3.2.5a Concentration of solutions

Concentration measures how much solute is packed into a solution

Definition

Solution

A mixture formed when a solute dissolves in a solvent.

Definition

Solute

The substance dissolved in a solvent to form a solution.

Many reactions take place in solution, so it helps to describe how much dissolved substance a solution contains.
A solute dissolves in a solvent to make the solution.
The concentration tells you how much solute is present in a given volume of that solution.

Key Idea

More solute in the same volume makes a more concentrated solution.
The same solute spread through a larger volume makes a more dilute solution.

Mass concentration is measured in grams per cubic decimetre

Definition

Concentration

The mass of solute present per unit volume of solution, usually measured in $g/dm3\text{g}/\text{dm}^3$ for this calculation.

Concentration in $g/dm3\text{g}/\text{dm}^3$ is the mass of solute divided by the volume of solution, or $\dfrac{m}{V}$ .
Here $m$ is the mass of solute in grams and $V$ is the volume of solution in $dm3\text{dm}^3$ .

Example

Dissolving $g20\ \text{g}$ of salt in $dm30.5\ \text{dm}^3$ of water gives a concentration of $g/dm3\dfrac{20}{0.5} = 40\ \text{g}/\text{dm}^3$ .

Convert the volume from $cm^3$ to $dm^3$ before you start

One cubic decimetre equals $cm31000\ \text{cm}^3$ , so divide a volume in $cm3\text{cm}^3$ by $1000$ to get $dm3\text{dm}^3$ .
For example, $cm3250\ \text{cm}^3$ is $dm3\dfrac{250}{1000} = 0.25\ \text{dm}^3$ .

Exam technique

Convert every volume to $dm3\text{dm}^3$ first, as using $cm3\text{cm}^3$ makes the concentration a thousand times too small.
Always write the unit $g/dm3\text{g}/\text{dm}^3$ with a mass concentration answer.

Finding the mass of solute in a solution

Rearranging the formula gives the mass of solute as $\times V$ .
For $250 cm3250\ \text{cm}^3$ $250 cm^{3}$ of a $40 g/dm340\ \text{g}/\text{dm}^3$ $40 g / dm^{3}$ solution, first write the volume as $0.25 dm30.25\ \text{dm}^3$ $0.25 dm^{3}$ .
1. The mass of solute is $40 \times 0.25 = 10\ \text{g}$ .

Self review

What does the concentration of a solution tell you?
How do you convert a volume in $cm3\text{cm}^3$ into $dm3\text{dm}^3$ ?
Find the concentration when $g30\ \text{g}$ of solute is dissolved to make $dm32\ \text{dm}^3$ of solution.
What mass of solute is in $cm3500\ \text{cm}^3$ of a $g/dm320\ \text{g}/\text{dm}^3$ solution?

3.2.5b Relating mass, volume and concentration

Concentration, solute mass and volume are tied together

Definition

Concentration

The mass of solute present per unit volume of solution, usually measured in $g/dm3\text{g}/\text{dm}^3$ for this calculation.

The three quantities are linked by $\dfrac{m}{V}$ , so knowing any two lets you find the third.
Concentration $c$ is in $g/dm3\text{g}/\text{dm}^3$ , mass $m$ is in grams and volume $V$ is in $dm3\text{dm}^3$ .

Key Idea

Concentration goes up when you add solute and goes down when you add solvent, because it is a mass shared over a volume.

More solute raises the concentration

Definition

Solute

The substance dissolved in a solvent to form a solution.

At a fixed volume, concentration is directly proportional to the mass of solute.
Doubling the mass of solute in the same volume doubles the concentration.

Example

Going from $g10\ \text{g}$ to $g20\ \text{g}$ of solute in $dm31\ \text{dm}^3$ raises the concentration from $10$ to $g/dm320\ \text{g}/\text{dm}^3$ .

A larger volume lowers the concentration

Definition

Solution

A mixture formed when a solute dissolves in a solvent.

At a fixed mass of solute, concentration is inversely proportional to the volume of solution.
Adding more solvent dilutes the solution, so the same solute spread through a bigger volume gives a lower concentration.

Exam technique

When asked to explain a change, name which quantity you kept fixed and which you changed.
Check the volume is in $dm3\text{dm}^3$ before rearranging, or the mass or volume you find will be wrong by a factor of a thousand.

Rearranging to find a mass or a volume

To find a mass of solute, use $m=c×Vm = c \times V$ $m = c \times V$ .
1. In $cm3200\ \text{cm}^3$ ( $dm30.2\ \text{dm}^3$ ) of a $g/dm315\ \text{g}/\text{dm}^3$ solution, the mass of solute is $15 \times 0.2 = 3\ \text{g}$ .
To find a volume, use $V=mcV = \dfrac{m}{c}$ $V = \frac{m}{c}$ .
1. A $g/dm325\ \text{g}/\text{dm}^3$ solution holds $g10\ \text{g}$ of solute in $dm3\dfrac{10}{25} = 0.4\ \text{dm}^3$ , which is $cm3400\ \text{cm}^3$ .

Self review

How does increasing the mass of solute change the concentration at fixed volume?
Why does diluting a solution with water lower its concentration?
What mass of solute is in $cm3100\ \text{cm}^3$ of a $g/dm330\ \text{g}/\text{dm}^3$ solution?
What volume of a $g/dm350\ \text{g}/\text{dm}^3$ solution contains $g20\ \text{g}$ of solute?

3.2.5a Concentration of solutions

Concentration measures how much solute is packed into a solution

Definition

Solution

A mixture formed when a solute dissolves in a solvent.

Definition

Solute

The substance dissolved in a solvent to form a solution.

Many reactions take place in solution, so it helps to describe how much dissolved substance a solution contains.
A solute dissolves in a solvent to make the solution.
The concentration tells you how much solute is present in a given volume of that solution.

Key Idea

More solute in the same volume makes a more concentrated solution.
The same solute spread through a larger volume makes a more dilute solution.

Mass concentration is measured in grams per cubic decimetre

Definition

Concentration

The mass of solute present per unit volume of solution, usually measured in $g/dm3\text{g}/\text{dm}^3$ for this calculation.

Concentration in $g/dm3\text{g}/\text{dm}^3$ is the mass of solute divided by the volume of solution, or $\dfrac{m}{V}$ .
Here $m$ is the mass of solute in grams and $V$ is the volume of solution in $dm3\text{dm}^3$ .

Example

Dissolving $g20\ \text{g}$ of salt in $dm30.5\ \text{dm}^3$ of water gives a concentration of $g/dm3\dfrac{20}{0.5} = 40\ \text{g}/\text{dm}^3$ .

Convert the volume from $cm^3$ to $dm^3$ before you start

One cubic decimetre equals $cm31000\ \text{cm}^3$ , so divide a volume in $cm3\text{cm}^3$ by $1000$ to get $dm3\text{dm}^3$ .
For example, $cm3250\ \text{cm}^3$ is $dm3\dfrac{250}{1000} = 0.25\ \text{dm}^3$ .

Exam technique

Convert every volume to $dm3\text{dm}^3$ first, as using $cm3\text{cm}^3$ makes the concentration a thousand times too small.
Always write the unit $g/dm3\text{g}/\text{dm}^3$ with a mass concentration answer.

Finding the mass of solute in a solution

Rearranging the formula gives the mass of solute as $\times V$ .
For $250 cm3250\ \text{cm}^3$ $250 cm^{3}$ of a $40 g/dm340\ \text{g}/\text{dm}^3$ $40 g / dm^{3}$ solution, first write the volume as $0.25 dm30.25\ \text{dm}^3$ $0.25 dm^{3}$ .
1. The mass of solute is $40 \times 0.25 = 10\ \text{g}$ .

Self review

What does the concentration of a solution tell you?
How do you convert a volume in $cm3\text{cm}^3$ into $dm3\text{dm}^3$ ?
Find the concentration when $g30\ \text{g}$ of solute is dissolved to make $dm32\ \text{dm}^3$ of solution.
What mass of solute is in $cm3500\ \text{cm}^3$ of a $g/dm320\ \text{g}/\text{dm}^3$ solution?

3.2.5b Relating mass, volume and concentration

Concentration, solute mass and volume are tied together

Definition

Concentration

The mass of solute present per unit volume of solution, usually measured in $g/dm3\text{g}/\text{dm}^3$ for this calculation.

The three quantities are linked by $\dfrac{m}{V}$ , so knowing any two lets you find the third.
Concentration $c$ is in $g/dm3\text{g}/\text{dm}^3$ , mass $m$ is in grams and volume $V$ is in $dm3\text{dm}^3$ .

Key Idea

Concentration goes up when you add solute and goes down when you add solvent, because it is a mass shared over a volume.

More solute raises the concentration

Definition

Solute

The substance dissolved in a solvent to form a solution.

At a fixed volume, concentration is directly proportional to the mass of solute.
Doubling the mass of solute in the same volume doubles the concentration.

Example

Going from $g10\ \text{g}$ to $g20\ \text{g}$ of solute in $dm31\ \text{dm}^3$ raises the concentration from $10$ to $g/dm320\ \text{g}/\text{dm}^3$ .

A larger volume lowers the concentration

Definition

Solution

A mixture formed when a solute dissolves in a solvent.

At a fixed mass of solute, concentration is inversely proportional to the volume of solution.
Adding more solvent dilutes the solution, so the same solute spread through a bigger volume gives a lower concentration.

Exam technique

When asked to explain a change, name which quantity you kept fixed and which you changed.
Check the volume is in $dm3\text{dm}^3$ before rearranging, or the mass or volume you find will be wrong by a factor of a thousand.

Rearranging to find a mass or a volume

To find a mass of solute, use $m=c×Vm = c \times V$ $m = c \times V$ .
1. In $cm3200\ \text{cm}^3$ ( $dm30.2\ \text{dm}^3$ ) of a $g/dm315\ \text{g}/\text{dm}^3$ solution, the mass of solute is $15 \times 0.2 = 3\ \text{g}$ .
To find a volume, use $V=mcV = \dfrac{m}{c}$ $V = \frac{m}{c}$ .
1. A $g/dm325\ \text{g}/\text{dm}^3$ solution holds $g10\ \text{g}$ of solute in $dm3\dfrac{10}{25} = 0.4\ \text{dm}^3$ , which is $cm3400\ \text{cm}^3$ .

Self review

How does increasing the mass of solute change the concentration at fixed volume?
Why does diluting a solution with water lower its concentration?
What mass of solute is in $cm3100\ \text{cm}^3$ of a $g/dm330\ \text{g}/\text{dm}^3$ solution?
What volume of a $g/dm350\ \text{g}/\text{dm}^3$ solution contains $g20\ \text{g}$ of solute?

3.2.5 Concentration of solutions

3.2.5a Concentration of solutions

Concentration measures how much solute is packed into a solution

Mass concentration is measured in grams per cubic decimetre

Convert the volume from $cm^3$ to $dm^3$ before you start

Finding the mass of solute in a solution

3.2.5b Relating mass, volume and concentration

Concentration, solute mass and volume are tied together

More solute raises the concentration

A larger volume lowers the concentration

Rearranging to find a mass or a volume

Review 3.2.5 Concentration of solutions by teaching Genie

Recap your knowledge with an interactive lesson

Remember key concepts with flashcards

3.2.5 Concentration of solutions

3.2.5a Concentration of solutions

Concentration measures how much solute is packed into a solution

Mass concentration is measured in grams per cubic decimetre

Convert the volume from $cm^3$ to $dm^3$ before you start

Finding the mass of solute in a solution

3.2.5b Relating mass, volume and concentration

Concentration, solute mass and volume are tied together

More solute raises the concentration

A larger volume lowers the concentration

Rearranging to find a mass or a volume

Review 3.2.5 Concentration of solutions by teaching Genie

Recap your knowledge with an interactive lesson

Remember key concepts with flashcards

3.2.5 Concentration of solutions

3.2.5a Concentration of solutions

Concentration measures how much solute is packed into a solution

Mass concentration is measured in grams per cubic decimetre

Convert the volume from cm3cm^3cm3 to dm3dm^3dm3 before you start

Finding the mass of solute in a solution

3.2.5b Relating mass, volume and concentration

Concentration, solute mass and volume are tied together

More solute raises the concentration

A larger volume lowers the concentration

Rearranging to find a mass or a volume

Review 3.2.5 Concentration of solutions by teaching Genie

Recap your knowledge with an interactive lesson

Remember key concepts with flashcards

3.2.5 Concentration of solutions Revision Guide

3.2.5 Concentration of solutions

3.2.5a Concentration of solutions

Concentration measures how much solute is packed into a solution

Mass concentration is measured in grams per cubic decimetre

Convert the volume from cm3cm^3cm3 to dm3dm^3dm3 before you start

Finding the mass of solute in a solution

3.2.5b Relating mass, volume and concentration

Concentration, solute mass and volume are tied together

More solute raises the concentration

A larger volume lowers the concentration

Rearranging to find a mass or a volume

Review 3.2.5 Concentration of solutions by teaching Genie

Recap your knowledge with an interactive lesson

Remember key concepts with flashcards

3.2.5 Concentration of solutions Revision Guide

Convert the volume from $cm^3$ to $dm^3$ before you start

Convert the volume from $cm^3$ to $dm^3$ before you start