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.
F is 2 mixture of two inorganic salts. Carry out the following exercises on F. Record your observations and identify any gas(es) evolved. State the conclusions you draw from the result of each test.
(a) Put all of F in a beaker and add about 10 cm\(^3\) of distilled water. Stir well and filter. Keep the filtrate and the residue.
(b)(i) To about 2cm\(^3\) of the filtrate. add NaOH\(_{(aq)}\) in drops and then in excess.
(ii) To another 2cm\(^3\) portion of the solution, add a few drops of NH3\(_{(aq)}\) in drops and then in excess.
(c) To about 2cm\(^3\) of the solution, add a few drops of HNO\(_{3(aq)}\) followed by few drops of the drops of AgNO\(_{3(aq)}\)
(d)(i) Put all the residue into a clean test-tube and add HNO\(_{3(aq)}\)
(ii) To a portion of the solution from (d)(i)) add NaOH\(_{(aq)}\) in drops and then in excess.
Explanation
| TEST | OBSERVATION | INTERFERENCE | |
| (a) |
F + distil water + stir + filter |
Effervescence (bubbling) occurs. Colourless and odourless gas evolved after filtration pale blue/colourless filtrate and green residue | |
| (b)(i) |
Filtrate + NaOH\(_{(aq)}\) in drops Then in excess |
White precipitate formed Precipitate insoluble in excess NaOH\(_{(aq)}\) |
Ca\(^{2+}\)/pb\(^{2+}\) Ca\(^{2+}\) present |
| (b)(ii) |
Filtrate + NH\(_3\) \(_{(aq)}\) in drops Then in excess |
No visible reaction No visible reaction |
Ca\(^{2+}\) present Ca\(^{2+}\) confirmed |
| (b)(i) |
Filtrate + NaOH\(_{(aq)}\) in drops Then in excess |
Blue gelatinous precipitate formed Precipitate insoluble in excess |
Cu\(^{2+}\) is present |
| (b)(ii) |
Filtrate + NH\(_3\) \(_{(aq)}\) in drops Then in excess |
Pale (light) blue gelatinous precipitate formed Precipitate dissolves to form a deep blue solution
|
Cu\(^{2+}\) Cu\(^{2+}\) confirmed |
| (c) |
Filtrate + NHO\(_3\) \(_{(aq)}\) + AgNO\(_3\)\(_{(aq)}\) |
No visible reaction No gas involved White precipitate formed |
Cl\(^{-}\) present |
| (d)(i) | Residue + HNO\(_{3(aq)}\) | Effervescence occurs, colourless and odourless gas evolves that turn blue litmus paper to red and turns lime water milky |
CO\(_{3(g)}\) CO\(_{3^{2-}}\) present |
| (d)(ii) |
Solution from (d)(i) + NaOH\(_{(aq)}\) in drops Then in excess |
Blue precipitate formed present Precipitate insoluble in excess NaOH\(_{(aq)}\) |
Cu\(^{2+}\) Cu\(^{2+}\) present |