CIE iGCSE Co-Ordinated Science C8.1 Arrangement of elements Exam Style Questions Paper 3
Question
(a) Potassium is an element in the Periodic Table.
Use numbers from the list to complete the sentences about potassium.
Each number may be used once, more than once, or not at all.
1 2 3 8 19 20 39
(i) Potassium is an element in group … of the Periodic Table.
▶️Answer/Explanation
Potassium is an element in Group 1 of the Periodic Table because it is an alkali metal.
(ii) A potassium atom has a total of … electrons.
▶️Answer/Explanation
A potassium atom has a total of 19 electrons because its atomic number is 19.
(iii) A potassium ion has a positive charge of ….
▶️Answer/Explanation
A potassium ion has a positive charge of 1 because it loses one electron to form K⁺.
(b) Sodium and chlorine react to form sodium chloride.
Fig. 8.1 shows the electronic structure of a sodium atom and a chlorine atom.
(i) Complete the diagrams in Fig. 8.2 to show the electronic structure of the ions in sodium chloride.
▶️Answer/Explanation
Sodium ion (Na⁺): 2,8 (lost one electron)
Chloride ion (Cl⁻): 2,8,8 (gained one electron)
This transfer of electrons forms an ionic bond.
(c) Fig. 8.3 shows the electrolysis of concentrated aqueous sodium chloride.
(i) Complete Fig. 8.3 by labelling the:
- Anode
- Cathode
- Electrolyte
▶️Answer/Explanation
Anode (Positive Electrode): Where oxidation occurs
Cathode (Negative Electrode): Where reduction occurs
Electrolyte: Concentrated aqueous sodium chloride (NaCl solution).
(ii) Hydrogen gas is one of the electrode products of this electrolysis. State the name of the other electrode product.
▶️Answer/Explanation
The other electrode product is chlorine gas (Cl₂), which is released at the anode.
(iii) Describe the chemical test for hydrogen gas. State the observation for a positive result.
▶️Answer/Explanation
Test: Hold a lighted splint near the gas.
Observation: If hydrogen gas is present, it will produce a ‘pop’ sound as it burns.