Question

How many grams of ${Na}_2{S}_2{O}_3$ are needed to prepare five litres of an 8% solution (by mass) having density $=1.075g/mL$?

• A. $43.0g$
• B. $430g$
• C. $400g$
• D. $40g$

Answer 1

The correct option is B $430g$

$N{a}_2{S}_2{O}_3$ molar mass is 140 gram

8% solution by mass means 8 gram solute dissolved in 100 gram of solution

density = 1.075 g/ml means, 1075 grams soluton in one litre

Thus one gram solution contains 8/100 gram of solute

or 1075 gram solution contains ($1075\times 8/100=86$) gram solute

5 litre solution or $(1075\times 5=5375)$ gram solutions contains $86\times 5=430$ gram solute