1.

Calculate the molecular mass of the following : (i) `H_(2)O` (ii) `CO_(2)` (iii) `CH_(4)`

Answer» Step I. Calculation of mass of methanol `(CH_(3)OH)`
Molar mass of methanol `(CH_(3)OH)=12 + 4 xx 1 + 16 = 32 "g mol"^(-1)`
Molarity of solution `= 0.25 M = 0.25 "mol L"^(-1)`
Volume of solution = 2.5 L
Molarity of solution `= ("Mass of methanol/Molar mass")/("Volume of solution in Litres")`
`(0.25 "mol L"^(-1))=(W)/((32"g mol"^(-1))xx("2.5 L"))`
`W = (0.25 "mol L"^(-1))xx("32 g mol"^(-1))xx("2.5 L")=20 g`
Step II. Calculation of volume of methanol
Mass of methanol = 20 g = 0.002 kg
Density of methanol `= 0.793 "kg L"^(-1)`
Volume of methanol `= ("Mass")/("Density")=((0.002kg))/((0.793 "kg L"^(-1)))=0.0025 L`.


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