Cleaning Capacity Of A Soap Class 10th Science Lab Manual CBSE Solution

Class 10th Science Lab Manual CBSE Solution

Lab Experiment 9
Question 1.

AIM

To study of the similar cleaning capacity of a sample of soap in soft and hard water.


Answer:

MATERIALS REQUIRED


Tap water, distilled water, calcium hydrogen carbonate, calcium chloride, calcium sulfate, soap sample, spatula, physical balance, weight box, five test tubes, three beakers, glass rods, measuring cylinder, a measuring scale.


THEORY


1. The hardness of water is due to the presence of salts of calcium and magnesium in water. These salts are soluble in water.


2. When a soap solution is added to hard water, it forms scum. This scum is insoluble in water. Therefore, floats on the top of the surface of the water.


3. The formation of scum is due to the formation of insoluble calcium and magnesium salts of fatty acids, follows:





4. Therefore, the presence of calcium and magnesium salts in water is responsible for precipitates of the soap led to reducing its cleaning power and Hence, reducing foaming capacity


PROCEDURE


1. Take three beakers and mark them as ‘A,’ ‘B’ and ‘C.’


2. Add 50 ml tap water in Beaker A.


3. Add 50 ml distilled water in beaker B.


4. Prepare 30 ml of soap solution by adding 1g soap to water in a beaker C.


5. Take 5 test tubes – A, B, C, D, E in a test tube stand.


6. By using a dropper, pour 4 ml of tap water in test tube A and 4 ml distilled water in each of the remaining 4 test tubes – B, C, D and E.


7. Add a pinch of calcium hydrogen carbonate, calcium chloride and calcium sulphate respectively in the test tubes – B, C, D and E.


8. Mix all the solutions well using a glass rod. Use separate glass rod for each test tube.


9. Add 2 ml of soap solution to the test tube A and record the observation in the observation table.



10. Shake the test tube A for 15 to 20 times and observe the length of the foam formed.

11. Repeat the above step for each test tube and measure the length of the foam in each test tube using a scale & record your observations in the observation table.


OBSERVATIONS


1. The volume of water samples taken in test tube = 4 ml.


2. The volume of soap solution added to each test tube = 2 ml.



3. The observations are shown below:



RESULTS



For cleaning action by the soap, the foam needs to be produced to remove the dirt. The formation of foam in a solution depends upon the availability of a hydrophobic portion of the soap.

In hard water, the foam is trapped due to the formation of scum. Thereby, making hard water is not suitable for cleaning purpose.


PRECAUTIONS


1. Use similar soap samples for both water


2. Take equal volumes of water samples.


3. The number of soap samples taken in all the solution should be the same.


4. Measure the length of foam should be measured immediately after shaking.



Viva Questions
Question 1.

Why can’t hard water be used for washing purposes?


Answer:

Hard water cannot be used for washing and cleaning because a large amount of soap gets washed away due to the formation of scum. Apart form this, it also sticks to the fibres of clothes.



Question 2.

What causes permanent hardness of water?


Answer:

Permanent hardness of water is caused by the presence of chlorides and sulphates of calcium and magnesium. It can be removed by using and ion exchanger.



Question 3.

How can temporary hardness of water be removed?


Answer:

Temporary harness of water is caused by the presence of calcium and magnesium bicarbonates in water. It can be removed by boiling or adding sodium carbonate to hard water.



Question 4.

Out of water obtained from rain, pond, tap and hand pump, which one is best suited for cleaning purposes?


Answer:

Rain water is best suited for cleaning purposes as it is distilled water and does not contain calcium and magnesium ions.



Question 5.

State the reason for deposition of white scale in the interior of boilers after prolong use?


Answer:

Scales are deposited in the interior of boilers after prolonged use due to the deposition of calcium carbonate and calcium sulphate.



Question 6.

State some units of hardness.


Answer:

Hardness can be measured in parts per million, Degree Clarke and Degree French.



Question 7.

Which type of water is associated with heart diseases?


Answer:

Soft water is linked to high incidences of heart diseases. It is also not considered suitable for drinking purposes.



Question 8.

On what factor does the production of foam depend?


Answer:

Production of foam depends upon free availability of a hydrophobic portion of the soap. Hydrophobicity is the property of a molecule to repel water. A long hydrocarbon chain is hydrophobic in nature.



Question 9.

State some advantages of hard water.


Answer:

Though hard water is not ideal for cleaning and drinking purposes, it has some advantages which are as below:

(a) It is good for health as it is a rich source of dietary minerals.


(b) Calcium and magnesium are needed by the body for bone and muscle growth.


(c) It also helps in regulating blood pressure.



Question 10.

Why is scum formed when hard water is treated with soap?


Answer:

Scum is formed when hard water is treated with soap because calcium and magnesium ions present in hard water react with soap to produce insoluble precipitate scum.



Question 11.

What are the positives of water softeners?


Answer:

Some of the benefits of water softeners are:

(a) Cleaner laundry.


(b) No soapy buildup on appliances which increases its lifetime.



Question 12.

State some negative effects of using water softeners.


Answer:

Some of the negative effects associated with water softeners are:

(a) They are costly, and maintenance of such systems involves a huge amount of effort.


(b) Health issues related to soft water.


(c) After softening of hard water, essential minerals like calcium and magnesium are removed.



Question 13.

What is the role of buffer solution in measuring the hardness of water?


Answer:

A buffer solution maintains the pH between 9-10 and improves the quality of water hardness testing by insulating against changes in pH or temperature.



Question 14.

What are the other names of temporary and permanent hardness?


Answer:

Temporary and permanent hardness are also known as carbonate and non-carbonate hardness.



Question 15.

Why is soft water not considered good for swimming pools?


Answer:

Soft water can greatly damage the pool as for when water is too soft it causes staining and resistance to chlorine.



Question 16.

Write the equation for the formation of scum?


Answer:

The scum is a white soild waste formed when soap is reacted with hard water. The reaction is given below:



Question 17.

How can you soften the hard water?


Answer:

Yes, hard water can be softened by chemical treatment.



Question 18.

Give any two difference between hard water and soft water?


Answer:

1. Hard water has very high mineral content whereas soft water has very less mineral content.


2. Hard water forms scum with soap whereas soft water forms lather with soap.



Question 19.

Which will form more foam – rain water or distilled water?


Answer:

Distilled water will form more foam as it does not contain magnesium and calcium ions. These ions decrease the foam forming capacity.



Question 20.

Can you write the formula for sodium stearate?


Answer:

Sodium Stearate has the chemical formula : C17H35COONa.


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