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WM test Flashcards

1
Q

Why do we measure melting point?

A

To determine purity.

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2
Q

What is the first step of melting point measuring?

A

Small sample of solid into glass capillary tube then place inside heating element.

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3
Q

What is the second step of melting point measuring?

A

Increase temperature until solid turns to liquid then measure melting range.

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4
Q

Do pure solids have a specific melting point?

A

Yes.

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5
Q

Why do impure solids not have a specific melting point?

A

As they disrupt the order, so they melt over a range.

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6
Q

What is thin layer chromatography used for?

A

To separate mixtures.

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7
Q

What is the stationary phase of thin layer chromatography?

A

Silicon dioxide or aluminium oxide.

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8
Q

What is the first step of chromatography?

A

Draw pencil line at bottom, put drop of each mixture on the line on TLC plate.

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9
Q

What is the second step of chromatography?

A

Place in beaker of solvent.

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10
Q

What is the third step of chromatography?

A

As solvent moves up the plate, resulting in chromatogram.

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11
Q

How can we reveal colourless chemicals on the TLC plate?

A

Using UV light or iodine.

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12
Q

How does UV reveal the colourless chemicals?

A

TLC plates have fluorescent dye, so the spots of chemicals will glow under UV light.

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13
Q

How does iodine show the colourless chemicals?

A

Sticks to chemicals on the plate, appearing as purple spots.

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14
Q

What is the calculation for Rf value?

A

Distance travelled by substance / distance travelled by solvent.

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15
Q

Why use refluxing?

A

To avoid losing volatile organic substances.

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16
Q

Describe the apparatus for refluxing.

A

Pour reaction mixture in round bottom flask with anti-bumping granules and attach a condenser vertically.

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17
Q

Describe the first step of reflux.

A

Gently heat the solution so it continuously evaporates then condenses back into the flask.

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18
Q

What is the purpose of distillation?

A

To separate substances with different boiling points.

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19
Q

Describe the apparatus for distillation.

A

Reaction mixture in round bottom flask attached to a condenser that has a conical flask underneath to collect pure product.

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20
Q

What is the first step of distillation?

A

Heat gently so substances evaporate in order of boiling point.

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21
Q

What is the second step of distillation?

A

Evaporated substances enter the condenser where they condense into a liquid and are collected in the conical flask.

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22
Q

How can distillation be used for primary alcohols?

A

React further in carboxylic acids using distillation again.

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23
Q

What is the purpose of redistillation?

A

To purify volatile liquids.

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24
Q

What is the first step of redistillation?

A

After distillation, product still has impurities, so you can use distillation to heat impure product.

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25
What is the second step of redistillation?
The liquid boils and condenses so you can collect the pure product.
26
What is the purpose of filtration?
To isolate solid organic products.
27
What is the first step of filtration?
Pour reaction mixture into Buchner funnel with filter paper.
28
What is the second step of filtration?
Reduced pressure in flask caused by vacuum forces liquid through the funnel.
29
What is the first step of separation?
Pour reaction mixture in a funnel and add water.
30
What is the second step of separation?
Water soluble impurities dissolve in aqueous layer that floats on top.
31
What is the third step of separation?
Open stopper of separating funnel to run aqueous layer, so left with product.
32
How can you remove water from a purified product?
By drying it.
33
What is the first step of drying?
Add anhydrous salt e.g., CaCl2 or MgSO4 as it acts as a drying agent.
34
What is the second step of drying?
Add drying agent until small lumps form, then filter to remove the drying agent.
35
What is the first step of recrystallization?
Add hot solvent to impure solid until it dissolves.
36
What is the second step of recrystallization?
Gives saturated solution of impure product.
37
What is the third step of recrystallization?
Leave to cool so crystals form.
38
What is the fourth step of recrystallization?
Remove crystals by filtration and wash in ice cold solvent, then leave to dry.
39
Describe phenol structure.
Benzene ring with OH attached.
40
What is the general formula for phenol?
C6H5OH.
41
Describe the test for phenols.
Add phenol to iron (III) chloride solution and shake; a purple solution is made.
42
What type of acid are phenols?
Weak.
43
What will form if you dissolve a phenol in water?
Phenoxide ion and water.
44
How acidic is the solution formed from phenol in water?
Weakly.
45
What creates water and salt?
Phenol and alkali.
46
How can you tell phenols apart from carboxylic acids?
Phenols don't react with carbonate, whereas carboxylic acids do.
47
What does a phenol and acid anhydride form?
Ester and carboxylic acid.
48
What else will phenols not react with?
Carboxylic acids.
49
What can primary alcohols be oxidised to?
Aldehydes and carboxylic acids.
50
What can secondary alcohols be oxidised to?
Ketones.
51
How to make ethanal?
Heat ethanol and potassium dichromate solution and sulfuric acid in a flask.
52
How to turn ethanal into ethanoic acid?
Distill so the aldehyde evaporates off, then distill immediately and vigorously oxidise under reflux.
53
Dehydrating alcohols forms what?
Alkenes.
54
Describe a dehydration reaction.
Ethanol vapour passed over aluminium oxide catalyst or reflux ethanol with concentrated sulfuric acid at 170°C.
55
What does the concentrated sulfuric acid act as?
A dehydrating agent in an elimination reaction.
56
What do you heat with an alcohol to form an ester?
Carboxylic acid.
57
Describe the reaction of carboxylic acid + alcohol.
Heated in the presence of an acid catalyst.
58
What can the acid catalyst be?
Concentrated sulfuric acid or hydrochloric acid.
59
What type of reaction is the esterification?
Esterification.
60
What does an alcohol and a carboxylic acid also make?
Water.
61
What else reacts with an alcohol to form an ester?
Acid anhydride.
62
What will form if you react an alcohol with an acid anhydride?
Carboxylic acid and an ester.
63
Describe the steps of converting an alcohol into a haloalkane.
Alcohols react with a compound that has a halide, so the OH (hydroxyl) group is replaced by the halide (e.g., Cl) to form a haloalkane.
64
What type of reaction forms a haloalkane?
Substitution reaction.

Chemistry (1 decks)

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