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AQA GCSE · Question 02.7 · Quantitative chemistry
The student used a solution of sodium hydroxide of concentration 4.00 g/dm³. Calculate the mass of sodium hydroxide in 25.0 cm³ of this solution. (1 dm³ = 1000 cm³)
The student used a solution of sodium hydroxide of concentration 4.00 g/dm³. Calculate the mass of sodium hydroxide in 25.0 cm³ of this solution. (1 dm³ = 1000 cm³)
How to approach this question
1. The concentration is in g/dm³ but the volume is in cm³. You must first convert the volume to dm³ by dividing by 1000.\n2. Rearrange the concentration formula (concentration = mass / volume) to make mass the subject: mass = concentration × volume.\n3. Substitute the values for concentration and the converted volume into the formula to calculate the mass.
Full Answer
First, convert the volume from cm³ to dm³:\nVolume = 25.0 cm³ / 1000 cm³/dm³ = 0.0250 dm³\n\nNext, use the formula: mass = concentration × volume\nMass = 4.00 g/dm³ × 0.0250 dm³\nMass = 0.100 g
The relationship between mass, concentration, and volume is given by the formula:\nConcentration = Mass / Volume\n\nWe need to find the mass, so we rearrange the formula:\nMass = Concentration × Volume\n\nFirst, we must ensure the units are consistent. The concentration is in g/dm³, so the volume must be in dm³.\nVolume in dm³ = 25.0 cm³ ÷ 1000 = 0.0250 dm³\n\nNow, we can calculate the mass:\nMass = 4.00 g/dm³ × 0.0250 dm³\nMass = 0.100 g
Common mistakes
✗ Forgetting to convert the volume from cm³ to dm³.\n✗ Dividing concentration by volume instead of multiplying.
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