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A-Level Chemistry [OCR B Salters] (sorry for any spelling mistakes - there are many) > [Year 1] WM > Flashcards

[Year 1] WM Flashcards

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1
Q

How do you identify an alcohol?

A

R-OH

Suffix: -ol
ethanol, CH₃CH₂OH

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2
Q

How do you identify an aldehyde?

A

R-COH

Suffix: -al
propanal, CH₃CH₂CHO

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3
Q

How do you identify a ketone?

A

R-CO-R’

-one
propanone, CH₃COCH₃

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4
Q

How do you identify a carboxylic acid?

A

R-COOH

Suffix: -oic acid
butanoic acid, CH₃CH₂CH₂COOH

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5
Q

How do you identify an acid anhydrides?

A

(R-CO)₂O

-oic anhydride
ethanoic anhydride, (CH₃CO)₂

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6
Q

How do you identify an ether?

A

R-O-R’

-oxy-
methoxyethane, CH₃OCH₂CH₃

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7
Q

How do you identify an ester?

A

R-COO-R’

alkyl-____-anoate
methyl ethanoate, CH₃COOCH₃

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8
Q

What makes an alcohol primary?

A

If the carbon it is connected to, is connected to one other carbon.

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9
Q

What makes an alcohol secondary?

A

If the carbon it is connected to, is connected to two other carbons.

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10
Q

What makes an alcohol tertiary?

A

If the carbon it is connected to, is connected to three other carbons.

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11
Q

What happens when you oxidise primary alcohol?

A

Becomes an aldehyde (distillation) then carboxylic acid (reflux with excess oxidising agent).

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12
Q

What happens when you oxidise secondary alcohol?

A

Becomes a ketone (reflux).

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13
Q

What happens when you oxidise tertiary alcohol?

A

Cant be oxidised (unless you burn it).

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14
Q

What is used to oxides alcohols?

A

Acidified potassium dichromate (K₂Cr₂O₇).

  • acts as the oxidising agent, so it reduces itself.
  • Turn from orange (dichromate ions) to green (chromium ions).
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15
Q

What are you doing when you distil something?

A

You are removing the desired product as it is formed.

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16
Q

What are you doing when you reflux something?

A

Heating reactants and condensing any volatile products/reactants to carry on the reaction.

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17
Q

What type of reaction forms alkenes from alcohols?

A

An elimination reaction.

  • By refluxing with sulfuric acid or phosphoric acid.
  • By passing alcohol vapour over a solid catalyst (Al₂O₃). (need to be able to draw this).
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18
Q

Describe the mechanism to dehydrate alcohols using elimination.

A
  • Lone pair on Oxygen attack H⁺ from the acid catalyst.
  • The intermediate formed has a + charge on the oxygen.
  • This oxygen can pull electrons in the C-O bond strongly to break the bond.
  • This leaves an unstable carbocation intermediate. (water leaves)
  • The carbocation loses a H⁺ from a neighbouring carbon to form a C=C bond as the electrons from the bond move.
  • This leaves an alkene, water, and reforms the H⁺ from the acid catalyst.
19
Q

How can esters be made from alcohols?

A

Reacting them with a carboxylic acid:

  • using a sulfuric acid catalyst.
  • -OH from carboxylic acid is removed.
  • -OR from alohol bond in its place.
  • The removed -OH bonds with -H from alcohol.

Or acid anhydride:

  • A C-O bond in the acid anhydride is broken.
  • -R from the alcohol takes its place.
  • the remaining -OH in the alcohol bonds with the smaller fragment to form a carboxylic acid.

Know how to draw these.

20
Q

How can haloalkanes be made from alcohols?

A

Via a substitution reaction (e.g. HBr).

  • -OH replaced by -Br.
  • -OH forms water with remaining -H.
21
Q

What is phenol and how are they numbered?

A
  • A benzene ring with an alcohol group.

- carbon with the alcohol is the 1-carbon.

22
Q

How do you test for phenols?

A

Add iron(III) chloride.

If phenol exists a purple colour should form.

23
Q

Why can phenols react with NaOH?

A
  • They are weak acids as they are able to dissociate partially to form a phenoxide ion.
  • This phenoxide ion can then bond to Na⁺.

(an react with other strong bases too)

24
Q

How can you tell the difference between phenols and carboxylic acids?

A

Carboxylic acids can react with weak bases whilst phenols cannot.

So you react carbonates with them to identify.

25
Q

How do you tell the difference between an alcohol and a phenol?

A
  • Phenols can react with acid anhydrides and make an ester and carboxylic acid.

BUT

  • Phenols cannot react with carboxylic acids.

WHILST
- alcohols can react with both.

THEREFORE
- you react them with carboxylic acids (using acid anhydrides as a control)

26
Q

What apparatus is used during reflux and when is it used?

A
  • Liebig condenser.
  • Heating mantle or water bath.

Used when you need to heat volatile substances without losing them.

27
Q

When is distillation used?

A

Used to separate substances with different boiling points.

Useful when you want to extract a chemical before it reacts any further.

28
Q

How can we purify a volatile substance?

A

Distilation and separation.

29
Q

Describe the method used for separation.

A
  • Clamp separating funnel to a clam stand and add the products from distillation.
  • Add water to dissolve soluble impurities. This forms an aqueous solution of impurities.
  • Allow time for the solution to settle and 2 layers will form:
    • The top layer is of impure products
    • The bottom layer is of aqueous later containing water-soluble impurities.
  • Remove the stopper and drain off aqueous layer.
30
Q

After separation, you are left with impure products.

What must you do next? Describe the method.

A

Purification.

  • Add impure products to a round-bottomed flask.
  • Add anhydrous CaCl₂ as a dehydrating agent.
    • This will remove all aqueous substances still remaining.
  • Invert flask and leave for 20-30 mins.
31
Q

After purification, you are left with impure products.

What must you do next? Describe the method.

A

(vacume) Filtration.
- Connect Buchner funnel and vacuum to a flask.
- Add filter paper to the Buchner funnel and dampen slightly to seal.
- Pour the reaction mixture through the top of the funnel with the vacuum line on.
- The vacuum creates a reduced pressure in the flask that pulls liquid through the filter paper leaving the solid in the Buchner funnel.

32
Q

If you want the solid after vacuum filtration, what must you do next?

A

Purify the solid.

33
Q

How do you purify a solid? Describe the method.

A

Recrystilation.

  • Choose an appropriate solvent such that will dissolve the solid when hot but no when cold.
  • Add just enough hot solvent to allow the impure solid to dissolve to get a saturated solution of impure product.
  • Hot filter to get rid of insoluble impurities.
  • Cool the solution slowly to allow crystals to form.
  • Soluble impurities will remain dissolved as there is a smaller quantity fo them so takes longer to crystalise
  • Filter and collect solid purified crystals.
  • Wash with very cold to remove any remaining soluble impurities solvent and dry them off.
34
Q

How can you measure the purity of a compound?

A
  • Measuring the melting point.

- TLC

35
Q

Describe the method for determining the purity of a compound via melting point analysis.

A
  • Add a sample of a solid product to capillary tube and place in the heating element of a melting point apparatus.
  • Slowly increase the temperature until the substance starts to melt.
  • This will be a range from when the solid just starts to melt to full melts.
  • Compare the melting points against data book values.
  • If substance contains impurities the melting point be lower and the range will be larger.
36
Q

Describe the method for determining the purity of a compound via TLC.

A
  • Draw a pencil line on stationary phase (silicon dioxide or aluminium dioxide plate).
  • Dissolve your solid product in a suitable solvent.
  • Using a capillary tube, pipette solution of your product and a solution of known pure product onto the pencil line.
  • Place in beaker and add mobile phase (liquid solvent) below the pencil line.
  • Place lid over beaker to prevent evaporation.
  • Allow solvent to move up close to the top and remove from beaker.
  • Mark the solvent front and allow to dry.
  • If the compound is colourless, observe with iodine (locating agent) or UV (using a fluorescent dye).
37
Q

After chromatography how do you analyse it quantitatively?

A

By calculating its Rf value and comparing it with a library of known Rf values.

Rf = distance travelled by spot / distance travelled by solvent

(also dependent on temp, solvent used, make up of TLC plate)

38
Q

It is difficult to use TLC for separating larger quantities.

What can be done instead?

A

Column Chromatograph.
- Pack burette with silica or alumina (stationary phase)

  • Run mixture and solvent (mobile phase) through continuously.
  • The different compound in the mixture run through the column at different rates.
  • So you can collect the pure compounds at the bottom at different times.
39
Q

What’s plotted during IR spectroscopy and how is it analysed?

A

Absorption of IR (which increases vibrational energy in covalent bonds) against Wavenumber (cm⁻¹).

There will be different peaks for different bonds in different functional groups.

40
Q

What’s plotted during mass spectroscopy and how is it analysed?

A

Relative abundance - Mass/Charge ratio

It peaks at different m/z depending on the Mr of the fragments.

The M+ peak is for the molecular ion peak.

The M+1 peak is for the molecular ion peak but with carbon-13

41
Q

What happens during fragmentation?

A
  • A positive fragment and a radical are made.

- Only the positive charged fragment is detected.

42
Q

When combining IR and mass spec, what order should they be analysed in?

A
  1. Find the functional groups present using IR.

2. Identify the structure from fragment patterns.

43
Q

What are the 12 principals of green chemistry?

A
  • Better atom economy: More feedstock incorporated into product and less waste.
  • Prevention of waste products: Better than treating/disposing of waste.
  • Less hazardous chemical synthesis: Using less hazards chemicals in reactions
  • Design safer chemical products: Less toxic and hazardous products
  • Use fewer solvents: Minimise use of organic solvents.
  • Lower energy usage: Lower temp and pressure processes.
  • Use renewable feedstock: Instead of depleting natural resources.
  • Reduce reagents used and number of steps: As these can generate waste.
  • Use catalysts, and more selective ones: Generally reduce energy usage and waste products.
  • Design chemical products for degradation: when released into environment, should break down into innocuous products.
  • Employ real-time process monitoring: To reduce waste products.
  • Use safer chemical processes: that minimise releasing of gases, fires and explosions

A-Level Chemistry [OCR B Salters] (sorry for any spelling mistakes - there are many) (14 decks)

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