What is the concentration of a solution which contains 0.28g of potassium hydroxide in 100 cm$^{3}$ of solution [KOH = 56]

Step 1: Analyze the question We need the molar concentration (mol dm⁻³) of KOH, given the mass dissolved and the volume of solution.

Step 2: Concept Concentration (mol dm⁻³) = number of moles ÷ volume in dm³ Number of moles = mass ÷ molar mass

Step 3: Solution

Moles of KOH = 0.28 g ÷ 56 g/mol = 0.005 mol

Volume = 100 cm³ = 100 ÷ 1000 = 0.1 dm³

Concentration = 0.005 ÷ 0.1 = 0.05 mol dm⁻³

Alternatively, using the mass concentration route:

• Mass concentration = 0.28 g ÷ 0.1 dm³ = 2.8 g/dm³
• Molar concentration = 2.8 ÷ 56 = 0.05 mol dm⁻³

Step 4: Answer The correct option is **B. 0.

Tip: Always convert cm³ to dm³ first by dividing by 1000. Many students get option A or D by forgetting this conversion or mixing up the steps. Remember the formula triangle: moles = concentration × volume (in dm³).