Decaying Papers
Librarians are worried about their books. Many of the old book in their collections are crumbing. The situation is so bad, in fact, that about one-third of the books in the U.S. Library of Congress cannot be circulated because the pages are too brittle. Why are the books deteriorating?
Until the latter part of the eighteenth century. Practically all paper produced in the western hemisphere was made from rags of linen or cotton, which is mostly cellulose. Cellulose is a polymer comprised of glucose (C6 H12 O6) units joined together in a specific fashion
As the demand for paper grew, wood pulp was substituted for rags as a source of cellulose. Wood pulp also contains lignin , an organic polymer that imparts rigidity to the paper , but lignin oxidizes easily, causing the paper to discolor. Paper made from wood pulp that has not been treated to remove the lignin is used for books and newspapers for which a long life is not an important consideration.
Another problem with paper made from wood pulp is that it is porous. Tiny holes in the surface of the paper soak up ink from a printing press, spreading it over a larger area than is intended. To prevent ink creep, a coating of aluminum sulfate [Al2(SO4)3] and rosin is applied to some paper to seal the holes. This process, called sizing , results in a smooth surface. You can reality tell the difference between papers with and without sizing by feeling the surface of a newspaper and this page. (Or try to write an them with a felt-tip pen.) Aluminum sulfate was chosen for the treatment because it is colorless and cheap. Because paper without sizing does not crumble, aluminum sulfate must be responsible for the slow decay. But how?
Chemical Clues
1.when books containing “sized” paper are stored in a high-humidity environment,Al2(SO4)3 absorbs moisture , which eventually leads to the prixluetion of H+ ions. The H+ ions catalyze the hydrolysis of cellulose by attaching to the shaded O atoms in cellulose. The long chain unit of glucose units breaks apart , resulting in the crumbling of the paper. Write equations for the production of H+ ions from Al2(SO4)3
2.To prevent papers from decaying, the obvious solution is to treat them with a base. However , both NaOH (a strong base) and NH, (a weak base) are unsatisfactory choices. Suggest how you could use these substances to neutralize the acid in the paper and describe their drawbacks.
3. after much testing .chemists developed a compound that stabilizes paper diethyzinc [Zn(C2 H5)2]. Diethylzinc is volatile so it can be sprayed onto books. It reacts with water to form zinc oxide (ZnO) gaseous ethane (C2 H6),(a) Write an equation for this reaction (b) ZnO is an amphoteric oxide . What is its reaction with H+ ions?
4. One disadvantage of diethylzinc is that it is extremely flammable in air. Therefore oxygen must not be present when this compound is applied. How would you remove oxygen from a room before spraying diethylzinc onto stacks of books in a library?
5. Nowadays papers are sized with titanium dioxide (TiO2), which like ZnO, is a nontoxic white compound that prevent the hydrolysis of cellulose. What advantage does TiO2 have over ZnO?
ช่วยสรุปบทความเป็นภาษาอังกฤษให้หนูหน่อยคะ(หนูจะส่งแล้วคะ)
Librarians are worried about their books. Many of the old book in their collections are crumbing. The situation is so bad, in fact, that about one-third of the books in the U.S. Library of Congress cannot be circulated because the pages are too brittle. Why are the books deteriorating?
Until the latter part of the eighteenth century. Practically all paper produced in the western hemisphere was made from rags of linen or cotton, which is mostly cellulose. Cellulose is a polymer comprised of glucose (C6 H12 O6) units joined together in a specific fashion
As the demand for paper grew, wood pulp was substituted for rags as a source of cellulose. Wood pulp also contains lignin , an organic polymer that imparts rigidity to the paper , but lignin oxidizes easily, causing the paper to discolor. Paper made from wood pulp that has not been treated to remove the lignin is used for books and newspapers for which a long life is not an important consideration.
Another problem with paper made from wood pulp is that it is porous. Tiny holes in the surface of the paper soak up ink from a printing press, spreading it over a larger area than is intended. To prevent ink creep, a coating of aluminum sulfate [Al2(SO4)3] and rosin is applied to some paper to seal the holes. This process, called sizing , results in a smooth surface. You can reality tell the difference between papers with and without sizing by feeling the surface of a newspaper and this page. (Or try to write an them with a felt-tip pen.) Aluminum sulfate was chosen for the treatment because it is colorless and cheap. Because paper without sizing does not crumble, aluminum sulfate must be responsible for the slow decay. But how?
Chemical Clues
1.when books containing “sized” paper are stored in a high-humidity environment,Al2(SO4)3 absorbs moisture , which eventually leads to the prixluetion of H+ ions. The H+ ions catalyze the hydrolysis of cellulose by attaching to the shaded O atoms in cellulose. The long chain unit of glucose units breaks apart , resulting in the crumbling of the paper. Write equations for the production of H+ ions from Al2(SO4)3
2.To prevent papers from decaying, the obvious solution is to treat them with a base. However , both NaOH (a strong base) and NH, (a weak base) are unsatisfactory choices. Suggest how you could use these substances to neutralize the acid in the paper and describe their drawbacks.
3. after much testing .chemists developed a compound that stabilizes paper diethyzinc [Zn(C2 H5)2]. Diethylzinc is volatile so it can be sprayed onto books. It reacts with water to form zinc oxide (ZnO) gaseous ethane (C2 H6),(a) Write an equation for this reaction (b) ZnO is an amphoteric oxide . What is its reaction with H+ ions?
4. One disadvantage of diethylzinc is that it is extremely flammable in air. Therefore oxygen must not be present when this compound is applied. How would you remove oxygen from a room before spraying diethylzinc onto stacks of books in a library?
5. Nowadays papers are sized with titanium dioxide (TiO2), which like ZnO, is a nontoxic white compound that prevent the hydrolysis of cellulose. What advantage does TiO2 have over ZnO?