Describe how mild analgesics function.

(i)     Outline why this substance is more soluble than standard aspirin in water.

 

(ii)     Deduce the balanced ionic equation for the reaction that occurs between soluble aspirin and the acid in the stomach.

(i)     Deduce two named functional groups present in both aspirin and diamorphine.

 

 

(ii)     Deduce one named functional group present in morphine but not in diamorphine.

 

(iii)     State two short-term advantages and two long-term disadvantages of using codeine as a strong analgesic.

 

Short-term advantages:

 

 

 

 

Long-term disadvantages:

 

 

 

 

(iv)     Explain the increased potency of diamorphine compared to morphine.

intercepts pain stimulus at source / inhibits release of substances/prostaglandins that cause pain/swelling/fever;

(i)     ionic compound (which dissociates);

(ii)     \({{\text{C}}_9}{{\text{H}}_7}{\text{O}}_4^ - {\text{(aq)}} + {{\text{H}}^ + }{\text{(aq)}} \to {{\text{C}}_9}{{\text{H}}_8}{{\text{O}}_4}{\text{(aq)}}\);

Ignore state symbols.

Ignore arrow.

(i)     phenyl/benzene ring;

Do not allow just benzene or arene or the formula C₆H₆.

ester;

Do not allow –COO– or carbonyl/CO.

(ii)     hydroxyl / phenol; [1]

Allow alcohol/hydroxy but not hydroxide.

Do not allow –OH.

(iii)     Award any [1] for any two short-term advantages from:

strong/powerful (pain reliever);

fast-acting / effective;

has a wide safety margin;

can quickly stop diarrhoea;

can be used in cough mixtures/medicines / antitussive properties;

works effectively with paracetamol/acetaminophen;

Award [1] for any two long-term disadvantages from:

(regular use) can lead to addiction/dependence/withdrawal symptoms;

tolerance can lead to toxic dosages;

can result in depression / apathy;

can cause mental health problems;

can result in constipation;

can result in sterility/sexually related problems;

memory loss;

serious health risk to babies who are breastfed;

Award [1 max] for one correct advantage and one correct disadvantage.

(iv)     two (polar) hydroxyl groups in morphine replaced by less polar ester groups in diamorphine/heroin;

Do not allow hydroxide for hydroxyl.

Accept alcohols for hydroxyl groups.

diamorphine/heroin more soluble in non-polar lipids / diamorphine/heroin more soluble in non-polar environment of central nervous system/CNS;

Reference to solubility required.

diamorphine/heroin can penetrate blood-brain barrier more quickly / diamorphine/heroin can act more quickly in CNS (leading to increased potency);

In Q15, the function of mild analgesics was well understood but few stated that the calcium salt is ionic and fewer still managed the ionic equation. The named functional groups were usually correctly identified although “benzene” was one of the incorrect answers as was “esther”. For the short-term advantages there was a tendency to repeat the stem of the question but the long-term disadvantages were better understood. Many scored one mark by including one correct short-term and one correct long-term answer. One respondent suggested that asking candidates about codeine was unfair – but this was regarded as a reasonable extension of D.3.4. Answers about the increased potency of diamorphine over morphine were better than in the past but if a mark were to be lost it would be for not commenting on the greater solubility of diamorphine in lipids specifically.

In Q15, the function of mild analgesics was well understood but few stated that the calcium salt is ionic and fewer still managed the ionic equation. The named functional groups were usually correctly identified although “benzene” was one of the incorrect answers as was “esther”. For the short-term advantages there was a tendency to repeat the stem of the question but the long-term disadvantages were better understood. Many scored one mark by including one correct short-term and one correct long-term answer. One respondent suggested that asking candidates about codeine was unfair – but this was regarded as a reasonable extension of D.3.4. Answers about the increased potency of diamorphine over morphine were better than in the past but if a mark were to be lost it would be for not commenting on the greater solubility of diamorphine in lipids specifically.

In Q15, the function of mild analgesics was well understood but few stated that the calcium salt is ionic and fewer still managed the ionic equation. The named functional groups were usually correctly identified although “benzene” was one of the incorrect answers as was “esther”. For the short-term advantages there was a tendency to repeat the stem of the question but the long-term disadvantages were better understood. Many scored one mark by including one correct short-term and one correct long-term answer. One respondent suggested that asking candidates about codeine was unfair – but this was regarded as a reasonable extension of D.3.4. Answers about the increased potency of diamorphine over morphine were better than in the past but if a mark were to be lost it would be for not commenting on the greater solubility of diamorphine in lipids specifically.