1.Which anion is normally present in deionized water and can be precipitated by

Question

1.Which anion is normally present in deionized water and can be precipitated by silver ions? (Note: Air is always dissolved in deionized water exposed to the atmosphere. Air is made up of 78% nitrogen, 21% oxygen and 1% other substances, including carbon dioxide).

Select one:

a. chloride ion;

b. carbonate ion;

c. nitrate ion;

d. hydroxide ion;

e. All options are incorrect

2.How can we quantitatively determine the chloride content in an unknown soluble salt by gravimetric analysis?

Select one:

a. dissolve the unknown salt in water, titrate the solution with silver nitrate and calculate the chloride content in the original salt based on the titration curve;

b. dissolve the unknown salt in water, measure the absorbance of the solution and calculate the chloride content in the original salt based on the Beer-Lambert law;

c. dissolve the unknown salt in water, precipitate the chloride ion as silver chloride, collect silver chloride and calculate the chloride content in the original salt by using stoichiometry;

d. all options are incorrect;

e. add dilute nitric acid in the solution;

3.If the color of the AgCl precipitate changes from white to violet, it means ____ .

Select one:

a. the AgCl precipitate was oxidized by oxygen in the air;

b. the AgCl precipitate absorbed moisture from air;

c. the AgCl precipitate was decomposed to silver in the presence of light;

d. all options are incorrect;

Explanation / Answer

1. d. hydrooxide ion. H2O + OH- = H2O + OH-  so hydroxide ion is free in deionise water.

2. a

3. a. the AgCl precipitate was Oxidize by oxygen in the air.

AgCl + O2 = Ag2O

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