Reversing the calculations
4 marks · NormalA student has 0.00800 mol of citric acid dissolved in water to make a solution. She needs to prepare the solution so that its concentration is exactly 0.200 mol/dm³.
Write the rearranged formula used to calculate the volume required in dm³, in terms of moles and concentration.
Calculate the required volume of solution, in dm³, to make the desired concentration.
Convert your answer from (b) to cm³.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) volume (dm³) = moles / concentration
(b) 0.0400 dm³
(c) 40.0 cm³
Common mistakes: Inverting the rearranged formula; Incorrect decimal moving in conversion
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correctly writes the formula: volume = moles / concentration.
M1 (b) · 1 mark · Substitutes the correct values into the rearranged formula.
A1 (b) · 1 mark · Correct calculation for the volume in dm³.
A2 (c) · 1 mark · Correct conversion of dm³ to cm³. (follow-through)
Worked solution
a) volume (dm³) = moles / concentration
b) volume = 0.00800 mol / 0.200 mol/dm³ = 0.0400 dm³
c) 0.0400 dm³ × 1000 = 40.0 cm³