Chapter 2 – Acids, Bases and Salts

1) What will occur when washing soda crystals get disclosed to air?

Ans – When washing soda crystals [sodium carbonate decahydrate (Na₂CO₃·10H₂O)] are uncovered to the outer air, they undergo a chemical reaction denoted as efflorescence.

The below chemical equation can depict this transition:

The loss of water will turn the crystals into white & powdery features creating an anhydrous sodium carbonate due to the impact of efflorescence.

2) What do you mean by efflorescence? Justify that.

Ans – Efflorescence is often depicted as the loss of water components during the crystallization of a hydrated salt upon revealing it to air, ending in a powdery residue over the surface.

It occurs when the hydrated salt has higher vapor pressure than the partial pressure of water vapor in the external air, causing the water molecules to evaporate from the crystal structure.

For instance, imagine you left a damp cloth with washing soda in the air. As time passes, you may witness a white, powdery layer formed on the cloth surface. This powder known as the anhydrous sodium carbonate is created from the washing soda’s efflorescence.

3) What’s the reason for having sodium hydrogen carbonate as their key component in antacids?

Ans – Antacids usually have sodium hydrogen carbonate (called sodium bicarbonate, NaHCO₃) as a key component due to its basic nature. Along with hydrochloric acid (HCl), this combines with your stomach to nullify additional acid. The below equation represents the neutralization reaction:

4) While an acid reacts with any metal, what’s the name of the gas that gets liberated? Give an example. How can you test the liberated gas to confirm its presence?

Ans – Hydrogen gas (H₂) is typically liberated when a metal and acid react. This reaction is a characteristic of most metals reacting with acids, producing hydrogen gas and salt.

For example,

Zn + Cl₂ → ZnCl₂ + H₂

Check out the above equation, where zinc combines with hydrochloric acid to create zinc chloride & hydrogen gas.

We can perform the “pop test” to confirm the inclusion of hydrogen gas.  We just have to bring a lit splint or match near the mouth of the container where the gas is collected. If hydrogen gas is present, it will ignite with a distinctive ‘pop’ sound.

5) Compound X upon electrolysis in an aqueous solution forms a strong base Y while liberating gases A and B. B is used to produce bleaching powder. Write the chemical equations identifying X, Y, A, and B.

Ans – The chemical equations can be written as:

2NaCl (aq) + 2H₂O → 2NaOH (aq) + Cl₂ (g) + H₂ (g)

Here,
X → NaCl
Y → NaOH
A → H₂
B → Cl₂

6) Record your observations when –

a. We test a solution of sodium sulfate with red litmus

Ans – There will be no change in color since the solution of water and Na₂SO₄ is almost neutral.

b. Dil HCL is introduced to Methyl orange.

Ans – Methyl orange will change into a reddish color.

c. Ferric chloride solution is tested with blue litmus.

Ans – FeCl₃ solution will produce HCL and Ferric hydroxide when added to water. This acid will make the solution acidic, thereby turning blue litmus red.

7) A sodium compound X is used in the kitchen typically to make crispy pakoras. Also, it can cure stomach acidity. What is X? Write its chemical formula. Also, state the chemical reaction taking place when it is cooked.

Ans – Here, compound X is baking powder, also known as baking soda, chemically called sodium hydrogen carbonate. (NaHCO₃).

When cooked or heated, the following reaction takes place –

8) Metallic compound A when reacts with dilute HCL forms effervescence. The evolved gas can extinguish a candle. Write the balanced chemical reaction for it, if one of the resultant compounds can be denoted as calcium chloride.

Ans – Since one of the products is calcium chloride, it’s obvious that metallic compound A is a calcium salt. Also, it extinguishes a burning candle when added to dilute HCL, indicating the formation of carbon dioxide. Hence, the end products are calcium chloride and carbon oxide.

Thus, compound A is calcium carbonate. Here’s the balanced chemical equation for it –

CaCO₃ + HCl → CaCl₂ + CO₂ + H₂O

9) Compound A upon heating at 370K produces B used to plaster fractured bones. Upon mixing B with water, it changes back to A. What are A and B? Answer along with the balanced chemical reaction. 

Ans – The reaction can be written as:

10) Write in words & balanced equations for the below chemical reactions:

a. Dilute sulphuric acid combined with zinc granules

Ans: Zinc+ Sulphuric acid → Zinc sulphate + Hydrogen

Zn + H₂SO₄ → ZnSO₄ + H₂

b. Magnesium ribbon added to dilute hydrochloric acid

Ans: Magnesium + Sulphuric acid → Magnesium chloride + Hydrogen gas

Mg+ 2HCI → MgCl₂ + H₂

c. Dilute sulphuric acid with aluminium powder

Ans: Aluminum + Sulphuric acid → Aluminum sulphate + Hydrogen gas

2AI + 3H₂SO₄ → AI₂(SO₄)₃ + 3H₂

d. Dilute hydrochloric acid merged into iron fillings

Ans: Iron + Hydrochloric acid → Iron chloride + Hydrogen

Fe + 2HCI → FeCl₂ + H₂