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Chemistry > Chemical analysis > Flashcards

Chemical analysis Flashcards

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1
Q

Pure substance

A

A single element/ compound
Not mixed with anything else

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2
Q

Pure vs impure substances

A

Pure = it will melt at a specific point/ boil at a specific point
Whereas impure = melts/boils at a range of temps

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3
Q

How to find if a substance is pure?

A

Increase the temperature
Record at what point it melts
Record what point it boils
If the temperatures are fixed = pure substance

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4
Q

What do heating graphs for impure substances look like?

A

When it’s changing state, it’s not at a fixed point.
It may slope upwards showing it’s not at a fixed point

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5
Q

Formulation

A

Complex mixture that has been designed as a useful product

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6
Q

How do we design formulations and why?

A

Quantity of each component has been carefully measured
So it has the properties we need

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7
Q

Examples of formulations

A

Fuels
Cleaning products
Paints
Medicine
Alloy
Fertiliser
Food

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8
Q

Physical separation techniques list

A

Filtration
Crystallisation
Distillation
Chromatography

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9
Q

What is the use of chromatography?

A

Allows us to separate substances based on their different solubilities
Ie ink into their different colours

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10
Q

How does chromatography work?

A

When the solvent travels up the paper
It dissolves the inks, carrying them up the paper
So it separates the colours

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11
Q

Stationary phase of chromatography

A

The paper because it doesn’t move

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12
Q

What is the mobile phase in chromatography?

A

The solvent (water) because it moves up the paper

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13
Q

Using chromatography, how do we determine if it’s a pure or impure colour?

A

A pure compound produces a single spot in all solvents
In an impure compound the compounds separate into different spots depending on the solvent

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14
Q

Do different solvents effect chromatography?

A

Yes
The positions could be further up or down the paper

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15
Q

Why use pencil in chromatography?

A

Using pen causes pen ink to move up the paper as well

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16
Q

Why exactly does paper chromatography work?

A

Because substances with a higher solubility can move further up the paper
And those with lower solubility will not go as high

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17
Q

How can we find out what an unknown chemical is in chromatography?

A

Do the chromatography of the unknown chemical
Draw the solvent line (where the water got to)
Measure distance from pencil line to the chemical
The measure how far the solvent moved from pencil line
Calculate Rf value and find out what that substance is

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18
Q

How to find Rf value

A

Distance moved by substance
———————————————
Distance moved by solvent

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19
Q

Problem with the method of finding Rf value

A

Several substances have same Rf value
Repeat using different solvent to narrow it down further
Newly found substance shave no Rf value to find

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20
Q

Test for hydrogen

A

Insert a burning splint into bung with hydrogen
Hydrogen will burn and make a pop sound

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21
Q

Test for oxygen

A

Use a glowing splint
Place it in oxygen and the splint will relight (burst into flames)

22
Q

What is limewater?

A

Calcium hydroxide dissolved in water

23
Q

Testing for carbon dioxide

A

Put some limewater into pipettes bubble the gas through limewater
Repeat several times = cloudy

24
Q

Testing for chlorine

A

Insert damp litmus paper
It will be bleached (white)

25
Q

What is the point of flame tests?

A

To find the metal ion in an unknown ionic compound

26
Q

How to do a flame test?

A

Put a small amount of ionic compound onto wire
Place this in a blue Bunsen burner flame
This changes the colour which we can use to identify the metal

27
Q

Colour lithium produces in flame test

A

Li = CRIMSON

28
Q

Colour sodium produces in flame test

A

Na = YELLOW

29
Q

Colour potassium produces in flame test

A

K = LILAC

30
Q

Colour calcium produces in flame test

A

Ca = ORANGE/RED

31
Q

Colour copper produces in flame test

A

Cu = GREEN

32
Q

Problems with flame test

A

-Colours hard to distinguish esp if there is low concentration of the metal compound
-Sample may contain mixture of metal ions which masks flame colour

33
Q

What do scientists do instead of flame tests?

A

Flame emission spectroscopy

34
Q

How does flame emission spectroscopy work.

A

Compound is put in flame
Light given out by flame passes through spectroscope
Converts it into line spectrum
Position of these lines in a spectrum is specific to different metals

35
Q

What else can flame emission spectroscopy tell us?

A

Concentration of metal ion
Because lines become more intense at higher concentration

36
Q

what is flame emission spectroscopy an example of?

A

Instrumental method
Aka carries out by a machine

37
Q

Advantages of instrumental methods

A

Quicker than by hand if we did flame tests
Sensitive so will work even if the compound is small
More accurate and correct than by hand

38
Q

Metal hydroxide tests

A

Used for metals that don’t work for flame tests

39
Q

How do metal hydroxide tests work?

A

Add sodium hydroxide to the substance
They produce a white precipitate which we then differentiate

40
Q

How to find aluminium ions

A

Add sodium hydroxide to make white precipitate
Add more sodium hydroxide and it will re dissolve thus become colourless again

41
Q

How to find magnesium ions

A

Add sodium hydroxide
Makes white precipitate
Adding more won’t redissolve it

42
Q

Testing for copper ii

A

Add sodium hydroxide
Forms blue precipitate of copper II hydroxide

43
Q

Testing for Iron II ions

A

Add sodium hydroxide
Forms green precipitate iron II hydroxide

44
Q

Testing for Iron III ions

A

Forms brown precipitate of iron III hydroxide

45
Q

Identifying non metal ions

A

Carbonate
Halide
Sulfate

46
Q

how to identify carbonate ion?

A

Add dilute acid
The carbonate will react to form carbon dioxide gas, by effervescence
So bubble this gas through limewater to see if it turns colours

47
Q

How to identify halide ions?

A

Add dilute nitric acid
Add dilute silver nitrate solution
Each halide produces different coloured precipitate

48
Q

What colours do chloride ions produce in silver chloride?

A

White precipitate

49
Q

What colours do bromide ions in silver bromide produce ?

A

Cream precipitate

50
Q

What colours do iodide ions produce in silver iodide

A

Yellow

51
Q

How to identify sulfate ion

A

Add dilute HCl
Add barium chloride solution
Forms white precipitate

Chemistry (46 decks)

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