Class 8 Basic Science Chapter 13 Important Questions Kerala Syllabus Acids, Bases, Salts

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Acids, Bases, Salts Extra Questions and Answers Class 8 Basic Science Chapter 13 Kerala Syllabus

Acids, Bases, Salts Class 8 Important Questions

Question 1.
Which organic acid is responsible for the sour taste in tamarind?
a) Citric acid
b) Lactic acid
c) Acetic acid
d) Tartaric acid
Answer:
d) Tartaric acid

Question 2.
Which is the common component present in all acids that is responsible for their acidic properties?
a) Oxygen
b) Hydrogen
c) Chlorine
d) Sulphur
Answer:
(b) Hydrogen.

Question 3.
Substances that can increase the
concentration of hydroxide ions (OH^–) in an aqueous solution are called:
a) Acids
b) Salts
c) Alkalis
d) Non-metal oxides
Answer:
(c) Alkalis.

Question 4.
When an acid reacts with a highly reactive metal (like Zinc), it produces a gas. How is this gas identified?
a) It turns lime water milky.
b) It turns blue litmus red.
c) It puts out a burning matchstick with a ‘pop’ sound.
d) It forms a brown ring.
Answer:
(c) It puts out a burning matchstick with a ‘pop’ sound (This is the test for Hydrogen, H₂).

Question 5.
Statement 1: Acids have a sour taste and turn blue litmus red.
Statement 2: Bases have a bitter taste and turn red litmus blue.
a) Both statements are correct.
b) Only Statement 1 is correct.
c) Only Statement 2 is correct.
d) Both statements are incorrect.
Answer:
(a) Both statements are correct.

Question 6.
Statement 1: Metal oxides (like MgO) generally show basic properties.
Statement 2: Non-metal oxides (like CO₂) generally show acidic properties.
a) Both statements are correct.
b) Only Statement 1 is correct.
c) Only Statement 2 is correct.
d) Both statements are incorrect.
Answer:
(a) Both statements are correct.

Question 7.
Statement 1: A solution with a pH value of 3 is acidic.
Statement 2: A solution with a pH value of 9 is also acidic.
a) Both statements are correct.
b) Only Statement 1 is correct.
c) Only Statement 2 is correct.
d) Both statements are incorrect.
Answer:
(b) Only Statement 1 is correct. (Statement 2 is incorrect; pH > 7 is basic).

Question 8.
Classify the following substances as Acidic, Basic, or Neutral:
(Lemon juice, Soap solution. Water, Vinegar, Lime water)
Answer:
Acidic: Lemon juice, Vinegar.
Basic: Soap solution, Lime water (Calcium hydroxide).
Neutral: Water.

Question 9.
Match the food substance with the organic acid responsible for its sour taste.

Substance	Acid
1. Tamarind	a. Lactic acid
2. Vinegar	b. Citric acid
3. Yoghurt	c. Tartaric acid
4. Lemon juice	d. Acetic acid

Answer:
1 – c, 2 – d, 3 – a, 4 – b.

Substance	Acid
1. Tamarind	c. Tartaric acid
2. Vinegar	d. Acetic acid
3. Yoghurt	a. Lactic acid
4. Lemon juice	b. Citric acid

Question 10.
Find the acid and base that must be reacted to obtain the salt Sodium Sulphate (Na₂SO₄).
Answer:
Acid: Sulphuric acid (H₂SO₄)
Alkali/Base: Sodium hydroxide (NaOH)

Question 11.
Find and correct the error in this statement:
“Acids turn red litmus paper blue, and bases turn blue litmus paper red.”
Answer:
Error: The colors are swapped. Correction: Acids turn blue litmus paper red, and bases turn red litmus paper blue.

Question 12.
Find and correct the error in this statement:
“A pH value of 8 indicates an acidic solution.”
Answer:
Error: Acidic.
Correction: A pH value greater than 7 indicates a basic solution.

Question 13.
Find and correct the error in this statement:
“When acids react with carbonates (like marble), hydrogen gas is liberated.”
Answer:
Error: Hydrogen gas.
Correction: When acids react with carbonates, carbon dioxide gas (CO₂) is liberated.

Question 14.
Why does taking an antacid (like milk of magnesia) relieve indigestion or heartburn?
Answer:
Indigestion is often caused by excess hydrochloric acid (HCl) in the stomach. Antacids (like milk of magnesia, Mg(OH)₂) are bases. The base reacts with the excess acid in a neutralisation reaction, reducing the acidity and providing relief.

Question 15.
Why is soda water considered acidic?
Answer:
Soda water is made by dissolving carbon dioxide (CO₂) (a non-metal oxide) in water. The CO₂ reacts with the water (H₂O) to form carbonic acid (H₂CO₃), which gives soda water its acidic nature.

Question 16.
Why do farmers sometimes add slaked lime (calcium hydroxide) to agricultural soil?
Answer:
Farmers add slaked lime (a base) to reduce the acidity of acidic soil. This neutralisation reaction helps bring the soil pH to a level that is suitable for growing certain crops.

Question 17.
Complete the chemical equation for the dissociation of Sulphuric acid in water:
H₂SO₄ → ……………..+…………..
Answer:
H₂SO₄ → 2H⁺ + SO₄^2-.

Question 18.
Complete the chemical equation for the neutralisation reaction between dilute nitric acid and sodium hydroxide.
NaOH + HNO₃ → ……………..+…………..
Answer:
NaOH + HNO₃ → NaNO₃ + H₂O. (The products are a salt, Sodium Nitrate, and water).

Question 19.
A salt solution forms a white precipitate when Barium Chloride (BaCl₂) is added. This precipitate does not dissolve when dilute HCl is added. Which ion is present in the salt? (Sulphate ion or Carbonate ion?)
Answer:
The Sulphate ion (SO₄^2-). (Both ions form a white precipitate with BaCl₂, but only Barium Sulphate (BaSO₄) does not dissolve in HCl).

Question 20.
Describe the experiment to identify a carbonate salt.
Answer:
Take a little of the salt solution (e.g., sodium carbonate) in a test tube.
Add a few drops of dilute hydrochloric acid (HCl).
Observation 1: Bubbles (effervescence) will form, indicating a gas is liberated.
Confirmation: Pass this gas through clear lime water (Ca(OH)₂ solution) using a delivery tube.
Observation 2: The clear lime water will turn milky. This confirms the gas is Carbon Dioxide (CO₂) and the salt is a carbonate.

Question 21.
Describe the procedure to test if a salt (like KCl) contains the chloride ion (Cl ).
Answer:
Take a small amount of the salt solution (e.g., KCl) in a test tube.
Add a few drops of silver nitrate (AgNO₃) solution to it.
Observation: A white precipitate of silver chloride (AgCl) will be formed.

Question 22.
Describe the procedure to test if a salt (like Ammonium Sulphate) contains the sulphate ion (SO₄^2-).
Answer:
Take a small amount of the salt solution in a test tube and mix it with water. Add barium chloride (BaCl₂) solution to it.
Observation 1: A white precipitate (Barium Sulphate, BaSO₄ will form.
Confirmation: Add a few drops of dilute hydrochloric acid (HCl) to the precipitate.
Observation 2: The white precipitate will not dissolve.

Question 23.
Match the food substance in Column A with the acid it contains in Column B.

Column A	Column B
(i) Vinegar	(a) Lactic acid
(ii) Lemon juice	(b) Tartaric acid
(iii) Yoghurt	(c) Acetic acid
(iv) Tamarind	(d) Citric acid

Answer:
(i) – c, (ii) – d, (iii) – a, (iv) – b

Column A	Column B
(i) Vinegar	(c) Acetic acid
(ii) Lemon juice	(d) Citric acid
(iii) Yoghurt	(a) Lactic acid
(iv) Tamarind	(b) Tartaric acid

Question 24.
Match the common name in Column A with its chemical formula in Column B.

Column A	Column B
(i) Caustic soda	(a) Ca(OH)2
(ii) Milk of lime	(b) KOH
(iii) Caustic potash	(c) NaOH

Answer:
(i) – c, (ii) – a, (iii) – b

Column A	Column B
(i) Caustic soda	(c) NaOH
(ii) Milk of lime	(a) Ca(OH)2
(iii) Caustic potash	(b) KOH

Question 25.
Match the ion being tested with the correct observation.

Ion	Observation
(i) Chloride (Cl–)	(a) Bubbles of gas that turn lime water milky.
(ii) Sulphate (SO42-)	(b) A brown ring forms at the liquid junction.
(iii) Carbonate (CO32-)	(c) A white precipitate forms when silver nitrate is added.
(iv) Nitrate (NO3–)	(d) A white precipitate forms when barium chloride is added.

Answer:
(i) – c, (ii) – d, (iii) – a, (iv) – b

Ion	Observation
(i) Chloride (Cl–)	(d) A white precipitate forms when barium chloride is added.
(ii) Sulphate (SO42-)	(a) Bubbles of gas that turn lime water milky.
(iii) Carbonate (CO32-)	(b) A brown ring forms at the liquid junction.
(iv) Nitrate (NO3–)	(c) A white precipitate forms when silver nitrate is added.

Question 26.
Statement (i): Acids have a sour taste and turn red litmus blue.
Statement (ii): Bases have a bitter taste and turn blue litmus red.
a) Both statements (i) and (ii) are correct.
b) Statement (i) is correct, but statement (ii) is incorrect.
c) Statement (ii) is correct, but statement (i) is incorrect.
d) Both statements (i) and (ii) are incorrect.
Answer:
(d) Both statements are incorrect. (Acids turn blue to red, and bases turn red to blue).

Question 27.
Statement (i): The chemical reaction between an acid and a base to form salt and water is called neutralisation.
Statement (ii): A solution with a pH value of 7 is considered basic.
a) Both statements (i) and (ii) are correct.
b) Statement (i) is correct, but statement (ii) is incorrect.
c) Statement (ii) is correct, but statement (i) is incorrect.
d) Both statements (i) and (ii) are incorrect.
Answer:
(b) Statement (i) is correct, but statement (ii) is incorrect. (A pH of 7 is neutral).

Question 28.
Statement (i): Non-metal oxides (like CO₂) react with water to form substances that are generally acidic.
Statement (ii): Metal oxides (like MgO) react with water to form substances that are generally basic.
a) Both statements (i) and (ii) are correct.
b) Statement (i) is correct, but statement (ii) is incorrect.
c) Statement (ii) is correct, but statement (i) is incorrect.
d) Both statements (i) and (ii) are incorrect.
Answer:
(a) Both statements (i) and (ii) are correct.

Question 29.
What is the chemical definition of an acid, and what ion is the basis for all its general properties?
Answer:
Acids are substances that can increase the concentration of hydrogen ions (H⁺) in an aqueous solution. The H⁺ ion (or hydronium ion, H₃O⁺) is the basis for the general properties of acids.

Question 30.
Match the following appropriately.

Substances	Acid responsible for the sour taste
a. Lemon juice	i) Acetic acid
b.Yoghurt / Buttermilk	ii) Tartaric acid
c. Tamarind	iii) Citric acid
d.Vinegar	iv) Lactic acid

A. a – (ii) c – (iii), d – (iv) b – (i)
B. a – (i) (b) – (ii), c – (iii), d – (iv)
C. a – (iii), b – (ii) c – (iv) d – (i)
D. a – (iii), b – (iv), c – (ii) d – (i)
Answer:
D. a – (iii) b – (iv) c – (ii) d – (i)

Substances	Acid responsible for the sour taste
a. Lemon juice	iii) Citric acid
b.Yoghurt / Buttermilk	iv) Lactic acid
c. Tamarind	ii) Tartaric acid
d.Vinegar	i) Acetic acid

Question 31.
From the characteristics given below, find out those suitable for acids.
a) Turns blue litmus red
b) Soapy to touch
c) Have bitter taste
d) Have sour taste
(i) a, b
(ii) b, c
(iii) a, d
(iv) a, c
Answer:
(iii) a, d

Question 32.
Why are antacids, like Milk of Magnesia (magnesium hydroxide), used to treat indigestion?
Answer:
Indigestion is often caused by an excess of hydrochloric acid in the stomach. Antacids are basic substances.

They undergo a neutralisation reaction with the excess acid, reducing the acidity and providing relief.

Question 33.
Why does a farmer add slaked lime (calcium hydroxide) to soil that has a pH value of 5?
Answer:
A pH value of 5 is acidic (since it is less than 7). Slaked lime is a base. The farmer adds it to the soil to neutralize the excess acidity, making the soil suitable for growing crops.

Question 34.
Soda water is prepared by dissolving CO₂ gas under high pressure in water.
A. Which is the acid present in soda water? What is its chemical formula?
B. Write the chemical equation of the reaction.1
Answer:
A. Carbonic acid.
H₂CO₃
B. H₂O + CO₂ → H₂CO₃

Question 35.
Acid rain causes many environmental problems.
a) Explain how acid rain is formed.
b) Write any one environmental issue caused by acid rain.
Answer:
a) The gases like SO₂, NO₂ emitted from factories, motor vehicles thermoelectric power stations into air dissolve in rain water and cause acid rain.

b)

• Plants lose their ability to produce carbohydrate through photosynthesis as their leaves are destroyed.
• Severe acid rain destroys the greenery of a region.
• The acidic nature of water causes the death and distruction of fish and corals.

Question 36.
Calcium oxide reacts with water.
A. What is the product obtained by the reaction?
B. Property of which of the following it has?
(Acid, Alkali, Neutral solution)
Answer:
A. Calcium hydroxide (Ca(OH)₂)
B. Alkali

Question 37.
What are the situations in our day to day life in which neutralisation is made use of?
Answer:
In the agricultural field we use suitable manures according to the crops. The acid-alkaline properties are checked before applying the fertilizer. Similarly the acidic property is neutralised by adding alkaline substances like slaked lime. The acidity in our stomach is removed by treating with antacids. Antacids remove the acidity by neutralisation. In the laboratories in case of burning due to acids, weak alkalies are used as a first aid for its treatment. Here also neutralisation is made use of.

Question 38.
Describe the experiment to identify a carbonate salt.
Answer:
Take a little of the salt solution (e.g., sodium carbonate) in a test tube.
Add a few drops of dilute hydrochloric acid (HCl).
Observation 1: Bubbles (effervescence) will form, indicating a gas is liberated.
Confirmation: Pass this gas through clear lime water Ca(OH)₂ solution) using a delivery tube.
Observation 2: The clear lime water will turn milky. This confirms the gas is Carbon Dioxide (CO₂) and the salt is a carbonate.

Question 39.
Describe the experiment to identify a sulphate salt.
Answer:
Take a little of the salt solution in a test tube.
Add a few drops of barium chloride (BaCl₂) solution.
Observation 1: A white precipitate (Barium Sulphate, BaSO₄ will form.
Confirmation: Add a few drops of di-lute hydrochloric acid (HCl) to the precipitate.
Observation 2: The white precipitate will not dissolve.

Question 40.
The pH of solutions P, Q, Rare given.

Solution	PH
P	4
Q	9
R	7

A. Among them which is the neutral solution?
B. Among them which solution gives CO₂ when reacts with Na₂CO₃? Why?
C. Which solution has more concentration of OH^– ions?
Answer:
A. R
B. Solution P. Because it being an acid reacts with Na₂CO₃ and gives CO₂
C. Q

Question 41.
20mL of NaOH is taken in a conical flask and two drops of phenolphthalein are added. Then dilute HCl is added drop by drop, continuously shaking the beaker.
a) NaOH solution is turned into pink colour when phenolphthalein is added. Which nature of the solution is indicated here?
b) As HCl is added, the intensity of pink colour of solution decreases and finally disappeares. Why? Explain.
c) Write the chemical equation of the reaction that has occured here?
Answer:
a) Basic nature
b) Acidic HCl reacts with basic NaOH to form neutral salt and water. As the concentration of base decreas-es the pink colour fades and finally disappears due to neutralisation reaction.
c) NaOH + HCl → NaCl + H₂O

Question 42.
At the initial stages of cultivation the pH value o the soil is found. What is the need of it?
Answer:
In the case of farming, the pH value of the soil has an important role. A particular pH range is required for the healthy growth of certain crops. Certain crops grow well in the soil that is acidic in nature. But certain other crops grow well in the soil that is basic in nature. In situations like this, soil samples are collected in a suitable manner. The samples are mixed and water is added to get a solution. The pH value of the solution is found out to determine the pH value of the soil.

Question 43.
The pH of a soil is measured during soil testing.
a) Why the pH of soil is measured?
b) Suggest a method to increase the pH of soil with pH = 5.
Answer:
a) The pH of soil is an important factor for crops. It is important to identify whether the soil of a region is suitable for a particular crop. For some crops, soil with acidic nature is suitable and for some other crops, soil with alkaline nature is suitable.

b) Sprinkling of slaked lime.

Question 44.
A student adds a piece of magnesium ribbon to a test tube containing dilute sulphuric acid.
a) What is the main observation?
b) How can the gas produced be identified?
Answer:
a) The student will observe bubbles (effervescence) as the magnesium reacts with the acid,
b) The gas produced is hydrogen (H₂). It can be identified by holding a burning matchstick at the mouth of the test tube. The gas will extinguish the flame with a ‘pop’ sound.

Question 45.
Match the following appropriately.

Common name	Chemical name
a. Caustic soda	i) Magnesium hydroxide
b. Milk of lime	ii) Potassium hydroxide
c. Caustic Potash	iii) Sodium hydroxide
d. Milk of magnesia	iv) Calcium hydroxide

A. a – (ii), b – (i), c – (iii), d – (iv)
B. a – (i), b – (ii), c – (iii), d – (iv)
C. a – (iii), b – (ii), c – (iv), d – (i)
D. a – (iii), b – (iv), c – (ii) d – (i)
Answer:
D. a – (iii), b – (iv) c – (ii) d – (i)

Common name	Chemical name
a. Caustic soda	iii) Sodium hydroxide
b. Milk of lime	iv) Calcium hydroxide
c. Caustic Potash	ii) Potassium hydroxide
d. Milk of magnesia	i) Magnesium hydroxide

Question 46.
Complete the chemical equation for the reaction between magnesium and sulphuric acid.
Mg + H₂SO₄ → ……………. + …………..
Answer:
Mg + H₂SO₄ → MgS0₄ + H₂.

Question 47.
Complete the equation for the reac-tion when Carbon dioxide (CO₂) gas is passed through water. Name the product formed.
CO₂ + H₂O → ……………. + …………..
Answer:
CO₂ + H₂O → H₂CO₃ (Carbonic acid).

Question 48.
Complete the following neutralisation reaction and identify the salt formed.
KOH + HNO₃ → ……………. + …………..
Answer:
KOH + HNO₃ → KNO₃ + H₂O. The salt formed is Potassium Nitrate.

Question 49.
From the chapter, write the chemical formulas for the following acids:
(a) Sulphuric acid
(b) Phosphoric acid
(c) Nitric acid
Answer:
a) H₂SO₄
b) H₃PO₄
c) HNO₃

Question 50.
How many H⁺ (hydrogen) ions and SO₄^2- (sulphate) ions are liberated when 3 molecules of Sulphuric Acid (H₂SO₄) dissolve in water?
Answer:
One molecule of H₂SO₄ liberates 2H⁺ ions and SO₄^2- ion.
Therefore, 3 molecules will liberate:
3 \times 2 = 6H⁺ ions.
3 \times 1 = 3 SO₄^2- ions

Question 51.
Identify the chemical formulas of the acid and base needed to form the salt Aluminium Sulphate (Al₂(SO₄)₃).
Answer:
Acid: Sulphuric acid (H₂SO₄
Base: Aluminium hydroxide (Al(OH)₃)

Question 52.
What is the characteristic effect of an acid on blue litmus paper?
(A) Turns blue
(B) Turns red
(C) No change
(D) Turns yellow
Answer:
(B) Turns red

Question 53.
Which ion is primarily responsible for the general properties of acids in an aqueous solution?
(A) Cl^–
(B) OH^–
(C) H⁺
(D) Na⁺
Answer:
(C) H⁺

Question 54.
Which organic acid is responsible for the sour taste in Tamarind?
(A) Lactic acid
(B) Citric acid
(C) Acetic acid
(D) Tartaric acid
Answer:
(D) Tartaric acid

Question 55.
Which substance is commonly used as an Antacid to reduce excessive stomach acidity?
(A) Hydrochloric acid (HCl)
(B) Magnesium hydroxide (Mg(OH)₂)
(C) Sodium hydroxide (NaOH)
(D) Sulphuric acid (H₂SO₄)
Answer:
(B) Magnesium hydroxide (Mg(OH)₂)

Question 56.
Complete the following chemical reaction which shows an acid reacting with a highly reactive metal.
Zn + 2HCl → ZnCl₂ + ___________
Answer:
Zn + 2HCl → ZnCl₂ + H₂(Hydrogen gas (H₂) is liberated when acids react with highly reactive metals like Zinc.)

Question 57.
Define amphoteric oxides and give one example.
Answer:
Amphoteric oxides are oxides that have both acidic and basic properties. This means they can react with both acids and bases.
Example: Al₂O₃ (Aluminium oxide) or ZnO (Zinc oxide).

Question 58.
Write the balanced chemfcqi equation for the reaction of Sulphur dioxide (SO₂) gas with water (H₂O).
Answer:
SO₂ + H₂O → H₂SO₃ (Sulphurous acid)

Question 59.
What is the pH value of a neutral solution? What characteristics do solutions with a pH value greater than 7 show?
Answer:
The pH value of a neutral solution is 7. Solutions with a pH value greater than 7 show basic characteristics.

Question 60.
Explain what Acid Rain is, and state two negative effects it has on the environment.
Answer:
Acid Rain:
Acid rain is the result of nonmetal oxide gases like SO₂ (Sulphur dioxide) and NO₂ (Nitrogen dioxide) reaching the atmosphere, dissolving in rainwater, and falling to the earth as acids.

Two Environmental Effects:

1. It damages plant leaves, which reduces the ability of plants to produce starch through photosynthesis.
2. It increases the acidity of water sources, which in turn causes the death of aquatic life like fish and coral reefs.

Question 61.
Define Neutralisation Reaction and complete the chemical equation for the reaction between Sodium Hydroxide (NaOH) and Hydrochloric Acid (HCl).
NaOH + HCl → _________ + ______
Answer:
Neutralisation Reaction:
A neutralisation reaction is the chemical reaction in which an acid and a base react and lose their characteristic properties to form water and a salt.
Complete the equation:
NaOH + HCl → NaCl + H₂O
(The products are Sodium Chloride (NaCl), which is the salt, and Water (H₂O).)