O-LevelChemistryStoichiometry5070/22 · May/June 2018 · Q48 Marks

Phosphorus is a non-metal in Group V of the Periodic Table.

(a)Phosphorus can be manufactured from calcium phosphate, Ca3(PO4)2. 2Ca3(PO4)2 + 6SiO2 + 10C → 6CaSiO3 + 10CO + P4 What is the maximum mass of phosphorus that can be made using 300g of silicon dioxide, SiO2? mass of phosphorus ..................................................... g[2]
(b)Phosphorus, P4, is a simple molecular substance. Suggest two physical properties of phosphorus.[2]
(c)Using ideas about structure and bonding, suggest why calcium phosphate, Ca3(PO4)2, has a high melting point.[2]
(d)Complete the table about the number of electrons, neutrons and protons in two particles. particle `30 P / 15` number of electrons number of neutrons number of protons[2]

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[2] 4(a) moles of SiO2 = 5 OR 300/60 OR moles of P4 = 300/360 OR 0.83 (1) mass of P4 (= moles of SiO2 × 124 ÷ 6 OR = moles of P4 × 124) = 103.3 (1)
[2] 4(b) Any two from: • low melting point / low boiling point (1) • poor conductor of electricity / poor conductor of heat (1) • does not dissolve in water (1)
[2] 4(c) has a giant (ionic) structure (1) strong attraction between ions / difficult to break attraction between ions / lot of energy needed to overcome (strong) attractive forces between ions (1)
[2] 4(d) particle `30 p / 15` `31p3- / 15` number of electrons 15 18 number of neutrons 15 16 number of protons 15 15 (1) (1)

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