4 This question is about Group 1 elements.
4-1 Give two observations you could make when a small piece of potassium is added to water. [2 marks]
ANSWER
The potassium react with water, releasing hydrogen gas and forming a solution containing a metal hydroxide;
metal + water → metal hydroxide + hydrogen;
e.g. 2K + 2H2O → 2NaOH + H2.
The solution of the metal hydroxide that is formed is alkaline.
Potassium burns with lilac flame.
4-2 Complete the equation for the reaction of potassium with water.
You should balance the equation.
K + H2O → +
[2 marks]
ANSWER
2K + 2H2O → 2KOH + H2
4-3 Explain why the reactivity of elements changes going down Group 1.
[4 marks]
ANSWER
Reactivity of Group 1 increases going down the group because the outer electron / shell is further from the nucleus so there is less force of attraction between the nucleus and the valence electron so the atom loses an electron more easily.
4-4 Sodium reacts with oxygen to form sodium oxide which is an ionic compound.
Oxygen is a Group 6 element.
Draw a dot and cross diagram to show what happens when atoms of sodium and oxygen react to produce sodium oxide.
[4 marks]
Diagram
ANSWER
4-5 Why is oxygen described as being reduced in the reaction between sodium and oxygen? [1 mark]
ANSWER
Oxygen is being reduced because oxygen gains electron.
4-6 Explain why sodium oxide has a high melting point. [3 marks]
ANSWER
Sodium oxide is a giant structure of ionic compound with strong electrostatic forces of attraction between oppositely charged ions so large amounts of energy is required to break the bonds.
