Chemical Formulae, Equations and Calculations Part 1
4 marks · NormalAnswer the questions about the compound sodium sulfate, Na2SO4.
State the relative atomic masses (Ar) of sodium (Na), sulfur (S), and oxygen (O).
Calculate the relative formula mass (Mr) of sodium sulfate, Na2SO4.
State the Mr of Na2SO4 to 1 decimal place.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Na = 23, S = 32, O = 16
(b) 142
(c) 142.0
Common mistakes: addition errors; incorrect Ar values
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correct Ar for each element: Na = 23, S = 32, O = 16
M1 (b) · 1 mark · Sets up correct calculation: (2×23) + 32 + (4×16)
A1 (b) · 1 mark · Correct addition for Mr = 142
A2 (c) · 1 mark · States Mr to 1 decimal place: 142.0 (follow-through)
Worked solution
a) Ar(Na) = 23, Ar(S) = 32, Ar(O) = 16
b) Na2SO4 has 2 sodium, 1 sulfur, 4 oxygen:
c) To 1 decimal place, Mr = 142.0