3. Determination of Total, Permanent and Temporary Hardness of Water sample

VIVA – VOICE QUESTIONS & ANSWERS

3. Determination of Total, Permanent and Temporary Hardness of Water sample

1. Define hardness of water.

Hardness is the property (or) characteristics of water, which does not produce lather with soap.

2. Define hard water and soft water.

(a) Hard water

Water, which does not produce lather with soap solution but produces white precipitate (scum) is called hard water.

This is due to the presence of dissolved Ca and Mg. salts.

 (b) Soft water

Water, which produces lather readily with soap solution is called soft water.

This is due to the absence of Ca and Mg salts.

3. What are the salts responsible for carbonate and non-carbonate hardness of water.

Carbonate hardness: Ca(HCO₃)₂ and Mg(HCO₃) ₂

Non-Carbonate hardness: CaCl₂, CaSO₄, MgCl₃, MgSO₄.

4. How is hardness of water expressed.

The concentration of hardness producing salts are usually expressed interms of an equivalent amount of CaCO₃.

Significance: Its molecular weight is whole number and it is the most insoluble salt. If the concentration of hardness producing salt is X mgs/lit, then

5. How is temporary hardness removed? Give example.

It can be removed by (i) boiling the water (ii) adding lime to the water.

The above two processes convert the bicarbonates into insoluble carbonates and hydroxides, which can be removed by filtering.

6. What are the units of hardness.

1. Parts per million (ppm)

2. Milligrams per litre (mgs/lit)

3. Clarke's degree (°C)

4. French degree (°Fr)

7. Draw the structure of EDTA.

8. How will you calculate temporary hardness.

Temporary hardness of the water sample is calculated by subtracting permanent hardness from total hardness.

Temporary hardness = Total hardness – Permanent hardness.

9. What is the colour change when EBT is added to hard water. Write its equation.

The indicator forms a weak complex with the metal ions present in the hard water and gives wine red colour.

10. What is a buffer solution.

Buffer solution is a solution which resists the change in pH by the addition of acid or base i.e., Buffer solution maintains the constant pH of a solution.

11. What buffer is used in EDTA titration. Why?

EDTA make complex with Ca⁺⁺ & Mg⁺⁺ ions only at pH 8 - 10. This range can be maintained by adding ammonia buffer (NH₄Cl + NH₄OH).

12. Hardness is expressed in terms of CaCO₃ equivalent - comment.

The concentration of hardness producing salts are usually expressed interms of an equivalent amount of CaCO₃. CaCO₃ is chosen as a standard because,

(i) Its molecular weight (100) and equivalent weight (50) are whole numbers, so the calculations in water analysis can be simplified.

(ii) It is the most insoluble salt, that can be precipitated in water treatment.

13. What is the colour change, when EDTA is added to hard water containing EBT. Write its equation.

When EDTA is added into the hard water, the metal ions form a stable metal complex with EDTA by leaving the indicator. When all the metal ions are taken by EDTA from the indicator metal ion complex, the wine red colour changes into steel blue.