Question

1.a) Calculate the molar mass, in g mol-1, of the following compounds, give your answers to 1dp:

i) Methane, CH4

ii) Calcium carbonate, CaCO3

iii) Potassium permanganate, KMnO4

iv) Ammonium sulphate, (NH4)2SO4

v) Iron(III)nitrate, Fe(NO3)3


b) Calculate the number of moles in the following, give your answers to 2 sig figs:


i) 23g of Na

ii) 36g of H2O

iii) 304g of Cr2O3 (chromium (III)oxide)

iv) 10g of CO2

v) 82g of C2H5OH (ethanol)

c) Calculate the mass, in g, of the following:

i) 2 moles of NH3 (ammonia)

ii) 0.5 moles of H2SO4 (sulphuric acid)

iii) 1.5 moles of NaCl (sodium chloride)

iv) 15 moles of Li2O (lithium oxide)

v) 3.45 moles of Sr(NO3)2 (strontium nitrate)

Answer 1

1. Calculate the molar mass as follows:

i) Mr (CH₄)=Ar(C)+4Ar(H)=12+4*1=16 g/mol

ii) Mr (CaCO₃)=Ar(Ca)+Ar(C)+3Ar(O)= 40+12+3*16=40+12+48=100 g/mol

iii)Mr(KMnO₄)=Ar(K)+Ar(Mn)+4Ar(O)= 39+55+4*16=39+55+64= 158 g/mol

iv)М((NH4)₂SO₄) = 2*Ar(N) + 4*2*Ar(H) + Ar(S) + 4*Ar(O) = 2*14 + 8*1 + 32 + 4*16 =28+8+32+64=132 g/mol

v)М(Fe(NO₃)₃) = Ar(Fe) + 3*Ar(N) + 3*3*Ar(O) =56+3*14+9*16=56+42+144= 242 g/mol

2.Calculate the number of moles as follows:

v=m/Mr

i) v(Na)=23g/23g/mol=1mol

ii)v(H₂0)=36g/(2*1+16)g/mol=36 g/18g/mol=2mol

iii)v(Cr₂O₃)=304g/(2*52+3*16)g/mol=304g/152g/mol=2mol

iv)v(CO₂)=10g/(12+2*16)g/mol=10g/44g/mol=0.2mol

v)v(C₂H₅OH)=82g/(2*12+5*1+16+1)g/mol=82g/46g/mol=1.8mol

3.Calculate the mass as follows:

m=v*Mr

i)m(NH₃)=2mol*(14+3*1)g/mol=2*17=34 g

ii)m(H₂SO₄)=0.5mol*(2*1+32+4*16)g/mol=2*98=196 g

iii)m(NaCl)=1.5mol*(23+35)g/mol=1.5*58=87 g

iv)m(Li₂O)=15mol*(2*7+16)g/mol=15*30=450 g

v)m(Sr(NO₃)₂) =3.45*(88+2*14+2*3*16)g/mol=3.45*212=731.4 g