7 This question is about silicon and compounds of silicon.
The reactivity series sometimes includes non-metals such as carbon, hydrogen and silicon.
Silicon can be extracted by reducing silicon dioxide with different substances.
The equation for one possible reaction is:
2 C(s) + SiO2(s) → Si(s) + 2CO(g)
7-1 Explain what this reaction shows about the position of silicon in the reactivity series.
[2 marks]
ANSWER
Silicon is less reactive than carbon because carbon displaces silicon from silicon dioxide.
7-2 Aluminium also reduces silicon dioxide.
Carbon is used rather than aluminium to reduce silicon dioxide because carbon is cheaper than aluminium.
Carbon can be obtained by heating coal. Aluminium is obtained from aluminium oxide.
Explain why aluminium is more expensive than carbon.
[2 marks]
ANSWER
More energy is needed to obtain aluminium because) aluminium is obtained from aluminium oxide by electrolysis.
Magnesium also reduces silicon dioxide
The equation for the reaction is:
2 Mg(s) + SiO2(s) → Si(s) + 2 MgO(s)
7-3 Give one reason why the products are difficult to separate if magnesium is used to reduce silicon dioxide
[1 mark]
ANSWER
Both products are solid in state.
7-4 Calculate the minimum mass in grams of magnesium needed to completely reduce 1.2 kg of silicon dioxide.
Relative atomic masses (Ar): O = 16 Mg = 24 Si = 28
[5 marks]
ANSWER
Now by seeing the molar ratio of Mg and Si from balanced equation, we get
Mg : Si = 2:1
Therefore,
7-5 Si2H6 is a covalent compound of silicon and hydrogen.
Complete Figure 9 to show the outer shell electrons in a molecule of Si2H6
[1 mark]
Figure 9
ANSWER
“X” represent electron of Silicon
“ ” represent electron of Hydrogen
7-6 Si2H6 reacts with oxygen.
The equation for the reaction is:
2Si2H6(g) + 7O2(g) → 4SiO2(s) + 6H2O(g)
30 cm3 of Si2H6 is reacted with 150 cm3 (an excess) of oxygen.
Calculate the total volume of gases present after the reaction.
All volumes of gases are measured at the same temperature and pressure.
[4 marks]
ANSWER
