3 Questions about Chemistry (The best will get 20 marks)

Question

1. For each of the following pairs of solid samples, suggest a test to distinguish between them. State your expected observations in each case.
(a) Sodium chloride and sodium sulphate
(b) Calcium carbonate and calcium hydrogencarbonate
(c) Potassium carbonate and sodium carbonate.

Please answer in English, thanks!!!

Answer 1

1a put them into silver nitrate solution with excess dilute nitric acid. The one has white would be sodium chloride
1b put them into calcium hydroxide solution the one which gives out carbon dioxide would be calcium carbonate
1c put them on a nichrome / platinum wire . Put the wire to the Bunsen flame
The one with golden yellow flame would be sodium carbonate
The one with lilac(purple) flame would be potassium carbonate

Answer 2

Answer 1b is absolutely wrong.
CaCO3 is insoluble in water, while Ca(HCO3)2 soluble. Both of them do not react with Ca(OH)2.
He/she gave a worse answer, but titled the best answer. 原因是 .... ?

Answer 3

(a)Dissove two samples into water. Add acidifried silver nitrate sloution and then excess nitric acid on each.White ppt from on sodium chloride solution.
NaCl + AgNO3 --> AgCl(s) + NaNO3

(b) Add water in each sample.CaHCO3 dissolved but CaC03 have not dissoolved.

(C)Dissolved tw osamples into water.To have a flame test.The potassium carbonate solution burns with lilac flame while sodium carbonate solution burn with golden yellow flame.

Answer 4

(a)
Dissolve each compound in distilled water to form solution. Add separately each solution into a test tube of silver nitrate solution which is acidified with dilute nitric acid.
Sodium chloride : A white precipitate of silver chloride is formed.
... Ag^+(aq) + Cl^-(aq) → AgCl(s)
Sodium sulphate : There is no observable change.

(b)
Add separately each solid to distilled water, and shake for a few minutes.
Calcium carbonate : It is insoluble in water. If the mixture is filtered, the filtrate does not react with dilute hydrochloricacid.
Calcium hydrogencarbonate : It is soluble in water. If the mixture is filtered, the filtrate reacts with dilute hydrochloric acid, bubbles of carbon dioxide are given off.
... HCO3^-(aq) + H^+(aq) → H2O(l) + CO2(g)
(Note that both calcium carbonate and calcium hdyrocarbon do not react with calcium hydroxide solution.)

(c)
Perform flame test for these two solid samples.
Potassium carbonate : It shows a lilac flame (crimson flame when viewed under cobalt glass.)
Sodium carbonate : It shows a bright yellow flame.