Science – Acids, Bases and Salts
Very Short Answer Type Questions
Q.1) Why does an aqueous solution of an acid conduct electricity?
Ans) The presence of hydrogen ions (H) or hydronium ions (H₃O) in the aqueous solution of an acid are responsible for conducting electricity.
Q.2) Why does dry HCl gas not change the colour of dry litmus paper?
Ans) The separation of H⁺ ions from HCl molecules cannot occurs in the absence of water. Hence, dry HCI has no hydrogen ions. Therefore, dry HCl gas does not change the colour of dry litmus paper because it has no hydrogen ions (H⁺) in it.
Q.3) How is the concentration of hydronium ions (H₃O⁺) affected when a solution of an acid is diluted?
Ans) When an acid is diluted, the concentration of hydronium ions (H₃O⁺) per unit volume decreases. This means that the strength of the acid decreases. When water is added, the H⁺ ions of acid react with hydroxyl ions (OH⁻) of water to form water molecule. Hence, concentration of (OH/H₃O⁺) in acid decreases on dilution with water.
Q.4) How is the concentration of hydroxide ions (OH⁻) affected when excess base is dissolved in a solution of sodium hydroxide ?
Ans) The concentration of hydroxide ions (OH⁻) would increase when excess base is dissolved in a solution of sodium hydroxide. Water-soluble bases produce OH⁻ ions on dissolving in water. Thus, when NaOH is dissolved in NaOH solution, the concentration of OH⁻ ions increases.
NaOH (s) → H₂O → Na⁺ (aq) + OH⁻ (aq)
Q.5) Do basic solutions also have H⁺ (aq) ions? If yes, then why are these basic?
Ans) Yes, basic solution also has H⁺ ions. However, their concentration is less as compared to the concentration of OH ions that makes the solution basic.
Q.6) Name the substance which on treatment with chlorine, yields bleaching powder.
Ans) Calcium hydroxide [Ca(OH)₂].
Q.7) Name the sodium compound which is used for softening hard water.
Ans) Washing soda (Na₂CO₃.10H₂O).
Q.8) What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.
Ans) When sodium hydrogen carbonate is heated then sodium carbonate and water is formed along with the evolution of carbon dioxide gas.
2NaHCO₃ → Heat → → Na2CO3 + H₂O + CO₂
Q.9) Write an equation to show the reaction between plaster of Paris and water.
Ans) CaSO₄. ½ H₂OHO + 1½ H₂OHO → Heat → CaSO₄.2H₂O
Plaster of Paris + Water → Gypsum
Q.10) When does acid rain occur? Write reasons and its effects
Ans) When pH of rain water is less than 5 6, it is called acid rain. Acid rain is caused by chemical reactions that begins when gases like sulpher dioxide and nitrogen oxide are released into air from factory etc. These gases rise very high into atmosphere, where they combine with moistured oxygen in atmosphere and other substance to form more acidic pollutants, known as acid rain. Commercial activities like factory, air conditioners and other human activities are the main causes of acid rain. Effects – Acid rain is very harmful to agriculture and human beings health etc.
Q.11) Which types of acid find in the following natural source? (i) Lemon, (ii) Ant sting.
Ans) (i). Lemon – In lemon citric acid is found.
(ii). Ant sting – In ant sting, formic acid is found.
Q.12) How can you identify acids and bases? Write any two methods.
Ans) Two common methods to identify acids and bases are using litmus paper and pH indicators.
- Acids will turn blue litmus paper red, while bases will turn red litmus paper blue.
- pH indicator, change colour depending on the solution’s acidity or alkalinity, with acids. Showing a pH less than 7 and bases a pH greater than 7.