Combined 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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