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Year 7 Science: Solutions and Mixtures

Acids and Alkalis

Homework may be marked on Firefly – check your feedback and make corrections to your work! This is your responsibility!

Solutions and Mixtures AND Acids and Alkalis – Revision Checklist

Dissolving as the breaking up of a substance in to small particles, the particles spreading out and being surrounded by particles of the solvent.

Meanings of the terms: SOLUBLE - a substance which dissolves in a solvent. INSOLUBLE - a substance which does not dissolve in a solvent. SOLVENT - a liquid that will dissolve something. SOLUTE - the substance which dissolves in a solvent. SOLUTION - a mixture of a solvent and a solute.

Solutions are clear. Clear as not meaning the same a colourless. Dissolving can be made to occur faster by:

Breaking the solute up into smaller lumps. Using a hot solvent. Stirring the mixture.

Solvents other than water exist If the temperature of the solvent is increased the amount of solute that will dissolve in the solvent

will also increase. The meaning of the term saturated solution - a solution in which no more of a given solute will

dissolve at that temperature. Cooling of a hot saturated solution will result in recrystallisation because at the lower temperature

not all of the solute can be dissolved. Rock salt as an impure substance (a mixture of salt, mud and sand). Purification of rock salt

(dissolve, filter and then evaporate solvent). Filtration as a method of removing undissolved solids from a solution. The meaning of the term filtrate (liquid collected as a result of filtration).

Evaporation as a method of obtaining a solute from a solution. If a solution is heated so that the solvent evaporates, and the solvent vapour is then cooled so that

it turns back to a liquid, then we can obtain the solvent from a solution. This process is called simple distillation. The meaning of the term distillate (the liquid collected during distillation).

The test for purity of water – boils at exactly 100oC at atmospheric pressure. The separation of miscible liquids by fractional distillation. The liquid with the lower boiling point

evaporates first and is then condensed. Separation of coloured substances by chromatography. Pupils should be familiar with both radial

and ascending paper chromatography. Samples of the same dye will travel the same distance along the paper.

Use of universal indicator to test solutions to determine pH number and describe as a strong/weak acid/alkali

Name some common acids and alkalis. Know what an indicator is and the colour changes associated with UI and red cabbage

Describe what a neutralisation reaction is and give examples of some neutralisation reactions (such as indigestion relief, bee/wasp stings)

Dissolving

Word Meaningthe breaking up of a substance in to small particles, the particles spreading out and being surrounded by particles of the solvent.a liquid that will dissolve something.

the substance which dissolves in a solvent

a mixture of a solvent and a solute

A property of a chemical: it is capable of dissolving in a solvent

A property of a chemical: it is not capable of dissolving in a solvent

Practical: Testing Different SolventsThere are many different solvents you can try and use to dissolve a substance.

Solvent Are the following soluble or insoluble in this solvent?Tippex Marker pen White paint Engine oil

White spiritEthanol

Water

Solutions and Mixtures Topic: Important Words

Use a dictionary or text book to find the meanings to these words. Put them into your own words; don’t just copy. Make sure you understand them

Word Meaning

Saturated solution

Condensation (in terms of water)

Pure (in terms of a chemical)

Miscible

Immiscible

Practical: DissolvingDissolving can be made to occur faster by:

• Breaking the s _ _ _ _ _ _ up into smaller lumps (this increases the s _ _ _ _ _ _ _ a _ _ _)

• Increasing the temperature of the s _ _ _ _ _ _.• S _ _ _ _ _ _ _ the mixture.

Aim: to see how much of a solute (copper sulphate) can dissolve in a solvent (water) at different temperatures

What is our independent variable?

What is our dependent variable?

List 3 control variables

Table:

Conclusion and explanation:

Questions: Dissolving

Saturated Solutions and RecrystalisationMethod:

1) Use a small volume of hot water from the kettle (around 10ml). This volume is roughly half an egg-cup full. Be careful pouring hot water into a small container!

2) Use sugar or salt and stir it in a small amount at a time until no more will dissolve.3) Leave the mixture to cool down in a warm place (next to a radiator?)4) Set up the same experiment but this time leave the mixture to cool down in a cooler

place (on a windowsill?)

Questions:

1) In step one, which of your glossary words can you use to describe the water

2) In step two, which of your glossary words can you use to describe the salt

3) In step two, which of your glossary words can you use to describe the salt water?

4) In step two, what kind of solution have you made?

Task:

Make a poster to show what you did in your experiment. It needs to include:

A description of what you did Photographs Answers to the questions above Observation – what do you notice happens to the solution you have left to cool down

in a cooler place compared to a hotter place? Attach a copy of your poster to this task

Bonus tasks for commendations:

Make a time-lapse video of your solutions are they cool down

Filtration

Practical: Rock SaltRock salt is an impure substance (a mixture of salt, mud and sand).

Aim: To find out what % of the rock salt is salt

You should be able to puzzle out a way of separating the salt from the mud and sand

Extension: complete a calculation to find out what % of the rock salt is salt.

Questions: Filtration

Distillation• A s _ _ _ _ _ _ _ is heated so that the solvent e _ _ _ _ _ _ _ _ _ _

• The solvent vapour is then c _ _ _ _ _ so that it c _ _ _ _ _ _ _ _ (turns back to a liquid)

• The liquid that is collected during distillation is called d _ _ _ _ _ _ _ _ _

Questions: Distillation

ChromatographyChromatography is a technique used to separate out a mixture of different solutes using a

solvent.

Setting up:

Analysing results:

Questions: Chromatography

The pH ScaleThe pH scale is a measure of how acid or alkali a substance is

1 2 3 4 5 6 7 8 9 10 11 12 13 14

IndicatorsYou could use a machine called a pH probe to measure the pH of a liquid to find out how acid or alkali something is, or you could use an indicator. An indicator is a chemical that will change colour letting you know whether something is an acid or an alkali. There are lots of different indicators and each one changes colour differently.

Find out what colour the following indicators change in different liquids and complete the table:

Different Indicators Turn Different Colours!Indicator pH

1pH 2

pH 3

pH 4

pH 5

pH 6

pH 7

pH 8

pH 9

pH 10

pH 11

pH 12

pH 13

pH 14

Universal indicatorRed Cabbage

Phenolpthalein

Red Litmus

Blue Litmus

Neutralisation Reactions

Practical: Indigestion Tablets

Questions: Indicators and the pH scale