Fig. 1.1 shows part of the Periodic Table.
(a) Answer the following questions using only the elements in Fig. 1.1. Each symbol of the element may be used once, more than once or not at all. Give the symbol of the element that:
(i) is in brass
(ii) produces an orange-red colour in a flame test
(iii) is a reactant in a fuel cell
(iv) has an atom with only three occupied electron shells
(v) forms an ion that gives a red-brown precipitate on addition of aqueous ammonia
(vi) forms an ion with a charge of 1-.
(b) Explain why Li, K and Rb have similar chemical properties.
▶️ Answer/Explanation
(a)
(i) Zn – Brass is an alloy of copper and zinc.
(ii) Ca – Calcium produces an orange-red flame color in flame tests.
(iii) H – Hydrogen is a reactant in fuel cells, combining with oxygen to produce electricity.
(iv) Al – Aluminum has electrons in three shells (2,8,3).
(v) Fe – Iron(III) ions form a red-brown precipitate with aqueous ammonia.
(vi) I – Iodine forms I⁻ ions with a 1- charge.
(b) Li, K and Rb have similar chemical properties because they are all in Group I (alkali metals) of the periodic table. This means they have the same number of electrons in their outer shell (1 electron each). Elements in the same group have similar chemical properties because chemical reactions primarily involve the outer shell electrons, and when these are the same, the elements behave similarly in chemical reactions.
Detailed Explanation:
1. For part (a), we need to identify elements based on their specific properties:
- Brass contains zinc (Zn) along with copper
- Calcium (Ca) gives characteristic orange-red color in flame tests
- Hydrogen (H) is used in fuel cells
- Aluminum (Al) has three electron shells occupied (n=1,2,3)
- Iron (Fe) forms Fe³⁺ which gives red-brown precipitate with NH₃
- Iodine (I) forms I⁻ ions commonly
2. For part (b), the key points are:
- Group I elements have identical outer electron configuration (ns¹)
- This similar electron configuration leads to similar chemical behavior
- All readily lose one electron to form +1 ions
- All react vigorously with water to form alkaline solutions
The periodic trend explains why elements in the same group behave similarly despite having different numbers of electron shells.
The table shows some properties of four Group I elements.
(a)(i) Complete the table by estimating:
- the boiling point of sodium
- the relative hardness of lithium. [2]
(ii) Predict the physical state of lithium at 200°C.
Give a reason for your answer. [2]
(b) Potassium reacts with water.
2K + 2H2O → 2KOH + H2
Describe two observations when potassium reacts with water.[2]
1
2
(c) Lithium is extracted by the electrolysis of molten lithium chloride.
(i) Name a non-metal used to make the electrodes.[1]
(ii) Give one property, other than the conduction of electricity, that makes this substance suitable for use as an electrode.[1]
(iii) State the products of the electrolysis of molten lithium chloride at:[2]
the negative electrode (cathode)
the positive electrode (anode)
(d) Lithium chloride conducts electricity when molten and when in aqueous solution.
Give two other physical properties of lithium chloride that show it is an ionic compound.[2]
▶️ Answer/Explanation
(a)(i) Ans:
- Boiling point of sodium: 900-1200°C (trend shows increase down Group I)
- Hardness of lithium: 0.8-1.2 MPa (harder than Na but softer than K)
(a)(ii) Ans: Liquid
Lithium melts at 180°C and boils at 1342°C. At 200°C (between these points), it exists as a liquid.
(b) Ans: Two observations
1. Violent fizzing (hydrogen gas evolution)
2. Lilac flame (exothermic reaction ignites hydrogen)
(c)(i) Ans: Graphite
Graphite is commonly used as it conducts electricity and is inert.
(c)(ii) Ans: High melting point
Graphite remains solid at high temperatures (melts at ~3600°C).
(c)(iii) Ans:
Cathode: Lithium metal (Li+ + e– → Li)
Anode: Chlorine gas (2Cl– → Cl2 + 2e–)
(d) Ans: Ionic properties
1. High melting point (605°C) due to strong ionic bonds
2. Soluble in polar solvents (e.g., water) but insoluble in organic solvents