Test for Presence of Urea in Urine

You might have heard of urea fertilisers which play a crucial role in the growth and development of crops. Despite their usefulness to plants, they are waste products for us. In mammalian urine, it is found abundantly as a naturally occurring molecule produced by protein metabolism. All mammals excrete the substance not only through their urine but also through their bile, blood, sweat, and milk.

Proteins are broken down so that amino groups are removed from amino acids. The liver converts these amino groups into urea, which is toxic to the body and must be converted back to ammonia. The urea is excreted in the urine by passing through the kidneys.

Table of Content

• Aim

• Theory

• Materials required

• Procedure

• Observation

• Result

• Precautions

Aim

The following experiment is conducted to test for the presence of urea in urine.

Theory

Nitrogen from amino acids is mainly excreted as urea by the kidneys. Ammonia is a highly toxic compound converted into urea after removing amino groups from amino acids. Despite urine having an acidic pH, when released into the atmosphere, it splits, releasing ammonia, and resulting in alkaline urine.

Urease test: When temperature and pH are optimum, urea decomposes by the enzyme urease into ammonia and carbon dioxide, forming ammonium carbonate, which changes the acidic solution into an alkaline one. The colour of the solution changes from yellow to pink when phenol red is used as an indicator.

Sodium hypobromite test: Urine contains an excess of sodium hydroxide released as carbon dioxide and nitrogen gas when treated with sodium hypobromite solution. Carbon dioxide, after reacting with sodium hydroxide, gives sodium bicarbonate.

1. Urease Test

Apparatus Required

1. Test tubes

2. Urine sample

3. 2% Na2CO3 solution

4. 2% acetic acid

5. Soybean powder

6. Phenol red

7. Dropper

8. Test tube stand

Procedure

1. Take 2 ml of urine and 2 ml of water in two separate test tubes.

2. Add a single drop of red phenol indicator to both tubes.

3. You should add 2% Na2CO3 solution drop by drop to both test tubes until the pink colour develops (just alkaline).

4. Add 2% acetic acid drop by drop to the test tubes until the pink colour disappears (just acidic).

5. Add soybean powder (containing the urease enzyme) to each test tube or add urease enzyme powder to both tubes. Rotate the tubes between your palms or heat them to about 60°C.

Observation and Result

The pink colour can be seen in the urine tube but not in the water tube.

2. Sodium Hypobromite Test

Apparatus Required

1. Urine sample

2. Sodium hypobromite

3. Test tube

4. Dropper

5. Test tube stands

Procedure

1. Take a clean test tube and add 2 ml of the urine sample.

2. Add two drops of alkaline sodium hypobromite solution with the help of a dropper to the same test tube.

Observation and Result

Upon testing the sample, a brisk effervescence of nitrogen occurs, indicating the presence of urea.

Precautions

1. Use clean test tubes for the experiment.

2. Ensure your hands are clean before and after collecting each sample.

3. Urease test: One should not overheat the sample to avoid the denaturation of enzymes.

Lab Manual Questions

1. What is the urine reaction with sodium hypobromite?

Ans. Urine reaction with sodium hypobromite results in the effervescence of nitrogen which confirms the presence of urea.

2. Why does pink appear in the test tube containing the urine sample?

Ans. urea decomposes by the enzyme urease into ammonia and carbon dioxide, forming ammonium carbonate, which changes the acidic solution into an alkaline one. The colour of the solution changes from yellow to pink when phenol red is used as an indicator.

3. Why does effervescence occur when sodium hypobromite is added to urine?

Ans. Urine contains an excess of sodium hydroxide released as carbon dioxide and nitrogen gas when treated with sodium hypobromite solution. Carbon dioxide, after reacting with sodium hydroxide, gives sodium bicarbonate. The nitrogen gas formed in the reaction produces effervescence.

4. What happens if you overheat the mixture of a urine sample and soybean powder?

Ans. The enzyme urease in the soybean powder gets denatured if we overheat the mixture of a urine sample and soybean powder.

Viva Questions

1. What is the normal value of urea nitrogen in urine?

Ans. The normal urea nitrogen value in urine ranges from 428.4 to 714 mmol/day.

2. Which enzyme helps in the digestion of urea? 

Ans. Urease helps in the digestion of urea.

3. What is the sodium hypobromite formula?

Ans. Sodium hypobromite formula is NaBrO.

4. What is the normal pH range of urine?

Ans. The normal pH range of urine ranges from 4.5 and 8.

5. What happens when the urease enzyme digests urea?

Ans. When the urease enzyme digests, urea carbon dioxide and ammonia are formed.

6. What is the normal urea level in urine?

Ans. The normal urea level in urine ranges from 12 to 20 g/24 h.

7. What happens if the liver fails to convert ammonia into urea?

Ans. If the liver fails to convert ammonia into urea, a high amount of ammonia is accumulated in the body, which may reach the blood and cause liver damage.

8. Why is soybean powder added to the test tube containing urine?

Ans. Since soybean contains a urease enzyme, it is added to the urine test tube for the urease test.

9. What is urea?

Ans. Urea is a crystalline and colourless  compound that is produced as a result of protein metabolism and is passed through the urine.

10. Why ammonia is converted to urea?

Ans. Since ammonia is toxic to the body, it should be removed. So the liver converts ammonia into urea which is not toxic as ammonia.

Practical-Based Questions

1. Which is the organ that converts ammonia into urea?

1. Kidney

2. Liver

3. Heart

4. Intestine

Ans: B) Liver

2. What colour change occurs when you add a phenol red indicator?

1. Pink to yellow

2. Yellow to orange

3. Yellow to pink

4. Pink to blue

Ans: C) Yellow to pink

3. Which compound is used in the urease test?

1. Acetic acid

2. Benzoic acid

3. Sulphuric acid

4. Hydrochloric acid

Ans: A) Acetic acid

4. Nitrogen is mainly excreted from the body in the form of ___?

1. Ammonia

2. Urea

3. Amino Acids

4. Proteins

Ans: B) Urea

5. Which is the product formed when carbon dioxide reacts with sodium hydroxide?

1. Sodium carbonate

2. Sodium chloride

3. Sodium hypobromite

4. Sodium bicarbonate

Ans: D) Sodium bicarbonate

6. Urea is produced in which process?

1. Breakdown of DNA

2. Breakdown of proteins

3. Breakdown of RNA

4. Breakdown of lipids

Ans: B) Breakdown of proteins

7. Which among the following is a urea test?

1. Urease test

2. Sodium hypobromite test

3. Biuret test

4. All the above

Ans: D) All the above

8. What will you observe when alkaline sodium hypobromite solution is added to the urine sample?

1. Colour of the solution changes

2. Precipitation formation

3. Effervescence formation

4. Froth formation

Ans: C) Effervescence formation

9. Which among the following compounds is added to the urine sample in urease test?

1. Sodium hydroxide

2. Sodium bicarbonate

3. Sodium carbonate

4. Sodium hypobromite

Ans: C) Sodium carbonate

10. What is the name of the indicator used in the urease test?

1. Phenolphthalein

2. Methyl orange

3. Methyl red

4. Phenol red

Ans: D) Phenol red

Summary

In mammalian urine, urea is found abundantly as a naturally occurring molecule produced by protein metabolism. The urea is excreted in the urine by passing through the kidneys. When temperature and pH are optimum, urea decomposes by the enzyme urease into ammonia and carbon dioxide, forming ammonium carbonate, which changes the acidic solution into an alkaline one. Carbon dioxide, after reacting with sodium hydroxide, gives sodium bicarbonate.