Science 8th grade
UNIT 8: Mixtures 8.5 Solutions
Science 8th grade
UNIT 8: Mixtures 8.5 Solutions
When you place a lump of sugar or some salt in water it seems to disappear. This is called dissolving. You get a colourless solution. The substance that dissolves is called the solute. The substance that it dissolves into is called the solvent.
A solution is a mixture. A sugar solution is a mixture of water and sugar. Although the sugar seems to disappear, it is still there. The sugar molecules have simply spread out among the water molecules.
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The diagrams below show what happens to sugar molecules when they dissolve.
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If you dissolve a coloured salt such as copper sulfate, the solution formed is coloured.
All solutions are transparent. This means you can see through them.
A liquid like milk is not a solution because it is not transparent.
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Activity 8.5 (Dissolving)
SE: 1) Place a watch glass or picce of paper on a top pan balance and find its mass. Add some salt. This is the solute. Find the mass of the salt. Record the mass.
2) Remove the salt. Now place a beaker of water on the top pan balance and find the mass of the water and beaker. The water is the solvent. Record the mass.
3) Add the salt to the water and find the mass.
Questions
${A_1}$: What was the mass of the salt used?
${A_2}$: What was the mass of the water and the beaker?
${A_3}$: What was the mass of the solution and the beaker?
${A_4}$: What does this tell you about the salt solution?
When salt is added to water and it dissolves, it has not disappeared. The salt particles are still in the water. The mass of a solution equals the total mass of the solute and the solvent. This is true for any solution.
mass of solute + mass of solvent = mass of solution
No mass has been lost. This is called conservation of mass.
Questions
1) In a solution of sugar and water, which is the solvent and which is the solute?
2) What mass of salt solution is made when $9g$ of salt is dissolved in $50g$ of water? Explain how you worked out your answer.
$A+I$: 3) A green powder was placed into a beaker of water. After it was stirred the water looked cloudy and lumps of powder could still be seen. Has a solution been formed? Explain your answer.