Common Operations and Wet Chemical Methods in Environmental Laboratories - Fundamentals of Environmental Sampling and Analysis - page 156

5. Explain the operational difference for pipets labeled as ''TD'' or ''TC''.
6. List all active and passive measures for a healthful and safe lab practice.
7. What action would you take in the following situation?
(a) Your labmate placed broken glass pipets (not the disposable ones) in the paper waste
bin.
(b) Your colleague went to a vending machine down stairs while he was performing a
COD reflux experiment.
(c) Your colleague is doing extraction using chloroform on her workbench.
(d) You saw a facility personnel rolling a gas cylinder while it is not capped.
(e) Your research assistant placed volumetric flasks in an oven to dry for the experiment
next day.
8. What is the primary difference between reflux and distillation?
9. What is the major difference between liquid-liquid separatory funnel extraction and
Soxhlet extraction in terms of the applicable type of sample matrices?
10. What oven temperature is used to dry samples for suspended solid measurement? Why
this constant temperature is important? Why different temperatures of 103 C, 180 C
and 550 C are used in solid measurement?
11. A 100-mL water sample was used for suspended solid measurement. The mass of
weighting bottle plus filter paper was 25.6257 g before filtration and 25.6505 g after
titration. What is the TSS in mg/L?
12. A sludge sample was collected after sludge was dewatered from a belt-dewatering
equipment, the moisture content was 12%. This sludge sample was further air-dried and
measured for its copper content at 80 mg/kg (dry basis). What is the copper concentra-
tion in mg/kg on a wet basis?
13. Explain why only a single titration step is needed for alkalinity measurement if the water
pH is lower than approximately 8.3.
14. Explain why acidity is not present if a water sample has a pH of greater than
approximately 8.5? What is the major difference between pH and acidity?
15. Discuss the major species responsible for the acidity in natural water and possible
contributing species in polluted water?
16. Discuss the major species responsible for the alkalinity in natural water and possible
contributing species in polluted water?
17. If 3.0 mL of 0.02 N H 2 SO 4 is required to titrate 200 mL of sample to the phenolphthalein
end point, what is the phenolthalein alkalinity as mg/L of CaCO 3 ? If additional 20.0 mL
of H 2 SO 4 is needed to reach the methyl orange point, what is the total alkalinity as mg/L
of CaCO 3 ?
18. Are Na þ and K þ included in the hardness calculation? Why or why not?
19. A water sample has Ca 2þ and Mg 2þ concentration of 25.0 mg/L and 17.0 mg/L.
Calculate the hardness in mg CaCO 3 /L (atomic weight: Ca¼40, Mg¼24).
20. A 25-mL groundwater sample was added to 25-mL DI water for a two-fold dilution. The
volume of 0.015 mol/L EDTA to reach the titration end point was 6.28 mL. Calculate the
water hardness in mmol/L and in mg CaCO 3 /L.