What is the number of moles of NaHCO3in 250cm3 of its solution if the solution contains 8.4 g of NaHCO3 in 1…

Analyze the question: We need the number of moles of NaHCO₃ in 250 cm³ of a solution that contains 8.4 g per 1 dm³.

Concept:

• Moles = mass ÷ molar mass
• 1 dm³ = 1000 cm³, so 250 cm³ is one quarter of a dm³.

Step 1: Molar mass of NaHCO₃ Na + H + C + 3(O) = 23 + 1 + 12 + 3(16) = 23 + 1 + 12 + 48 = 84 g/mol

Step 2: Moles in 1 dm³ n = 8.4 ÷ 84 = 0.1 mol (so the concentration is 0.1 mol/dm³)

Step 3: Moles in 250 cm³ n = 0.1 × (250 ÷ 1000) = 0.1 × 0.25 = 0.025 mol

Alternatively, using concentration × volume: 0.1 mol/dm³ × 0.25 dm³ = 0.025 mol.

Answer: 0.025 mol, which is option D.

Tip: Always convert cm³ to dm³ by dividing by 1000 before using n = C × V. A quick shortcut is that 250 cm³ is ¼ of a dm³, so just divide the moles per dm³ by 4 (0.1 ÷ 4 = 0.025).