LSC: Mixtures, Elements and Compounds Assignment

1 Here is a list of mixtures:
a) maize meal and salt
b) dirty water
c) iron and copper filings
d) currants and rice.
Describe, in each case, a process you could use to get the substance in italics in a pure form out of the mixture.
2 If you mixed two substances together and then heated them, describe two observations that you could make if you wanted to know whether a chemical reaction had taken place.
3 Here is part of the label on a packet of potato chips.
Nutritional information Per 100 g
Calcium 100 mg
Magnesium 125 mg
Iron 27 mg
Phosphorus 420 mg

Use Fig. 6.1. showing the Periodic Table to answer these questions:
a) Write down the chemical symbols for calcium, magnesium, iron and phosphorus.
b) These substances are all elements, but one is different from the other three. State  which one is different and describe what it is that makes it different.
4 Look at the chemicals listed below and answer the questions about them. You can use
Fig. 6.1 showing the Periodic Table to help you.
iron water
sand oxygen
gold carbon dioxide
helium carbon
rust sea water
a) Name the two metals.
b) Name a gas that is not an element.
c) Name two compounds.
d) Name a mixture.
e) Name a non-metallic element that is a solid.
5 Here is a crossword puzzle to help you remember the names and symbols of some common elements.

i) Write the names of the elements that have the following symbols:
Across
1. H 3. Au 6. Na 11. Fe 12. Zn 15. Cu 17. Pb 24. I 25. Ca 26. K
Down
2. O 4. Li 5. Ag 8. C 10. N 14. U 16. Pt 19.
He 20. S 23. Sn
ii) Write down the symbols of the following elements:
Across
9. chlorine 18. a metal that is a liquid 22. neon 30. magnesium 31.bromine
Down
7. manganese 13. cobalt 21. a metal used in coins
27. argon 28. silicon 29. a metal that burns brightly in air
6 What does this term mean? Give an example.
a) filtrate
b) residue
7 You have a solution of sugar in water. You want to obtain the sugar from it.
a) Explain why filtering will not work.
b) Which method will you use instead?
8 Describe how you would crystallise potassium nitrate from its aqueous solution.
9 How would you separate salt and sugar? Mention any special safety precaution you would take.
10 Now see if you can think of a way to get clean sand from a mixture of sand and little bits of iron wire.
11 Seawater can be purified using this apparatus:

a) i) What is the maximum temperature recorded on the thermometer, during the distillation?
ii) How does this compare to the boiling point of the seawater?
b) In which piece of apparatus does evaporation take place? Give its name.
c) i) Which is the condenser, A, B, or C?
ii) Where does the supply of cold water enter?
d) Distillation is used rather than filtration, to purify seawater for drinking. Why?
12 Argon, oxygen, and nitrogen are obtained from air by fractional distillation. Liquid air, at -250 °C, is warmed up, and the gases are collected one by one.
a) Is liquid air a mixture, or a pure substance?
b) Explain why fractional distillation is used, rather than simple distillation.
c) During the distillation, nitrogen gas is obtained first, then argon and oxygen. What can you say about the boiling points of these three gases?