Lab Exercise 7 to 11

Question 1

Which is false?
A.Groundwater dissolves the iron from soil and minerals. B.Iron also contributes to water hardness since it is a divalent ion.
C.Iron has harmful effects in humans.
D.Iron imparts a certain taste that will cause water rejection.

Answer 1

C

Question 2

Which was not used @ Iron Det? For remaining, do sequence them :)
A. glass beads
B. NH4Ac buffer & phenanthroline
C. conc & hydroxylamine HCl
D. methyl orange

Answer 2

D. Orange shade kasi yung final color!! :))

C,A,B

Question 3

Which forms red orange color @ Fe det?
A. NH4Ac buffer
B. Hydroxylamine hydrochloride
C. phenanthroline
D. methyl orange

Answer 3

C, upon rxn with Fe

Question 4

Which is reducing agent @ Fe det?
A. NH4Ac buffer
B. Hydroxylamine hydrochloride
C. phenanthroline
D. methyl orange

Answer 4

B

Question 5

@ iron det: NH4Ac buffer maintains pH @ __

Answer 5

3.5

Question 6

False about chloride determination
A.via precipitation titration
B.excess AgNO3 is needed to react with K2CrO4
C.Colored precipitate happens before equivalence point
D.Reagent blank: ideally has no Ag

Answer 6

C - AFTER EQUIVALENCE
POINT
o At equivalence point, [Ag] = [Cl]
o Excess [Ag] is needed to form a precipitate with
chromate
o Thus the need for blank to measure the excess [Ag]

Question 7

Which is false?
A. Cl standard for drinking H2O & irrigation H2O is the same
B. Chloride content increases as mineral content increases
C. Chloride has no significant health effects
D. Spray from ocean is carried inlands as droplets which constantly replenish the chloride content of inland waters

Answer 7

A
250 mg/L for drinking water
Less than 250 mg/L for water of irrigation

Question 8

how can over pumping of groundwater increase Cl content

Answer 8

Overpumping of groundwater –> intrusion of seawater –> increase chloride content

Question 9

identify determination method of:
A. chloride
B. sulfate

Answer 9

A. chloride - precipitation titration

B. sulfate - turbidimeter/colorimetric method

Question 10

identify determination method of:
C. fluoride
D. iron

Answer 10

C. fluoride - colorimetric method

D. iron - colorimetric method

Question 11

Not a conditioning reagent in sulfate determination
A.HCl
B.NaCl 
C.BaCl2
D.glycerol

Answer 11

C

Question 12

Which is not an effect of sulfate @ envi & health?
A.May hard scales in boilers & heat exchangers
B.Odor problems
C.Corrosion of sewers
D.Increase prevalence of NCDs
E.Acid rain

Answer 12

D

Question 13

Iron, sulfate & fluoride determined via colorimetric method. What are their end colours, respectively?

Answer 13

iron - red orange
sulfate - blue
fluoride - red

Question 14

Iron, sulfate & fluoride determined via colorimetric method. In what wavelengths are they read, respectively?

Answer 14

Fe - 510 nm
sulfate - 340 nm
F - 570 nm

Question 15

respective standard values for:
A. fluoride
B. sulfate

Answer 15

A. 4 mg/L for drinking water

B. Less than or equal to 750 ppm. 250 mg/L for drinking water

Question 16

What is chlorine demand & how is it determined?

Answer 16

 Amount of chlorine used up to oxidize substances in water

 Determined through iodometric method

Question 17

reactions @ iodometric method - identify

Answer 17

Cl2 + 2I- –> I2 + 2Cl-

I2 + starch –> blue color

Question 18

breakpoint chlorination denotes the ff except:
A.The point where the curve starts to rise again
B.The end of reaction of chlorine with impurities in water
C.the start of disinfecting ability of chlorine
D.NOTA

Answer 18

D

Question 19

How is breakpoint chlorination determined?

Answer 19

iodometric method

Question 20

What is residual chlorine?

Answer 20

Amount of chlorine remaining after some of the chlorine has reacted with substances in water

Question 21

in residual chlorine, what was the titrant?

Answer 21

std. sodium thiosulfate solution (0.025 N)

Question 22

Why do some samples have no breakpoint chlorination? enumerate two reasons

Answer 22

Some have no breakpoint chlorination maybe because:
o Breakpoint is found before the starting mL
o Water sample may contain different organic molecules
that react at different rates