Class 10 Acids, Bases and Salts Mock Test (ICSE)

Topics in Acids, Bases and Salts

• Acids and their classification
• Bases and alkalis
• pH scale and indicators
• Preparation of salts
• Normal, acid and basic salts

Acids, Bases and Salts practice questions with answers

1. Q1Multiple choice·1 mark
   8 g of sodium hydroxide (molar mass $40\ \text{g mol}^{-1}$) is completely neutralised by dilute hydrochloric acid. The mass of sodium chloride (molar mass $58.5\ \text{g mol}^{-1}$) formed is

   1. (a)$11.7\ \text{g}$
   2. (b)$5.85\ \text{g}$
   3. (c)$23.4\ \text{g}$
   4. (d)$58.5\ \text{g}$
   Show answer and step marks

   1. Correct option: (a) $11.7\ \text{g}$ (moles of NaOH $= 8/40 = 0.2$ mol; moles of NaCl formed $= 0.2$ mol; mass $= 0.2 \times 58.5 = 11.7\ \text{g}$)+1

   Answer: (a)
2. Q2Multiple choice·1 mark
   Which of the following salts is prepared by the method of direct combination (synthesis)?

   1. (a)Zinc sulphate
   2. (b)Copper(II) sulphate
   3. (c)Iron(III) chloride
   4. (d)Lead(II) chloride
   Show answer and step marks

   1. Correct option: (c) Iron(III) chloride. It is prepared by the direct action of dry chlorine gas on heated iron ($2Fe + 3Cl_2 \rightarrow 2FeCl_3$).+1

   Answer: (c)
3. Q3Multiple choice·1 mark
   An example of a dibasic organic acid is:

   1. (a)Formic acid
   2. (b)Oxalic acid
   3. (c)Citric acid
   4. (d)Acetic acid
   Show answer and step marks

   1. Correct option: (b) Oxalic acid ($H_2C_2O_4$ or $(COOH)_2$). It is an organic acid containing two replaceable hydrogen ions per molecule.+1

   Answer: (b)
4. Q4Multiple choice·1 mark
   Which of the following is an example of an acid salt?

   1. (a)Basic copper chloride
   2. (b)Sodium chloride
   3. (c)Sodium hydrogen sulphate
   4. (d)Sodium acetate
   Show answer and step marks

   1. Correct option: (c) Sodium hydrogen sulphate ($NaHSO_4$). Acid salts are formed by the partial replacement of replaceable hydrogen ions of a polybasic acid by a basic radical.+1

   Answer: (c)
5. Q5Short answer·2 marks
   State two differences between a base and an alkali. Give one example of each.
   Show answer and step marks

   1. First difference, any one of: a base may be insoluble in water (e.g. CuO), whereas an alkali is a base that dissolves in water; an alkali dissolves to give $OH^-$ ions in solution, whereas an insoluble base gives no $OH^-$ ions; an alkali turns moist red litmus blue, whereas an insoluble base has no effect on it; or any other valid difference.+0.5
   2. Second difference, a different one from the same list.+0.5
   3. Example of a base (insoluble in water), any one of: copper(II) oxide ($CuO$); iron(III) hydroxide ($Fe(OH)_3$); zinc oxide ($ZnO$); or any other valid insoluble base.+0.5
   4. Example of an alkali, any one of: sodium hydroxide ($NaOH$); potassium hydroxide ($KOH$); calcium hydroxide ($Ca(OH)_2$); ammonium hydroxide ($NH_4OH$); or any other valid alkali.+0.5

   Answer: Any two of: a base may be insoluble in water while an alkali is a water-soluble base; an alkali gives $OH^-$ ions in solution while an insoluble base does not; an alkali turns red litmus blue while an insoluble base does not. Examples: base $CuO$; alkali $NaOH$.
6. Q6Long answer·4 marks
   (a) What is meant by the term 'pH'? State the pH value of pure water at $25^\circ\text{C}$. [1] (b) State the colour change observed when phenolphthalein indicator is added to an aqueous solution having a pH of $12$. [1] (c) Solutions P, Q, and R have pH values of $3.5$, $7.0$, and $12.0$ respectively. (i) Identify the solution which is the most alkaline. (ii) Which solution would liberate carbon dioxide gas when reacted with sodium carbonate? Give a reason. [2]
   Show answer and step marks

   1. (a) pH is the negative logarithm to the base 10 of the hydrogen ion concentration in moles per litre ($\text{pH} = -\log_{10}[\text{H}^+]$).+0.5
   2. (a) The pH of pure water at $25^\circ\text{C}$ is $7$.+0.5
   3. (b) Phenolphthalein turns from colourless to pink (magenta) in a solution of pH $12$.+1
   4. (c)(i) Solution R (pH $12.0$) is the most alkaline.+1
   5. (c)(ii) Solution P.+0.5
   6. (c)(ii) Reason: P is acidic (pH $3.5$, below $7$), and acids react with metal carbonates such as sodium carbonate to liberate carbon dioxide.+0.5

   Answer: (a) pH is the negative logarithm (base 10) of the hydrogen ion concentration; pure water has pH $7$. (b) Colourless to pink. (c)(i) Solution R. (c)(ii) Solution P, because it is acidic and acids react with carbonates to evolve $\text{CO}_2$.

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