Volumetric Viva question and answers PDF

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Lab questions and answers for the final exam. This is the volumetric part....

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Volumetric Experiments (Part-B)

Dr. M. Vinuth

M.Sc., PGDHRM, Ph.D.

ESTIMATION OF TOTAL HARDNESS OF WATER BY EDTA COMPLEXOMETRIC METHOD VIVA QUESTIONS AND ANSWERS

1. What is hardness of water? It is the property of water in which hardness is caused by the presence of dissolved salts of Magnesium and Calcium. 2. How do you differentiate hard water from soft water? It can be easily differentiated by treating with soap. Soft water forms lather easily with soap solution, while hard water doesn’t give much lather with soap. 3. What are the types of hardness? How are they caused? There are two types of hardness of water. (a) Temporary hardness caused by the bicarbonates of calcium and magnesium. (b) Permanent hardness caused due to the chlorides and sulfates of magnesium and calcium. 4. How hardness of water is expressed? Hardness of water is generally expressed in ppm (parts per million) of CaCO3. 5. What does EDTA stands for? Ethylene diamine tetra acetic acid. 6. Write the structure of EDTA.

7. Why disodium salt of EDTA is used instead of EDTA in determining the total hardness of water? EDTA is sparingly soluble in water, therefore disodium salt of EDTA which is readily soluble in water. Hence It is used in determination of total hardness of water.

Engineering Chemistry Laboratory

Volumetric Experiments (Part-B)

Dr. M. Vinuth

M.Sc., PGDHRM, Ph.D.

8. What are buffers? These are the solutions in which resists the changes in pH when small amounts of acid or alkali is added to it. 9.

Give an example for acidic buffer and basic buffer. Acidic buffer: CH3COOH-CH3COONa buffer Basic buffer: NH3-NH4Cl buffer

10. Name the indicator used in determination of total hardness of water. Eriochrome Black-T (EBT) 11. Give an example for metal ion indicator. Eriochrome Black-T (EBT) 12. What are the ill effects of hard water? The main ill effects are skin irritation, cardiovascular disease, heart disease and high blood pressure etc. Especially in adults and children, there is an increased risk of reproductive failure and growth retardation was observed. 13. Account for the colour change when indicator is added to hard water and at the end point. Wine red to clear blue formation due to the formation of weak metal ion indicator complex. At the end, it turns blue colour due to the release of free indicator. Since the weak wine-red complex is attacked and broken by the strong chelating agent EDTA. 14. What is standard solution? Standard solutions are solutions that contain a known and accurate amount (i.e. concentration) of a substance or element. 15. Define Normality and Molarity? Normality is defined as the number of equivalent mass of the solute dissolved in 1 litre/1000cm3/ dm3 Normality = Mass X 1000 Eq. Mass X Volume

Engineering Chemistry Laboratory

Volumetric Experiments (Part-B)

Dr. M. Vinuth

M.Sc., PGDHRM, Ph.D.

Molarity is defined as the number of molecular mass of the solute dissolved in 1 litre/1000cm3/ dm3 Molarity

=

Mass X 1000 Mol. Mass X Volume

16. What is total hardness of water? Total hardness is the sum of temporary hardness (due to bicarbonates of calcium and Magnesium) and permanent hardness (due to chlorides, sulphates etc., of Calcium and Magnesium). 17. How temporary and permanent hardness can be removed? Temporary hardness can be removed by simple physical process like boiling Mg/Ca(HCO3)

Mg/CaCO3 + H2O + CO2

Permanent hardness can be removed only by chemical methods like soda-lime process, ion exchange process and Clark’s method. 18. Name the deposition formed when hard water is boiled? Write its reaction. Scale and sludge formation take place. Ca(HCO3)2(aq) Mg(HCO3)2(aq)

CaCO3 (s) + CO2 (g) + H2O MgCO3(s) + CO2 (g)+ H2O

19. Why pH gets altered in the experiment? The reaction involves the liberation of H+ ions and the indicator is sensitive to the concentration of H+ ions of the solution and this will directly affect the variation in the pH during the experiment. 20. Why and how pH is maintained in the experiment? The reaction involves the liberation of H+ ions and the indicator is sensitive to the concentration of H+ ions of the solution and this will directly affect the variation in the pH during the experiment. However, a constant pH around 10 has to be maintained for completion of reaction. For this purpose, ammonia-ammonium chloride buffer is used. Engineering Chemistry Laboratory

Volumetric Experiments (Part-B)

Dr. M. Vinuth

M.Sc., PGDHRM, Ph.D.

ESTIMATION OF CALCIUM OXIDE (CaO) BY RAPID EDTA METHOD VIVA QUESTIONS AND ANSWERS

1. What is cement? Write its composition. The major constituents are silicates of calcium, magnesium, aluminum and iron with a small quantity of oxides of alkali metals. The average composition of Portland cement as follows CaO - 63.90%; SiO2 - 20.7%; Al2O3- 5.6%; Fe2O3 – 2.5% MgO – 3.75%; TiO2 – 0.23%; Na2O – 0.21%; K2O – 0.51% 2. What is the purpose of using? (a) Glycerol

(b)Diethylamine

(c) NaOH

in the estimation of CaO in cement solution? Glycerol avoids the coprecipitation of indicator with Mg(OH)2 precipitate and helps in getting the sharp end point. Diethylamine is used maintain the pH of the solution in the range of 12 - 14. NaOH is added to avoid the interference of Mg+2 ions, thereby precipitating Mg+2 ions as Mg(OH)2 precipitate [Mg+2 + 2NaOH

Mg(OH)2 + 2Na+

3. Name the product after addition of sodium hydroxide? Mg(OH)2 precipitate [Mg+2 + 2NaOH

Mg(OH)2 + 2Na+]

4. Why percentage of CaO has to be determined in cement sample and what is its importance? Lime or calcium oxide (CaO) is the most important composition of cement. The cement contains 59 to 63% of lime in it.

Engineering Chemistry Laboratory

Volumetric Experiments (Part-B)

Dr. M. Vinuth

M.Sc., PGDHRM, Ph.D.

If CaO concentration is very high then cement becomes unsound as well as expansion and disintegration of cement will occur. If CaO concentration is very low, strength of cement will reduce and also setting time of cement will decrease. 5. Why EBT is not used in CaO determination? EBT forms a very weak and unstable complex with Ca +2 at pH between 12 - 14 and the change of colour is not sharp. It gives the total concentration of both Ca/Mg+2 ions. 6. Name the indicator used in CaO determination in cement solution. Patton and Reeder’s indicator. 7. Why the titration is called rapid EDTA method? We could easily determine the percentage of Ca+2 (CaO) ions very quickly using std. EDTA solution. Moreover, the reaction mixture with a pinch of Patton Reeder’s indicator against EDTA gives the sharp color change from wine red to clear blue. Hence it is called as rapid EDTA method.

Engineering Chemistry Laboratory

Volumetric Experiments (Part-B)

DETERMINATION

Dr. M. Vinuth

OF

PERCENTAGE

OF

COPPER

M.Sc., PGDHRM, Ph.D.

IN

BRASS

SOLUTION USING STANDARD SODIUM THIOSULPHATE SOLUTION VIVA QUESTIONS AND ANSWERS

1. What is brass? Mention its constituents. Brass is an alloy of copper and zinc. Along with Cu and Zn, trace quantities of Sn, Pb, and Fe. 2. What is an alloy? Give examples. It is a homogeneous mixture of two or more metals or metal with a nonmetal. E.g.: Steel, Bronze, and Brass 3. What is the purpose of alloying the metals? The main purpose is to be enhance the properties like tensile strength, hardness, abrasion resistance and corrosion resistance. 4. What are iodometric and iodimetric titrations? Iodimetric titrations are those in which standard iodine solution is used as oxidizing agent whereas, in iodometric titration some oxidizing agent Cu +2 liberates iodine(I2) from iodide solution (KI) and then the liberated iodine is titrated against std. reducing agent (Na2S2O3) 5. What is the purpose of adding urea to the brass sample? Urea is added to neutralize the dissolved oxides of nitrogen which can oxidize KI to I2. 6. Why is NH4OH added to brass solution in the determination of copper? NH4OH is added to neutralize mineral acid HNO3. 7. Why is acetic acid added to brass solution in the determination of Copper? Acetic acid dissolves the Cu(OH)2 ppt and maintains slightly acidic medium required for redox titration.

Engineering Chemistry Laboratory

Volumetric Experiments (Part-B)

Dr. M. Vinuth

M.Sc., PGDHRM, Ph.D.

8. Classify the following into oxidizing and reducing agents. Cu+2, I-, I2 and Na2S2O3 Cu+2 and I2 = Oxidizing agents I- and Na2S2O3 = Reducing agents 9. Give an example for redox indicator Starch is the example for redox indicator. 10. Why starch indicator is added towards the endpoint in iodometric titrations? Because, it forms water insoluble complex with I2 at higher concentration of I2 and it cannot be easily dissociated by the thiosulphate solution.

Engineering Chemistry Laboratory

Volumetric Experiments (Part-B)

Dr. M. Vinuth

M.Sc., PGDHRM, Ph.D.

DETERMINATION OF CHEMICAL OXYGEN DEMAND (COD) OF WASTE WATER VIVA QUESTIONS AND ANSWERS

1. What is COD? Write its unit. It is defined as the amount of oxygen which is required for the complete oxidation of inorganic and organic waste/compounds present in waste water by a strong oxidizing agent. It is expressed in ppm or mg/dm3. 2. What is the role of mercuric sulphate and Ag2SO4 in the determination of COD? Mercuric sulphate avoids the precipitation of silver ions as AgCl and Ag2SO4 acts as catalyst. 3. What is the significance of COD? It is the quick parameter used in detect the pollution level and indicates the pollution strength of wastewater sample. 4. Which is the indicator used in COD experiment? Ferroin indicator 5. What is the colour change at the endpoint in the determination of COD? Blue green to reddish brown 6. Why blank titre value is higher than the back titre value? In back titration only unreacted K 2Cr2O7 is estimated, whereas in blank titration the whole amount of K2Cr2O7 is estimated. 7. What is the chemical name, formula, molecular weight and equivalent weight of Mohr’s salt? Chemical name: Ferrous ammonium sulphate [FeSO4. (NH4)2 SO4. 6H2O] Molecular weight: 392 g and Equivalent weight: 392 g 8. Why dil. H2SO4 is used to dissolve FAS crystals while preparing the standard solution? To avoid the hydrolysis of ferrous ions (Fe+2 ions). Engineering Chemistry Laboratory...