CBSE in its latest sample papers has changed the pattern of the question papers and the markings of questions. Now the 5 marks questions will be descriptive and analytical. Rote learning and memorisation will not work at all.
Therefore,
We have created “Acids Bases And Salts 5 Marks Questions Answers” so that you get an idea about the changed pattern. Practice the questions to get good marks.
Before attemting the question,
Prepare the short notes and practice other question formats given below:
- Acids, Bases And Salts Short Notes
- Acids, Bases And Salts MCQs Quiz
- Acids, Bases And Salts 2 Marks questions
- Acids, Bases And Salts 3 Marks questions
- Acids, Bases And Salts 4 marks questions
Question 1.
The following reaction occurs when a metal compound A reacts with dilute hydrochloric acid:
A(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)
Answer the following:
(a) Identify the chemical name and formula of compound A.
(b) What observation confirms the evolution of gas?
(c) Why does the gas turn lime water milky?
(d) What happens when excess gas is passed through lime water?
(e) Write the balanced equation for the reaction between the gas and lime water, and for the subsequent reaction with excess gas.
Show Answer
(a) Compound A is calcium carbonate, with formula CaCO₃.
(b) The gas evolved extinguishes a burning candle, confirming it is carbon dioxide.
(c) CO₂ reacts with calcium hydroxide to form insoluble calcium carbonate, which causes milkiness.
(d) On passing excess CO₂, milkiness disappears because calcium carbonate converts to soluble calcium hydrogen carbonate.
Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)
CaCO₃(s) + H₂O(l) + CO₂(g) → Ca(HCO₃)₂(aq)
Question 2.
Consider the reaction:
2NaOH(aq) + Zn(s) → Na₂ZnO₂(aq) + H₂(g)
Answer the following:
(a) What is the common name of Na₂ZnO₂?
(b) Why is hydrogen gas evolved even though NaOH is a base?
(c) Can all metals react with bases to produce hydrogen? Justify.
(d) What test confirms the presence of hydrogen gas?
(e) Write a similar reaction using aluminium instead of zinc.
Show Answer
(a) Na₂ZnO₂ is called sodium zincate.
(b) Zinc is amphoteric, so it reacts with strong bases like NaOH to liberate hydrogen gas.
(c) No, only amphoteric metals like Al, Zn, and Pb react with bases to produce H₂.
(d) Hydrogen burns with a pop sound when a burning candle is brought near it.
2NaOH(aq) + 2Al(s) + 2H₂O(l) → 2NaAlO₂(aq) + 3H₂(g)
Question 3.
The reaction during the chlor-alkali process is:
2NaCl(aq) + 2H₂O(l) → 2NaOH(aq) + Cl₂(g) + H₂(g)
Answer the following:
(a) Why is this process called chlor-alkali?
(b) Identify the products formed at anode and cathode.
(c) What is the use of Cl₂ gas in daily life?
(d) Why is an aqueous solution of NaCl used, not solid NaCl?
(e) Write the chemical equation for the reaction of Cl₂ with dry slaked lime.
Show Answer
(a) It is called chlor-alkali because it produces chlor (chlorine) and alkali (sodium hydroxide).
(b) Cl₂ gas is formed at the anode, and H₂ gas at the cathode.
(c) Chlorine is used to manufacture bleaching powder, which disinfects drinking water.
(d) Ions are free to move only in aqueous solution, enabling electrolysis.
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
Question 4.
On heating, baking soda decomposes as:
2NaHCO₃(s) → Na₂CO₃(s) + H₂O(g) + CO₂(g)
Answer the following:
(a) What is the chemical name of NaHCO₃?
(b) Why is this reaction useful in baking?
(c) What type of salt is NaHCO₃—acidic, basic, or neutral?
(d) How does it act as an antacid?
(e) Write the reaction when baking powder (NaHCO₃ + tartaric acid) is mixed with water.
Show Answer
(a) Sodium hydrogencarbonate.
(b) CO₂ gas makes cakes rise, making them soft and spongy.
(c) It is a mild non-corrosive basic salt.
(d) It neutralises excess stomach acid due to its basic nature.
NaHCO₃ + H⁺ → CO₂ + H₂O + sodium salt of acid
Question 5.
The reaction of bleaching powder with water is implied in its use. The formation reaction is:
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
Answer the following:
(a) What is the common name of CaOCl₂?
(b) What is the raw material used to make it?
(c) Why is it used to disinfect drinking water?
(d) Is it stable in air? Justify.
(e) Write the reaction that shows its bleaching action and What chemical property enables this?(hint: it releases Cl₂ in presence of acid).
Show Answer
(a) Bleaching powder.
(b) Dry slaked lime [Ca(OH)₂] and chlorine gas.
(c) It kills germs due to its oxidising action.
(d) It reacts with CO₂ in air, so must be stored in airtight containers.
CaOCl₂ + H₂SO₄ → CaSO₄ + Cl₂ + H₂O
It acts as an oxidising agent.
Question 6.
The reaction between copper oxide and dilute HCl is:
CuO(s) + 2HCl(aq) → CuCl₂(aq) + H₂O(l)
(a) What colour change is observed?
(b) Why is CuO called a basic oxide?
(c) What type of reaction is this?
(d) Can this reaction be used to produce hydrogen gas? Why?
(e) Write a general equation for metal oxide + acid.
Show Answer
(a) The solution turns blue-green.
(b) Because it reacts with acid to form salt and water, like a base.
(c) It is a neutralisation reaction.
(d) No, because no hydrogen gas is evolved—only water is formed.
Metal oxide + Acid → Salt + Water
Question 7.
When CO₂ is passed through lime water:
Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)
(a) What is lime water chemically?
(b) What causes milkiness?
(c) Why does milkiness disappear on excess CO₂?
(d) Write the second reaction with excess CO₂.
(e) Name a natural substance that contains CaCO₃.
Show Answer
(a) Calcium hydroxide solution.
(b) Formation of insoluble white CaCO₃ precipitate.
(c) Because CaCO₃ converts to soluble Ca(HCO₃)₂.
CaCO₃(s) + H₂O(l) + CO₂(g) → Ca(HCO₃)₂(aq)
(e) Limestone, chalk, or marble.
Question 8.
Reaction of Na₂CO₃ with HCl:
Na₂CO₃(s) + 2HCl(aq) → 2NaCl(aq) + H₂O(l) + CO₂(g)
(a) What gas is evolved?
(b) How is it tested?
(c) Is Na₂CO₃ acidic or basic in nature?
(d) What is its common name?
(e) Give one industrial use of Na₂CO₃.
Show Answer
(a) Carbon dioxide.
(b) It turns lime water milky.
(c) It is basic (salt of strong base and weak acid).
(d) Washing soda (when hydrated).
(e) Used in glass, soap, and paper industries.
Question 9.
The reaction:
Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)
(a) What type of reaction is this?
(b) Why is hydrogen displaced?
(c) What test identifies H₂?
(d) Can Cu replace H in acids? Why?
(e) Write a general equation for metal + acid.
Show Answer
(a) Displacement reaction.
(b) Because Zn is more reactive than hydrogen.
(c) Burns with a pop sound.
(d) No, because Cu is less reactive than H.
Acid + Metal → Salt + Hydrogen gas
Question 10.
Heating hydrated copper sulphate:
CuSO₄·5H₂O(s) → CuSO₄(s) + 5H₂O(g)
(a) What is the colour before and after heating?
(b) What is water of crystallisation?
(c) What happens when water is added to the heated product?
(d) How many water molecules are in one formula unit?
(e) Name another salt with water of crystallisation.
Show Answer
(a) Blue → white.
(b) Fixed number of water molecules present in one formula unit of a salt.
(c) Blue colour is restored.
(d) Five.
(e) Gypsum (CaSO₄·2H₂O).
Question 11.
The reaction of a metal carbonate A with hydrochloric acid is represented as:
A(s) + xHCl(aq) → CaCl₂(aq) + yH₂O(l) + zCO₂(g)
Answer the following:
(a) Identify the chemical formula of A.
(b) Using atom balance, determine the values of x, y, and z.
(c) What observation confirms the evolution of gas?
(d) What happens when this gas is passed through lime water?
(e) Name a natural substance that contains A.
Show Answer
(a) A is calcium carbonate, CaCO₃.
(b) Balancing atoms:
Ca: 1 = 1 → OK
C: 1 = z → z = 1
O: 3 = y + 2z → 3 = y + 2 → y = 1
H: x = 2y → x = 2
Cl: x = 2 → consistent
Thus, x = 2, y = 1, z = 1.
(c) The gas extinguishes a burning candle.
(d) It turns lime water milky due to formation of insoluble CaCO₃.
(e) Marble, chalk, or limestone.
CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)
Question 12.
The thermal decomposition of baking soda is given as:
2NaHCO₃(s) → aNa₂CO₃(s) + bH₂O(g) + cCO₂(g)
Answer the following:
(a) Using atom balance, find the values of a, b, and c.
(b) What is the common name of NaHCO₃?
(c) Why is this reaction used in baking?
(d) Is NaHCO₃ acidic, basic, or neutral? Justify.
(e) Give one medicinal use of this compound.
Show Answer
(a) Balancing:
Na: 2 = 2a → a = 1
H: 2 = 2b → b = 1
C: 2 = a + c → 2 = 1 + c → c = 1
O: 6 = 3a + b + 2c = 3 + 1 + 2 = 6 → OK
So, a = 1, b = 1, c = 1.
(b) Baking soda.
(c) CO₂ gas makes cakes soft and spongy.
(d) It is basic because it is a salt of strong base (NaOH) and weak acid (H₂CO₃).
(e) Used as an antacid to neutralise excess stomach acid.
2NaHCO₃(s) → Na₂CO₃(s) + H₂O(g) + CO₂(g)
Question 13.
The formation of bleaching powder is:
Ca(OH)₂(s) + Cl₂(g) → CaOCl₂(s) + dH₂O(l)
Answer the following:
(a) Using atom balance, find d.
(b) What is the chemical name of Ca(OH)₂?
(c) What is the common name of CaOCl₂?
(d) Give two uses of bleaching powder.
(e) Why must it be stored in airtight containers?
Show Answer
(a) Left: Ca = 1, O = 2, H = 2, Cl = 2
Right: Ca = 1, O = 1 (in CaOCl₂?) + d, H = 2d, Cl = 2
But per standard and PDF, d = 1 (as written).
Balancing H: 2 = 2d → d = 1.
(b) Calcium hydroxide (dry slaked lime).
(c) Bleaching powder.
(d) (i) Disinfecting drinking water, (ii) Bleaching cotton in textile industry.
(e) It reacts with CO₂ in air, so decomposes.
Ca(OH)₂(s) + Cl₂(g) → CaOCl₂(s) + H₂O(l)
Question 14.
In the chlor-alkali process, the reaction is:
pNaCl(aq) + qH₂O(l) → rNaOH(aq) + sCl₂(g) + tH₂(g)
Answer the following:
(a) Using atom balance, determine the values of p, q, r, s, and t.
(b) Why is this process called chlor-alkali?
(c) Which gas is produced at the anode?
(d) Which gas at the cathode?
(e) Give one industrial use of NaOH.
Show Answer
(a) Balance:
Na: p = r
Cl: p = 2s
H: 2q = r + 2t
O: q = r
From O: q = r
From Na: p = r = q
From Cl: p = 2s → s = p/2
From H: 2q = q + 2t → q = 2t → t = q/2
Choose smallest integers: let q = 2 → r = 2, p = 2, s = 1, t = 1
So p = 2, q = 2, r = 2, s = 1, t = 1.
(b) It produces chlor (chlorine) and alkali (NaOH).
(c) Chlorine gas at anode.
(d) Hydrogen gas at cathode.
(e) Used in soap, paper, or textile industries.
2NaCl(aq) + 2H₂O(l) → 2NaOH(aq) + Cl₂(g) + H₂(g)
Question 15.
The reaction of hydrated copper sulphate on heating is:
CuSO₄·xH₂O(s) → CuSO₄(s) + yH₂O(g)
Answer the following:
(a) Using knowledge from the text, what is the value of x?
(b) Hence, find y.
(c) What colour change is observed on heating?
(d) What happens when water is added to the heated product?
(e) What is the term for the fixed number of water molecules in a salt?
Show Answer
(a) The formula is CuSO₄·5H₂O, so x = 5.
(b) All water is released, so y = 5.
(c) Blue → white.
(d) Blue colour is restored.
(e) Water of crystallisation.
CuSO₄·5H₂O(s) → CuSO₄(s) + 5H₂O(g)
Question 16.
The thermal decomposition of baking soda is represented as:
2NaHCO₃(s) → Na₂CO₃(s) + aH₂O(g) + bCO₂(g)
(a) Determine a and b using atom balance.
(b) What is the chemical name of NaHCO₃?
(c) Why is this reaction used in baking?
(d) Is NaHCO₃ acidic, basic, or neutral? Justify.
(e) Write the reaction when baking powder (NaHCO₃ + tartaric acid) is added to water.
Show Answer
(a) Na: 2 = 2 → OK
H: 2 = 2a → a = 1
C: 2 = 1 + b → b = 1
O: 6 = 3 + a + 2b = 3 + 1 + 2 = 6 → balanced
So, a = 1, b = 1.
(b) Sodium hydrogencarbonate.
(c) CO₂ gas makes cakes soft and spongy.
(d) It is a mild basic salt because it is formed from strong base (NaOH) and weak acid (H₂CO₃).
2NaHCO₃(s) → Na₂CO₃(s) + H₂O(g) + CO₂(g)
Question 17.
In the chlor-alkali process:
pNaCl(aq) + qH₂O(l) → rNaOH(aq) + sCl₂(g) + tH₂(g)
(a) Using atom balance, find p, q, r, s, t.
(b) Why is it called the chlor-alkali process?
(c) Which gas is formed at the anode?
(d) Which at the cathode?
(e) Give one industrial use of NaOH.
Show Answer
(a) Na: p = r; Cl: p = 2s; H: 2q = r + 2t; O: q = r
Let r = 2 → p = 2, q = 2, s = 1, t = 1
So, p = 2, q = 2, r = 2, s = 1, t = 1.
(b) It produces chlor (chlorine) and alkali (NaOH).
(c) Chlorine gas at anode.
(d) Hydrogen gas at cathode.
(e) Used in soap, paper, or textile industries.
2NaCl(aq) + 2H₂O(l) → 2NaOH(aq) + Cl₂(g) + H₂(g)
Question 18.
Hydrated copper sulphate decomposes as:
CuSO₄·xH₂O(s) → CuSO₄(s) + yH₂O(g)
(a) What is the value of x as per the text? Hence find y.
(b) What colour change occurs on heating?
(c) What happens when water is added to the heated product?
(d) What is the term for x?
(e) Name another salt with water of crystallisation.
Show Answer
(a) x = 5, so y = 5.
(b) Blue to white.
(c) Blue colour is restored.
(d) Water of crystallisation.
(e) Gypsum (CaSO₄·2H₂O).
CuSO₄·5H₂O(s) → CuSO₄(s) + 5H₂O(g)
Question 19.
A base reacts with zinc as:
2NaOH(aq) + Zn(s) → Na₂ZnOₓ(aq) + yH₂(g)
(a) Balance to find x and y.
(b) What is the name of Na₂ZnOₓ?
(c) Why does zinc react with a base?
(d) What test identifies the gas?
(e) Name another metal that behaves similarly.
Show Answer
(a) Na: 2 = 2; Zn: 1 = 1; O: 2 + x = x? Wait—standard formula is Na₂ZnO₂.
Atoms: Left O = 2 (from 2NaOH), Right O = x.
H: 2 = 2y → y = 1.
O: 2 = x → x = 2.
So, x = 2, y = 1.
(b) Sodium zincate.
(c) Zinc is amphoteric—reacts with acids and bases.
(d) Burns with a pop sound.
(e) Aluminium.
2NaOH(aq) + Zn(s) → Na₂ZnO₂(aq) + H₂(g)
Question 20.
Plaster of Paris reacts with water:
CaSO₄·½H₂O + xH₂O → CaSO₄·yH₂O
(a) Find x and y.
(b) What is the common name of the product?
(c) Why is it used for fractured bones?
(d) Why must it be stored moisture-proof?
(e) What does “½H₂O” signify chemically?
Show Answer
(a) Left H₂O = 0.5 + x; Right = y.
Standard: y = 2, so x = 1.5 = 3/2, but written as:
CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O.
So x = 3/2, y = 2 → integers: 2CaSO₄·H₂O + 3H₂O → 2CaSO₄·2H₂O.
But per text: x = 1½, y = 2.
Accept x = 3/2, y = 2 or x = 1.5, y = 2.
(b) Gypsum.
(c) It forms a hard solid mass that supports bones.
(d) It reacts with moisture and hardens prematurely.
(e) Two formula units share one water molecule.
CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O
Question 21.
A student is given three test tubes containing distilled water, an acidic solution, and a basic solution. Only red litmus paper is available.
(a) Describe a method to identify all three.
(b) Why does basic solution turn red litmus blue?
(c) What is the effect of dilution on H⁺ ion concentration?
(d) Why is universal indicator better than litmus?
(e) What pH range indicates a strong base?
Show Answer
(a) Add red litmus to each:
– Turns blue → basic
– No change → test this with a drop of known base; if turns blue, it’s water; if still no change, it’s acid (since acid doesn’t change red litmus).
(b) Bases produce OH⁻ ions, which change litmus dye structure.
(c) Decreases H⁺ concentration, increasing pH.
(d) It gives exact pH value, not just acid/base.
(e) pH 12–14.
