A teacher shows convection in a liquid using a glass tube, as in Fig. 1.1.
The tube is filled with water and left undisturbed for ten minutes. A purple crystal is then put into the mouth of the tube. This crystal dissolves and makes the water around it turn purple. The tube is then heated gently, as shown in Fig. 1.1.
(a)[1]
Suggest why the water is allowed to stand for ten minutes before the crystal is placed in the tube.
(b)[1]
When the water is heated, it is only heated gently. Suggest why.
(c)[1]
On Fig. 1.1, add an arrow to indicate the direction in which the purple colour travels through the water.
(d)[1]
State one safety precaution the teacher should use for this demonstration.
Worked solution & mark scheme
This 4-mark question has a full step-by-step worked solution and mark scheme. One marking point: “If the water is moving or disturbed, the colour would spread.” …