مراجعة للاختبارات

Question 1

Compound X is an anhydrous white solid. When heated, the white solid releases a colourless vapour which condenses to a colourless liquid. Upon further heating, a colourless gas is produced, leaving a white solid residue. What could be compound X?

Answer 1

Calcium hydrogencarbonate.
Calcium hydrogencarbonate —> calcium oxide + water vapour + carbon dioxide

Question 2

Explain why the mass of calcium oxide formed is less than the original mass of limestone.

Answer 2

Carbon dioxide gas escapes.

Question 3

State the name of the rock which is largely calcium carbonate.

Answer 3

Marble / limestone / chalk

Question 4

How to distinguish magnesium carbonate and magnesium chloride.

Answer 4

Add dilute hydrochloric acid to each substance. Magnesium carbonate give gas bubbles.
Magnesium chloride gives no observable change.

Question 5

Precautions to deal with corrosive chemicals

Answer 5

-Carry out the procedures in the fume cupboard
-Wear protective gloves / laboratory coat / safety goggles when handling corrosive chemicals (especially the concentrated acids)
-Do not heat the glass portion of the nichrome wire
-Do not add water in the acid directly when washing containers of concentrated hydrochloric acid.

Question 6

What is washing soda?

Answer 6

Sodium carbonate

Question 7

Crystallisation (process)

Answer 7

1. Heat the solution to evaporate some of the water. It becomes more concentrated.
2. Heat until the solution becomes saturated. Stop heating.
3. Leave the saturated solution to cool. Crystals start to form in it as the temperature falls.
4. Separate the crystals form the remaining solution by filtration. Wash the crystals into a small amount of cold deionised water. Dry the crystals using filter paper.

Question 8

Why is a second time of fractional distillation needed to separate oxygen and argon?

Answer 8

Their boiling points are very close

Question 9

Suggest why the air coming out of the lime kiln has a greater percentage of carbon dioxide than the air entering the kiln.

Answer 9

Carbon dioxide comes from the decomposition of limestone.

Question 10

Test for carbon dioxide

Answer 10

Pass the gas sample into limewater. It turns from colourless to milky.

Question 11

Explain how the plaster became even harder with age.

Answer 11

Carbon dioxide in the air reacted with slaked lime. Calcium carbonate was formed. The water exported.

Question 12

Test for carbonates

Answer 12

1. Add dilute hydrochloric acid to each solid.
2. Potassium carbonate gives out gas bubbles.
3. Potassium chloride gives no observable change.

Question 13

Distillation of seawater

Answer 13

When sea water is heated, the water vapour which escapes passes through the inner tube of the cone near. This is called by the cold water flowing around it. The water vapour condenses to form liquid water.

Question 14

(Fractional distillation)
Suggest why the air is compressed, cooled and allowed to expand.

Answer 14

To liquefy the air

Question 15

(Fractional distillation)
Suggest why the air is compressed, cooled and allowed to expand.

Answer 15

To liquefy the air

Question 16

Heat flammable liquid

Answer 16

Use a hot water bath, never heat them directly with a flame.

Question 17

Why should we avoid loose clothing in the laboratory?

Answer 17

You would knock things out more easily. Loose clothing is more likely to fall into flames and catches fire.

Question 18

Why should we wash our hands thoroughly after experiments, especially after handling chemicals?

Answer 18

We may accidentally get some toxic chemicals on your hands.

Question 19

Hazard warning labels

Answer 19

Flammable: these chemicals burn easily.
Corrosive: these chemicals can damage living tissue upon contact.
Irritant: these chemicals give you blisters.
Toxic: these chemicals can kill you.
Oxidising: this chemical gives away so that other substances can burn.

Question 20

Why do we need hazard warning Llanelli?

Answer 20

To warn the danger

Question 21

Definition of micro scale experiments

Answer 21

Experiments carried out on a reduced scale using minute quantities of materials

Question 22

Why do water vapour and carbon dioxide are removed before the gases are compressed and cooled?

Answer 22

Because both of them at at solid state and will block the pipe

Question 23

Why does the air have to be filtered before the gases are separated?

Answer 23

To remove dust/gas particles