Ans) Curd and other sour substances contain acids. Therefore, when they are kept in brass and copper vessels, the metal reacts with the acid to liberate hydrogen gas and harmful products, thus spoiling the food.

Ans) When HCl or HNO₃ are mixed with water, they dissolve in water to form H⁺ or H₃O⁺ ions, which shows their acidic character. For example—

HCl(aq) → H⁺ + Cl⁻

H⁺ + H₂O → H₃O⁺

When alcohol or glucose are mixed with water, they do not dissolve to form ions. Hence, they do not show acidic character.

Ans) The process of dissolving an acid in water is exothermic, hence it is always recommended that acid should be added to water. If water is added to acid then it is possible that because of large amount of heat generated, the mixture splashes out and causes burns.

Ans) If the concentration of H⁺ (aq.) ions is increased (>10-7) then the solution will become acidic and if the concentration of H⁺ (aq) ions is decreased (<10-7) then the solution will become basic in nature.

Ans) If the soil is acidic and improper for cultivation, then to increase the basicity of soil, the farmer would treat the soil with calcium, hydroxide or quick lime. Caclium hydroxide is basic in nature. Hence, it will be used to neutralise the acidic nature of soil as the reaction of acid and base is Neutralisation reaction.

Ans) Distilled water is pure and does not contain dissolved salts hence, it cannot conduct electricity because it does not contain ions, while rain water conducts electricity as it contains ions due to the presence of dissolved salts in it.

Ans) Acids do not show acidic behaviour in the absence of water because the dissociation of hydrogen ions in an acid takes place only in presence of water.

Ans) The pH of milk is 6. When the milk changes into curd, its pH will reduce because curd is acidic in nature. The acids present in it will decrease the pH. Conversion of milk into curd produces lactic acid, due to which the curd is acidic and pH value of acids is low. Therefore, the pH of curd will reduce.

Ans) The milkman shifts the pH of the fresh milk from 6 to slightly alkaline because in this condition milk does not set as curd easily.

Ans) Since this milk is slightly basic than usual milk, acids produced to set the curd are neutralized by the base. Thus, this milk takes a longer time to set as curd.

Ans) Plaster of Paris should be stored in a moisture-proof container because it absorbs water from moisture and turns into a hard substance (gypsum). The following equation represents it: –

CaSO₄·½H₂O + 1½ H₂O → Heat → CaSO₄·2H₂O

Plaster of Paris + Water → Gypsum

Ans) A reaction in which an acid and a base react together to give salt and water is termed as neutralization reaction, e.g.

(i) NaOH + HCI → NaCl + H₂O

(ii). HNO₃ + KOH → KNO₃ + H₂O

Ans) Uses of washing soda: –

• It is used for removing permanent hardness of water.
• It is used as a cleaning agent for domestic purposes.

Uses of baking soda: –

• It is used in making of baking power.
• It is also used in soda-acid fire extinguishers.

Ans) CaOCl₂ {Bleaching powder}

Ans) CaSO₄.½H₂O {Plaster of Paris}

Ans) Chemical name of bleaching powder – Calcium oxy chloride.

Formula of the bleaching powder – CaOCl₂

Uses of bleaching powder: –

• For bleaching clothes and papers.
• As an insecticide.