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chemistry > chemical analysis (p2) > Flashcards

chemical analysis (p2) Flashcards

1
Q

What is a pure substance?

A

A single element or compound that is not mixed with any other substance

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2
Q

What type of substances melt and boil at specific temperatures?

A

Pure substances

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3
Q

If a substance boils between 55 and 58 ᵒC, will it be pure or impure?

A

impure

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3
Q

What type of substances melt and boil over a range of temperatures?

A

Impure substances

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4
Q

Is carbon dioxide pure or impure?

A

pure

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5
Q

Is oxygen pure or impure?

A

pure

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6
Q

What is a formulation?

A

A mixture that has been designed as a useful product

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6
Q

Is water from a tap pure or impure?

A

Impure as contains dissolved salts

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7
Q

Are formulations pure or impure?

A

Impure

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8
Q

What is chromatography used to separate?

A

Mixtures of soluble susbtances

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9
Q

Name the two phases in chromatography

A

Stationary phase - where molecules can’t move
Mobile phase - where molecules can move

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10
Q

What phase is the paper in chromatography?

A

Stationary phase

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11
Q

What phase is the water in chromatography?

A

Mobile phase

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12
Q

Why do substances separate in paper chromatography?

A

Substances move up the paper when they are dissolved in the solvent
The different substances have different solubilities in the solvent
Therefore they travel different distances up the paper

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13
Q

How could you tell if a substance was impure by looking at a chromatogram?

A

There would be more than one spot in a vertical column above the original spot

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14
Q

How could you tell if a substance was pure by looking at a chromatogram?

A

There would be only one spot in a vertical column above the original spot

15
Q

Why should the baseline be drawn in pencil?

A

Pencil is insoluble
If it was drawn in pen the ink would dissolve and so the line would run

16
Q

Why should the level of water be below the baseline?

A

If it was above the baseline the spots would wash off the paper

17
Q

What is the solvent front?

A

The distance travelled by the solvent

18
Q

When should you remove the chromatography paper?

A

When the solvent has nearly reached the top

19
Q

Why is the chromatography paper often attached to a glass rod when carrying out chromatography?

A

So that it stands up in the water

20
Q

Why should a lid be placed on the beaker during chromatography?

A

To saturated the atmosphere in the beaker with solvent vapour

prevent evaporation

21
Q

The higher the Rf value the ………. the distance travelled by the substance

A

Greater

22
Q

What equation is used to calculate Rf values?

A

Rf value = distance travelled by spot ÷ distance travelled by solvent

23
Q

How many spots will a pure susbtances produce on a chromatogram?

A

one

24
Q

Describe how you would set up a chromatogram

A
  • Draw a baseline in pencil near the bottom of a piece of filter paper
  • Add a spot of ink to this line and allow it to dry
  • Place the paper in a beaker of solvent (usually water), make sure the level of solvent is below the baseline
  • Add a lid to the beaker to stop the solvent evaporating
  • Allow the solvent to run up the paper
  • Remove the paper from the beaker just before the solvent reaches the top of the paper
24
Q

What is the test for oxygen?

A
  • Use a glowing splint
  • If oxygen gas is present the glowing splint will relight
25
Q

What is the test for hydrogen?

A
  • Use a burning splint
  • If hydrogen is present it will burn with a squeaky pop
26
Q

What is the test for carbon dioxide?

A
  • Bubble gas through limewater (calcium hydroxide solution)
  • If the gas is carbon dioxide the limewater will turn from colourless to milky
27
Q

What is the test for chlorine?

A
  • Add damp litmus paper
  • If chlorine gas is present the litmus paper is bleached and turns white

chemistry (15 decks)

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