1The Diagram Represents the Substances Found in the Air

HELP

1The diagram represents the substances found in the air.

aHow does the diagram show that air is a mixture?

bHow many different substances are shown in the diagram?

cHow many of them are not molecules?

dHow many oxygen molecules are shown?

eName the three elements shown.

fiHow many different compounds are shown?

iiName them.

CORE

2aThe list below contains both mixtures and pure substances. Make a table with ‘Mixture’ and ‘Pure’ as headings. Then add each substance below to the correct column in your table.

bThe sentences below describe how pure ethanol (alcohol) can be obtained from fermented sugar, by distilling the solution and collecting the ethanol in it. The sentences are in the wrong order. Rewrite them in the correct order.

ACool the condenser with tap water.

BCollect only the vapour that condenses at 78°C.

CHeat the fermented sugar solution in a flask.

DWhen the thermometer reads 100°C, stop collecting the ethanol.

EPass the vapour into a condenser.

This worksheet may have been altered from the original on the CD-ROM.

EXTENSION

3Sammy investigated some fruit juice. A panelon the carton had information about theingredients.

Sammy measured the pH of the fruit drink andfound that it was between pH 4 and pH 5. Shefiltered the fruit drink. She measured out100 cm3 of the filtrate and heated it until it wasdry. She was left with 165 mg of an orangeresidue in the evaporating basin. Next, Sammydistilled 100 cm3 of the fruit drink. She collected99.2 cm3 of a clear, colourless liquid that boiledat exactly 100°C. Sammy sent the liquid to ananalytical laboratory that did some more testson it. They reported that it contained hydrogenand oxygen in the ratio 2:1. Sammy wonderedabout how she could find out if there really wasonly one type of food colouring in the juice.

aWhich substance was responsible for the pH that Sammy measured?

bWhat did Sammy remove when she filtered the juice?

ciWhy did filtering the juice not remove the residue obtained after evaporation?

iiHow much residue would Sammy have obtained if she had heated 1 litre of juice?

diWhat does the boiling point of the colourless liquid suggest that it might be?

iiExplain how the information from the analytical laboratory helps to identify the colourless liquid.

eDescribe how Sammy could find out if there was another yellow colouring in the juice. (Hint: this revises a process you first met in Year 7.)

fiWhich of the substances mentioned in the information is definitely pure?

iiExplain how you know this.

gSuggest a reason why water was put first in the list of ingredients.

This worksheet may have been altered from the original on the CD-ROM.