(a) List three pieces of apparatus required for the evaporation of sodium chloride solution to dryness. (b)(i) List two normal salts which when dissolved in...
Question 1 Report
(a) List three pieces of apparatus required for the evaporation of sodium chloride solution to dryness.
(b)(i) List two normal salts which when dissolved in water turn red litmus blue.
(ii) State the phenomenon that is responsible for the action on the litmus in (b)(i).
(c) State what would be observed on adding BaCl\(_2\) solution to a portion of a saturated Na\(_2\)CO\(_3\), followed by dilute HCI in excess.
(i) A gas Q decolourized acidified KMnO\(_4\) solution. Suggest what Q could be.
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 \(KMnO_4\).)
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