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GCSE Chemistry 🧪 > Separating Substances 🔥 > Flashcards

Separating Substances 🔥 Flashcards

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1
Q

What is a pure substance?

A

A substance which consists of a single element or compound which contains no other substances.

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2
Q

What is a mixture?

A

Two or more elements or compounds that are physically mixed together, they are not chemically bonded.

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3
Q

What is air an example of?

A

A mixture

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4
Q

What is a characteristic of pure substances?

A

Melt and boil at specific and sharp temperatures e.g pure water has a boiling point of 100°C and a melting point of 0°C.

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5
Q

What would a pure substance look like on a heating/cooling curve?

A

The horizontal part of the graph would show a sharp melting point.

E.g https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1280,f=auto/uploads/2020/02/Purity-Pure-Substance-Cooling-Curve.png

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6
Q

What would an impure sample look like on a heating/cooling curve?

A

Produce a gradual decrease/increase in temperature.

E.g https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1280,f=auto/uploads/2020/02/Purity-ImPure-Substance-Cooling-Curve.png

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7
Q

What is a compound?

A

Contains two or more types of atom bonded/joined together.

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8
Q

What is simple distillation used to separate?

A

A liquid and a soluble solid from a solution
OR
A pure liquid from a mixture of liquids

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9
Q

Give a brief outline of simple distillation.

A
  • solution is heated and pure water evaporates producing a vapour which rises.
  • the vapour passes through the condenser, where it cools and condenses, turning into the pure liquid that is collected.
  • only the solid solute will be left behind.
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10
Q

What is fractional distillation used to separate?

A

Different liquids from a mixture of liquids.

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11
Q

Give a brief outline of fractional distillation.

A
  • the solution is heated to the temp of the substance with the lowest boiling point.
  • this substance will rise and evaporate first, and vapours will pass through a condenser and will be collected.
  • this leaves behind the other component(s) of the mixture.
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12
Q

What is filtration used to separate?

A

An insoluble solid from a liquid.

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13
Q

Give a brief outline of filtration.

A
  • A piece of filter paper is placed in a filter funnel above a beaker.
  • The mixture is poured into the filter funnel.
  • The filter paper will only allow small liquid particles to pass through a filtrate.
  • solid particles are too large so will stay behind as a residue.
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14
Q

What is crystallisation used to separate?

A

A dissolved solid from a solution

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15
Q

Give a brief outline of crystallisation.

A
  • A solution is placed in an evaporating basin and heated.
  • Some water evaporates and solid particles begin to form.
  • All the water evaporates which labels solid crystals.
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16
Q

What is paper chromatography used to separate?

A

Mixtures of soluble substances. (E.g inks)

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17
Q

Why is pencil used in paper chromatography to draw a start line?

A

Ink would run into the chromatogram along with the samples.

18
Q

Should the pencil line sit above or below the level of solvent?

A

Above so the samples don’t wash into the solvent container.

19
Q

Will substances with higher solubility travel further?

A

Yes

20
Q

How many spots will an impure substance show up with?

A

More than one

21
Q

What is the stationary phase in paper chromatography?

A

The paper

22
Q

What is the mobile phase in paper chromatography?

A

The solvent

23
Q

Give a brief outline of paper chromatography.

A
  • pencil line is drawn and spots of ink are placed on it.
  • the paper is lowered into the solvent container.
  • the solvent travels up the paper taking some coloured substances with it.
  • substances will spread apart, showing different components of the ink / dye .
24
Q

How many spots does a pure substance produce on a chromatogram?

A

One spot

25
Q

What is the equation for the Rf value?

A

distance travelled by substance / distance travelled by solvent

26
Q

What number must Rf values always be below?

A

1

27
Q

What does Rf stand for?

A

Retention factor

28
Q

Why do we use the Rf value?

A

To identify substances because it can be compared with Rf values of known substances. (Reference values)

29
Q

What does it mean if the Rf value is close to 1?

A

The more soluble the component in the solvent is. Attracted to the solvent (mobile phase)

30
Q

What is potable water?

A

Water that is safe to drink.

31
Q

What 3 processes are involved in treating water in order?

A

Filtration, sedimentation, chlorination

32
Q

What does filtration remove from water?

A

Large insoluble particles

33
Q

What is used to filter water in filtration?

A

Layers of sand and gravel.
Sometimes mesh filters.

34
Q

What does sedimentation remove from the water?

A

Large insoluble particles sink to the bottom of the tank of water.

35
Q

What does chlorination do to treat water?

A

Kills bacteria and microorganisms which are too small to be trapped by the filters.

36
Q

Diagram of purifying water.

A

https://cdn.savemyexams.co.uk/cdn-cgi/image/w=1280,f=auto/uploads/2020/01/Water-treatment-1.png

37
Q

How can we attain pure water from sea water?

A

By using simple distillation

38
Q

What is a disadvantage of using simple distillation to attain pure water?

A

It is expensive because large amount of energy are needed to heat seawater.

39
Q

Why is distilled water useful in the laboratory for dissolving substances?

A

It does not contain any dissolved ions that might interfere with chemical analysis.

40
Q

Water used in analysis must not contain any?

A

Dissolved salts

GCSE Chemistry 🧪 (11 decks)

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