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Chemistry > C2.1 Purity and Separating Mixtures > Flashcards

C2.1 Purity and Separating Mixtures Flashcards

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1
Q

What is Relative atomic mass (Ar)?

A

The mean mass of an atom of an element compared to 1/12 the mass of a carbon-12 atom( 12/6 C)

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2
Q

What does a chemical formula tell you?

A

How many atoms of each element there are in a unit of substance.
E.G. Chemical formula of water is H2O
-this means each molecule of water contains 2 hydrogen atoms bonded to 1 Oxygen atom

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3
Q

What is Relative Formula Mass? (Mr)

A

the mean mass of a unit of a substance compared to 1/12 the mass of a carbon-12 atom.

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4
Q

How to calculate Mr?

A

add all the Ar values for all the atoms in a substance.

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5
Q

Units

A

Ar and Mr do not have any units

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6
Q

What is an empirical formula?

A

The simplest Whole-number ratio of the atoms of each element in a compound.
They are simplified by HCF

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7
Q

What does a balanced equation show?

A

the formulae and number of units for all the substances in a reaction

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8
Q

How do balanced equations also help?

A

They give you a way to check that you have correctly calculated Mr.

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9
Q

What is a pure substance?

A

A substance which has not been processed of change.

A pure substance consists of just ONE element or compound.

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10
Q

What is an impure substance?

A

A substance which contains more than one element or compound

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11
Q

What is an alloy?

A

A mixture of a metal with one or more other elements.
Most metals you use are alloys.
EG - mixture of gold and copper is used in jewellery

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12
Q

What is Melting point

A

The temperature at which it changes from solid to liquid

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13
Q

Melting point of a pure substance:

A

A single temperature without any variation

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14
Q

Melting Point of an impure substance:

A

(1) melting point is less than that of the pure substance
(2) It often melts over a range of temperatures NOT ONE temperature.
(3) Greater the difference between measured melting point and accepted MP - the lower its purity

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15
Q

How to determine MP?

A

Heat the substance and then either measure the temperature at which it melts, or the temperature at regular intervals.

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16
Q

What is it important to do when Measuring MP?

A

(1) Heat the substance slowly - allows temp of whole sample to increase
(2) Stir the substance as it melts - ensures the entire sample is at the same temperature

They both help improve accuracy.

17
Q

How is a solution formed?

A

When a solute (Substance which dissolves) dissolves in a solvent (substance it dissolves in).

18
Q

What happens when a substance dissolves?

A

Its particles separate and become completely mixed with particles of the solvent

19
Q

What is it meant when a substance is soluble?

A

Soluble - When a substance can dissolve in a particular solvent

20
Q

What is it meant when a substance is insoulble?

A

Insoluble - When a substance cannot dissolve in a particular solvent

21
Q

What does filtration do?

A

Separates insoluble substance in solid state from substances in liquid state

22
Q

How does filtration work?

A

Filter paper has tiny microscopic holes which allow the smaller liquid molecules to go through and stops the larger insoluble solid particles from going through

23
Q

What is the solid left in filtration called?

A

Residue

24
Q

What is the liquid which goes through the filter paper called?

A

Filtrate

25
Q

What is a saturated solution?

A

When no more solute can be dissolved into the solvent

26
Q

What happens when you heat a solution?

A

If you heat a solution, solvent evaporates leaving the solute behind / or a powder (if heated too strongly).

If you allow solvent to evaporate slowly, you get a regularly shaped crystal

27
Q

How to do crystallisation?

A

Heat a solution gently until it becomes saturated.
Crystals will start forming at this point, so let the solution cool slowly.
As solution cools, solubility of solute decreases, so more crystals form.

28
Q

Two types of distillation:

A

Simple and Fractional

29
Q

Simple Distillation:

A

(1) separates solvent from a solution.
(2) Relies on Solvent having much lower BP than solute.
(3) When heated, solvent boils but solute does not.
(4) solvent escapes solution in gas state and is then cooled and condensed back into a liquid by a Condenser

30
Q

Why is Simple distillation useful?

A

If you want to purify a solvent

E.G.
Providing purified water for chemists - tap water contains nacl and other dissolved salts.

31
Q

Fractional Distillation:

A

(1) Separates 2 or more liquids (EG ethanol and water)
(2) relies on each substance having different BP
(3) Uses fractioning column :
- the vapours condense on the inside surface, heating it up
- when inside temp reaches BP of ethanol, ethanol vapour cannot condense any more, but water can
- Water droplets fall back into flask and ethanol vapour pass into the condensor
(4) ethanol vapor is cooled and condensed into liquid. and drops into collecting container

32
Q

Fractions

A

Each substance separated by Frac Distil

33
Q

Types of Chromatography:

A

1) paper - separate coloured substances in Ink or dye
2) Thin-Layer - Separate sample into components for identification or analysis
3) Gas - Separates components of a mixture and also measures their amounts

34
Q

Two chemical phases:

A

Stationary phase

Secondary phase

35
Q

Stationary phases:

A

PC - absorbent paper
TLC - Silica or alumina power spread over a plate of glass or plastic
GC: Silica or alumina power packed into metal column

36
Q

Mobile Phases:

A

PC - Solvent in the liquid
TLC - Solvent in liquid
GC - Carrier gas which does not react W/ sample

37
Q

TLC in depth

A

1) Put solvent into a chromatography tank to depth of 1cm
2) Add small amount of sample to baseline, not damaging the power on the plate
3) Let solvent travel through the power, take plate out before it reaches the top
4) Analyse the pattern of coloured spots, chromatogram

38
Q

Rf values

A

used to compare different spots on a chromatogram - 2 identical spots have same Rf value and are the same colour.

39
Q

Rf formula

A

Distance travelled by substance / Distance travelled by solvent

Chemistry (20 decks)

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