TEST OF PRACTICAL KNOWLEDGE QUESTION (a) List three pieces of apparatus required for the evaporation of sodium chloride solution to dryness. (b)(i) List two...

Answer Details

(a) Three pieces of apparatus for evaporating sodium chloride solution to dryness

Evaporating dish (basin), tripod stand and Bunsen burner. (Wire gauze and a glass stirring rod are also acceptable.)

(b)(i) Two normal salts that turn red litmus blue

Sodium trioxocarbonate(IV), \(Na_2CO_3\), and potassium trioxocarbonate(IV), \(K_2CO_3\). (Sodium ethanoate, \(CH_3COONa\), is also acceptable.) Their aqueous solutions are alkaline.

(b)(ii) Phenomenon responsible

Salt hydrolysis (specifically anionic hydrolysis): being salts of a strong base and a weak acid, they hydrolyze in water to give an alkaline solution.

(c) Adding BaCl2 to saturated Na2CO3, then excess dilute HCl

On adding barium chloride solution, a white precipitate of barium trioxocarbonate(IV) forms:

\[BaCl_{2(aq)} + Na_2CO_{3(aq)} \to BaCO_{3(s)} + 2NaCl_{(aq)}\]

On then adding dilute hydrochloric acid in excess, the white precipitate dissolves with effervescence, giving off a colourless gas (carbon(IV) oxide) that turns limewater milky:

\[BaCO_{3(s)} + 2HCl_{(aq)} \to BaCl_{2(aq)} + H_2O_{(l)} + CO_{2(g)}\]

(i) Gas Q that decolourizes acidified KMnO4

Q is a reducing gas; it could be sulphur(IV) oxide (sulphur dioxide, \(SO_2\)). (Hydrogen sulphide, \(H_2S\), or an unsaturated gas such as ethene would also decolourize acidified \(KMnO_4\).)