A student wanted to prepare a 3.2 % (m/m) solution of ammonium chloride using 100.0 g of water. How many grams of NH4Cl must the student use?

Question

Enter your answer with the proper number of significant figures.

Answer 1

3.2% (m/m) means 3.2 g NH4Cl per 100 g of solution

If you use 100 g H2O, the total mass of solution will be 100 g + x g NH4Cl

This must then be equal to 3.2% (0.032 or 3.2 g/100 g)

x g NH4Cl / 100 g + x g = 0.032

3.2 + 0.032x = x

0.968x = 3.2

x = 3.31 g NH4Cl

Check the answer:

Find % (m/m) if you dissolve 3.31 g NH4Cl in 100 g H2O

Total mass = 3.31 g + 100 g = 103.31 g

%(m/m) = 3.31 g / 103.31 (x100) = 3.2% √