litmus papers to test whether the solution has acidic or basic nature. Write down your observation.
Answer:
After dissolving sodium chloride in water, a litmus paper test would show no change in colour for either red or blue litmus paper.
Question 44.
Examine whether the solutions of the salts given below are acidic or basic in nature and complete the table.
Answer:
| Salt solution | Change in the colour of blue litmus paper when it is in contact with the solution. | Change in the colour of red litmus paper when it is in contact with the solution. | Nature of solutions (Acidic nature / basic nature / neutral) |
| NaCl | No change in colour | No change in colour | Neutral |
| NH4Cl | Turns red | No change in colour | Acidic |
| Na3CO3 | No change in colour | Turns blue | Basic |
Certain salts when dissolved in water do not exhibit acidic or basic nature. Such salts are called neutral salts. Salt hydrolysis is the process by which the anions, cations or both of a salt react with wafer to form a solution that has acidic or basic nature.
| Salts that undergo hydrolysis when dissolved in water to give an acidic solution are called acid salts. |
Question 45.
Which acid and base react to produce NaCl?
Answer:
Acid – Hydrochloric acid (HCl)
Base – Sodium Hydroxide (NaOH)
Here, acid and base are strong.
Question 46.
Which acid and base react to produce NH4Cl?
Answer:
Acid – Hydrochloric acid (HCl)
Base – Ammonium Hydroxide (NH4OH)
Question 47.
Which of these is stronger, the acid or the base?
Answer:
Acid
Question 48.
Which acid and base react to produce Na2CO3?
Answer:
Acid – Carbonic acid (H2CO3)
Base – Sodium Hydroxide (NH4OH)
Question 49.
Which of these is stronger, the acid or the base?
Answer:
Base
| The salt formed by the reaction of a strong acid and a strong base will be neutral. The salt formed from strong acid and weak base will be acidic. The salt formed from weak acid and strong base will be basic. |
Question 50.
Can plants utilise fertilizers that are insoluble in water?
Answer:
Yes, plants can use fertilizers that are insoluble in water, but the process is slower. These are often called slow-release fertilizers.
Plants can only absorb nutrients that are dissolved in water. Insoluble fertilizers break down gradually in the soil through microbial activity and chemical reactions, making the nutrients available to the plants over time.
This slow breakdown has several benefits:
- Sustained nutrient supply
- Reduced nutrient runoff
- Lower risk of damaging the plant’s roots
Question 51.
If a fertilizer decomposes too quickly, will it be beneficial to plants?
Answer:
A fertilizer that decomposes too quickly is harmful to plants. It can cause root damage from “fertilizer burn,” lead to nutrient leaching that pollutes water, and provides only a short-lived nutrient boost instead of the steady supply plants need for healthy growth.
Essential qualities of fertilizers
- The elements present in the compounds in fertilizer should be easily available to plants.
- The fertilizer should be soluble in water.
- The compounds in fertilizer must be stable and remain in the soil for a long time, making them available to plants
- They should not cause significant variations to the pH of the soil.
- They should not be toxic to plants.
Chemical fertilizers are used to make the primary nutrients available to plants in the right quantities. Such fertilizers are classified as nitrogenous feritlizers, phosphate fertilizers and potash fertilizers. These are combined to produce mixed fertilizers. These are also called NPK mixed fertilizers.
| Types of fertilizers | Effect of fertilizer on plants | Examples |
| Nitrogenous fertilizers | • Accelerates the growth of plants. | Ammonium sulphate, calcium cyanamide, urea, sodium nitrate, calcium nitrate, potassium nitrate |
| Phosphate fertilizers | • Helps the growth of plants • Increases productivity |
Ammonium phosphate, triple super phosphate |
| Potash fertilizers | • Helps the growth of plants • Increases productivity • Boosts immunity |
Potassium chloride (Muriate of potash), potassium sulphate, potassium – magnesium sulphate |
Std 10 Chemistry Chapter 7 Notes – Extended Activities
Question 1.
A graph of the reaction H2(g) + I2(g) \(\text { ⇌ }\) 2HI(g) is given below.
At the start of this chemical reaction (time = 0), the concentration of hydrogen is greater than that of iodine.
(i) What do the curves C, D and E indicate?
(ii) What is the nature of the chemical reaction from the time indicated by line AB?
Answer:
(i) C, D represents the forward reaction.
E represents the backward reaction.
(ii) After AB, the concentrations of H2, I2, and HI remain constant, indicating a dynamic equilibrium between the forward and backward reactions.
Question 2.
Discuss with farmers and the agriculture officer and prepare a note on the fertilisers used for any four crops at different stages of their growth.
Answer:
Paddy (Rice):
- Basal stage: Urea, Super Phosphate, Potash — for root growth.
- Mid stage: Urea — for leaf development and healthy tillers.
- Grain filling stage: Potash and Zinc — for good yield and quality grains.
Maize (Corn):
- Sowing stage: Potash — for root and early growth.
- Vegetative stage: Urea — for strong stems and leaves.
- Silking stage: Potash, micronutrients — for grain development.
Banana:
- Planting stage: Urea, Super Phosphate — for soil fertility and early growth.
- Vegetative stage: Urea, Potash — for leaf and stem growth.
- Fruiting stage: Potash, micronutrients — for fruit size and sweetness.
Tomato:
- Basal stage: Compost, Super Phosphate, Potash — for root establishment.
- Vegetative stage: Urea — for leafy growth.
- Flowering stage: Potash, calcium nitrate — for fruit set and quality.
- Fruiting stage: Micronutrients, Potash — for ripening and yield.
Question 3.
Some chemical reactions that attain chemical equilibrium are given below. Explain the effect of pressure on these.
(Hint: The effect of pressure on compounds that exist in the solid and liquid states is so small that it cannot be considered.)
i. CO2(g) + C(s) \(\text { ⇌ }\) 2CO(g)
ii. CaCO3(s) \(\text { ⇌ }\) CaO(s) + CO2(g)
iii. COCl2 \(\text { ⇌ }\) CO(g) + Cl2(g)
Answer:
(i) CO2(g) + C(s) \(\text { ⇌ }\) 2CO(g)
- Forward reaction increases the number of gas molecules (1 → 2).
- Increasing pressure shifts the equilibrium backwards (towards fewer gas molecules)
(ii) CaCO3(s) \(\text { ⇌ }\) CaO(s) + CO2(g)
- Only CO2 is gaseous on the product side.
- Increasing pressure shifts the equilibrium backwards (towards CaCO3) because it reduces gas volume.
(iii) COCl2(g) \(\text { ⇌ }\) CO(g) + Cl2(g)
- Forward reaction increases the number of gas molecules (1 → 2).
- Increasing pressure shifts the equilibrium backwards (towards COCl2).
Question 4.
If sodium acetate is added to very dilute vinegar, will the resulting solution be more or less acidic than the dilute vinegar? Justify.
Answer:
Less acidic
Vinegar contains acetic acid (CH3COOH). Adding sodium acetate (CH3COONa) adds acetate ions, shifting the equilibrium backwards. This reduces the concentration of H+ ions, making the solution less acidic than dilute vinegar.
Question 5.
The main components of a chemical fertilizer are ammonium phosphate ((NH4)3PO4) and ammonium sulphate ((NH4)2SO4).
(i) What is the minimum number of raw materials needed to manufacture it industrially?
(ii) What are these raw materials?
(iii) Explain the industrial preparation of these raw materials that are described in the unit.
Answer:
(i) Minimum number of raw materials required is 2
(ii) Ammonium phosphate: Ammonium hydroxide (NH4OH) and Phosphoric acid (H3PO4).
Ammonium sulphate: Ammonium hydroxide (NH4OH) and Sulphuric acid (H2SO4).
(iii) Ammonia: Prepared by the Haber process
N2 + 3H2 \(\text { ⇌ }\) 2NH3
(high pressure, catalyst, 450 °C).
Sulphuric acid: Manufactured by the Contact process.
Steps involved are.
S + O2 → SO2
2SO2 + O2 \(\text { ⇌ }\) 2SO3 (catalyst V2O5… )
SO3 + H2SO4 → H2S2O7 (Oleum) H2S2O7 + H20 → H2SO4
Some Compounds of Industrial Importance Class 10 Notes
Some Compounds of Industrial Importance Notes Pdf
Ammonia (NH3)
- Prepared in the lab from NH4Cl + Ca(OH)2.
- Physical properties: colourless, pungent smell, lighter than air, highly soluble in water.
Chemical properties: - Basic → turns red litmus blue.
- Soluble in water → forms ammonium hydroxide (NH4OH).
Uses: manufacture of fertilizers (urea, ammonium salts), nitric acid, explosives.
Industrial preparation of ammonia: Haber process
- N2 + 3H2 \(\text { ⇌ }\) 2NH3 (with Fe catalyst, high T & P).
- Nitrogen from air, Hydrogen from water/naphtha.
- Stored as liquid ammonia.
- Uses: fertilizers (urea, ammonium salts), refrigerant, rayon/nylon, petroleum refining, nitric acid manufacture.
Equilibrium
- Reversible reaction: Takes place in both directions.
Example: N2 + 3H2 \(\text { ⇌ }\) 2NH3 - Irreversible reaction: Takes place only in one direction (e.g., NaOH + HCl → NaCl + H20).
Chemical equilibrium:- Forward rate = backward rate,
- Dynamic (both reactions continue at equal rate).
Factors affecting equilibrium (Le Chatelier’s principle)
- Concentration:
- Add reactant → forward reaction increases,
- Add product → backward reaction increases,
- Remove product → forward reaction increases.
- Pressure (for gases):
- Equilibrium shifts to side with fewer molecules,
- If molecules are equal (e.g., H2 + I2 \(\text { ⇌ }\) 2HI), pressure has no effect.
- Temperature:
- Increase in temperature will increase the rate of endothermic reaction.
- Decrease in temperature will increase the rate of exothermic reaction.
- Catalyst:
- Speeds up both forward & backward equally.
- Helps reach equilibrium faster but does not shift the position of equilibrium.
Sulphuric Acid (H2SO4)
- Called “King of Chemicals”; used in fertilizers, detergents, paints, fibres, medicines, and petroleum refining.
- Manufactured by Contact Process
- S + O2 → sO2
- 2SO2 + O2 \(\text { ⇌ }\) 2SO3 (catalyst V2O5)
- SO3 + H2SO4 → H2S2O7 (Oleum)
- H2S2O7 + H2O → H2SO4
- Properties: Colourless, viscous, denser than water, soluble in water.
- Chemical Properties: Dehydrating agent, Drying agent, Reacts with salt, Oxidising agent.
Basicity of Acids
- Basicity = number of replaceable H+ ions in an acid.
- Examples:
- HNO3, HCl → Monobasic (1H+)
- H2SO4 → Dibasic (2 H+)
- H3PO4 → Tribasic (3 H+)
- Alkalies = water-soluble bases (NaOH, Ca(OH)2, NH4OH).
- Acids → give H+, Bases → give OH– in water (Arrhenius theory).
Sodium Hydroxide (NaOH)
- Prepared by the Chlor-alkali process (electrolysis of brine using a membrane cell).
Reactions:- At anode: 2Cl– → Cl2 + 2e–
- At cathode: 2H2O + 2e– → H2 + 2OH–
- Sodium hydroxide is formed in the right chamber by the combination of Na+ ions and OH– ions.
Na+ + OH– → NaOH - Overall: NaOH, Cl2, H2 formed.
- Uses: Soaps, detergents, paper, rayon, aluminium extraction, medicines (aspirin).
Hydrochloric Acid (HCl)
- Prepared by direct combination: H2 + Cl2 → 2HCl (exothermic, in HCl burner).
- Uses: refining salt, dyes, PVC, aqua regia, fertilizers, refining metals, organic/inorganic synthesis.
Salts
- Neutralisation:
Acid + Base → Salt + Water.
HCl + NaOH → NaCl + H2O. - Nature of salt solution:
- NaCl → Neutral
- NH4Cl → Acidic
- Na2CO3 → Basic
- Formation;
- HCl + NaOH (both strong) → NaCl
- HCl (strong acid) + NH4OH (weak base) → NH4Cl (Acidic)
- H2CO3 (weak acid) + NaOH (strong base) → Na2CO3 (Basic)
Fertilizers
- Natural or artificial substances that provide nutrients to plants are called fertilizers.
- Nutrients for plants:
- Natural nutrients – H, O, C (from water & CO2).
- Primary nutrients – N, P, K (needed in large amounts),
- Secondary nutrients – Ca, Mg, S (small amounts),
- Micro nutrients – Fe, Mn, etc.
- Plants absorb nutrients only when dissolved in water.
- Qualities of good fertilizers: soluble, stable, non-toxic, pH neutral.
- Types:
- Nitrogenous → Accelerates the growth of plants, (e.g., urea, ammonium sulphate),
- Phosphate → Increases productivity, root growth (e.g., ammopium phosphate, superphosphate),
- Potash → Helps the growth of plants, boosts immunity (e.g., KCl, K2SO4).
- NPK mixed fertilizers supply all 3 primary nutrients.
INDRODUCTION
The Industrial Revolution and the Green Revolution significantly altered human life. They marked the move from a traditional lifestyle to a modern one. Long ago, wide paddy fields were a common sight, but today farming has changed a lot. Agriculture is something that humans have learned from nature. Our country is rich in farming and has become self-sufficient in food production through the adoption of improved methods.
Chemistry has a major role in this progress. Fertilizers are needed for healthy crop growth and better yield. In the chapter Some Compounds of Industrial Importance, we will study ammonia and its industrial preparation, equilibrium and the factors affecting it, the industrial preparation of sulphuric acid, sodium hydroxide, and hydrochloric acid, as well as fertilizers and their essential properties.
Ammonia and Its Industrial Preparation
- Ammonia is an important nitrogen compound used in fertilizers.
- Industrially prepared by the Haber process, combining nitrogen and hydrogen under high pressure, temperature, and a catalyst.
- Used in fertilizers, explosives, cleaning agents, and refrigeration.
Equilibrium and Factors Affecting Equilibrium
- Chemical equilibrium occurs when the forward and backward reactions balance each other.
- Le Chatelier’s Principle explains how changes in temperature, pressure, and concentration affect equilibrium.
- Very important in industrial processes (e.g., Haber process, Contact process).
Industrial Preparation of Sulphuric Acid
- One of the most important industrial chemicals, called the “King of Chemicals.”
- Prepared by the Contact process.
- Used in fertilizers, dyes, paints, petroleum refining, and batteries.
Basicity of acids
- The presence of H+ ions is the basis for the characteristic properties of acids.
- The basicity of an acid is the number of hydrogen ions that the molecule of the acid can donate. If basicity is 1, the acid is called a monobasic acid.
- If the basicity of an acid is 2, it is called a dibasic acid.
- If the basicity of an acid is 3, it is called a tribasic acid.
Industrial Preparation of Sodium Hydroxide
- Also known as caustic soda.
- Prepared by the Chlor-alkali process (electrolysis of brine solution).
- Widely used in soap making, the paper industry, textiles, and cleaning agents.
Industrial Preparation of Hydrochloric Acid
- Prepared by dissolving hydrogen chloride gas in water.
- Produced as a by-product in industries (e.g., during the manufacture of sodium hydroxide).
- Used to prepare dyes, to manufacture PVC, to prepare organic and inorganic compounds.
Salts
- Salt hydrolysis is the process by which the anions, cations or both of a salt react with water to form a solution that has an acidic or basic nature.
- The salt formed by the reaction of a strong acid and a strong base will be neutral.
- The salt formed from a strong acid and a weak base will be acidic.
- The salt formed from a weak acid and a strong base will be basic.
Fertilizers and Their Essential Properties
- Fertilizers supply essential nutrients like nitrogen, phosphorus, and potassium.
- Types: Nitrogenous, Phosphate and Potash fertilizers.
- Good fertilizers are water-soluble, easily absorbed, and should improve crop yield without harming the soil.
AMMONIA
Ammonia is a chemical used for the production of nitrogenous fertilizers which are required for the growth of plants.
INDUSTRIAL PREPARATION OF AMMONIA (HABER PROCESS)
In this process, nitrogen and hydrogen, in the ratio 1 : 3, are made to combine at very high pressure and temperature to produce ammonia. Sponge iron is used as the catalyst.
N2(g) + 3H2(g) \(\text { ⇌ }\) 2NH3(g) + heat
Atmospheric air is the source of nitrogen. Petroleum products like naphtha are used as sources of hydrogen. Hydrogen obtained by the electrolysis of water is also used.
The ammonia produced by the Haber process is liquefied under high pressure and stored as liquid ammonia.
Liquor ammonia is a concentrated aqueous solution of ammonia. Ammonia gas can be easily liquefied by applying pressure. Liquefied ammonia is known as liquid ammonia.
Uses of ammonia
- For the preparation of chemical fertilizers such as ammonium sulphate, ammonium phosphate and urea.
- As a refrigerant.
- For the production of artificial fibres such as nylon and rayon.
- In the refining of petroleum.
- As the main raw material in the industrial preparation of nitric acid by the Ostwald process.
EXPREMENT
Take some ammonium chloride in a test tube. Add a little sodium hydroxide solution to the test tube. Observe the colour and odour of the gas produced. Bring a moist red litmus paper to the mouth of the test tube. Heat the test tube gently. Then, introduce a glass rod dipped in con. hydrochloric acid to the mouth of the test tube. Observe the experiment well and complete the following table. Conduct the experiment according to your teacher’s instructions.
| Colour of the gas produced. | Colourless |
| Odour of the gas produced. | Pungent or Irritating |
| The change in colour of the moist red litmus paper when shown to the mouth of the test tube. | The moist red litmus paper turns blue. |
| Nature of the gas produced. | Basic or Alkaline (since it turns red litmus blue) |
| What did you observe when the glass rod dipped in con. hydrochloric acid was shown to the mouth of the test tube? | Dense white fumes are produced. |
| Write the chemical equation of this reaction. | NH3 + HCl → NH4Cl |
REVERSIBLE REACTION
Reactions taking place in both directions simultaneously are called reversible reactions.
Example: The formation of ammonia by the reaction of nitrogen and hydrogen is a reversible reaction.
N2(g) + 3H2(g) \(\text { ⇌ }\) 2NH3(g)
IRREVERSIBLE REACTION
An irreversible reaction is a reaction in which reactants form products, but the products cannot change back into reactants
Consider the chemical reactions given below:
NaOH + HCl → NaCl + H2O
C + O2 → CO2
NaCl + AgNO3 → NaNO3 + AgCl
In all these reactions, reactants react to give products. However, at the same conditions, the products do not change to reactants. Such type of reactions are called irreversible reactions.
CHEMICAL EQUILIBRIUM
The stage at which the rate of forward reaction becomes equal to reaction is called chemical equilibrium.
The scientist Le Chatelier has proposed an important principle related to chemical equilibrium.
DYNAMIC EQUILIBRIUM.
At equilibrium, forward and backward reactions occur simultaneously at the same rate and are referred to as dynamic equilibrium.
| LE CHATELIER’S PRINCIPLE “When the concentration, pressure or temperature of a system at equilibrium is changed, the system will readjust itself so as to nullify the effect of that change and attain a new state of equilibrium.” This is Le Chatelier’s principle. |
CHARACTERISTICS OF EQUILIBRIUM
- At equilibrium, both the reactants and the products coexist.
- The rates of forward and backward reactions are equal at equilibrium.
- Even after attaining equilibrium, the reactant molecules react to form product molecules and, at the same rate, the product molecules react to form reactant molecules. Hence, chemical equilibrium is a dynamic equilibrium at the molecular level.
- When nothing new is added to a system and nothing is removed from the system, such a system is called a closed system. Equilibrium is possible only in a closed system.
FACTORS AFFECTING EQUILIBRIUM
- Concentration
- Pressure
- Temperature
- Catalyst
INFLUENCE OF CONCENTRATION ON EQUILIBRIUM
Examine the chemical equation given below.
N2(g) + 3H2(g) \(\text { ⇌ }\) 2NH3(g)
If the concentration of one of the reactants, nitrogen, is increased in this system at equilibrium, what changes are made by the system to rearrange itself according to Le Chatelier’s principle? Tick (✓) only the correct ones in the Table.
| More ammonia will be formed. | ✓ |
| More hydrogen will be used. | ✓ |
| The rate of the forward reaction will increase. | ✓ |
| The rate of the backward reaction will increase. | ✗ |
TEMPERATURE AND EQUILIBRIUM
N2(g) + 3H2(g) \(\text { ⇌ }\) 2NH3(g) + Heat
CATALYST AND EQUILIBRIUM
Catalysts are substances that increase the rate of reactions. In a reversible reaction, catalysts increase the rate of both forward and backward reactions to the same extent. As a result, the system reaches equilibrium very fast.
SULPHURIC ACID (H2SO4)
Sulphuric acid is an important chemical used in the production of many substances like chemical fertilizers, paints, fibres, medicines, fabrics, detergents etc and in petroleum refining. Sulphuric acid is often called the ‘King of Chemicals’ because it is an industrially important chemical.
Sulphuric acid is manufactured by the Contact process.
Important steps in Contact process
- Molten sulphur is burnt in purified and moisture free atmospheric air and converted to sulphur dioxide.
S(s) + O2(g) → SO2 (g) - Sulphur dioxide formed in the first step combines with oxygen, in presence of the catalyst vanadium pentoxide (V2O5), to form sulphur trioxide.
- SO3 is dissolved in concentrated sulphuric acid to produce oleum (H2S2O7).
SO3 (g) + H2SO4(l) → H2S2O7(l) - The oleum thus obtained is dissolved in water to produce sulphuric acid.
H2S2O7(l) + H2O(l) → 2H2SO4(l)
BASICITY OF ACIDS
The presence of H+ ions is the basis for the characteristic properties of acids.
SODIUM HYDROXIDE
Sodium hydroxide is industrially produced by chlor-alkali process. In this, concentrated aqueous solution of sodium chloride (brine) is subjected to electrolysis. In modern industries, membrane cell is used for the electrolysis of brine. A diagram of the membrane cell is given in the figure.
In this, the two chambers are separated using a membrane which allows the passage of specific ions only.
HYDROCHLORIC ACID (HCl)
The product obtained when hydrogen and chlorine react is Hydrochloric acid (HCl)
The balanced chemical equation for this reaction is
H2 + Cl2 → 2HCl
Hydrogen chloride is manufactured by the direct combination of hydrogen and chlorine. Since it is an exothermic process, the reactor where the process takes place will always be hot. Hence the reactor is known as ‘HCl oven’ or ‘HCl burner’. The hydrogen chloride formed in the HCl burner is dissolved in deionised water to produce concentrated hydrochloric acid.
Uses
- To refine table salt.
- To prepare dyes.
- For manufacturing PVC.
- To prepare aquaregia which is used to dissolve Some Compounds of Industrial Importance like gold and platinum.
- For preparing organic and inorganic compounds.
- To produce fertilizers.
- For refining Some Compounds of Industrial Importance.
FERTILIZERS
- Natural or artificial substances that provide nutrients to plants are called fertilizers.
- Water (H2O) contains the elements hydrogen (H) and oxygen (O).
- Carbon dioxide (CO2) contains the elements carbon (C) and oxygen (O)
- These elements are available to plants from nature itself. They can be absorbed from air and water. These three elements are called natural nutrients,
- Nitrogen (N), phosphorus (P) and potassium (K) are the three elements that plants need in large quantities. These are called primary nutrients.
- The soil contains low amounts of calcium (Ca), magnesium (Mg) and sulphur (S). Plants need these only in small amounts. These three elements are called secondary nutrients.
- Some elements are needed to plants only in very small amounts. Hence, they are called micro nutrients.
Eg. Iron, manganese
