Colourimetry (testing for glucose in urine) - Biology A-level Required Practical

Summary

In this video, a practical experiment is conducted to determine the concentration of glucose in three urine samples using a quantitative Benedict's solution. The process involves creating a dilution series of known glucose concentrations, measuring absorbance through a colorimeter, and plotting a calibration curve. This technique is used to estimate the glucose concentration in the urine samples, which could help diagnose conditions like diabetes. The experiment showcases the preparation of test tubes, mixing of solutions, heating, and the use of a colorimeter to collect quantitative data.

Takeaways

• 🔬 The experiment aims to identify the concentration of glucose in three unknown urine samples using a calibration curve and quantitative Benedict's solution.
• 🧪 The urine samples are prepared by measuring 2 milliliters of urine and mixing it with 2 milliliters of quantitative Benedict's solution.
• 📉 A dilution series is created using a stock glucose solution of 10 millimolar concentration, with dilutions down to 0 millimolar.
• ⚗️ Quantitative Benedict's solution, unlike traditional Benedict's, produces a white precipitate and reduces the blue color when reacting with glucose.
• 🌡️ The reaction occurs in a water bath for 4 minutes, with no significant visible color change but increasing white precipitate with higher glucose concentrations.
• 🧴 The absorbance of each sample is measured using a colorimeter set to a red filter, as blue solutions absorb red light best.
• 📊 The reference (0 millimolar glucose) sample is used to blank the colorimeter, ensuring accurate absorbance readings.
• 🔍 Absorbance readings are taken for each known glucose concentration, ranging from 0 to 10 millimolar, to plot a calibration curve.
• 💧 Absorbance readings for the unknown urine samples (from Tom, Dick, and Harry) are compared against the calibration curve to estimate glucose concentrations.
• 📈 The calibration curve is used to determine the glucose concentration in each urine sample by matching their absorbance values to the graph.

Q & A

What is the purpose of the experiment described in the script?

The purpose of the experiment is to identify the concentration of glucose in three urine samples using a technique involving quantitative Benedict's solution and a calorimeter to produce a calibration curve.

What is the significance of measuring glucose concentration in urine?

Measuring glucose concentration in urine can help identify if someone has high levels of glucose over a long period, which might indicate a diagnosis of diabetes.

What is quantitative Benedict's solution and how is it different from traditional Benedict's solution?

Quantitative Benedict's solution is a test for reducing sugars like glucose. Unlike traditional Benedict's solution, which produces a range of color changes, quantitative Benedict's solution produces a white precipitate and causes the blue color to fade, with the effect being greater with stronger glucose concentration.

How is the urine sample prepared for the experiment?

The urine sample is prepared by decanting it into a beaker, measuring out two milliliters accurately into a test tube, and then adding an equal volume of quantitative Benedict's solution.

What is a dilution series and why is it used in this experiment?

A dilution series is a set of solutions with known and decreasing concentrations of a substance. It is used in this experiment to create a range of known glucose concentrations to create a calibration curve.

How are the known glucose concentration samples prepared?

The known glucose concentration samples are prepared by diluting a stock solution of 10 millimolar glucose to create six test tubes with decreasing concentrations, and then adding an equal volume of quantitative Benedict's solution to each.

What happens when the test tubes are heated in the water bath?

When the test tubes are heated in the water bath, a white precipitate forms, and the blue color fades, indicating the presence of glucose. This reaction is part of the quantitative Benedict's test.

How is the absorbance of the samples measured?

The absorbance of the samples is measured using a calorimeter with a red filter. The calorimeter provides a quantitative data readout of how much light is absorbed by the samples.

Why is a red filter used in the calorimeter?

A red filter is used because the blue solution absorbs all other wavelengths of light. To see a change in absorbance, a filter of the complementary color, red, is chosen.

How are the absorbance readings of the unknown urine samples used?

The absorbance readings of the unknown urine samples are used to estimate the glucose concentration by comparing them to the calibration curve plotted from the known glucose concentrations and their absorbance readings.

What is a calibration curve and how is it used in this experiment?

A calibration curve is a graph plotting known concentrations of a substance against their corresponding measurements, such as absorbance. In this experiment, it is used to estimate the glucose concentration in the urine samples by comparing their absorbance readings to the curve.