The relative formula mass of NaOH is 40 - OCR Gateway - GCSE Chemistry Combined Science - Question 10 - 2018 - Paper 1

To find the mass of sodium hydroxide in the solution, we can use the formula:

$ext{Mass} = ext{Moles} imes ext{Relative Molecular Mass}$

First, we need to calculate the number of moles in 100 cm³ of a 0.5 mol/dm³ solution. Since 1 dm³ is equal to 1000 cm³, we convert 100 cm³ to dm³:

ext{Volume in dm³} = rac{100 ext{ cm}^3}{1000} = 0.1 ext{ dm}^3

Now we calculate the number of moles:

$ext{Moles} = ext{Concentration} imes ext{Volume} = 0.5 ext{ mol/dm}^3 imes 0.1 ext{ dm}^3 = 0.05 ext{ moles}$

Using the relative formula mass of NaOH (40 g/mol):

$ext{Mass} = 0.05 ext{ moles} imes 40 ext{ g/mol} = 2.0 ext{ g}$

Therefore, the mass of sodium hydroxide in the solution is 2.0 g.