兩條關於Acids and Alkalis的簡單化學問題

Tieria

2009-05-02 9:42 pm

Describe what would be observed in each of the following cases.

1. Adding copper (II) oxide to dilute sulphuric acid.

1. A student carries out a series of experiment on a mixture of two substances, A and B, as follows:

Procedure

Observations

Step1

Add water to the mixture.

A is soluble while B is insoluble.

Step2

Add dilute sodium hydroxide solution to a solution of A and heat the mixture.

A pungent smelling gas C evolves. The gas turns moist red litmus paper blue.

Step3

Add silver nitrate solution to a solution of A.

A white precipitate D forms.

Step4

Carry out a flame test on solid B.

B gives a brick red colour flame.

Step5

Add dilute hydrochloric acid to another sample of B.

A gas E evolves. The gas turns limewater milky due to the formation of a precipitate F.

(a) Identify substance A. Explain your answer with appropriate equation(s). (5 marks)

回答 (1)

老爺子

2009-05-03 12:24 am

✔ 最佳答案

1.
The black copper(II) oxide solid dissolves in the dilute sulphuric acid to give a blue solution.

1. (a)
A is ammonium chloride (NH4Cl).

A contains ammonium ion (NH4+ ion). This is because ammonium ion reacts with heated sodium hydroxide solution to give pungent ammonia gas, which turns red litmus paper blue.
NH4+(aq) + OH-(aq) → NH3(g) + H2O(l)
or NH4Cl(aq) + NaOH(aq) → NaCl(aq) + NH3(g) + H2O(l)

A contains chloride ion (Cl- ion). This is because chloride ion reacts with silver ion to give a white precipitate of silver chloride.
Ag+(aq) + Cl-(aq) → AgCl(s)
or AgNO3(aq) + NH4Cl(aq) → AgCl(s) + NH4NO3(aq)

A may also be ammonium carbonate ((NH4)2CO3).
Carbonate ion can also react with silver ion to give a white precipitate (silver carbonate).
2Ag+(aq) + CO32-(aq) → Ag2CO3(s)
2AgNO3 + (NH4)2CO3(aq) → Ag2CO3(s) + 2NH4NO3(aq)
However, if the silver nitrate solution is acidified, no precipitate of Ag2CO3 will be formed.
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