Lab Questions

Question 1

How is the Rf value calculated?

Answer 1

Rf = distance of spot/distance of solvent

Question 2

Which compounds travel further on TLC plates?

Answer 2

Non-polar substances

Question 3

If TLC liquid is more polar, do polar substances travel more or less distance?

Answer 3

More distance

Question 4

What is the equation to find the concentration?

Answer 4

n = m/GFM

Question 5

What are equivalents?

Answer 5

Equivalents assess which reactant is limiting and which is in excess

Question 6

What details are needed for a correct graph?

Answer 6

Title
Labelled axises
Units on axis
Axis takes up half of graph paper

Question 7

How does p-aminophenol become paracetamol?

Answer 7

P-aminophenol is acylated to form paracetamol

Question 8

How is paracetamol purified?

Answer 8

By recrystallisation

Question 9

Why is ethanoic acid water soluble?

Answer 9

Carboxylic acid is hydrophilic

Question 10

Why is paracetamol not very water soluble?

Answer 10

Aromatic ring is hydrophobic

Question 11

How is para-aminophenol formed?

Answer 11

Phenol is nitrated to form ortho and para nitrophenol
P and O nitrophenol are separated
P-nitophenol is reduced to p-aminophenol (NO2 becomees NH2)

Question 12

How is percentage yield calculated?

Answer 12

% yield = recrystallised yield/actual yield x100

Question 13

How can impurities be checked for?

Answer 13

Low MP and larger MP range

Question 14

Why is sulphuric acid added to powered plant?

Answer 14

To convert the free base to a salt

Question 15

Why was DCM used?

Answer 15

As an organic solvent to remove impurities as free base is in salt form so aqueous soluble

Question 16

Why was anhydrous sodium sulphate used?

Answer 16

As a drying agent

Question 17

Why is the vitali-morin’s test done?

Answer 17

To test for the presence of tropane alkaloids

Question 18

What colour is the Vitali-morin’s test?

Answer 18

Purple

Question 19

Why was TLC done for the alkaloids?

Answer 19

To examine the the resulting alkaloids for the presence of atropine and hyoscine

Question 20

What can be concluded about hyoscine?

Answer 20

Hyoscine is very non-polar as it travelled very far up the plate

Question 21

Why was methanol added to the dried solid?

Answer 21

As an organic solvent to extract the free base

Question 22

Why are barbiturates acid?

Answer 22

They can donate a proton

Question 23

How is the barbiturate molecule stabilised?

Answer 23

Electrons are delocalised around the ring to stabilise the molecule

Question 24

Why was analysis done at different pHs?

Answer 24

To mimic different body parts

Question 25

When are barbiturates ionised?

Answer 25

In basic solutions

Question 26

How do barbital and phenobarbital differ?

Answer 26

Phenobarbital has an aromatic ring so is more lipophilic, has higher logP and is less water soluble than barbital

Question 27

Why was the first solution scanned at multiple dilutions?

Answer 27

To construct an absorbance vs concentration calibration curve Used to determine concentration later in the experminent

Question 28

Why was the spectrometer blanked?

Answer 28

To give λ max to analyse further dilutions

Question 29

What happens to the concentration in aqueous as pH increases?

Answer 29

Drug aqueous concentration increases as pH increases

Question 30

What happens to %ionisation as pH increases?

Answer 30

As pH increases, % ionisation increases as barbiturates are ionised in basic solutions

Question 31

What does SMILES stand for?

Answer 31

simplified molecular-input line-entry system

Question 32

Why molecular weight under 500?

Answer 32

Follows Lipinski's rule of 5

Question 33

Why is logP not the best measure of lipophilicity of drugs?

Answer 33

logP can only be used for unionised molecules and most drugs are ionised at physiological pH

Question 34

What is the percentage ionisation of a drug when pKa=physiological pH?

Answer 34

50%

Question 35

What is the percentage ionisation of an acidic drug when pH = pKa + 2?

Answer 35

99%

Question 36

What is the percentage ionisation of a basic drug when pH = pKa - 1?

Answer 36

90%

Question 37

Why was concentrated ammonia added?

Answer 37

To convert the salt to a free base