CIE iGCSE Co-Ordinated Science C9.2 Uses of metals Water Exam Style Questions Paper 3

(a)(i) potassium

Potassium (K) has atomic number 19 with electronic structure 2.8.8.1, placing it in Group I (alkali metals).
From the given list, only potassium belongs to Group I of the Periodic Table.
Sodium is also a Group I element but is not in the list.

(a)(ii) carbon

Diamond is one of the allotropes of carbon, consisting of carbon atoms bonded in a giant covalent lattice.
Each carbon atom forms four covalent bonds in a tetrahedral arrangement, giving diamond its extreme hardness.
This is purely a carbon structure — no other element from the list is found in diamond.

(a)(iii) nitrogen

Clean (dry) air is composed of approximately 78% nitrogen \((\text{N}_2)\), 21% oxygen, and 1% other gases.
Nitrogen is the most abundant gas in the atmosphere by volume.
Oxygen makes up the second largest proportion at approximately 21%.

(a)(iv) potassium

The flame test for potassium produces a characteristic lilac (violet) colour.
Sodium gives yellow, calcium gives brick-red, and copper gives blue-green in flame tests.
Potassium’s lilac flame is often observed through blue cobalt glass to filter out any sodium contamination.

(a)(v) copper

Copper is the most commonly used metal in electroplating due to its excellent electrical conductivity and relatively low cost.
In electroplating, copper ions from a copper anode are deposited onto the cathode object.
The equation for copper electroplating involves \(\text{Cu}^{2+} + 2e^- \rightarrow \text{Cu}\) at the cathode.

(a)(vi) sulfur

Sulfur is a key raw material in the manufacture of sulfuric acid \((\text{H}_2\text{SO}_4)\) via the Contact Process.
In the Contact Process, sulfur is first burned to form sulfur dioxide: \(\text{S} + \text{O}_2 \rightarrow \text{SO}_2\).
This is then oxidised to sulfur trioxide and reacted with water to produce sulfuric acid.

(b) electrons; protons; electrons

Electrons occupy shells (energy levels) around the nucleus and are arranged in the order 2, 8, 8, … from the innermost shell.
Protons are found in the nucleus and carry a positive charge of \(+1\); neutrons are also in the nucleus but are neutral.
Electrons have negligible mass (approximately \(\frac{1}{1836}\) of a proton), making them the particles with the smallest mass.