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Year 7

Dissolving

I can use the particle model to explain both how solutions form and how solutions differ from a suspension.

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New
New
Year 7

Dissolving

I can use the particle model to explain both how solutions form and how solutions differ from a suspension.

Download all resources
Share activities with pupils

Lesson details

Key learning points

  1. Suspensions are not solutions, as solid particles can be seen, and eventually will settle over time.
  2. Forces of attraction between solute particles have to be overcome for something to dissolve.
  3. In a mixture, one particle may fit into spaces between another type, making the total volume less than expected.
  4. Not every substance can be dissolved (is soluble) in a solvent.
  5. Dissolving is not the same as melting, but both are physical processes.

Common misconception

Forces of attraction are broken when a substance dissolves.

Forces of attraction are *overcome*. They are still acting between the particles, but weaker than before so a different particle arrangement

Keywords

  • Dissolve - Occurs when a substance's particles separate and spread throughout the particles of a solvent resulting in it no longer being seen.

  • Insoluble - If a substance does not dissolve in a particular solvent, it is described as insoluble.

  • Melting - Melting occurs when a substance in the solid state is heated and its particles move into the arrangement of a substance in the liquid state.

  • Force of attraction - A force of attraction is a pulling force that keeps things, such as particles, close together.

  • Suspension - A mixture of an insoluble solid and liquid in which the solid particles are dispersed in the liquid and settle upon the mixture standing.

Demo the dissolving of 5g of sugar in 400mL water; then demo the melting of 5g sugar and ask pupils to record observations. They then write a comparison paragraph using key terms: particles, forces of attraction, melting, dissolving, physical change.
Teacher tip

Content guidance

  • Risk assessment required - equipment

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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Starter quiz

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6 Questions

Q1.
Which of the following statements is true of a solution?
It has particles that are visible to the naked eye.
Correct answer: It is made of two or more substances mixed evenly at the particle level.
It separates into layers when left standing.
It can only be made with liquids.
Q2.
Arrange the following states of substances based on their increasing ability to flow, starting with the state that cannot flow.
1 - Substances in the solid state.
2 - Substances in the liquid state.
3 - Substances in the gas state.
Q3.
is the ability of a substance to dissolve in a solvent.
Correct Answer: solubility
Q4.
Match the term with its description.
Correct Answer:Solvent,A substance into which a solute dissolves.

A substance into which a solute dissolves.

Correct Answer:Solute,A substance that has dissolved into a solvent.

A substance that has dissolved into a solvent.

Correct Answer:Solution,When a solute and solvent combine, this is formed.

When a solute and solvent combine, this is formed.

Correct Answer:Soluble,When a solute dissolves, it is described as this.

When a solute dissolves, it is described as this.

Q5.
What happens to the total mass of substances that are mixed together?
They lose mass.
They gain mass.
Correct answer: Their total mass stays the same.
Their total mass is halved.
Q6.
What is the term for the random motion of particles suspended in a medium?
Correct Answer: brownian motion, Brownian motion

Exit quiz

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6 Questions

Q1.
Why is a suspension not considered a solution?
It has a fixed melting point.
Correct answer: Solid particles are visible and can settle.
It changes state over a range of temperatures.
It contains impurities.
Q2.
Match the term with its characteristic.
Correct Answer:Solubility,Ability to dissolve in a solvent.

Ability to dissolve in a solvent.

Correct Answer:Dissolving,Overcoming forces of attraction between solvent particles.

Overcoming forces of attraction between solvent particles.

Correct Answer:Melting,Changing from a solid to a liquid state.

Changing from a solid to a liquid state.

Q3.
Dissolving is not the same as melting, but both are processes.
Correct Answer: physical
Q4.
Why is it incorrect to say that every substance can be dissolved in a solvent?
Lack of stirring.
Correct answer: Differences in solubility.
High temperature.
Presence of impurities.
Q5.
During the dissolving process, why does a solute dissolve in a solvent?
Solute-solvent forces of attraction are weaker than solute-solute.
The solute particles are larger than the solvent particles.
Correct answer: Solute-solvent forces of attraction are stronger than solute-solute.
The solute particles do not collide with the solvent particles.
Q6.
Why might the total volume of a mixture be less than the sum of the volumes of its individual components?
Evaporation occurs.
Correct answer: Particles fit into spaces between each other.
Chemical reaction reduces volume.
Measurement error.
Some solvent is spilled when forming the mixture.