Answers to viva questions

ANSWERS TO VIVA QUESTIONS

1. Hardness is the amount of dissolved calcium and magnesium ions in water (Ca2+, Mg2+). Hardness in water is caused due to contact of flowing water with soil and rocks. It is expressed as ppm of CaCO3. Hard water is unfit for bathing and laundry purposes due to high consumption of soap and residue on utensils. Hard water is unfit for use in textile and beverage industries and should not be used for boiler feed.
2. Temporary hardness is due to dissolved Calcium and Magnesium ions (Calcium hydrogen carbonate and Magnesium hydrogen carbonate). It is called temporary because it can be removed by boiling
3. Permanent hardness is hardness due to presence of Chlorides, Nitrates and Sulphates of Calcium and Magnesium which cannot be removed by boiling. Permanent hardness can be removed by base-exchange process or by the use of silicon zeolites
4. Dissolved Oxygen is the amount of gaseous oxygen (O2) dissolved in the water. Oxygen enters the water by direct absorption from the atmosphere, by rapid movement, or as a waste product of plant photosynthesis
5. At 0℃ the saturation value of DO in water is 14.6 PPM
6. Biochemical Oxygen Demand or BOD refers to the amount of biologically degradable organic matter present in the water. It is a measure of the strength of the sewage and indicates organic matter present in the water sample. It takes five days to determine BOD. This is known as BOD₅ which reflects about 70 - 75% BOD. This is adopted as a standard. However, complete oxidation takes more than three weeks and is known as ultimate BOD and is represented as BODu
7. Chemical Oxygen Demand (COD) refers to the amount of chemically oxidizable matter present in the water. It is ALWAYS greater than BOD
8. Alkalinity refers to the capacity to neutralize acids. It occurs due to carbonate (CO₃²⁻), bicarbonate (HCO₃⁻) and hydroxides (OH⁻)
9. Turbidity is defined as the extent to which light is either scattered or absorbed by suspended suspended matter in water.
10. Residual chlorine refers to the excess amount of chlorine in water after break-point chlorination
11. The significance of jar test is that it helps to determine the optimum dosage of coagulant to be added to the water for obtaining the most clear water after sedimentation and coagulation processes
12. Sedimentation refers to the removal of suspended matter in water by allowing it to stand still in a quiescent pond for period known as 'detention period'
13. Coagulation refers to the addition of a chemical called "coagulant" that traps the very finely suspended particles (that do not settle easily) in a gel. Examples of coagulants are alum and ferric chloride
14. When the coagulated chunks called flocs in the coagulation tank are stirred, all the flocs come together to form bigger flocs. This process is called flocculation
15. The ill-effects of hard water in domestic use are it forms precipitates requiring excessive use of soap in washing and bathing. In industries, hard water causes encrustation and formation of scales in pipes and boilers
16. BOD is Biochemical Oxygen Demand and it is the amount of Oxygen required to decompose organic matter
17.  BOD is the amount of Oxygen required while DO is the amount of Oxygen present in water in a dissolved state. If BOD is high, DO is low (Inversely proportional)
18. BOD and COD refer to the amount of Oxygen REQUIRED for oxidation of organic matter biologically and chemically respectively. COD is always higher than BOD because COD oxidizes organic matter BOTH biologically and chemically active organic matter while BOD refers to only biologically active organic matter
19. Turbidity plays a very important role in wastewater treatment. It indicates the amount of suspended sediment in water. Water with high turbidity block sunlight to aquatic plants and carry contaminants and pathogens
20. Dissolved Oxygen (DO) is measured using a method called "Azide modification method" or 'winkler's method'
21. Coagulation refers to aggregation of particles. It is mainly used in the treatment of water containing colloids
22. The permissible value of residual chlorine is 0.1 to 0.2 ppm or mg/l
23. The permissible value for chloride content in water is 250 ppm
24. The amount of chlorine in water decreases initially till ALL the bacteria are killed and then starts increasing as chlorine appears as free chlorine. This point is known as break point chlorination
25. A graph is plotted in jar test to accurately determine the optimum dosage of coagulant
26. The source of chlorides in water is the dissolution of rocks as water flows on land
27. Minimum DO to support aquatic life is 2 ppm
28. The saturation value of DO at 25 C is 8.1 ppm
29. Alkalinity is the capacity to neutralise an acid. Alkalinity plays an important role in chemical coagulation and biological waste treatment processes
30. Standardization is the process of determining the exact concentration of a solution. 
31. Normality is the ratio of molecular weight of a substance to the number of gram equivalents of that substance
32. Dilution ratio is the ratio of volume of the mixture to volume of the concentrate. It is used in determining BOD of very strong wastes
33. Hypochlorous acid is a weak acid formed during the process of chlorination. It is mainly used for disinfection of water,
34. During the determination of residual chlorine, in one of the steps, potassium dichromate is added as a reagent and the solution is kept in the dark to prevent photochemical oxidation of potassium dichromate 
35. Standardization of a reagent is done to adjust the concentration of a reagent to the specific value required for the reaction. Usually stock solutions required for a reaction are prepared in bulk of a concentration greater than the requirement and hence it is required to calculate their precise concentration and adjust it accordingly as per the requirement for the particular experiment
36. Alkalinity is caused due to carbonate, bicarbonate and hydroxide ions while hardness is caused due to divalent cations of Calcium and Magnesium
37. Hardness and Alkalinity are both expressed in mg/L of CaCO3
38. EDTA - Ethylene Diamine Tetra Acetic acid; EBT - Eriochrome Black T
39. Winklers test is conducted to determine dissolved oxygen in water and it is also known as Alkali Azide Modification Method
40. Saturation value for DO depends on temperature and its value is 8.1 at 25 C
41. Permissible value for chlorides in water is 250 ppm
42. The types of alkalinities are phenolphthalein alkalinity and methyl orange alkalinity
43. Carbonate, bicarbonate and hydroxide ions contribute to alkalinity in water
44. Turbidity is measured in NTU (Nephelo Turbidity Units)
45. 'Stock solution' refers to a standard solution prepared in bulk and used repeatedly. Stock solutions are prepared for frequent use in labs and they are usually of a higher concentration than needed. They should be standardised before use
46. If the solution has a higher value than the range for which the instrument is calibrated, the solution is diluted and the formula used is (A * (B+C))/C where A = Turbidity of diluted solition, B = Volume of dilution water in ml, C = Volume of sample that had been diluted
47. Alum is chemically called 'Aluminium Sulphate' and is used as a floccculant to remove unwanted colour and turbidity from water. It is used in combination with filtration in conventional water treatment processes
48. Coagulants function to neutralize negatively charged particles and destabilize the forces that keep the particles apart.
49. If too little of coagulant is added, all the suspended particles in water do not coagulate and if coagulant is added in excess, water acquires a bitter taste
50. Alkalinity and Hardness, both are expressed as mg/l of Calcium Carbonate