Help, chemistry c4,c5,c6 10th june 2013

Ok here you go.

Metal (positive) ions can be identified two ways.

1) Use a flame test. Sterilise the end of a nichrome wire with hydrochloric acid and dip into a solid compound that you wish to test. Place the tip under a blue Bunsen flame and observe the flame colour.

(L)ithium compounds give a crimson colour like (l)ipstick.
(S)odium compounds give the yellow colour of the (s)un.
(P)otassium compounds give a lilac colour like lavender in a flower (p)ot.
Calcium makes your bones strong like bricks. Calcium compounds give a brick red colour.
(B)arium compounds give a (b)amboo green colour.

2) Dissolve the compound in distilled water and add a few drops of dilute sodium hydroxide solution. If a precipitate is formed, observe its colour. (This time there is no easy way to remember the colours, just remember them)

Iron(II), Fe 2+, makes a green precipitate of iron(II) hydroxide.
Iron(III), Fe 3+, makes a brown precipitate of iron (III) hydroxide.
Copper(II), Cu 2+, makes a blue precipitate of copper(II) hydroxide.

Then we need to identify non-metal (negative) ions. There are three tests: identify a carbonate, sulfate or halide.

1) To identify a carbonate, add a few drops of dilute hydrochloric acid. If you notice fizzing, a gas is being given off. Test with limewater, which should go cloudy if the gas is carbon dioxide. If so, the compound had carbonate ions.

2) To identify a sulfate, add dilute hydrochloric acid, followed by barium chloride solution. A white precipitate of barium sulfate indicates there are sulfate ions in the compound.

3) To test for a halide, add nitric acid followed by silver nitrate solution and observe a precipitate colour.

White - silver chloride (so compound contains chloride ions)
Cream - silver bromide (so the compound contains bromine ions)
Yellow - silver iodide (so the compound contains iodide ions).

Hope that helps a lot!



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How is everyone feeling about the exam?

possible 6 marks-

Just revise everything! I think that they might ask us 6 marks on-
-Rate of reactions/using different methods to determine it
-The periodic table(HALOGENS vs ALKALI METALS)
-Which ore is the most economically viable to extract out of a table.
-Which metal is the most appropriate for this job?
-Exo/Endo reactions
-Correlation and cause and a random topic(THE DOGGY ONE)
-How can a factory owner make their yeild larger/improve efficiency...
-The different ways of extracting an ore-(ELECTROLYSIS/REDUCTION)

One of these is bound to come up!If not then we have all flopped the test like jan p4p5p6

How did everyone find it?

Pretty easy really I found. Just a slight blip in that I initially thought that if the energy of the products went down, it was an endothermic reaction, yet it's actually the opposite... So my answer was really messy as I had to change all the wording. (last 6 marker)

Have you wrote answers to these by any chance?

ahaha lol that doesn't matter.I think the six marks were great.They literally required no knowledge.I think i dropped odd 1 or 2 markers but overall i found it quite easy.I think grade boundaries are gona be 43/44 for an a*.