TEST OF PRACTICAL KNOWLEDGE QUESTION (a) State what would be observed when: (i) Chlorine is passed through a freshly prepared solution of FeCl\(_2\). (ii) S...
(i) Chlorine is passed through a freshly prepared solution of FeCl\(_2\).
(ii) SO\(_2\) is bubbled into a solution of FeCl\(_3\);
(iii) A few drops of water Is added to sodium hydroxide pellets in a test tube;
(iv) Dilute H\(_2\)SO\(_4\) is added to CaCO\(_{3(s)}\)
(b) Three test tubes contain solutions of SO\(_3^{2-}\), CO\(^{2-}_3\) and SO\(_4^{2-}\) respectively. Describe one chemical method that you would use to identify the solution containing SO\(_4^{2-}\)
(c)(i) Draw and label a diagram to illustrate the separation of a mixture of petrol and water
(ii) Which of the following will dissolve faster? 10g of NaOH pellets in 100 cm\(^3\) of water; 10g of NaOH powder in 50 cm\(^3\) of water. Give the reason for your answer.
(a) Observations
(i) Chlorine passed through freshly prepared FeCl\(_2\) solution: the pale green solution turns yellow-brown. Chlorine (an oxidising agent) oxidises iron(II) ions to iron(III) ions.
(ii) SO\(_2\) bubbled into FeCl\(_3\) solution: the yellow-brown solution turns pale green. Sulphur(IV) oxide (a reducing agent) reduces iron(III) ions to iron(II) ions.
(iii) A few drops of water added to sodium hydroxide pellets: the pellets dissolve and a large amount of heat is evolved (the process is strongly exothermic), so the test tube becomes warm/hot.
(iv) Dilute H\(_2\)SO\(_4\) added to CaCO\(_{3(s)}\): there is effervescence (brisk at first) and a colourless, odourless gas, CO\(_2\), is evolved which turns lime water milky. The reaction soon slows because insoluble calcium tetraoxosulphate(VI) coats the marble.
To each solution add dilute hydrochloric acid, then barium chloride solution. The carbonate and the sulphite react with the acid and give no lasting precipitate (the carbonate effervesces, evolving CO\(_2\); the sulphite evolves SO\(_2\), which has a choking smell). Only the tetraoxosulphate(VI) still gives a white precipitate of barium tetraoxosulphate(VI) that is insoluble in the dilute acid. The solution that gives the acid-insoluble white precipitate is the one containing SO\(_4^{2-}\).
(c)(i) Separation of a mixture of petrol and water
Petrol and water are immiscible liquids that form two distinct layers, so they are separated using a separating funnel. The mixture is poured into the funnel and allowed to settle: the denser water sinks to the bottom and the less dense petrol floats on top. The tap (stopcock) is opened to run the lower water layer into a beaker, then closed the moment the petrol reaches the tap, so that the petrol is left in the funnel.
Separation of immiscible petrol and water using a separating funnel: the lower water layer is run off through the tap, leaving petrol in the funnel.
(c)(ii) The 10 g of NaOH powder in 50 cm\(^3\) of water dissolves faster. The powder is broken into much finer particles than the pellets, so it exposes a far larger surface area to the water; more particles are attacked by the water molecules at the same time, giving a faster rate of dissolution. (The smaller volume of water also brings the particles into contact with the solvent more readily.)
(i) Chlorine passed through freshly prepared FeCl\(_2\) solution: the pale green solution turns yellow-brown. Chlorine (an oxidising agent) oxidises iron(II) ions to iron(III) ions.
(ii) SO\(_2\) bubbled into FeCl\(_3\) solution: the yellow-brown solution turns pale green. Sulphur(IV) oxide (a reducing agent) reduces iron(III) ions to iron(II) ions.
(iii) A few drops of water added to sodium hydroxide pellets: the pellets dissolve and a large amount of heat is evolved (the process is strongly exothermic), so the test tube becomes warm/hot.
(iv) Dilute H\(_2\)SO\(_4\) added to CaCO\(_{3(s)}\): there is effervescence (brisk at first) and a colourless, odourless gas, CO\(_2\), is evolved which turns lime water milky. The reaction soon slows because insoluble calcium tetraoxosulphate(VI) coats the marble.
To each solution add dilute hydrochloric acid, then barium chloride solution. The carbonate and the sulphite react with the acid and give no lasting precipitate (the carbonate effervesces, evolving CO\(_2\); the sulphite evolves SO\(_2\), which has a choking smell). Only the tetraoxosulphate(VI) still gives a white precipitate of barium tetraoxosulphate(VI) that is insoluble in the dilute acid. The solution that gives the acid-insoluble white precipitate is the one containing SO\(_4^{2-}\).
(c)(i) Separation of a mixture of petrol and water
Petrol and water are immiscible liquids that form two distinct layers, so they are separated using a separating funnel. The mixture is poured into the funnel and allowed to settle: the denser water sinks to the bottom and the less dense petrol floats on top. The tap (stopcock) is opened to run the lower water layer into a beaker, then closed the moment the petrol reaches the tap, so that the petrol is left in the funnel.
Separation of immiscible petrol and water using a separating funnel: the lower water layer is run off through the tap, leaving petrol in the funnel.
(c)(ii) The 10 g of NaOH powder in 50 cm\(^3\) of water dissolves faster. The powder is broken into much finer particles than the pellets, so it exposes a far larger surface area to the water; more particles are attacked by the water molecules at the same time, giving a faster rate of dissolution. (The smaller volume of water also brings the particles into contact with the solvent more readily.)
