c8 chemical analysis

Question 1

what is a pure substance in chemistry?

Answer 1

a single element or compound which is not mixed with any other substance

Question 2

how can you use melting or boiling point to tell you how pure a substance is?

Answer 2

1) a chemically pure substance will melt or boil at a specific temperature.
2) you can test the purity of a sample by measuring its MP and BP and comparing it with the MP or BP of the pure substance.
3) the closer the value is to the actual MP and BP, the purer your sample is.

Question 3

what do impurities in your sample cause?

Answer 3

• it will lower the MP and increase the melting range of your sample.
• they will also increase the BP and may result in your sample boiling over a range of temperatures

Question 4

what is a formulation?

Answer 4

useful mixtures with a precise purpose that are made by following a ‘formula’. each component in a formulation is present in a measured quantity, and contributes to the properties of the formulation so that it means its required function

Question 5

what are some examples of formulations?

Answer 5

fuels
cleaning agents
paint
medicines
alloys

Question 6

why are formulations important in the pharmaceutical industry?

Answer 6

by altering the formulation of a pill, chemists can make sure it delivers the drug to the correct part of the body at the right concentration, that its consumable and has a long shell life

Question 7

what is the importance of the part of a products packaging which tells you its composition?

Answer 7

• tells you that the product is a formulation.
• lets you choose a formulation with the right composition for your particular use

Question 8

what is the test for chlorine gas and what is the positive result?

Answer 8

• damp litmus paper
  POSITIVE RESULT: bleaches the litmus paper, turning it white

Question 9

what is the test for oxygen gas and what is the positive result?

Answer 9

• glowing splint
  POSITIVE RESULT: the glowing splint should relight

Question 10

what is the test for carbon dioxide and what is the positive result?

Answer 10

• limewater// calcium hydroxide
  POSITIVE RESULT: the limewater turns cloudy

Question 11

what is the test for hydrogen and what is the positive result?

Answer 11

• burning splint, squeaky pop
  POSITIVE RESULT: squeaky pop sound

Question 12

what are carbonates and how can you test for them?

Answer 12

1) carbonates are substances that contain CO3 ^2- ions.

2) you can test for them by adding a few drops of dilute acid to a test tube containing the mystery substance.
- then you can connect this test tube to one containing lime water.
-if carbonate ions are present, the reaction with the acid will release CO2 and will turn the limewater cloudy

Question 13

how to test for sulfates?

Answer 13

1) use a dropping pipette to add a couple drops of dilute HCl followed by a few drops of barium chloride solution to a test tube containing the mystery solution.
2) if sulfate ions are present, a white precipitate of barium sulfate will form

Question 14

how to test for halides? (chloride, bromide and iodide)

Answer 14

1) to identify a halide ion, add a couple drops of dilute nitric acid, followed by a couple drops of silver nitrate solution to your mystery solution.

• CHLORIDE: white precipitate of silver chloride.
  -BROMIDE: cream precipitate of silver bromide.
  -IODIDE: yellow precipitate of silver iodide.

Question 15

for the flame test, what colour is produced for:
1) lithium cations
2) sodium cations
3) potassium cations
4) calcium cations
5) copper cations

Answer 15

1) LITHIUM- crimson flame
2) SODIUM- yellow flame
3) POTASSIUM- lilac flame
4) CALCIUM- orange/ red flame
5) COPPER- green flame

Question 16

how do some metals form a coloured precipitate with NaOH?

Answer 16

1) many metal hydroxides are insoluble and precipitate out of solution when formed.
2) so you add a few drops of sodium hydroxide to a solution of your mystery compound to try to form an insoluble hydroxide.

Question 17

what is the metal ion and the colour of precipitate for the metal hydroxide?

Answer 17

calcium- white
copper (II)- blue
iron (II)- green
iron (III) brown
aluminium- white at first but adding excess NaOH forms a colourless solution.
magnesium- white

Question 18

how does the flame emission spectroscopy work?

Answer 18

1) a sample being placed in a flame.
2) as the ions heat up, the electrons move to higher energy levels.
3) when the electrons drop back to their original energy level, they release energy as light.
4) the light passes through a spectroscope, which can detect different wave lengths of light to produce a line spectrum.

Question 19

what do the combinations of wavelengths emitted by an ion depend on?

Answer 19

its charge and electron arrangement.
- since no 2 ions have the same charge and the same electron arrangement, different ions emit different wavelengths of light.
- so each ion produces a different pattern of wavelengths, and has a different line on the spectrum.

Question 20

what does the intensity of the spectrum indicate and what does this mean?

Answer 20

1) the concentration of that ion in solution.
- this means that line spectra can be used to identify ions in solution and calculate their concentrations

Question 21

why can flame emission spectroscopy be more useful than just flame tests?

Answer 21

because it can be used to identify different ions in mixtures, but flame tests only work for substances that only contain a single metal ion

Question 22

what are the advantages of using instrumental analysis’ instead of manual/ chemical analysis’ ?

Answer 22

1) very sensitive- they can detect even the tiniest amounts of substances.
2) very fast and the tests can be automated.
3) very accurate