chem 116 quiz 2

Question 1

simplified formula of Alum

Answer 1

M M,III (SO4)2 * 12H2O
M - alkali metal
M,III - trivalent ion

Question 2

alums (are/are not) water soluble

Answer 2

are

Question 3

taste of alums

Answer 3

astringent, acidic, sweet

Question 4

alums react as ? with litmus (i.e., ?)

Answer 4

acids; turn blue litmus red

Question 5

alums (are/are not) considered to be hydrate compounds

Answer 5

are

Question 6

percent yield equals

Answer 6

(actual yield / theoretical yield) x 100%

Question 7

alum used today for

Answer 7

hardening photographic film, preparing pickles, creating and fixing dyes

Question 8

in the synthesis of alum, initially, the aluminum metal is ? to the aluminum ion

Answer 8

oxidized

Question 9

alum reacts very slowly with acids because

Answer 9

it has an aluminum oxide coating that forms on it

Question 10

aluminum metal will react more quickly with ? to produce the tetrahydroxoaluminate ion [Al(OH)4]-, so that is what is done in this experiment

Answer 10

bases such as KOH

Question 11

slowly adding sulfuric acid to the tetrahydroxoaluminate solution causes ? to precipitate

Answer 11

aluminum hydroxide Al(OH)3

Question 12

if excess acid is added, the solid aluminum hydroxide reacts with it and the ? ion is formed; the insoluble aluminum hydroxide will be converted to the soluble ? ion (same answer)

Answer 12

Al 3+

Question 13

aluminum potassium sulfate dodecahydrate is (not soluble/very soluble) in hot water and (insoluble/soluble) in 95% ethanol

Answer 13

very soluble; insoluble

Question 14

to precipitate the alum, the solution containing the dissolved aluminum sulfate and potassium sulfate is (cooled/heated)

Answer 14

cooled

Question 15

filtration

Answer 15

the process by which a solid is separated from a liquid solution

Question 16

gravity filtration

Answer 16

the simplest form of filtration; the solution that is to be filtered is poured through a filter paper fit into a filter funnel

Question 17

gravity filtration is most often used when

Answer 17

the solid is being discarded and the filtrate (recovered solution) kept

Question 18

two ways to fold the paper that will be placed in the filter funnel

Answer 18

simple (fold in half twice) and fluted (fold in half twice and then fold into eighths)

Question 19

vacuum filtration

Answer 19

preferentially used to collect solids due to its speed and better drying capabilities

Question 20

vacuum filtration is (slower/faster) than gravity filtration and why

Answer 20

faster; the solution is forced through the filter paper by the application of a vacuum

Question 21

vacuum filtration is not used when?

Answer 21

to filter a solid from a liquid if it is the liquid that is to be kept and the liquid has a low boiling point

Question 22

synthesis

Answer 22

the conversion of one substance to another

Question 23

theoretical yield

Answer 23

the predicted amount of product that should be made using the stoichiometry of a reaction

Question 24

what can cause the actual yield to be smaller than the theoretical?

Answer 24

incomplete reaction or mechanical losses in transfers, spills, or splashing

Question 25

in this experiment the percent yield indicated the efficiency of

Answer 25

both the synthesis and recovery process

Question 26

goal of any synthesis reaction

Answer 26

high percent yield

Question 27

safety precautions of this lab

Answer 27

• eye protection
• wipe up any spills immediately with paper towels and rinse the area with water
• if you get the material on yourself, wash the area with copious quantities of water
• wash your hands before you leave the laboratory
• dispose of the liquids you collect in the waste container in the hood labeled for this purpose

Question 28

product and filter paper to be disposed of

Answer 28

in the trash can