This question is about metals.
(a) State three general physical properties common to most metals.[3]
(b) Metals are often used in the form of alloys.
(i) State the meaning of the term alloy.[1]
(ii) Explain in terms of their properties why alloys are used instead of pure metals.[1]
(iii) Stainless steel is an alloy.
Give one use of stainless steel.[1]
(c) Place these metals in order of their reactivity with oxygen.
copper
magnesium
potassium
zinc
Put the least reactive metal first.[2]
(d) When 4.8g of magnesium reacts with excess oxygen, 8.0g of magnesium oxide is formed.
Calculate the minimum mass of magnesium needed to produce 24.0g of magnesium oxide.
minimum mass = g [1] [Total: 9]
▶️ Answer/Explanation
(a) Ans: Any three of:
- Good conductors of electricity and heat
- Malleable (can be hammered into sheets)
- Ductile (can be drawn into wires)
- Lustrous/shiny surface
- High melting and boiling points
(b)(i) Ans: A mixture of a metal with one or more other elements
Alloys are created by combining metals with other elements to enhance properties.
(b)(ii) Ans: Alloys are harder/more resistant to corrosion than pure metals
The added elements disrupt the regular metal lattice, making it more durable.
(b)(iii) Ans: Cutlery/chemical plant equipment/surgical instruments
Stainless steel’s corrosion resistance makes it ideal for these applications.
(c) Ans: copper, zinc, magnesium, potassium
This follows the reactivity series: K (most reactive) > Mg > Zn > Cu (least reactive).
(d) Ans: 14.4 g
Using the given ratio (4.8g Mg → 8.0g MgO), we establish the proportion: (4.8/8.0) × 24.0 = 14.4g.
Alternatively, using molar masses: 2Mg + O₂ → 2MgO shows 48g Mg produces 80g MgO, so scaling up gives 14.4g.
The table shows some properties of four halogens.
(a) (i) Complete the table by predicting:
● the boiling point of chlorine
● the density of fluorine at its melting point.
(ii) Describe the trend in the melting points of the halogens down the group.
(iii) Deduce the physical state of iodine at 130°C.
Explain your answer.
(b) (i) Give the electronic structure of a fluorine atom.
(ii) Explain why a fluoride ion has a single negative charge.
(c) Magnesium reacts with excess fluorine to produce magnesium fluoride.
When 2.40g of magnesium is reacted, 6.20g of magnesium fluoride is produced. Calculate the mass of magnesium needed to produce 1.24g of magnesium fluoride.
mass of magnesium = ………………………… g
▶️ Answer/Explanation
(a)(i) Ans: Boiling point of chlorine: between –100°C and 10°C (e.g., –34°C).
Density of fluorine: between 0.20 g/cm³ and 1.55 g/cm³ (e.g., 1.50 g/cm³).
(a)(ii) Ans: The melting points increase down the group due to stronger London dispersion forces as the size of the molecules increases.
(a)(iii) Ans: Iodine is a liquid at 130°C because 130°C lies between its melting point (114°C) and boiling point (184°C).
(b)(i) Ans: The electronic structure of a fluorine atom is 2.7.
(b)(ii) Ans: A fluoride ion (F⁻) has a single negative charge because it gains one electron, resulting in 10 electrons (while retaining 9 protons).
(c) Ans: 0.48 g
Calculation:
Given:
2.40 g Mg → 6.20 g MgF₂
We need the mass of Mg for 1.24 g MgF₂.
Using proportion: \(\frac{2.40}{6.20} = \frac{x}{1.24}\)
\(x = \frac{2.40 \times 1.24}{6.20} = 0.48 \text{ g}\).