How to Perform Urea Detection in Urine: Methods and Significance for Class 11 Students
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
Test tubes
Urine sample
2% Na2CO3 solution
2% acetic acid
Soybean powder
Phenol red
Dropper
Test tube stand
Procedure
Take 2 ml of urine and 2 ml of water in two separate test tubes.
Add a single drop of red phenol indicator to both tubes.
You should add 2% Na2CO3 solution drop by drop to both test tubes until the pink colour develops (just alkaline).
Add 2% acetic acid drop by drop to the test tubes until the pink colour disappears (just acidic).
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
Urine sample
Sodium hypobromite
Test tube
Dropper
Test tube stands
Procedure
Take a clean test tube and add 2 ml of the urine sample.
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
Use clean test tubes for the experiment.
Ensure your hands are clean before and after collecting each sample.
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
Which is the organ that converts ammonia into urea?
Kidney
Liver
Heart
Intestine
Ans: B) Liver
What colour change occurs when you add a phenol red indicator?
Pink to yellow
Yellow to orange
Yellow to pink
Pink to blue
Ans: C) Yellow to pink
Which compound is used in the urease test?
Acetic acid
Benzoic acid
Sulphuric acid
Hydrochloric acid
Ans: A) Acetic acid
Nitrogen is mainly excreted from the body in the form of ___?
Ammonia
Urea
Amino Acids
Proteins
Ans: B) Urea
Which is the product formed when carbon dioxide reacts with sodium hydroxide?
Sodium carbonate
Sodium chloride
Sodium hypobromite
Sodium bicarbonate
Ans: D) Sodium bicarbonate
Urea is produced in which process?
Breakdown of DNA
Breakdown of proteins
Breakdown of RNA
Breakdown of lipids
Ans: B) Breakdown of proteins
Which among the following is a urea test?
Urease test
Sodium hypobromite test
Biuret test
All the above
Ans: D) All the above
What will you observe when alkaline sodium hypobromite solution is added to the urine sample?
Colour of the solution changes
Precipitation formation
Effervescence formation
Froth formation
Ans: C) Effervescence formation
Which among the following compounds is added to the urine sample in urease test?
Sodium hydroxide
Sodium bicarbonate
Sodium carbonate
Sodium hypobromite
Ans: C) Sodium carbonate
What is the name of the indicator used in the urease test?
Phenolphthalein
Methyl orange
Methyl red
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.
FAQs on Step-by-Step Guide: Testing for Urea Presence in Urine (Class 11 Biology, 2025-26)
1. How do you perform the test for the presence of urea in urine as per the Class 11 Biology practical syllabus for the 2025-26 session?
To test for urea in a urine sample, follow these steps which are crucial for the practical examination:
- Sample Preparation: Take 2 ml of fresh urine in a clean test tube.
- Enzyme Addition: Add a pinch of soybean powder or urease enzyme to the urine sample. The enzyme urease is the key reagent that acts on urea.
- Incubation: Shake the test tube well and allow it to stand for 5-10 minutes. This gives the enzyme time to react.
- Detection: Moisten a piece of red litmus paper and place it near the mouth of the test tube. Gently warm the test tube.
- Observation: If urea is present, the red litmus paper will turn blue, confirming a positive result.
2. What is the underlying principle of the urease test for urea, and why does the red litmus paper turn blue?
The principle of this important test is based on enzymatic action. The enzyme urease specifically hydrolyzes urea present in the urine into ammonia (NH₃) and carbon dioxide (CO₂). The chemical reaction is: CO(NH₂)₂ + H₂O → 2NH₃ + CO₂. Ammonia is an alkaline gas. When it is released from the solution upon gentle warming, it comes into contact with the moist red litmus paper, turning it blue. This colour change is the key indicator confirming the presence of urea.
3. What are the essential materials and reagents required for conducting the test for urea in urine in a laboratory?
For the Class 11 practical exam, you will need the following:
- Apparatus: Test tubes, test tube holder, test tube stand, and a spirit lamp or burner.
- Sample: A fresh sample of urine.
- Key Reagent: Urease enzyme source, which is typically soybean powder or pure urease extract.
- Indicator: Red litmus paper strips.
- Other: Distilled water for cleaning purposes.
4. From an examination perspective, what is the clinical significance of detecting abnormal levels of urea in urine?
While urea is a normal excretory product, its concentration is an important diagnostic marker. For a 2 or 3-mark question, you should mention:
- High Urea Levels: May indicate a high-protein diet, excessive tissue breakdown, or certain kidney conditions where the body is processing more nitrogenous waste.
- Low Urea Levels: Can suggest liver failure (as the liver synthesizes urea), malnutrition, or overhydration. Therefore, testing for urea concentration helps in assessing liver and kidney function, as well as the overall metabolic state of an individual.
5. Why is the enzyme urease so specific for this test? Could another enzyme be used instead?
The enzyme urease is highly specific because its active site is uniquely shaped to bind only with the urea molecule, acting as a lock and key. This specificity is a crucial concept for HOTS questions. It ensures that the test is reliable and that the ammonia produced is a direct result of urea breakdown only, not from other substances in the urine. No other enzyme could be used as a substitute because other enzymes will not catalyse the hydrolysis of urea.
6. What are two important precautions a student must take while performing the urea test to get an accurate result in the practical exam?
To ensure accurate and safe results in your board practicals, you must observe the following precautions:
- Avoid Overheating: The urine sample should be warmed very gently. Vigorous boiling can cause the liquid to splash out and may decompose other urinary components, leading to inaccurate results.
- Use a Fresh Sample: Use a fresh urine sample because if it is left standing for too long, bacteria can decompose the urea, releasing ammonia and giving a false positive result even before the test begins.
7. If urea is a normal constituent of urine, why is testing for its presence considered an important practical experiment in the CBSE syllabus?
This is a key conceptual question. While urea is always present in normal urine, this experiment is important for several reasons:
- Understanding Metabolism: It demonstrates the end-product of protein metabolism and the role of the liver and kidneys in excretion.
- Enzyme Action: It is a classic example of enzyme specificity (urease acting on urea), a fundamental concept in biology.
- Diagnostic Foundation: It teaches the principle behind quantitative analysis. While the school test is qualitative (presence/absence), it forms the basis for diagnostic tests that measure the *concentration* of urea to assess health.
