Lab Questions Flashcards
How is the Rf value calculated?
Rf = distance of spot/distance of solvent
Which compounds travel further on TLC plates?
Non-polar substances
If TLC liquid is more polar, do polar substances travel more or less distance?
More distance
What is the equation to find the concentration?
n = m/GFM
What are equivalents?
Equivalents assess which reactant is limiting and which is in excess
What details are needed for a correct graph?
Title
Labelled axises
Units on axis
Axis takes up half of graph paper
How does p-aminophenol become paracetamol?
P-aminophenol is acylated to form paracetamol
How is paracetamol purified?
By recrystallisation
Why is ethanoic acid water soluble?
Carboxylic acid is hydrophilic
Why is paracetamol not very water soluble?
Aromatic ring is hydrophobic
How is para-aminophenol formed?
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)
How is percentage yield calculated?
% yield = recrystallised yield/actual yield x100
How can impurities be checked for?
Low MP and larger MP range
Why is sulphuric acid added to powered plant?
To convert the free base to a salt
Why was DCM used?
As an organic solvent to remove impurities as free base is in salt form so aqueous soluble
Why was anhydrous sodium sulphate used?
As a drying agent
Why is the vitali-morin’s test done?
To test for the presence of tropane alkaloids
What colour is the Vitali-morin’s test?
Purple
Why was TLC done for the alkaloids?
To examine the the resulting alkaloids for the presence of atropine and hyoscine
What can be concluded about hyoscine?
Hyoscine is very non-polar as it travelled very far up the plate
Why was methanol added to the dried solid?
As an organic solvent to extract the free base
Why are barbiturates acid?
They can donate a proton
How is the barbiturate molecule stabilised?
Electrons are delocalised around the ring to stabilise the molecule
Why was analysis done at different pHs?
To mimic different body parts
When are barbiturates ionised?
In basic solutions
How do barbital and phenobarbital differ?
Phenobarbital has an aromatic ring so is more lipophilic, has higher logP and is less water soluble than barbital
Why was the first solution scanned at multiple dilutions?
To construct an absorbance vs concentration calibration curve
Used to determine concentration later in the experminent
Why was the spectrometer blanked?
To give λ max to analyse further dilutions
What happens to the concentration in aqueous as pH increases?
Drug aqueous concentration increases as pH increases
What happens to %ionisation as pH increases?
As pH increases, % ionisation increases as barbiturates are ionised in basic solutions
What does SMILES stand for?
simplified molecular-input line-entry system
Why molecular weight under 500?
Follows Lipinski’s rule of 5
Why is logP not the best measure of lipophilicity of drugs?
logP can only be used for unionised molecules and most drugs are ionised at physiological pH
What is the percentage ionisation of a drug when pKa=physiological pH?
50%
What is the percentage ionisation of an acidic drug when pH = pKa + 2?
99%
What is the percentage ionisation of a basic drug when pH = pKa - 1?
90%
Why was concentrated ammonia added?
To convert the salt to a free base
