Separate Chemistry - C8 Chemical Analysis Flashcards

1
Q

What is the chemical meaning of a ‘pure’ substance?

What is the every day meaning of a ‘pure’ substance?

A

In Chemistry: A single element or compound that is not mixed with any other substance.

In everyday language: A substance that hasn’t had anything added to it, e.g. pure milk.

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2
Q

What data can be used to prove a substance is ‘pure’ and not a mixture?

A

Melting and Boiling points (because pure substance melt and boil at specific temperatures)

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3
Q

What is a formulation?

A

A mixture that has been designed as a useful product.

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4
Q

Give three examples of formulations

A

Any three from:

Fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods.

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5
Q

Name the two phases in chromatography.

A
  • Stationary Phase
  • Mobile Phase
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6
Q

In Chromatography, how do you calculate the Rf value for a substance?

A

Rf = distance moved by substance / distance moved by solvent

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7
Q

What will the chromatogram of a pure substance look like?

A

A pure substance will only show a single spot on the chromatogram.

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8
Q

Explain how paper chromatography can be used to separate a mixture.

A
  • A substance is added to the chromatography paper (stationary phase).
  • Molecules within a substance dissolve in the solvent and move up the paper (mobile phase).
  • The molecules within the substance separate because different chemicals spend different amounts of time in the mobile and stationary phases and therefore move different distances up the paper.
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9
Q

Describe how you would test for Hydrogen.

A
  • Collect gas in a test tube
  • Hold a burning splint at the open end of a test tube.
  • You will hear a ‘pop’ sound if Hydrogen is present
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10
Q

Describe how you would test for Oxygen.

A
  • Collect gas in a test tube
  • Insert a glowing splint into the test tube
  • The splint will relight if oxygen is present
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11
Q

Describe the test for Carbon dioxide.

A
  • Bubble the gas through limewater (calcium hydroxide solution)
  • If the limewater turns milky (cloudy) then carbon dioxide is present
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12
Q

Describe the test for Chlorine.

A
  • Collect gas in a test tube
  • Place damp litmus paper in the test tube
  • If chlorine is present, the litmus paper is bleached and turns white
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13
Q

Separate Q. What type of ions are metal ions?

A

Cations

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14
Q

Separate Q. What would the flame test results be for the following metal compounds?

a) Lithium
b) Sodium
c) Potassium
d) Calcium
e) Copper

A

a) Crimson flame
b) Yellow flame
c) Lilac flame
d) Orange-red flame
e) Green flame

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15
Q

Separate Q. If a sample contains a mixture of metals, why might it be difficult to identify the metals using a flame test?

A

Some flame colours can be masked by others

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16
Q

Separate Q. Describe the results you would see when adding sodium hydroxide to compounds containing the following metals:

a) Aluminium
b) Calcium
c) Magnesium
d) Copper (II)
e) Iron (II)
f) Iron (III)

A

a) Aluminium: White precipitate
b) Calcium: White precipitate
c) Magnesium: White precipitate
d) Copper (II): Blue Precipitate
e) Iron (II): Green Precipitate
f) Iron (III): Brown Precipitate

17
Q

Separate Q. Name the solution added to metal compounds to test for metal ions.

A

Sodium hydroxide solution

18
Q

Separate Q. Aluminium, calcium and magnesium all form white precipitates when sodium hydroxide is added. If sodium hydroxide is added in excess, which precipitate will dissolve?

A

Aluminium hydroxide

19
Q

Separate Q. Complete the word equations for the reaction of sodium hydroxide with:

a) Calcium nitrate
b) Copper sulfate

A

a) calcium nitrate + sodium hydroxide → calcium hydroxide + sodium nitrate
b) copper sulfate + sodium hydroxide → copper hydroxide + sodium sulfate

20
Q

Separate Q. Describe the test for a carbonate.

A
  • Add dilute acid to the unknown compound.
  • Bubble gas produced through limewater.
  • If limewater turns milky (cloudy) then the compound is a carbonate.
21
Q

Separate Q. Describe the test for Halide ions.

A
  • Add silver nitrate and dilute nitric acid to your unknown solution.
  • If a precipitate is produced, the unknown solution contains Halide ions.
  • Silver chloride is white, silver bromide is cream, silver iodide is yellow.
22
Q

Separate Q. Complete the word equations for the following reactions:

Silver nitrate + Barium chloride →

Silver nitrate + Barium bromide →

Silver nitrate + Barium iodide →

A

Silver nitrate + Barium chloride → Silver chloride + Barium nitrate

Silver nitrate + Barium bromide → Silver bromide + Barium nitrate

Silver nitrate + Barium iodide → Silver iodide + Barium nitrate

23
Q

Separate Q. Describe the test for sulfate ions.

A
  • Add barium chloride and dilute hydrochloric acid to your unknown solution.
  • A white precipitate will form if sulfate ions are present.
24
Q

Separate Q. Give three advantages of using instrumental methods to identify substances.

A
  • Fast
  • Accurate
  • Sensitive
25
Q

Separate Q. Name the instrumental method that can be used to identify metal ions in solutions.

A

Flame emission spectroscopy

26
Q

Separate Q. Describe how flame emission spectroscopy works.

A
  • Sample is put in a flame
  • Light emitted by flame is passed through a spectroscope
  • Line spectrum output is produced by the machine
  • This line spectrum is used to identify the metal ions and measure their concentration in the solution.
27
Q

Separate Q. Identify the metal ion present in the solution using the flame emission spectrometry data below.

A

The unknown metal ion is Ion Y because the line spectrum for the unknown metal ion matches the reference spectrum for Ion Y.