Paper 2-SC10

Question 1

What colour is the flame for a Li+ ion?

Answer 1

Red

Question 2

What colour is the flame for a Na+ ion?

Answer 2

Oragne/yellow

Question 3

What colour is the flame for a K+ ion?

Answer 3

Lilacy Pink

Question 4

What colour is the flame for a Ca 2+ ion?

Answer 4

Red/Orange

Question 5

What colour is the flame for a Copper 2+ ion?

Answer 5

Green/Blue

Question 6

What colour is the flame for a Mg 2+ ion?

Answer 6

Colourless

Question 7

What type of data is the flame test?

Answer 7

Quantitative data

Question 8

Why are instruments used to determine a substance rather than a human?

Answer 8

Faster
More sensitive
Accurate

Question 9

What is Flame Photometry?

Answer 9

The flame photometer measures the light intensity of the flame colours produced by metal ions. Its data is used to determine the concentrations of the metal ion in a dilute solution.

Question 10

How do you identify the metal ions using a flame photometer.

Answer 10

In the flame photometer, the coloured light from a vaporised sample can be split to produce an emission spectrum. The different lines in an emission spectrum look like a coloured barcode. Each metal ion produces a unique emission spectrum.

Question 11

What precipitate colour with hydroxide is the metal ion Fe 2+?

Answer 11

Green

Question 12

What precipitate colour with hydroxide is the metal ion Fe 3+?

Answer 12

Brown

Question 13

What precipitate colour with hydroxide is the metal ion Al 3+?

Answer 13

White

Question 14

What precipitate colour with hydroxide is the metal ion Ca 2+?

Answer 14

White

Question 15

What precipitate colour with hydroxide is the metal ion Cu 2+?

Answer 15

Blue

Question 16

How do you tell if a substance is either Al 3+ and Ca 2+?

Answer 16

After the two drops of hydroxide add an excess amount of hydroxide. The aluminium stayed colourless because the precipitate dissolves, calcium precipitate stayed as a white colour.

Question 17

How do you test for ammonia?

Answer 17

Smell it, smells like when urea breaks down.

Damp litmus paper will turn blue.

Question 18

What tests can you do to find out a metal ion?

Answer 18

Precipitation reactions and a flame test.

Question 19

What is a precipitation reaction?

Answer 19

Involves sodium hydroxide solution that forms the base of a test to identify dissolved metal ions. A few drops at a time of dilute sodium hydroxide are added to the test solition, colour change happens depending on the metal ions present.

Question 20

What is a flame test?

Answer 20

Used to identify metal ions in substances. Work with solid samples and with solutions, solid are easier to see the colour.

Question 21

How do you carry out a flame test?

Answer 21

1. Light a bunsen burner and open the air hole to give a hot blue flame.
2. Pick up a small sample of the test substances using a wire loop.
3. Hold the sample in the edge of the flame and observe the flame colour.

Question 22

What do you have to do with the wire loop to make sure it is clean.

Answer 22

Place the wire loop in hydrochloric acid before testing each sample. Platinum wire has a high melting point and is unreactive. It also gives no colour to the flame. However, nichrome alloy is often used instead. Altough it produces its own faint orange colour, it is much cheaper.

Question 23

How do you test for carbonate ions?

Answer 23

A reaction between a carbonate and a dilute acid gives a salt, carbon dioxide and water. As carbon dioxide is produced, we can use the standard carbon dioxide test to work out if an unknown substance is a carbonate.

Question 24

How do you test for sulfate ions?

Answer 24

Add dilute hydrochloric acid to an unknown solution, removing carbonate ions. These could disrupt test results by forming a precipitate with the barium ions added in step 2.

Add barium chloride to the same solution.
If sulfates are present, the white precipitate barium sulfate will form:
Ba2+(aq) + SO42-(aq) → BaSO4(s)

Question 25

How do you test for halide ions?

Answer 25

Add dilute nitric acid to an unknown solution, removing any carbonate ions that could react with the ions added in step 2 and disrupt the test. Add silver nitrate, if halide ions are present, they will form a precipitate with the silver ions.

Question 26

What colour is the precipitate with the chloride halide ion?

Answer 26

white

Question 27

What colour is the precipitate with the bromide halide ion?

Answer 27

cream

Question 28

What colour is the precipitate with the iodide halide ion?

Answer 28

yellow

Question 29

What is the correct order to test the cations present in an unknown salt?

Answer 29

Flame test Coloured precipitates with sodium hydroxide Testing the gas evolved for ammonium

Question 30

What is the correct order to test the anions present in an unknown salt?

Answer 30

Test for carbonate - test for carbon dioxide gas to confirm a positive result Test for sulfates - the presence of a white barium sulfate precipitate confirms a positive result Test for halide ions - the colour of silver halide corresponds to halide anion in a positive result

Question 31

Why must the test for anions present be carried out in a logical way?

Answer 31

If any HCl or BaCl2 is added to test for carbonate or sulfate, there will be chloride ions in the solution. These will be tested and there will be a false positive result for chloride ions.

Question 32

What are 3 advantages of instrumental methods?

Answer 32

Greater sensitivity and accuracy. Quicker at producing results. Able to analyse tiny samples.

Question 33

What are 3 disadvantages of instrumental methods?

Answer 33

Expensive. Need special training on how to use them. The results are often only useful when compared to data from known substances.

Question 34

What is a nanoparticle?

Answer 34

A particle between 1 and 100 nanometres in size.

Question 35

What can be said about the nanoparticle surface area to volume ratio?

Answer 35

It is very large and can catalyse more efficiency than big lumps of the same substances.

Question 36

Why is nanoparticulate materials used to clean clothes?

Answer 36

The large surface area allows them to be used as good catalysts and therefore can catalyse the breakdown of dirt.

Question 37

What can nanoparticles also used for?

Answer 37

Suncream. Titanium dioxide in bulk is a white solid, it absorbs harmful UV radiation present in sunlight. It is transparent because they are very small, useful for almost=invisible suncream.

Question 38

What are the risks of nanoparticles?

Answer 38

They can be breathed in because they are so small and can pass through cell-surface membranes. Their larghe surface area to volume ratios may aloow them to catalyse harmful reactions, or to carry toxic subsrtances bound to their surfaces. The risks are difficult to dtermine because modern nanoparticulate materials haven't been in use for long.

Question 39

Theory behind testing for sulphate ions

Answer 39

Add barium ions to sample, is barium sulfate is produced (white precipitate) then sulphate ions are present

Question 40

Step one of testing for sulphate ions

Answer 40

Add dilute HCL to sample to remove carbonates and sulphate ions which could also react

Question 41

Step two of testing for sulphate ions

Answer 41

Add barium chloride

Question 42

Step one of testing for halide ions

Answer 42

Add dilute nitric acid to get rid of carbonate and sulphate impurities

Question 43

Second step of testing for halide ions

Answer 43

Add silver nitrate

Question 44

Theory of testing for halide ions

Answer 44

Silver ions from silver nitrate react with halide ions to form a precipitate

Question 45

What does colouir of precipitate formed by halide ions and nitrate depend on?

Answer 45

The halide ion present