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Dissolving and Separation Investigation

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Dissolving and Separation Investigation

A team is helping prepare a hands-on science display at an art gallery. Their job is to separate a mixed sample of salt, sand and iron filings, then explain what happens when salt dissolves. Use the evidence and plan a safe, sensible method. Do not taste any materials.

Explore the science

A dissolved substance has not vanished: its particles have spread through the liquid. The substance that dissolves is the solute; the liquid doing the dissolving is the solvent. Diffusion is the spreading of particles from an area of higher concentration to an area of lower concentration. A mixture can often be separated by choosing a method that uses a physical property.

1.Salt is stirred into water until the crystals can no longer be seen. Which statement best explains what has happened?

The salt has changed into water.
Salt particles have spread through the water, forming a solution.
The salt has been destroyed.
The salt has floated to the bottom.

2.In salt water, identify the solute and the solvent.

3.A drop of food colouring spreads through still water without stirring. Using the definition of diffusion in the science text, what is this spreading called? Explain what moves and in which direction the particles spread.

4.Match each material in the gallery sample to a useful separation method.

Iron filings
Sand mixed with water
Dissolved salt in water

Evaporate the water
Use a magnet
Filter through filter paper

5.True or false: Filter paper will separate dissolved salt from salt water. Give a reason for your answer.

TrueFalse

Plan the investigation

The gallery team has a mixture of salt, sand and iron filings. They can use water, a magnet, filter paper and safe warming equipment with adult supervision. Think about the order of steps: some methods work best before water is added.

6.Put these steps in a sensible order, numbering them 1–4: filter out the sand; add water and stir to dissolve the salt; use a magnet to remove iron filings; evaporate the water to recover salt.

7.Write a hypothesis for this test: What do you predict will happen to salt and sand when each is mixed with water and stirred? Give a reason for your prediction.

8.A group warms salt water in an evaporating dish and later sees crystals. What happened to the water, and why could the salt be collected?

9.The group wants to make the salt dissolve faster, without changing the amount of salt. Name two changes they could make and explain why each helps.

10.Record one observation that would show the sand was separated by filtration, and one observation that would show the salt was recovered by evaporation.

11.Suggest one safety rule for warming salt water in this investigation, and explain why it matters.

12.Finish the investigation summary using all four words: dissolve, solute, solvent, diffusion. Explain how salt water forms and how salt can later be recovered. Use the definition of diffusion in the science text.