Starter quiz
- A ______ material is composed of only one type of chemical.
- 'pure' ✓
- What is the name given to a substance found in a material in very small amounts, but which can alter the material’s properties?
- 'impurity' ✓
- Which diagram correctly represents a mixture of two metals in the solid state?
- Which of these statements about mixtures are true?
- Mixtures boil at a single, specific temperature.
- Mixtures contain a maximum of three types of chemicals.
- Mixtures boil over a range of temperatures. ✓
- Mixtures always include water.
- Mixtures must contain at least two types of chemicals. ✓
-
What is the highest temperature at which all of these substances are in the solid state?- -218C
- -210C ✓
- 0C
- 2950C
- never
-
- Starting from a substance in the gas state, can you put the states and the temperatures at which changes of state happen in order?
- 1⇔substance in the gas state
- 2⇔condensing point
- 3⇔substance in the liquid state
- 4⇔freezing point
- 5⇔substance in the solid state
Exit quiz
- A pure substance in chemistry is a single element or compound that is not mixed with any other substance. Which of the following are pure substances in chemistry?
pure beeswax
pure gold bars ✓
pure orange juice
pure water in the solid state ✓
The image shows the label of a pack of orange juice. What information on the label tells us it is not chemically pure?- it contains at least two types of carbohydrate ✓
- it contains 200 mg of potassium per 100 ml ✓
- it contains protein and vitamin C ✓
- it has one ingredient: orange juice
- it is NOT FROM CONCENTRATE
-
- Honey has a melting range of 35 to 40C and it decomposes before it boils. Using this information and what you know about pure substances, what makes honey an impure substance?
- it decomposes before it gets to boiling
- it is melting at 36C
- it has a melting range from 35 to 40C ✓
- it has another substance added to it
- it is made up of more than one type of compound ✓
-
- How is the melting point of a chemical substance represented on a graph?
- as a horizontal line on a cooling curve ✓
- as a horizontal line on a heating curve ✓
- as a sloped line on a cooling curve
- as a sloped line on a heating curve
-
A melting and freezing experiment is done with stearic acid. Put the stages of the experiment in order:- 1⇔Set up a beaker with water, heating up above a Bunsen burner to a gentle boil.
- 2⇔Clamp a boiling tube, with solid substance and thermometer below water level.
- 3⇔Record temperature at suitable time intervals until it reaches 70C.
- 4⇔Note the point at which the solid starts to melt.
- 5⇔Lift the clamp with the tube from the hot water.
- 6⇔Record the temperature at suitable time intervals until it reaches 50C.
- 7⇔Note the point at which the liquid starts to solidify.
- Honey can crystallise at room temperature, and starts to decompose (caramelise and smoke) at around 60C. How could you melt crystallised honey so this doesn't happen? Put the steps in order.
- 1⇔Heat water in a pan until 60C and turn off the heat.
- 2⇔Put honey in a glass bowl.
- 3⇔Place the bowl in the hot water.
- 4⇔Wait until all the honey has just melted and remove from the pan.
- 5⇔Enjoy! You can repeat this if it crystallises again.
Worksheet
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Presentation
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Video
Lesson Details
Key learning points
- A 'pure substance' in chemistry is a single element or compound not mixed with any other substance.
- The definition of 'pure' means something different in its everyday usage.
- Pure elements and compounds have specific melting and boiling points.
- Melting point data can be used to recognise substances with specific melting points as pure substances.
Common misconception
Pupils can struggle to decide on the scales needed for an axis on a graph.
Suggest a suitable scale that will fit on the graph paper they will use or use a computer to draw graphs.
Keywords
Pure substance - A pure substance in chemistry is a single element or compound that is not mixed with any other substance.
Property - A property is a feature or characteristic of a substance that can be used to classify it, or describe how it behaves.
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