CHEMISTRY

The following examples are very similar in style to the questions expected in Question 4. Example 8: Q: Natural gas is used as a fuel in many Irish homes. Name the hydrocarbon compound that is the main component of natural gas. A: Methane (CH4)

Q: When natural gas is burned completely, carbon dioxide and one other compound are formed. Name the other compound. A: Water (H2O) Example 9:

Q: Hard water causes a build up of limescale on heating elements, as in the picture below. What is hard water? A: Water that doesn’t easily form lather with soap. Q: State one method of removing hardness from water. A: Any of the following:

• Boiling

• Distilling

• Ion-exchange

• Deioniser

• Sodium carbonate (washing soda) Example 10:

Q: Ernest Rutherford (1871-1937) suggested the existence of the atomic nucleus in 1911. Give two properties of the atomic nucleus. A: Any 2 of the following:

• Centre of the atom.

• Contains most of the mass.

• Very small.

• Positive charge.

• Contains protons.

• Contains neutrons. Example 11: Q: Name each of the metallic elements with the chemical symbols below.

• Au: Gold

• Cu: Copper

• Fe: Iron

The following examples are very similar in style to the questions expected in Question 5.

Example 12: Q: A Science student investigated the solubility of two common substances, sugar and salt, in water for a range of temperatures. The data for the sugar are given in the table. Salt maintained a constant solubility of 40g/100g of water for the temperature range investigated, O°C to 100°C. Draw a graph of the effect of temperature on the solubility of sugar in the grid below.

A:

Q: Use the graph to estimate the increase in the solubility of sugar if the temperature of the solution is raised from 50°C to 70°C. A: See graph

50°C = 260 g/100 g of water 70°C = 320 g/100 g of water.

Q: Using the same grid, draw a graph of the effect of temperature on the solubility of salt. A: See graph Example 13:

The diagram below shows the arrangement of the appartus used for the preparation of oxygen gas in the laboratory.

Q: Name the solution labelled A.

A: Hydrogen peroxide. Q: Describe the apperance of the solution A. A: Colourless. Q: The manganese dioxide speeds up the rate of this reaction but is not used up at the end of the experiment. What name is given to a substance which acts this way.

A: Catalyst.

Q: A test tube of oxygen was collected. Two pieces of damp litmus paper (one red and one blue) were the placed into this test tube. Niether changed colour. What conclusion can be made from this observation?

A: Substance is neutral (pH = 7).

The following examples are very similar in style to the questions expected in Question 6.

Example 14: Q: Oxygen-16 and oxygen-17 are two isotopes of the element oxygen. What is meant by the term isotopes?

A: Atoms of the same element with the same atomic number and the same number of protons but with a different mass number and number of neutrons.

Q: How many protons are in an atom of oxygen- 17?

A:8.

Q: Oxygen gas consists of molecules of oxygen. Each molecule contains two oxygen atoms. In the space below, draw a diagram of a molecule of oxygen, clearly showing the locations of all the electrons. A: 2 electrons on the first energy level, 6 electrons on the outer energy level, must show overlapping of outer orbitals with four electrons being shared, two from each atom.