Separating Mixtures

Question 1

Define chromatography

Answer 1

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

Question 2

Why might we want to separate a mixture?

Answer 2

Identify, purify and quantify substances present.

Question 3

what do we call the 2 phases used in chromatography?

Answer 3

Mobile and stationary

Question 4

why do substance in a mixture move to different distances?

Answer 4

They have different affinities for the 2 phases

Question 5

Greater affinity for which phase means substance move more slowly?

Answer 5

Greater affinity for the stationary

Question 6

Why might a mixture of solvent be used ?

Answer 6

To separate substances that are equally soluble in 1 solvent

Question 7

Define adsorption

Answer 7

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

Question 8

Define polar/hydrophilic

Answer 8

a polar substance will dissolve in or mix with water.

Question 9

Define adsorbent

Answer 9

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

Question 10

What is one advantage of paper chromatography over other types?

Answer 10

it is cheaper

Question 11

In paper chromatography, what stationary phase?

Answer 11

water bound to the paper.

Question 12

In paper chromatography , what is the mobile phase?

Answer 12

A non-polar solvent or mixture of solvents

Question 13

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

Answer 13

Origin

Question 14

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

Answer 14

solvent front

Question 15

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

Answer 15

chromatogram

Question 16

what does Rf value mean?

Answer 16

Retention factor

Question 17

how is Rf value calculated?

Answer 17

Rf=distance travelled by substance/distance travelled by solvent

Question 18

how many decimal places are Rf values expressed to?

Answer 18

2 d.p

Question 19

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

Answer 19

Published literature values

Question 20

what do we mean by standard procedure?

Answer 20

• same solvent
• same stationary phase
• same run time
• same temperature

Question 21

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

Answer 21

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

Question 22

substances or processes that make spots on a chromatogram visible?

Answer 22

locating agents

Question 23

Give one example of a non-destructive locating agent

Answer 23

fluorescent substances can be seen with UV light

Question 24

Give examples of other locating agents

Answer 24

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

Question 25

what are the advantages of TLC over paper chromatography

Answer 25

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

Question 26

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

Answer 26

- Don't give positive identification of substances | - Qualitative not Quantitative results

Question 27

What is TLC?

Answer 27

Thin layer chromatography

Question 28

In TLC, what is the stationary phase?

Answer 28

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

Question 29

in TLC, what is the mobile phase?

Answer 29

`a non-polar solvent or mixture of solvents

Question 30

On what basis does gel electrophoresis separate DNA fragments?

Answer 30

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

Question 31

List the uses of gel electrophoresis and genetic fingerprinting

Answer 31

``` forensic science paternity testing genetic disease diagnosis pathogenic disease diagnosis tracing ancestry determining phylogenetic relationships between organisms ```

Question 32

What charge do DNA molecules have?

Answer 32

Negative

Question 33

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

Answer 33

the positive electrode (anode)

Question 34

What is the gel in gel electrophoresis made from?

Answer 34

agarose

Question 35

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

Answer 35

Shorter fragments

Question 36

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

Answer 36

restriction enzymes

Question 37

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

Answer 37

Wells

Question 38

What is added to complete the circuit?

Answer 38

Buffer solution

Question 39

Which electrode is placed near the wells?

Answer 39

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

Question 40

What is important about the electrical current applied?

Answer 40

direct current

Question 41

What is used to visualise the DNA fragments?

Answer 41

dye or radioactivity

Question 42

What unit of measurement is used for DNA fragments?

Answer 42

base pairs (bp)

Question 43

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

Answer 43

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

Question 44

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

Answer 44

Southern blotting

Question 45

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

Answer 45

DNA bands or banding pattern

Question 46

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

Answer 46

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

Question 47

What does PCR stand for?

Answer 47

polymerase chain reaction

Question 48

What is PCR used for?

Answer 48

to make millions of copies of a target piece of DNA

Question 49

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

Answer 49

nucleotides, primers, & polymerase

Question 50

How are DNA strands separated in PCR?

Answer 50

heat to 95oC for 2 minutes

Question 51

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

Answer 51

Primers

Question 52

Which enzyme is needed to form the new DNA copies?

Answer 52

Taq DNA polymerase

Question 53

Which organism does the DNA polymerase come from? 

Answer 53

Thermus aquaticus bacteria

Question 54

What is the advantage of using Taq DNA polymerase?

Answer 54

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

Question 55

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

Answer 55

2n (where n = the number of cycles)

Question 56

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

Answer 56

to allow the primers to attach/anneal