Theory & Procedure, Detection of Urea in Urine | Additional Study Material for NEET PDF Download

Objective

To detect the presence of urea in the given sample of urine.

Theory

Urine is a liquid produced by the kidneys to remove waste products from the bloodstream. Human urine is yellow in color and contains various chemical components. It primarily consists of water, organic substance such as urea, uric acid, trace amounts of enzymes, carbohydrates and hormones. The handling of urea by the kidneys is an important part of mammalian metabolism.

Let’s see how urea is produced in our body.

Urea is present mainly in the urine of all mammals, but it also occurs in blood, bile and milk. Urea is naturally produced during the process of breakdown of proteins. Due to this process, amino groups are removed from the amino acid present in the proteins. These amino groups are converted to highly toxic ammonia (NH3), and the ammonia thus produced is finally converted to urea by the liver. The urea thus formed then passes to the kidneys and is finally excreted from the body through the urine.

A healthy adult person normally excretes about 15g of nitrogen per day. Among this, about 95% of this nitrogen is excreted as urea through urine. If the liver is not healthy, it may not efficiently break down proteins. Similarly, if the kidneys are not healthy, they may not properly filter urea. Either of these problems leads to changes in the amount of urea nitrogen in our body.  If the urine is kept exposed to the atmosphere, it splits and ammonia gets released due to bacterial activity. Due to this process the stored urine becomes alkaline.  
Generally urease tests are used to detect the presence of urea in the urine sample. The enzyme urease decomposes urea into ammonia and carbon dioxide. On adding an alkaline substance, ammonium carbonate to it, changes the slightly acidic urine to an alkaline solution.  The colour of phenol red indicator changes from yellow to red in this reaction mixture.

Learning outcomes

• Students understand the characteristics of urea.
• Students understand how urea is produced in our body.
• Students understand the test to detect the presence of urea in the urine sample.
• Students will be able to do the experiment more accurately in the real lab once they understand the steps through the animation and simulation.

Sodium Hypobromite Test

Materials Required:

Procedure:

• Take 2 ml urine sample in a measuring cylinder from the urine sample bottle.
• Take a test tube and pour the urine sample into the test tube.
• Using a dropper, take sodium hypobromite solution.
• Add few drops of sodium hypobromide solution to the urine sample.
• Brisk effervescence of nitrogen appears in the test tube which indicates presence of urea in the urine.

Urease test

Materials required:

Procedure:

• Take 5 ml urine sample in a measuring cylinder from the urine sample bottle.
• Take a test tube and pour the urine sample into the test tube.
• Using a dropper, take some phenol red indicator.
• Add 4-5 drops of phenol red indicator to the test tube.
• Use a fresh dropper to take few drops of 2% Na₂CO₃.
• Add Na₂CO₃ solution drop by drop until a pink colour develops in the test tube.
• Take few drops of 1% acetic acid using a fresh dropper.
• Add 1% acetic acid to the test tube drop by drop until the pink colour disappears.
• Using a spatula, take some urease powder from the watch glass.
• Add urease powder to the test tube and shake it well.
• The pink or red colour appearing in the solution indicates the presence of urea in urine.

Simulator Procedure (as performed through the Online Labs)

You can select the type of test from the ‘Select type of test’ drop down list.

Sodium Hypobromite Test

• Drag the dropper containing the sodium hypobromite solution towards the test tube to pour the solution into it
• Click on the information icon to see the inference.
• You can redo the experiment by clicking on the ‘Reset’ button.

Urease Test

• Drag the dropper containing the Phenol red indicator towards the test tube to pour the indicator solution into it
• Drag the dropper containing the Na₂CO₃ towards the test tube to pour the solution into it
• Drag the dropper containing the Acetic acid towards the test tube to pour the solution into it
• Drag the spatula containing the urease powder towards the test tube to put the powder into it
• Drag the test tube to shake.
• Click on the information icon to see the inference.
• You can redo the experiment by clicking on the ‘Reset’ button.