Lakhmir Singh & Manjit Kaur Test: Acids, Bases & Salts - Class 9 MCQ

Metal oxides react with acid to form salt and water because most of the metal oxides are basic or amphoteric in nature.

- When an acid reacts with a base, a neutralization reaction occurs, producing water and a salt.
- This reaction is exothermic, meaning it releases heat.
- As a result:
- The temperature of the solution increases due to the release of heat.
- Salt formation takes place as the acid and base neutralize each other.
- Hence, both temperature increase and salt formation occur, making option D the correct choice.

It is an example of a double displacement reaction in which an acid (carbon dioxide) reacts with base (calcium hydroxide) to form salt and water.

Ferrous sulphate →FeSO₄⋅7H₂O

Copper sulphate →CuSO₄⋅5H₂O

Magnesium sulphate →MgSO₄⋅7H₂O

Sodium chloride →NaCl

- Neutral Salt: A neutral salt is formed when a strong acid reacts with a strong base, resulting in a salt with no acidic or basic properties in water.

- NaCl (Sodium Chloride):
- Formed from the reaction of hydrochloric acid (HCl), a strong acid, and sodium hydroxide (NaOH), a strong base.
- Does not affect the pH of the solution significantly, making it a neutral salt.

- Others:
- NH₄Cl: Acidic salt from a weak base (NH₃) and a strong acid (HCl).
- CaCl₂: Neutral salt from strong acid (HCl) and strong base (Ca(OH)₂).
- FeCl₃: Acidic salt, weakly acidic nature.

Correct answer: A: NaCl

Metal oxides react with acid to form salt and water because most of the metal oxides are basic or amphoteric in nature.

All carbonates react with acids to produce salt, water and carbon dioxide gas. H2SO4 + CuCO₃ —> CuSO₄ + H₂O + CO₂

pH above 7 confirms the compound to be alkaline in nature so it can be either sodium carbonate or sodium hydroxide as HCl and CH₃COOH are acidic in nature. Sodium hydroxide is a strong base, so it has the highest pH of about 14 while sodium carbonate is a weak base so it can have pH 9.

Groups IIA, IIIA, and IVA metals are less reactive than the neighbouring alkali metals. Thus Al and Zn are less reactive metals than Na, K and Mg.

- Water is a very weak acid.

- Acetic acid is a weak acid. It partially dissociates in water, releasing some protons.

- Hydrochloric acid (HCl) is a strong acid. It completely dissociates in water, releasing all its protons.

- The increasing order of acidic strength is based on their ability to donate protons:

- Water < Acetic acid < Hydrochloric acid

Thus, option A is correct.

 Reason: Zn + 2NaOH → Ma₂Zn0₂ (Sodium Zincate) + H₂

Calcium hydroxide reacts with carbon dioxide to form calcium carbonate.

Aqueous calcium hydroxide reacts with carbon dioxide to form a white precipitate, calcium carbonate, and water.

Ca(OH)₂(s) + CO₂(g) → CaCO₃(s) + H₂O(g)

NaCl is a neutral salt formed by the reaction between strong acid HCl and strong base NaOH.

Calcium hydroxide reacts with carbon dioxide to form calcium carbonate.

Aqueous calcium hydroxide reacts with carbon dioxide to form a white precipitate, calcium carbonate, and water.

Ca(OH)₂(s) + CO₂(g) → CaCO₃(s) + H₂O(g)

Answer: b) Release of hydrogen gas

When an acid reacts with a metal, the metal displaces hydrogen ions from the acid.
- This reaction results in the formation of a salt and the release of hydrogen gas.
- For example, when hydrochloric acid (HCl) reacts with zinc (Zn), zinc chloride (ZnCl₂) and hydrogen gas (H₂) are produced.
- Hence, the correct answer is B: Release of hydrogen gas.