3.4.1 Using concentrations of solutions in mol/dm³ (chemistry only) (HT only)

3.4.1 Concentration in mol/dm3

Concentration can be measured in moles per cubic decimetre

Definition

Molar concentration

The concentration of a solution measured in moles of solute per cubic decimetre of solution ( $mol/dm3\text{mol}/\text{dm}^3$ ).

Definition

Solution

A mixture formed when a solute dissolves in a solvent.

Chemists often give the concentration of a solution in $mol/dm3\text{mol}/\text{dm}^3$ rather than $g/dm3\text{g}/\text{dm}^3$ .
Measuring in moles is useful because reactions happen in whole-number mole ratios, not in equal masses.

Key Idea

A molar concentration tells you how many moles of solute sit in every cubic decimetre of the solution.

Moles, volume and concentration are linked by one formula

Definition

Mole

The amount of a substance, measured in mol, where one mole has a mass in grams numerically equal to its relative formula mass.

The concentration in $mol/dm3\text{mol}/\text{dm}^3$ is the moles of solute divided by the volume in $dm3\text{dm}^3$ , or $\dfrac{n}{V}$ .
Rearranging gives the moles as $\times V$ and the volume as $\dfrac{n}{c}$ .

Example

$mol0.5\ \text{mol}$ of sodium hydroxide in $cm3250\ \text{cm}^3$ ( $dm30.25\ \text{dm}^3$ ) has a concentration of $mol/dm3\dfrac{0.5}{0.25} = 2\ \text{mol}/\text{dm}^3$ .

Converting between g/dm3 and mol/dm3

Definition

Solute

The substance dissolved in a solvent to form a solution.

To change $g/dm3\text{g}/\text{dm}^3$ into $mol/dm3\text{mol}/\text{dm}^3$ , divide by the relative formula mass of the solute.
To change $mol/dm3\text{mol}/\text{dm}^3$ back into $g/dm3\text{g}/\text{dm}^3$ , multiply by the relative formula mass.

Exam technique

Change the volume to $dm3\text{dm}^3$ before using $\dfrac{n}{V}$ , as a volume in $cm3\text{cm}^3$ gives an answer a thousand times too small.
Label each concentration with its unit, since $mol/dm3\text{mol}/\text{dm}^3$ and $g/dm3\text{g}/\text{dm}^3$ are easy to mix up.

Example

The sodium hydroxide solution above is $2 mol/dm32\ \text{mol}/\text{dm}^3$ $2 mol / dm^{3}$ .
1. With $M_r = 40$ , this is $\times 40 = 80\ \text{g}/\text{dm}^3$ .
2. Working the other way, $g/dm380\ \text{g}/\text{dm}^3$ divided by $40$ returns $mol/dm32\ \text{mol}/\text{dm}^3$ .

Self review

What does a concentration in $mol/dm3\text{mol}/\text{dm}^3$ tell you?
Write the formula linking concentration, moles and volume.
Find the concentration of $mol0.2\ \text{mol}$ of solute in $cm3500\ \text{cm}^3$ of solution.
Convert $g/dm3117\ \text{g}/\text{dm}^3$ of sodium chloride ( $M_r = 58.5$ ) into $mol/dm3\text{mol}/\text{dm}^3$ .

Recap questions

1 of 5

A copper sulfate solution has a concentration of 0.40 mol/dm³. How many moles of solute are in 150 cm³ of this solution?

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A solution is a mixture formed when a solute dissolves in a solvent. Molar concentration tells you how many moles of solute are present in every cubic decimetre of solution.

The unit is $mol/dm3\text{mol}/\text{dm}^3$ . Measuring concentration in moles is useful because chemical reactions occur in whole-number mole ratios rather than equal masses.

The key relationship is:

\frac{n}{V}

Here, $c$ is concentration in $mol/dm3\text{mol}/\text{dm}^3$ , $n$ is amount in mol, and $V$ is volume in $dm3\text{dm}^3$ .

Flashcards

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21 flashcards

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What does a concentration of $mol/dm3\text{mol}/\text{dm}^3$ tell you?

3.4.1 Using concentrations of solutions in mol/dm³ (chemistry only) (HT only)

3.4.1 Concentration in mol/dm3

Concentration can be measured in moles per cubic decimetre

Definition

Molar concentration

The concentration of a solution measured in moles of solute per cubic decimetre of solution ( $mol/dm3\text{mol}/\text{dm}^3$ ).

Definition

Solution

A mixture formed when a solute dissolves in a solvent.

Chemists often give the concentration of a solution in $mol/dm3\text{mol}/\text{dm}^3$ rather than $g/dm3\text{g}/\text{dm}^3$ .
Measuring in moles is useful because reactions happen in whole-number mole ratios, not in equal masses.

Key Idea

A molar concentration tells you how many moles of solute sit in every cubic decimetre of the solution.

Moles, volume and concentration are linked by one formula

Definition

Mole

The amount of a substance, measured in mol, where one mole has a mass in grams numerically equal to its relative formula mass.

The concentration in $mol/dm3\text{mol}/\text{dm}^3$ is the moles of solute divided by the volume in $dm3\text{dm}^3$ , or $\dfrac{n}{V}$ .
Rearranging gives the moles as $\times V$ and the volume as $\dfrac{n}{c}$ .

Example

$mol0.5\ \text{mol}$ of sodium hydroxide in $cm3250\ \text{cm}^3$ ( $dm30.25\ \text{dm}^3$ ) has a concentration of $mol/dm3\dfrac{0.5}{0.25} = 2\ \text{mol}/\text{dm}^3$ .

Converting between g/dm3 and mol/dm3

Definition

Solute

The substance dissolved in a solvent to form a solution.

To change $g/dm3\text{g}/\text{dm}^3$ into $mol/dm3\text{mol}/\text{dm}^3$ , divide by the relative formula mass of the solute.
To change $mol/dm3\text{mol}/\text{dm}^3$ back into $g/dm3\text{g}/\text{dm}^3$ , multiply by the relative formula mass.

Exam technique

Change the volume to $dm3\text{dm}^3$ before using $\dfrac{n}{V}$ , as a volume in $cm3\text{cm}^3$ gives an answer a thousand times too small.
Label each concentration with its unit, since $mol/dm3\text{mol}/\text{dm}^3$ and $g/dm3\text{g}/\text{dm}^3$ are easy to mix up.

Example

The sodium hydroxide solution above is $2 mol/dm32\ \text{mol}/\text{dm}^3$ $2 mol / dm^{3}$ .
1. With $M_r = 40$ , this is $\times 40 = 80\ \text{g}/\text{dm}^3$ .
2. Working the other way, $g/dm380\ \text{g}/\text{dm}^3$ divided by $40$ returns $mol/dm32\ \text{mol}/\text{dm}^3$ .

Self review

What does a concentration in $mol/dm3\text{mol}/\text{dm}^3$ tell you?
Write the formula linking concentration, moles and volume.
Find the concentration of $mol0.2\ \text{mol}$ of solute in $cm3500\ \text{cm}^3$ of solution.
Convert $g/dm3117\ \text{g}/\text{dm}^3$ of sodium chloride ( $M_r = 58.5$ ) into $mol/dm3\text{mol}/\text{dm}^3$ .

Recap questions

1 of 5

A copper sulfate solution has a concentration of 0.40 mol/dm³. How many moles of solute are in 150 cm³ of this solution?

Previous Next

How was this guide?

Teach Genie

Review 3.4 Using concentrations of solutions in mol/dm³ (HT only) by teaching Genie

Teach it back in your own words, spot gaps, and remember it better.

Start teaching

Lesson

Recap your knowledge with an interactive lesson

8 minute activity

Start lesson

A solution is a mixture formed when a solute dissolves in a solvent. Molar concentration tells you how many moles of solute are present in every cubic decimetre of solution.

The unit is $mol/dm3\text{mol}/\text{dm}^3$ . Measuring concentration in moles is useful because chemical reactions occur in whole-number mole ratios rather than equal masses.

The key relationship is:

\frac{n}{V}

Here, $c$ is concentration in $mol/dm3\text{mol}/\text{dm}^3$ , $n$ is amount in mol, and $V$ is volume in $dm3\text{dm}^3$ .

Flashcards

Remember key concepts with flashcards

21 flashcards

Practice flashcards

What does a concentration of $mol/dm3\text{mol}/\text{dm}^3$ tell you?

3.4.1 Using concentrations of solutions in mol/dm3 (chemistry only) (HT only)

3.4.1 Concentration in mol/dm3

Concentration can be measured in moles per cubic decimetre

Moles, volume and concentration are linked by one formula

Converting between g/dm3 and mol/dm3

Recap questions

Review 3.4 Using concentrations of solutions in mol/dm³ (HT only) by teaching Genie

Recap your knowledge with an interactive lesson

Remember key concepts with flashcards

3.4 Using concentrations of solutions in mol/dm³ (HT only) Revision Guide

3.4.1 Using concentrations of solutions in mol/dm3 (chemistry only) (HT only)

3.4.1 Concentration in mol/dm3

Concentration can be measured in moles per cubic decimetre

Moles, volume and concentration are linked by one formula

Converting between g/dm3 and mol/dm3

Recap questions

Review 3.4 Using concentrations of solutions in mol/dm³ (HT only) by teaching Genie

Recap your knowledge with an interactive lesson

Remember key concepts with flashcards

3.4 Using concentrations of solutions in mol/dm³ (HT only) Revision Guide

3.4.1 Using concentrations of solutions in mol/dm³ (chemistry only) (HT only)

3.4.1 Using concentrations of solutions in mol/dm³ (chemistry only) (HT only)