Concentration of Solutions

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Concentration of Solutions — Free MYP5 Chemistry Practice Questions

1QuestionDilution concept and simple dilution calculationsConcept Practice

2 marks~3 minCriterion A

Three pieces of laboratory glassware are shown in the diagram: a beaker, a pipette, and a volumetric flask.

Identify the volumetric flask from the diagram. [1]

Explain why the volumetric flask, rather than the beaker, is used to prepare a diluted solution of precisely known concentration. [1]

Solutions

2QuestionCalculating moles from concentration and volumeAssessment Practice

4 marks~6 minCriterion D

A technician prepares a saline drip solution for a hospital ward. The solution contains sodium chloride (NaCl) dissolved in water. The volume of the solution is

0.50 \text{ L}

and its concentration is

2.0 \text{ mol/L}

Calculate the number of moles of NaCl in the solution using

n = c \times V

. [1]

A second bag contains

1.50 \text{ L}

of a NaCl solution with the same concentration. Deduce the total moles of NaCl across both bags. [1]

The recommended maximum daily intake of NaCl is

0.086 \text{ mol}

. Evaluate whether the combined NaCl from both bags poses a health concern, justifying your answer with a calculation. [2]

Solutions

3QuestionDefinition of concentration (mol/dm³ or g/dm³)Assessment Practice

5 marks~8 minCriterion C

A student prepares five copper(II) sulfate (

\text{CuSO}_4

) solutions by serial dilution of a

1.00\ \text{mol dm}^{-3}

stock solution. Absorbance is measured at

635\ \text{nm}

Concentration ( $\text{mol dm}^{-3}$ )	$1.00$	$0.50$	$0.25$	$0.125$	$0.0625$
Absorbance	$1.20$	$0.60$	$0.55$	$0.30$	$0.15$

Calculate the expected absorbance for each diluted solution, assuming absorbance is directly proportional to concentration. [2]

Identify the anomalous data point and explain, using the definition of concentration in

\text{mol dm}^{-3}

, why the measured absorbance indicates the actual concentration differs from the intended value. [2]

Evaluate whether the anomaly is more likely caused by an error in volume measurement or mass measurement during the dilution, justifying your reasoning. [1]

Solutions

4QuestionDilution concept and simple dilution calculationsAssessment Practice

3 marks~5 minCriterion B

A student dilutes 10 cm³ of a 1.0 mol dm⁻³ copper(II) sulfate solution by adding distilled water to reach four different final volumes.

Final volume (cm³)	20	40	60	80
Concentration (mol dm⁻³)	0.50	0.25	0.17	0.13

Calculate the number of moles of copper(II) sulfate present in the original 10 cm³ sample. [1]

Explain why the concentration decreases as the final volume increases. [1]

A student claims that doubling the final volume always halves the concentration. Evaluate this claim using the data provided. [1]

Solutions

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