Required Practical 11 Flashcards
(34 cards)
What is the main aim of Required Practical 11?
To create a dilution series of glucose and use colorimetric techniques to identify glucose concentration in an unknown urine sample.
What is the key test used in this practical to measure glucose concentration?
The quantitative Benedict’s test.
Why does glucose react in the Benedict’s test?
Because glucose is a reducing sugar.
What happens to Cu²⁺ ions in Benedict’s solution when glucose is present?
Cu²⁺ ions are reduced to insoluble copper (I) oxide.
What color change occurs in the Benedict’s test?
The solution changes from blue to brick red.
What does the extent of the color change depend on?
It depends on the concentration of glucose in the sample.
How is the color change measured in this practical?
Using a colorimeter to measure absorbance.
What equipment is needed for the dilution series?
10 mmol/dm³ glucose solution, distilled water, and six boiling tubes.
What is the first step in preparing the dilution series?
Create a dilution series using distilled water.
What glucose concentrations are prepared in the dilution series?
Concentrations range from 0 to 10 mmol/dm³.
How many boiling tubes are used for the dilution series?
Six boiling tubes.
What should be placed in each boiling tube for the test?
2 cm³ of the unknown urine sample.
How much Benedict’s solution should be added to each boiling tube?
2 cm³ of Benedict’s solution.
What is the next step after adding Benedict’s solution?
Place the boiling tubes in a water bath at 90°C for 4 minutes.
What should be used to remove the boiling tubes from the water bath?
Use tongs to carefully remove the tubes.
What should be done after removing the boiling tubes from the water bath?
Leave the tubes to cool.
How do you prepare the colorimeter for measurement?
Zero the colorimeter using a cuvette filled with distilled water.
What filter should be used for the colorimeter?
Set the colorimeter to the red filter.
What should be placed in the colorimeter to measure absorbance?
Known glucose samples in cuvettes.
What is plotted on the calibration curve?
Absorbance versus known glucose concentrations.
What do you need to create a calibration curve?
A plot of absorbance against known glucose concentrations.
After measuring the absorbance of known samples, what should you do next?
Measure the absorbance of the unknown samples.
How do you find the glucose concentration of unknown samples?
Use the calibration curve to match the absorbance to the glucose concentration.
What is the risk associated with Benedict’s solution?
It is an irritant to the skin and eyes.
