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Chemistry A2 Rafa > 6.3 Analysis > Flashcards

6.3 Analysis Flashcards

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1
Q

Rf value

A

Comparison between how far a component has moved compared to the solvent in thin layer chromatography

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2
Q

Retention time

A

Time taken for a component to travel from the inlet to the detector in a gas chromatohraph

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3
Q

Why do different substances travel different amounts in paper chromatography?

A
  • The more polar a compound is the greater affinity it has to the polar mobile phase
  • moves further up the paper with it
  • the less polar compounds aren’t as attracted and so don’t move as far
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4
Q

What are the components to thin-layer chromatography?

A
  • The stationary phase is a thin inert material, coated in an aDsorbent (taken onto surface) chemical
  • the mobile phase is an organic solvent
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5
Q

What are the components to gas chromatography?

A

Stationary phase is an inert solid or liquid coating on the inside of a thin long coiled tube
-the mobile phase is an unreactive gas (He or N)

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6
Q

How are the results of a gas chromatogram displayed?

A

x-axis shows retention time

y-axis shows abundance

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7
Q

What is qualtitative analysis?

A

Observable changes to a reaction/solution, observations not including the use of numerical values

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8
Q

How do you test for Alkenes?

A

Add a few drops of bromine water, shake, if the solution decolourises then it is an alkene

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9
Q

How do you test for a Haloalkane?

A

Add aqueous silver nitrate and ethanol, precipitate forms to show presence of halogen:
white precip-chloroalkane
cream precip-bromoalkane
yellow precip-iodoalkane

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10
Q

How do you test for a Carbonyl?

A

Add brady’s reagent (2-4,DNP), it will turn form a yellow/orange precipitate if the solution contains an aldhyde or ketone

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11
Q

How do you test for an Aldehyde?

A

Add fehlings solution: dark blue solution produces red precipitate
Tollens reagent: silver mirror forms

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12
Q

What is Tollen’s reagent and how does it work?

A

It is a solution of silver nitrate and ammonia, the silver nitrate is reduced as the aldehyde is oxidised to a carboxlyic acid, this reduction releases the silver ions which colourise the solution

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13
Q

How do you test for a Carboxylic acid?

A

Add Universal Indicator, pH colour of a weak acid will show

Adding a metal or metal carbonate will cause effervescence

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14
Q

What is TMS?

A

An internal standard that generates a reference peak for both Carbon and Proton NMR

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15
Q

What is ‘chemical shift’?

A

Scale comparing frequency of NMR absorption of compound with the frequency of the absorption of the reference peak

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16
Q

Why is TMS useful/good?

A
  • produces one sharp signal as hydrogen atoms are in a single environment and only one carbon environment as there is only one carbon atom
  • It is non toxic
  • low boiling point so is easily removed from sample
  • is inert so doesn’t interfere with test chemicals
  • has both carbon and hydrogen
17
Q

What can you deduce from a Carbon NMR graph

A

The shift of peaks can be compared to a data sheet to show what functional group it is, the height of peaks shows how many carbons there are of that environment/ functional group

18
Q

What are equivalent protons?

A

Hydrogen atoms bonded to the same atom, they therefore experience the same magnetic field in an NMR spectrometer and so show the same reading

19
Q

What can you deduce from a Proton NMR graph?

A

Shift compared to data sheet shows which atom it is bonded to,
Integration trace shows number of hydrogen atoms in particular environment
Split patterns: no. of split peaks -1 = no. of hydrogens on adjacent carbons

20
Q

How do you identify if a peak is formed by an -OH or -NH group in proton NMR?

A

Run a NMR test, then add D2O and shake vigorsously, run another NMR test and compare the resulting graphs, the peaks on the first graph that are -OH or -NH groups will have disappeared on the second graph

21
Q

4 factors to consider when making synthetic routes

A

No solvent
Non hazardous starting material
Fewer reaction steps
High yield

22
Q

What do we use when filtering something under reduced pressure?

A

A Buchner or Hirsh funnel on top of a filter flask

23
Q

Why is it ideal to use no solvent in a synthetic route?

A

The products do not have to be separated from the solvent at the end of the reaction

24
Q

Why is it ideal to use a non-hazardous starting material when designing a synthetic route?

A

Limits the danger to the chemist and the safety precautions necessary

25
Q

Why is it ideal to use few reaction steps in a synthetic route?

A

Saves money on equipment and time as well as producing fewer by-products

26
Q

Why is it ideal to have a high atomic yield in synthetic routes?

A

Saves money as largest amount of starting material is made into product

27
Q

What does Rf stand for?

A

Retention factor

28
Q

What is the coating in the long coiled tube in gas chromatography usually?

A

A hydrocarbon with a high boiling point as we tend to heat the mixture in gas chromatography

29
Q

How can we analyse gasses after they have been separated in gas chromatography?

A

We can attach the chromatograph to a mass spectrometer

30
Q

What does the area under a gas chromatogram represent?

A

The amount of the component that is present

31
Q

What must you do to the compounds you are investigating in NMR spectroscopy?

A

You must dissolve them

If they are organic you should dissolve them in an organic solvent

32
Q

Why cant we use most organic solvents as solvents in C NMR?

A

Because most organic solvents contain C13 atoms which would make the spectrums unreadable

33
Q

What molecule doesnt affect spin?

A

Deuterium

34
Q

What is a common solvent used in NMR?

A

heavy trichloromethane, CDCl3

35
Q

Bad thing about oxygen and nitrogen peaks on NMR?

A
  • Can appear almost anywhere on spectrum

- BROAD peaks which can be mistake for other peaks

36
Q

What can we use D2O for?

A

replaces H in compounds containing -OH or -NH so that they do not appear in spectrum

37
Q

How do we actually use D2O?

A

1) run original proton NMR spectrum]
2) Shake sample VIGOROUSLY with D2O as it is immiscible with CDCl3
3) Run the NMR spectrum again and any peaks due to -OH or -NH will have been removed

38
Q

What splitting pattern do -OH and -NH groups give and why?

A

Singlets

-the hydrogens on the OH or NH are too far away from other hydrogens to cause splitting patterns

39
Q

Why are the OH and NH peaks broad?

A

We cannot remove all traces of water from our solvent

Hydrogens bonds form between water and OH or NH and this broadens the peaks

Chemistry A2 Rafa (8 decks)

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