This set of Pulp and Paper Multiple Choice Questions and Answers (MCQs) focuses on “Bleaching Mechanical Pulps”.
1. __________ are most, sometimes conjugated double bond systems arising in the lignin of pulps.
a) Chromosomes
b) Chromophores
c) Chloroplasts
d) Chrome
View Answer
Explanation: Chromophores are the most often conjugated double bond systems present in the lignin of pulps.
2. Mechanical pulps are bleached with chemicals just to alter many of the chromophores.
a) True
b) False
View Answer
Explanation: Mechanical pulps are bleached with chemicals just to alter many of the chromophores.
3. Brightening of mechanical pulps is done by reducing agents like __________
a) Groundwood
b) Sulphite
c) Dithionite
d) Dissolving pulp
View Answer
Explanation: Brightening mechanical pulps is accomplished with the help of reducing agents, such as dithionite, or oxidants, such as hydrogen peroxide.
4. Brightened mechanical pulps are the ones subjected to colour reversion. Since the lignin is largely decoloured, but not removed, there is only a small loss of yield.
a) True
b) False
View Answer
Explanation: Brightened mechanical pulps are the ones subject to colour reversion because the lignin is largely de-coloured, but are not removed, there’s only a small loss of yield.
5. __________ (a common name in the industry, but dithionite is the preferred name) bleaching process is carried out with 0.5-1.0% dithionite on the wood.
a) Hydroslufite
b) Groundwood
c) Kraft
d) Sulphite
View Answer
Explanation: Hydroslufite (the common name in the industry, but dithionite is the preferred name) bleaching process is carried out with 0.5-1.0% dithionite on the wood.
6. In hydrosufite bleching Zn+2SO2andrarr; __________
a) ZnSO
b) Zn S2O4
c) Zn2SO4
d) ZnS2O4
View Answer
Explanation: Zinc dithionite is prepared in the pulp mill from zinc and sulfur dioxide as follows: Zn+2SO2andrarr; ZnS2O4
7. Chelating agents, such as __________ have the added gain of preventing pulp dis-coloration by binding together with ferric ion that could otherwise form a colored complex with the phenolic lignin structure.
a) Pulp
b) Lignin
c) Oxygen
d) EDTA
View Answer
Explanation: Chelating agents, such as EDTA, have the added gain of preventing pulp dis-coloration by binding together with ferric ion that could otherwise form a colored complex with the phenolic lignin structure.
8. __________ (5% on wood) is used usually after the addition of magnesium ion. The mechanism for inactivating the ions by __________ precipitating the ions, but, strictly speaking, it is not a chelating agent.
a) Sodium disulfate
b) Sodium peroxide
c) Sodium silicate
d) Sodium hydroxide
View Answer
Explanation: Sodium slicate (5% on wood) is used usually after the addition of magnesium ion. The mechanism for inactivating the ions by Sodium silicate precipitating the ions, but it is not a chelating agent.
9. __________ with sodium hydroxide and/or sodium peroxide is utilized to produce the high pH that is crucial to produce the active perhydroxyl ion, HOO–.
a) Hydrogen dioxide
b) Hydrogen peroxide
c) Hydrogen silicate
d) Hydrogen fluoride
View Answer
Explanation: Hydrogen peroxide with sodium hydroxide and/or sodium peroxide (NaOOH) is utilized to produce the high pH that is crucial to produce the active perhydroxyl ion, HOO–.
10. Pine and fir are difficult to brighten. Colour reduction occurs by altering __________ groups, the pulp is sometimes subsequently treated with SO2 to neutralize OH– and reduce any residual peroxide.
a) Chromosome
b) Chromophoric
c) Dithionite
d) Peroxide
View Answer
Explanation: Pine and fir are difficult to brighten. Colour reduction occurs by altering __________ groups, the pulp is sometimes subsequently treated with SO2 to neutralize OH– and reduce any residual peroxide.
Sanfoundry Global Education & Learning Series – Pulp and Paper.
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