Chemical analysis.

Question 1

What is a pure substance?

Answer 1

A single element or compound.

Question 2

How can you find out if a substance is impure?

Answer 2

They’re mixtures and don’t melt/boil at a specific temperature. This means they’re impure.

Question 3

What is a formulation?

Answer 3

Formulations are mixtures that have been carefully designed to have specific properties. Eg fuels, cleaning agents, paints.

Question 4

What two phases does chromatography involve?

Answer 4

A stationary phase-Which does not move.
A mobile phase-Which does move/

Question 5

(RP) Investigate how paper chromatography can be used to separate and tell the difference between coloured substances.

Answer 5

1)Draw a line with a pencil on a piece of absorbent paper.
2)Put 5 samples of known food and unknown (X)colouring on the line.
3) Dip paper into the solvent.
4) Wait for solvent to travel to the top of the paper.
5) Identify substance X by comparing the horizontal spots with the 5 other samples.

Question 6

What is the equation to find the Rf-value?

Answer 6

Rf = distance moved by substance
distance moved by solvent

Question 7

Gas tests (Hydrogen, Oxygen, carbon dioxide, chlorine).

Answer 7

Hydrogen- Burning splint held at the open end of a test tube of the gas. Burns rapidly with a pop sound.
Oxygen-Glowing splint and insert it into a test tube of
the gas. Relights in oxygen.
Carbon dioxide- Calcium hydroxide (lime water). CO2 is bubbled through limewater. Turns milky (cloudy) if co2 is present.
Chlorine-litmus paper. damp litmus paper put it into chlorine gas. litmus paper is bleached and turns white.

Question 8

What is a flame test used for?

Answer 8

Flame tests can be used to identify some metal ions (cations).

Question 9

(RP) Identify the ions in a single ionic compound using chemical test.

Answer 9

1)Dip the piece of nichrome wire in Hcl. pass it through the flame to clean it.
2) Dip wire into the compound.
3)Put into a busen flame and observe the colour.

Question 10

Identifying cations (positive results-colours).

Answer 10

• lithium- crimson flame
• sodium- yellow flame
• potassium-lilac flame
• calcium-orange-red flame
• copper-green flame.

Question 11

How can some of the colours of some ions be masked in a flame test?

Answer 11

If its a mixture of ions. Eg Solution had sodium and potassium ions the pale lilac colour from potassium ions can be hard to detect alongside the intense yellow from the sodium ions.

Question 12

What do Carbonates react with?

Answer 12

Carbonates react with dilute acids to form carbon dioxide gas.

Question 13

What are precipitates?

Answer 13

Insoluble solids that come out from a solution.

Question 14

What colour precipitations are formed when metal ions are mixed with sodium hydroxide?

Answer 14

Aluminium- Aluminium hydroxide-White-Dissovles if more NaOH is added.
Calcium- Calcium hydroxide-White
Magnesium- Magneisum hydroxide-White
Copper-Blue
Iron(II)-Green
Iron(III)-Brown

Question 15

Sulfate reaction.

Answer 15

Hcl + barium chloride is added to a solution containing sulfate ions. Forms white precipitate of barium sulfate.

Question 16

What precipitates do halides form?

Answer 16

Halide + Silver nitrates in the presence of dilute nitric acid=silver halide precipitates.
Chloride-white
Bromide-cream
Iodide-yellow

Question 17

How can elements and compounds be detected and identified?

Answer 17

By using instrumental methods. Instrumental methods are accurate, sensitive and rapid.

Question 18

What is Flame emission spectroscopy used for?

Answer 18

used to analyse solutions that contain metal ions. The sample is put into a flame and the light given out is passed
through a spectroscope.
Produces a line which can be used to
-identify the metal ions in the solution and measure the concentration of the metal ions.