Concentration measures solute per volume of solution

Definition

Concentration

The amount of solute dissolved in a stated volume of solution, measured in g/dm³ or mol/dm³.

Definition

Solute

The substance that dissolves in a solvent to make a solution.

A solution forms when a solute dissolves in a solvent, such as salt dissolving in water.
A concentrated solution has a lot of solute in a given volume, while a dilute solution has only a little.
Concentration can be measured in grams per cubic decimetre, written $g/dm3\text{g/dm}^3$ $g/dm^{3}$ .
1. One cubic decimetre is $cm31000\,\text{cm}^3$ , which is the same as one litre.
The volume used is the volume of the whole solution, not the volume of water that was added.
Concentration can also be given in $mol/dm3\text{mol/dm}^3$ , which uses the amount in moles of solute instead of its mass.

Key Idea

Concentration depends on two things only: how much solute there is and how much solution it is spread through.

Concentration equals mass of solute over volume

The relationship is: $(dm3)\text{concentration (g/dm}^3\text{)} = \frac{\text{mass of solute (g)}}{\text{volume of solution (dm}^3\text{)}}$
Convert a volume in $cm3\text{cm}^3$ $cm^{3}$ into $dm3\text{dm}^3$ $dm^{3}$ by dividing by 1000 before using the equation.
1. So $cm3250\,\text{cm}^3$ is $dm30.250\,\text{dm}^3$ .
Rearranging gives mass of solute $=$ concentration $×\times$ $\times$ volume, which tells you how much solid to weigh out.
1. Making $dm32.00\,\text{dm}^3$ of a $g/dm315.0\,\text{g/dm}^3$ solution needs $15.0 \times 2.00 = 30.0\,\text{g}$ of solute.
Give every answer with its unit, because a number alone does not say whether it is a mass, a volume or a concentration.

Example

Calculate the concentration of a solution made by dissolving $g5.00\,\text{g}$ of sodium chloride in water to make $cm3250\,\text{cm}^3$ of solution.
Convert the volume: $dm3250\,\text{cm}^3 \div 1000 = 0.250\,\text{dm}^3$ .
Divide mass by volume: $g/dm3\dfrac{5.00\,\text{g}}{0.250\,\text{dm}^3} = 20.0\,\text{g/dm}^3$ .

How solute mass and volume affect concentration

At a fixed volume, concentration is directly proportional to the mass of solute.
1. Dissolving twice the mass of solute in the same volume doubles the concentration.
For a fixed mass of solute, a larger volume of solution gives a lower concentration.
1. Spreading the same mass through twice the volume halves the concentration.
Doubling both the mass and the volume leaves the concentration unchanged.
A sample of any size taken from a well-mixed solution has the same concentration as the rest of it.

Example

Adding more squash to the same glass of water makes a stronger drink, while topping the glass up with water makes it weaker, although the amount of squash in the glass has not changed.

Diluting a solution lowers its concentration

When water is added, the mass of solute stays the same.
The volume of solution increases, so the concentration falls.
Evaporating some of the water has the opposite effect, raising the concentration because the volume decreases while the solute stays.
To find a new concentration, first work out the mass of solute present, then divide it by the new volume.

Example

Water is added to $cm350.0\,\text{cm}^3$ of a $g/dm340.0\,\text{g/dm}^3$ solution until its volume is $cm3200\,\text{cm}^3$ ; find the new concentration.
Mass of solute $40.0\,\text{g/dm}^3 \times 0.0500\,\text{dm}^3 = 2.00\,\text{g}$ .
New concentration $\dfrac{2.00\,\text{g}}{0.200\,\text{dm}^3} = 10.0\,\text{g/dm}^3$ .

Making a solution of known concentration

Weigh the solid accurately on a balance in a weighing boat or small beaker.
Dissolve it in a small volume of distilled water in a beaker, stirring until no solid remains.
Pour the solution into a volumetric flask and rinse the beaker and stirring rod into the flask, so no solute is left behind.
Add distilled water until the bottom of the meniscus sits on the line, then stopper and invert the flask to mix.
Divide the mass weighed by the volume of the flask in $dm3\text{dm}^3$ to find the concentration.

Exam technique

When a question asks how a change affects concentration, say what happens to the mass of solute and what happens to the volume of solution, then state the effect.

Self review

What does a concentration of $g/dm320.0\,\text{g/dm}^3$ mean?
What is the concentration of $g3.00\,\text{g}$ of solute in $cm3150\,\text{cm}^3$ of solution?
What happens to the concentration if the same mass of solute is dissolved in twice the volume?
Why does adding water lower the concentration of a solution?
What mass of solute is needed to make $cm3500\,\text{cm}^3$ of a $g/dm312.0\,\text{g/dm}^3$ solution?

Concentration measures solute per volume of solution

Definition

Concentration

The amount of solute dissolved in a stated volume of solution, measured in g/dm³ or mol/dm³.

Definition

Solute

The substance that dissolves in a solvent to make a solution.

A solution forms when a solute dissolves in a solvent, such as salt dissolving in water.
A concentrated solution has a lot of solute in a given volume, while a dilute solution has only a little.
Concentration can be measured in grams per cubic decimetre, written $g/dm3\text{g/dm}^3$ $g/dm^{3}$ .
1. One cubic decimetre is $cm31000\,\text{cm}^3$ , which is the same as one litre.
The volume used is the volume of the whole solution, not the volume of water that was added.
Concentration can also be given in $mol/dm3\text{mol/dm}^3$ , which uses the amount in moles of solute instead of its mass.

Key Idea

Concentration depends on two things only: how much solute there is and how much solution it is spread through.

Concentration equals mass of solute over volume

The relationship is: $(dm3)\text{concentration (g/dm}^3\text{)} = \frac{\text{mass of solute (g)}}{\text{volume of solution (dm}^3\text{)}}$
Convert a volume in $cm3\text{cm}^3$ $cm^{3}$ into $dm3\text{dm}^3$ $dm^{3}$ by dividing by 1000 before using the equation.
1. So $cm3250\,\text{cm}^3$ is $dm30.250\,\text{dm}^3$ .
Rearranging gives mass of solute $=$ concentration $×\times$ $\times$ volume, which tells you how much solid to weigh out.
1. Making $dm32.00\,\text{dm}^3$ of a $g/dm315.0\,\text{g/dm}^3$ solution needs $15.0 \times 2.00 = 30.0\,\text{g}$ of solute.
Give every answer with its unit, because a number alone does not say whether it is a mass, a volume or a concentration.

Example

Calculate the concentration of a solution made by dissolving $g5.00\,\text{g}$ of sodium chloride in water to make $cm3250\,\text{cm}^3$ of solution.
Convert the volume: $dm3250\,\text{cm}^3 \div 1000 = 0.250\,\text{dm}^3$ .
Divide mass by volume: $g/dm3\dfrac{5.00\,\text{g}}{0.250\,\text{dm}^3} = 20.0\,\text{g/dm}^3$ .

How solute mass and volume affect concentration

At a fixed volume, concentration is directly proportional to the mass of solute.
1. Dissolving twice the mass of solute in the same volume doubles the concentration.
For a fixed mass of solute, a larger volume of solution gives a lower concentration.
1. Spreading the same mass through twice the volume halves the concentration.
Doubling both the mass and the volume leaves the concentration unchanged.
A sample of any size taken from a well-mixed solution has the same concentration as the rest of it.

Example

Adding more squash to the same glass of water makes a stronger drink, while topping the glass up with water makes it weaker, although the amount of squash in the glass has not changed.

Diluting a solution lowers its concentration

When water is added, the mass of solute stays the same.
The volume of solution increases, so the concentration falls.
Evaporating some of the water has the opposite effect, raising the concentration because the volume decreases while the solute stays.
To find a new concentration, first work out the mass of solute present, then divide it by the new volume.

Example

Water is added to $cm350.0\,\text{cm}^3$ of a $g/dm340.0\,\text{g/dm}^3$ solution until its volume is $cm3200\,\text{cm}^3$ ; find the new concentration.
Mass of solute $40.0\,\text{g/dm}^3 \times 0.0500\,\text{dm}^3 = 2.00\,\text{g}$ .
New concentration $\dfrac{2.00\,\text{g}}{0.200\,\text{dm}^3} = 10.0\,\text{g/dm}^3$ .

Making a solution of known concentration

Weigh the solid accurately on a balance in a weighing boat or small beaker.
Dissolve it in a small volume of distilled water in a beaker, stirring until no solid remains.
Pour the solution into a volumetric flask and rinse the beaker and stirring rod into the flask, so no solute is left behind.
Add distilled water until the bottom of the meniscus sits on the line, then stopper and invert the flask to mix.
Divide the mass weighed by the volume of the flask in $dm3\text{dm}^3$ to find the concentration.

Exam technique

When a question asks how a change affects concentration, say what happens to the mass of solute and what happens to the volume of solution, then state the effect.

Self review

What does a concentration of $g/dm320.0\,\text{g/dm}^3$ mean?
What is the concentration of $g3.00\,\text{g}$ of solute in $cm3150\,\text{cm}^3$ of solution?
What happens to the concentration if the same mass of solute is dissolved in twice the volume?
Why does adding water lower the concentration of a solution?
What mass of solute is needed to make $cm3500\,\text{cm}^3$ of a $g/dm312.0\,\text{g/dm}^3$ solution?

5.1.3 Concentration of a solution in mol/dm3

Concentration measures solute per volume of solution

Concentration equals mass of solute over volume

How solute mass and volume affect concentration

Diluting a solution lowers its concentration

Making a solution of known concentration

Review 5.1.3 Concentration of a solution in mol/dm3 by teaching Genie

Recap your knowledge with an interactive lesson

Remember key concepts with flashcards

5.1.3 Concentration of a solution in mol/dm3

Concentration measures solute per volume of solution

Concentration equals mass of solute over volume

How solute mass and volume affect concentration

Diluting a solution lowers its concentration

Making a solution of known concentration

Review 5.1.3 Concentration of a solution in mol/dm3 by teaching Genie

Recap your knowledge with an interactive lesson

Remember key concepts with flashcards

5.1.3 Concentration of a solution in mol/dm3

Concentration measures solute per volume of solution

Concentration equals mass of solute over volume

How solute mass and volume affect concentration

Diluting a solution lowers its concentration

Making a solution of known concentration

Review 5.1.3 Concentration of a solution in mol/dm3 by teaching Genie

Recap your knowledge with an interactive lesson

Remember key concepts with flashcards

5.1.3 Concentration of a solution in mol/dm3 Revision Guide

5.1.3 Concentration of a solution in mol/dm3

Concentration measures solute per volume of solution

Concentration equals mass of solute over volume

How solute mass and volume affect concentration

Diluting a solution lowers its concentration

Making a solution of known concentration

Review 5.1.3 Concentration of a solution in mol/dm3 by teaching Genie

Recap your knowledge with an interactive lesson

Remember key concepts with flashcards

5.1.3 Concentration of a solution in mol/dm3 Revision Guide