A Level Biology Help
Benedict's Test Question
Method 1: Testing for reducing sugar
1. Label four boiling tubes A – D and place 4 cm3 of the corresponding samples into each using a fresh syringe each time.
2. Use a dropping pipette to add ̴̴ 2 cm3 Benedict’s reagent to each of the four samples.
3. Record your observations of each sample immediately after adding Benedict’s reagent.
4. Place all four boiling tubes into the water bath.
5. After 2 minutes record your observations of each sample, replacing the samples in the water bath afterwards.
6. After a further 2 minutes (4 minutes total incubation time) remove the tubes from the water bath and record your final observations of each sample and your conclusions about the presence or absence of reducing sugar in the samples (and therefore which letter corresponds to the glucose solution).
Method 2: Testing for non-reducing sugar
1. Put 4 cm3 of each of the samples, A – D, into its own labelled boiling tube using a fresh syringe each time.
2. Use a dropping pipette to add ̴̴ 2 cm3 of 2 mol dm-3 hydrochloric acid to each of the four samples.
3. Place all four boiling tubes into the water bath and incubate for 2 minutes.
4. Remove the tubes from the water bath and allow them to cool.
5. Next neutralise the acid by gradually adding sodium hydrogen carbonate to each sample until no more effervescence is observed.
6. Check the pH with indicator paper. If the pH is still lower than pH 7, repeat step 5. It does not matter if the pH has risen slightly above pH 7.
7. Use a dropping pipette to add ̴̴ 2 cm3 Benedict’s reagent to each of the four samples.
8. Record your observations of each sample immediately after adding Benedict’s reagent.
9. Place all four boiling tubes into the water bath.
10. After 2 minutes record your observations of each sample, replacing the samples in the water bath afterwards.
11. After a further 2 minutes (4 minutes total incubation time) remove the tubes from the water bath and record your final observations of each sample and your conclusions about the presence or absence of non-reducing sugar in the samples (and therefore which letter corresponds to the sucrose solution).
The actual question:
1. What improvements can you suggest to the method you were given for this qualitative test?
Method 1: Testing for reducing sugar
1. Label four boiling tubes A – D and place 4 cm3 of the corresponding samples into each using a fresh syringe each time.
2. Use a dropping pipette to add ̴̴ 2 cm3 Benedict’s reagent to each of the four samples.
3. Record your observations of each sample immediately after adding Benedict’s reagent.
4. Place all four boiling tubes into the water bath.
5. After 2 minutes record your observations of each sample, replacing the samples in the water bath afterwards.
6. After a further 2 minutes (4 minutes total incubation time) remove the tubes from the water bath and record your final observations of each sample and your conclusions about the presence or absence of reducing sugar in the samples (and therefore which letter corresponds to the glucose solution).
Method 2: Testing for non-reducing sugar
1. Put 4 cm3 of each of the samples, A – D, into its own labelled boiling tube using a fresh syringe each time.
2. Use a dropping pipette to add ̴̴ 2 cm3 of 2 mol dm-3 hydrochloric acid to each of the four samples.
3. Place all four boiling tubes into the water bath and incubate for 2 minutes.
4. Remove the tubes from the water bath and allow them to cool.
5. Next neutralise the acid by gradually adding sodium hydrogen carbonate to each sample until no more effervescence is observed.
6. Check the pH with indicator paper. If the pH is still lower than pH 7, repeat step 5. It does not matter if the pH has risen slightly above pH 7.
7. Use a dropping pipette to add ̴̴ 2 cm3 Benedict’s reagent to each of the four samples.
8. Record your observations of each sample immediately after adding Benedict’s reagent.
9. Place all four boiling tubes into the water bath.
10. After 2 minutes record your observations of each sample, replacing the samples in the water bath afterwards.
11. After a further 2 minutes (4 minutes total incubation time) remove the tubes from the water bath and record your final observations of each sample and your conclusions about the presence or absence of non-reducing sugar in the samples (and therefore which letter corresponds to the sucrose solution).
The actual question:
1. What improvements can you suggest to the method you were given for this qualitative test?
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