7H Solutions
Lesson 1: Dissolving
Learning objectives
 That when a solute dissolves mass is conserved
 That when a solute dissolves the solute and solvent particles intermingle
 That some solids dissolve in liquids and others do not
 How the particle theory can be used to model changes
Learning outcomes
 Name some solids that dissolve in water and some that do not
 State and explain that mass of solution is the same as that of solute + solvent
 Describe how solvent and solute particles mix.
Resources
For demonstration: 2 place balance, beaker of water and some salt.
Molecular models – Cubic ones joined together in a lump to
represent the closely arranged particles of salt in a grain of
salt.
For class practical: test tube rack with spatula full of a range of soluble and
insoluble solids (sugar, copper sulphate, flour and sulphur),
beakers (for adding water to test tubes, bungs for test tubes,
goggles.
Worksheets: “The dissolving story”, [Thinking through science book 1 © John
Murray] “Homework questions on concentration” [Thinking through science Book 1,
p.178]
Video S48 (Wolfreton School)
(Heinemann Book 1)
Lesson Outline
1. Demonstrate salt dissolving in water – elicit “dissolving” and a description of
what is seen happening. I.e. “it seems to disappear” How could we prove that
the salt is still present? – elicit “Mass” and “taste”
2. Demonstration: Weigh some salt. Place a beaker of water on a balance and
show that the measurement of mass indicates the presence of salt in the
mixture.
Or
Video: Programme 3(Mixtures) 00:30 – 02:15 could be used to prompt
the same line of questioning
3. Explanation/development of model
a. Thinking back to solid & liquid models from “S, L & G” and elicit
drawings of the particles in a grain of salt and in the beaker of water.
Use molecular models to show the two arrangements
b. Explain that salt particles are surrounded by water particles as they
are attracted to them. Show the particles of the salt grain model
separating and intermingling with the water particles
c. We can no longer see the salt particles as they are separated from
each other and are too small to see individually.
4. Show clip of video: 14.00 – 15.12 (which shows sand grains being broken up)
and/or look at the drawings on P89 of the textbook.
5. Class practical (can be done now or after next activity). Pupils add water to
range of soluble and insoluble solids. The aim of the exercise is to
discover/confirm that some substances are soluble and others are insoluble in
water
6. Worksheet 9.1:
a. Pupils read sheet and then work in pairs as instructed on the sheet to
produce a piece of creative writing under the heading “The dissolving
story”
b. Pupils evaluate each others work – discuss how it should be marked
Level 4 – I have shown that sugar disappears when is it placed in
water
Level 5 – I have said that sugar dissolves when it is added to water.
Level 6 – I have described the particles in a solid (sugar) and a liquid
(water). I have also shown that the particles become mixed up when
the sugar dissolves.
Level 7 – I have described the attraction between sugar and water
particles and I have explained how this causes the water particles to
surround the sugar particles and break the sugar grain into individual
particles.
7. Plenary question – Do all materials dissolve? How does the particle model
explain what happens when a solid does not dissolve?
Homework
Concentration worksheet