TEST OF PRACTICAL KNOWLEDGE QUESTION Credit will be given for strict adherence to the instructions, for observations precisely recorded, and for accurate in...
Credit will be given for strict adherence to the instructions, for observations precisely recorded, and for accurate inferences. All tests, observations, and inferences must be clearly centered in your answer book, at the time they are made.
C is a mixture of two salts. Carry outline following exercises on C. Record your observations and identify any gas(es) evolved. State the conclusion you draw from the result of each test.
(a) Put C into a beaker and add about \(10\ \text{cm}^3\) of distilled water, stir the mixture, and filter. Test the filtrate with litmus paper. Keep the residue and the filtrate.
(b)(i) To about \(2\ \text{cm}^3\) of the filtrate, add few drops of aqueous \(\mathrm{HNO_3}\) followed by \(\mathrm{AgNO_{3(aq)}}\)
(ii) Add excess \(\mathrm{NH_3}\) solution to the resulting mixture.
(c) To about half of the residue from (a) above, add about \(5\text{cm}^3\) of dilute \(\mathrm{HNO_3}\) in drops. Divide the resulting solution into two equal portions.
(d)(i) To the first portion add ammonia solution in drops and then in excess.
(ii) To the second portion add dilute hydrochloric acid.
Tests on C
C is a mixture of two salts.
Test
Observation
Inference / conclusion
(a) Add distilled water to C, stir and filter. Test the filtrate with litmus paper.
C partly dissolves, giving a colourless filtrate and a white residue. The filtrate has no effect on either red or blue litmus paper.
C contains a soluble salt and an insoluble salt. The soluble salt gives a neutral solution.
(b)(i) To the filtrate add dilute nitric acid, followed by aqueous silver nitrate.
No visible change occurs on adding nitric acid. A white precipitate forms on adding silver nitrate solution.
Chloride ions, \(\mathrm{Cl^-}\), may be present.
(b)(ii) Add excess aqueous ammonia to the mixture in (b)(i).
The white precipitate dissolves in excess ammonia solution to give a colourless solution.
\(\mathrm{Cl^-}\) is confirmed. The precipitate is silver chloride, \(\mathrm{AgCl}\).
(c) Add dilute nitric acid dropwise to the residue.
The white residue dissolves with effervescence. The gas evolved turns limewater milky.
The gas is carbon dioxide, \(\mathrm{CO_2}\). Carbonate ions, \(\mathrm{CO_3^{2-}}\), are present.
(d)(i) To the first portion of the solution from (c), add aqueous ammonia dropwise and then in excess.
A white precipitate forms. It is insoluble in excess ammonia solution.
\(\mathrm{Pb^{2+}}\) may be present.
(d)(ii) To the second portion of the solution from (c), add dilute hydrochloric acid.
A white chalky precipitate is formed.
\(\mathrm{Pb^{2+}}\) is confirmed, due to formation of lead(II) chloride, \(\mathrm{PbCl_2}\).
Gas evolved: Carbon dioxide, \(\mathrm{CO_2}\).
Overall conclusion: C contains a soluble neutral chloride, represented by sodium chloride, \(\mathrm{NaCl}\), and insoluble lead(II) trioxocarbonate(IV), \(\mathrm{PbCO_3}\).
(a) Add distilled water to C, stir and filter. Test the filtrate with litmus paper.
C partly dissolves, giving a colourless filtrate and a white residue. The filtrate has no effect on either red or blue litmus paper.
C contains a soluble salt and an insoluble salt. The soluble salt gives a neutral solution.
(b)(i) To the filtrate add dilute nitric acid, followed by aqueous silver nitrate.
No visible change occurs on adding nitric acid. A white precipitate forms on adding silver nitrate solution.
Chloride ions, \(\mathrm{Cl^-}\), may be present.
(b)(ii) Add excess aqueous ammonia to the mixture in (b)(i).
The white precipitate dissolves in excess ammonia solution to give a colourless solution.
\(\mathrm{Cl^-}\) is confirmed. The precipitate is silver chloride, \(\mathrm{AgCl}\).
(c) Add dilute nitric acid dropwise to the residue.
The white residue dissolves with effervescence. The gas evolved turns limewater milky.
The gas is carbon dioxide, \(\mathrm{CO_2}\). Carbonate ions, \(\mathrm{CO_3^{2-}}\), are present.
(d)(i) To the first portion of the solution from (c), add aqueous ammonia dropwise and then in excess.
A white precipitate forms. It is insoluble in excess ammonia solution.
\(\mathrm{Pb^{2+}}\) may be present.
(d)(ii) To the second portion of the solution from (c), add dilute hydrochloric acid.
A white chalky precipitate is formed.
\(\mathrm{Pb^{2+}}\) is confirmed, due to formation of lead(II) chloride, \(\mathrm{PbCl_2}\).
Gas evolved: Carbon dioxide, \(\mathrm{CO_2}\).
Overall conclusion: C contains a soluble neutral chloride, represented by sodium chloride, \(\mathrm{NaCl}\), and insoluble lead(II) trioxocarbonate(IV), \(\mathrm{PbCO_3}\).
