# Pulp & Paper Questions and Answers – Chlorine Bleaching

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This set of Pulp and Paper Multiple Choice Questions and Answers (MCQs) focuses on “Chlorine Bleaching”.

1. The pH is of utmost importance in _________ for several reasons. First the form of Cl in solution is dependent on the pH according to the following equilibrium reactions.
a) Chlorine bleaching
b) Peroxide bleaching
c) Alovera bleaching
d) Milk bleaching

Explanation: The pH is of utmost importance in chlorine bleaching for several reasons. First the form of Cl in solution is dependent on the pH according to the following equilibrium reactions.

2. The concentration of Cl in water at 25°Celcius is _________ at saturation (i.e., 1 atmosphere pressure of CI2).
a) 1.254 M
b) 5.324 M
c) 0.091 M
d) 4.542 M

Explanation: The concentration of Cl in water at 25°Celcius is 0.091 M at saturation i.e., one atmosphere pressure of CI2. Like the solubility of CO2, the solubility of CI2 is highly pH dependent.

3. A saturated chlorine solution in water, with addition of acid or base, has a pH of or 1.54, an actual chlorine concentration, Cy, of 0.062 M, a hydrochloric acid concentration of 0.029 M, and HOCl concentration of 0.029.
a) True
b) False

Explanation: Therefore, a saturated Cl solution in water, without addition of acid or base, has a pH of 1.54, an actual Cl concentration, Cy, of 0.062 M, a HCl concentration of 0.029 M, and a HOCl concentration of 0.029.

4. An eq. is easily solved at various pH is by utilization of the quadratic eq. At pH = 0, X = 0.00423 M. At pH 1.66, x = 0.0222 in agreement with the calc. above.
a) True
b) False

Explanation: This eq. is easily solved at various pH is by use of the quadratic equation. At pH = 0, X = 0.00423 M. At pH 1.66, x = 0.0222 in agreement with the calc. above.

5. The pH at intermediate amounts of base is given in the form of the _________equation; consequently, the ratio of HOCI to OCl is not concentration dependent.
a) Henderson-Hasselbalch
b) Kennedy-kraft
c) Jason-Hammer
d) Leigh-Mark

Explanation: The pH at intermediate amounts of base is given in the form of the Henderson-Hasselbalch equation; consequently, the ratio of HOCI to OCl is not concentration dependent except for the effect of activity coefficient from pH 5 to 9.

6. The desired reaction of substitution occurs most rapidly at the _________ pH values; however, acid hydrolysis of cellulose and hemicellulose also increases with decreasing pH.
a) High
b) Slightly above neutral
c) Slightly below neutral
d) Low

Explanation: The desired reaction of substitution occurs most rapidly at the lowest pH values; however, acid hydrolysis of cellulose and hemicellulose also increment with decreasing pH. Acid hydrolysis leads to a decrement in the cellulose viscosity.

7. The hydrolysis of chlorine is also temperature dependent. _________ in Pulping Processes gives the hydrolysis constants of CI2 as a function of temperature; they are 1.45 x 10-4 at 0°C and 9.75 x 10-4 at 60°C.
a) Francis
b) Walter
c) John
d) Rydholm

Explanation: The hydrolysis of chlorine is also temperature dependent. _________ in Pulping Processes gives the hydrolysis constants of CI2 as a function of temperature; they are 1.45 x 10-4 at 0°Celcius and 9.75 x 10-8 at 60°Celcius.

8. Fill in the blank.
K = (_________ x2) / (0.05 – x)
[H+] + K1x – 0.05K1 = 0
a) [H+]
b) [HOCl]
c) K1
d) K2

Explanation: The ratio of CI2 to HOCl as a function of pH where the source of the acid is immaterial is solved in the following manner, where x = [HOCl] = [CI]. At pH = 0, X = 0.00423 M.

9. Fill in the blank.
Ka = [H+][Cl] / [Cl2] = ([H+]3) / (0.091 – [H+])
a) [H+]
b) [HOCl]
c) K1
d) K2

Explanation: The concentration of chlorine in water at 25°C is 0.091 M at saturation (i.e., one atmosphere pressure of CI2). (Like the solubility of CO2, the solubility of CI2 is highly pH dependent.). Solving for [H+] gives [H+] = 0.029 M. Therefore, a saturated chlorine solution in water, without addition of acid or base, has a pH of 1.54, an actual chlorine concentration, [Cy, of 0.062 M, a hydrochloric acid concentration of 0.029 M, and a hypochlorous acid concentration of 0.029 M.

10. Fill in the blank.
pH = pKa + log (CA- / CA)
pH =7.46 + log ([OCl]) / (____________)
a) [H+]
b) [HOCl]
c) K1
d) K2

Explanation: The pH at intermediate amounts of base is given in the form of the Henderson-Hasselbalch equation; consequently, the ratio of HOCI to OCl is not concentration dependent (except for the effect of activity coefficients) from pH 5 to 9.

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