All your burette readings… | Chemistry

Question 1 Report

All your burette readings (initials and final) as well as the size of your pipette must be recorded but no account of experimental procedure is required. All calculations must be done in your answer booklet.

C is a mixture of two inorganic compounds. Carry out the following exercises on C. Record your observations and identify any gas(es) evolved. State the conclusions you draw from the result of each test.

(a) Put all of C in a boiling tube and add about \(10\ \text{cm}^3\) of distilled water. Shake thoroughly and filter. Keep both the residue and the filtrate.

(b)(i) To about \(2\ \text{cm}^3\) of the filtrate add a few drops of Silver trioxoitrate (V) followed by dilute \(\text{HNO}_3\)

(ii) Add excess \(\text{NH}_3\) solution to the resulting mixture in (b)(i).

(C)(i) Put the residue in a test tube, add about \(2\ \text{cm}^3\) of dilute HCl and shake.

(ii) Add \(\text{NH}_3\) Solution in drops to the mixture from (c)(i) and then in excess.

Answer

Analysis of Mixture C

Sketch of the separation and confirmatory tests

Separation of C into residue and filtrate, followed by the stated confirmatory tests.

Test	Observation	Inference / conclusion
(a) C was shaken with distilled water and filtered.	C dissolved partially, leaving a green residue and a colourless filtrate.	C contains a water-soluble salt and an insoluble green salt. The green residue may contain a copper(II) compound.
(b)(i) To 2 cm³ of the filtrate, silver trioxonitrate(V) solution was added, followed by dilute HNO₃.	A white precipitate formed and remained undissolved on adding dilute HNO₃.	Chloride ions, Cl⁻, are present. The white precipitate is silver chloride, AgCl.
(b)(ii) Excess aqueous ammonia was added to the mixture from (b)(i).	The white precipitate dissolved to give a colourless solution.	Cl⁻ is confirmed.
(c)(i) The residue was treated with dilute HCl.	The green residue dissolved with effervescence to give a blue solution. A colourless, odourless gas evolved and turned limewater milky.	Cu²⁺ ions are present. The gas is carbon dioxide, CO₂, showing the presence of CO₃²⁻ ions.
(c)(ii) A portion of the mixture from (c)(i) was treated with aqueous NH₃, first dropwise and then in excess.	A pale blue precipitate formed with a few drops of ammonia and dissolved in excess ammonia to give a deep blue solution.	Cu²⁺ ions are confirmed.

Equations

\(\mathrm{Ag^+(aq)+Cl^-(aq)\rightarrow AgCl(s)}\)

\(\mathrm{CuCO_3(s)+2HCl(aq)\rightarrow CuCl_2(aq)+H_2O(l)+CO_2(g)}\)

Final conclusion: C is a mixture containing a soluble chloride and insoluble copper(II) trioxocarbonate(IV), \(\mathrm{CuCO_3}\).

Read lesson note on Metals And Their Compounds (JAMB)

Read lesson note on Acids, Bases And Salts (JAMB)

Answer Details

Analysis of Mixture C

Sketch of the separation and confirmatory tests

Test	Observation	Inference / conclusion
(a) C was shaken with distilled water and filtered.	C dissolved partially, leaving a green residue and a colourless filtrate.	C contains a water-soluble salt and an insoluble green salt. The green residue may contain a copper(II) compound.
(b)(i) To 2 cm³ of the filtrate, silver trioxonitrate(V) solution was added, followed by dilute HNO₃.	A white precipitate formed and remained undissolved on adding dilute HNO₃.	Chloride ions, Cl⁻, are present. The white precipitate is silver chloride, AgCl.
(b)(ii) Excess aqueous ammonia was added to the mixture from (b)(i).	The white precipitate dissolved to give a colourless solution.	Cl⁻ is confirmed.
(c)(i) The residue was treated with dilute HCl.	The green residue dissolved with effervescence to give a blue solution. A colourless, odourless gas evolved and turned limewater milky.	Cu²⁺ ions are present. The gas is carbon dioxide, CO₂, showing the presence of CO₃²⁻ ions.
(c)(ii) A portion of the mixture from (c)(i) was treated with aqueous NH₃, first dropwise and then in excess.	A pale blue precipitate formed with a few drops of ammonia and dissolved in excess ammonia to give a deep blue solution.	Cu²⁺ ions are confirmed.