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applied science > Separating Mixtures > Flashcards

Separating Mixtures Flashcards

Unit 2

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1
Q

Define chromatography

A

Separation of the components of a mixture dissolved in the mobile phase carrying it through the stationary phase.

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2
Q

Why might we want to separate a mixture?

A

Identify, purify and quantify substances present.

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3
Q

what do we call the 2 phases used in chromatography?

A

Mobile and stationary

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4
Q

why do substance in a mixture move to different distances?

A

They have different affinities for the 2 phases

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5
Q

Greater affinity for which phase means substance move more slowly?

A

Greater affinity for the stationary

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6
Q

Why might a mixture of solvent be used ?

A

To separate substances that are equally soluble in 1 solvent

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7
Q

Define adsorption

A

when a substance (e.g.gas, liquid or solute)binds or attaches to another (usually solid)

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8
Q

Define polar/hydrophilic

A

a polar substance will dissolve in or mix with water.

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9
Q

Define adsorbent

A

describes the stationary phase in chromatography because substances become adsorbed to it during separation

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10
Q

What is one advantage of paper chromatography over other types?

A

it is cheaper

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11
Q

In paper chromatography, what stationary phase?

A

water bound to the paper.

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12
Q

In paper chromatography , what is the mobile phase?

A

A non-polar solvent or mixture of solvents

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13
Q

What do we call the line drawn at the bottom of the where the solvent has travelled to?

A

Origin

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14
Q

what is the name of the line at the top of the paper where the solvent has travelled to?

A

solvent front

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15
Q

what do we call the paper that has the separated substances on it at when chromatography has been carried out?

A

chromatogram

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16
Q

what does Rf value mean?

A

Retention factor

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17
Q

how is Rf value calculated?

A

Rf=distance travelled by substance/distance travelled by solvent

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18
Q

how many decimal places are Rf values expressed to?

A

2 d.p

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19
Q

when chromatography is carried out using a stardoms procedure, what can Rf values be compared to identify substances in a mixture?

A

Published literature values

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20
Q

what do we mean by standard procedure?

A
  • same solvent
  • same stationary phase
  • same run time
  • same temperature
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21
Q

Another way of identifying substances in a mixture is by using reference standards; what are reference standards.

A
  • samples of pure substances (standards) applied the origin next to the mixture
  • to compare distance travelled by spots
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22
Q

substances or processes that make spots on a chromatogram visible?

A

locating agents

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23
Q

Give one example of a non-destructive locating agent

A

fluorescent substances can be seen with UV light

24
Q

Give examples of other locating agents

A

ninhydrin (shows amino acids),iodine (shows starch)

25
Q

what are the advantages of TLC over paper chromatography

A
  • faster run time
  • better separation of substances
  • choice of absorbents
  • TLC plate self-supporting/ easy to manipulate
  • TLC more durable
26
Q

what’re the disadvantages of Bothe paper chromatography and TLC?

A
  • Don’t give positive identification of substances

- Qualitative not Quantitative results

27
Q

What is TLC?

A

Thin layer chromatography

28
Q

In TLC, what is the stationary phase?

A

silica gel, powder cellulose or alumina/aluminium oxide attached to glass or plastics.

29
Q

in TLC, what is the mobile phase?

A

`a non-polar solvent or mixture of solvents

30
Q

On what basis does gel electrophoresis separate DNA fragments?

A

gel electrophoresis separates DNA fragments based on the size of the fragments

31
Q

List the uses of gel electrophoresis and genetic fingerprinting

A 
forensic science  
paternity testing 
genetic disease diagnosis 
pathogenic disease diagnosis 
tracing ancestry 
determining phylogenetic relationships between organisms
32
Q

What charge do DNA molecules have?

A

Negative

33
Q

When DNA fragments are placed in an electrical field, which electrode are they attracted to?

A

the positive electrode (anode)

34
Q

What is the gel in gel electrophoresis made from?

A

agarose

35
Q

Which DNA fragments can move through the pores in the gel matrix more easily (and can therefore move further in a set time)?

A

Shorter fragments

36
Q

What is the name of the enzymes that are used to cut DNA molecules into fragments before gel electrophoresis?

A

restriction enzymes

37
Q

What are the DNA fragments placed into at one end of the gel?

A

Wells

38
Q

What is added to complete the circuit?

A

Buffer solution

39
Q

Which electrode is placed near the wells?

A

the negatively charged electrode(cathode) is placed near the wells

40
Q

What is important about the electrical current applied?

A

direct current

41
Q

What is used to visualise the DNA fragments?

A

dye or radioactivity

42
Q

What unit of measurement is used for DNA fragments?

A

base pairs (bp)

43
Q

Why is a ‘size reference standard’ mix of DNA fragments used in one of the lanes in gel electrophoresis?

A

to estimate the size of the DNA fragments in the other lanes

44
Q

What process is used to make a permanent record of the gel?

A

Southern blotting

45
Q

What do we call the position or pattern of the DNA fragments in the gel?

A

DNA bands or banding pattern

46
Q

When looking at genetic fingerprints created by gel electrophoresis, how do we know that 2 individuals are closely related?

A

they have (more) bands (DNA fragments) in common

47
Q

What does PCR stand for?

A

polymerase chain reaction

48
Q

What is PCR used for?

A

to make millions of copies of a target piece of DNA

49
Q

What 3 things must be added to the DNA for PCR to be carried out?

A

nucleotides, primers, & polymerase

50
Q

How are DNA strands separated in PCR?

A

heat to 95oC for 2 minutes

51
Q

To start the replication process, what must attach or anneal to the DNA?

A

Primers

52
Q

Which enzyme is needed to form the new DNA copies?

A

Taq DNA polymerase

53
Q

Which organism does the DNA polymerase come from?

A

Thermus aquaticus bacteria

54
Q

What is the advantage of using Taq DNA polymerase?

A

It doesn’t denature at high temperatures (needed to separate DNA strands)

55
Q

What is the formula for calculating the number of DNA molecules after a certain number of PCR cycles?

A

2n (where n = the number of cycles)

56
Q

Why is it necessary to cool the mixture after heating to separate the DNA strands?

A

to allow the primers to attach/anneal

applied science (3 decks)

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