Chapter Two · Firstly: Qualitative chemical analysis: practice questions

In the detection of the sulphite anion, what is the observation when a paper wet with potassium dichromate acidified by sulphuric acid is exposed to the evolved gas?

• AThe paper turns black
• BThe paper turns blue
• CThe paper turns green
• DThe paper turns yellow

In the classical scheme of cation analysis, which reagent is used as the group reagent to precipitate the cations of the first analytical group (such as Ag⁺ and Pb²⁺) as insoluble chlorides?

• ASodium hydroxide (NaOH)
• BAmmonium hydroxide (NH₄OH)
• CHydrogen sulphide (H₂S)
• DDilute hydrochloric acid (dilute HCl)

Which reagent is used to confirm the presence of sulphide (S²⁻) ions in a solution?

• APotassium dichromate acidified by sulphuric acid.
• BPotassium permanganate.
• CSilver nitrate solution.
• DStarch paper.

In the brown ring test for the nitrate ion, concentrated sulphuric acid is carefully poured down the side of the tube. The brown ring formed at the junction of the two liquids is due to the formation of:

• Asilver chloride (AgCl)
• Blead(II) sulphide (PbS)
• Cthe brown-ring compound FeSO₄.NO
• Dbarium sulphate (BaSO₄)

Why is the qualitative analysis of a mixture more complex than that of a pure substance?

• ABecause mixtures always require gravimetric analysis before qualitative analysis.
• BBecause mixtures must first be separated into their components before identifying them using suitable indicators.
• CBecause pure substances cannot be identified by physical constants like boiling point.
• DBecause qualitative analysis is not applicable to mixtures containing more than two components.

A solution contains a single anion. It gives no precipitate with barium chloride, a white precipitate with silver nitrate that dissolves in concentrated ammonia, and no gas with dilute acid. The anion is the:

• Asulphide ion
• Bchloride ion
• Csulphate ion
• Dcarbonate ion

Which of the following observations distinguishes a nitrite (NO₂⁻) from a nitrate (NO₃⁻)?

• AOnly the nitrate gives a white precipitate with barium chloride.
• BOn adding dilute hydrochloric acid, only the nitrite evolves a colourless gas that turns reddish-brown at the mouth of the tube.
• COnly the nitrate turns lead(II) acetate paper black.
• DOnly the nitrate decolourises potassium permanganate acidified with conc. sulphuric acid.

Consider the following two reactions involving sodium thiosulphate: (1) reaction with dilute HCl yielding a yellow precipitate, and (2) reaction with iodine solution where the brown colour is removed producing sodium tetrathionate. Which species is specifically responsible for the yellow precipitate in the first reaction?

• ASilver sulphide (Ag₂S)
• BSilver sulphite (Ag₂SO₃)
• CSuspended sulphur (S)
• DNitrogen dioxide (NO₂)

A solution contains a mixture of Fe³⁺ and Al³⁺ ions. Sodium hydroxide solution is added slowly until it is in large excess. Which of the following correctly describes the sequence of observations?

• ANeither hydroxide precipitates because both are amphoteric
• BBoth hydroxides precipitate; the reddish-brown Fe(OH)₃ dissolves in excess, leaving white Al(OH)₃
• CBoth hydroxides precipitate; the white Al(OH)₃ dissolves in excess, leaving a reddish-brown Fe(OH)₃ precipitate
• DOnly Fe(OH)₃ precipitates; the Al³⁺ stays in solution throughout

If you have an unknown solid inorganic salt and you add dilute hydrochloric acid, no gas evolves. Then you test a solution of the salt with silver nitrate solution, and it forms a yellow precipitate that is insoluble in ammonia solution. Which anion is most likely present?

• AIodide (I¯)
• BChloride (Cl¯)
• CBromide (Br¯)
• DSulphite (SO3)2-