paper 1 practicals/ techniques

Question 1

Suggest a method to measure the quantity of sugar in a solution

Answer 1

• carry out benedict’s test as above, then filter and dry precipitate
• find mass/weight

Question 2

Describe a method to identify the concentration of glucose in an unknown solution.

Answer 2

1. Make sugar solutions of known concentrations (e.g. dilution series)
2. Heat a set volume of each sample with a set volume of Benedict’s solution for same time
3. Use colorimeter to measure absorbance of light of each known concentration
4. Plot calibration cruve - conc on x axis , absorbance on y
5. Draw line of best fit. Repeat Benedict’s test with unknown sample and measure absorbance.
6. Red off calibration cruve to find conc associated with unknown sample’s absorbance

Question 3

Outline how chromatography could be used to identify the amino acids in a mixture

Answer 3

1. Prepare the chromatography paper by drawing a pencil line near the bottom and placing small spots of the amino acid mixture and known amino acid standards along the line.
2. Place paper in solvent (e.g., ethanol), ensuring the solvent level is below the spots. Leave it to develop in a covered container.
3. As the solvent travels, different amino acids move at different rates depending on their solubility
4. When the solvent has nearly reached the top, remove the paper and mark the solvent front. Dry the paper.
5. Spray with a locating agent (e.g., ninhydrin) to make the amino acid spots visible.
6. Compare the positions of the unknown spots with those of the known standards or calculate Rf values and match them to known Rf values.

Question 4

Name 5 factors that affect the rate of enzyme-controlled reactions

Answer 4

• enzyme concentration
• substrate concentration
• concentration of inhibitors
• pH
• temperature

Question 5

Common questions 1-4:

1. Describe how temperature can be controlled.
2. Describe how pH can be controlled.
3. Why were the enzyme & substrate solutions left in the water bath for 10 mins before mixing?
4. Describe a control experiment.

RP1: investigation into the effect of a named variable on rate of enzyme reactions

Answer 5

1. Use a thermostatically controlled water bath + Monitor using a thermometer at regular intervals and
   add hot / cold water if temperature fluctuates
2. Use a buffer solution+ Monitor using a pH meter at regular intervals
3. So solutions equilibrate / reach the temperature of
   the water bath
4. Use denatured enzymes (eg. by boiling)
5. Everything else same as experiment, eg. same conc. /
   volume of substrate (at start) and enzyme, same
   type / volume of buffer solution, same temperature

Question 6

common questions

1. Suggest a safety risk and explain how to reduce this risk.
2. Explain why using a colorimeter to measure colour change is better than comparison to colour standards.
3. Explain a procedure that could be used to stop each reaction.

Answer 6

1. Handling enzymes may cause an allergic reaction. Avoid contact with skin by wearing gloves and eye protection
2. Not subjective + More accurate
3. Boil / add strong acid / alkali -+ denature enzyme. Put in ice - lower kinetic energy so no E-S complexes form. Add high concentration of inhibitor -+ no E-S complexes form

Question 7

state the formula for pH.

Answer 7

pH = −log10 ([H+])

H+ = hydrogen ion concentration of a solution