exp 3 hydrates

Question 1

what does efflorescent mean?

Answer 1

gives off h2o to the atmosphere, Ph20atm < ph20

Question 2

what does hygroscopic mean?

Answer 2

absorbs h20, ph20 atm > ph20 crystal

Question 3

what changes may a compound go through as it loses water?

Answer 3

color change
form of crystal change, usually results in dry powdery solid
may dissolve in water which will evaporate and leave an anhydrate
may decompose causing a color change or emitting colored vapors, this is undesirable

Question 4

flame test results

Answer 4

violet means K

green means Cu

Question 5

basic steps

Answer 5

1. determine h2o present
2. qualitative heating
3. find initial mass of hydrate
4. qualitative heating of hydrate
5. determine anions

Question 6

how do we know if C03 is in it?

Answer 6

1. add HNO3. colorless gas will be evolved
2. add BaSO4, no reaction
3. add AgNO3, should have colorless gas and white ppt

Question 7

how do we know if the S04 anion is in it?

Answer 7

1. add HNO3, no reaction
2. add Ba(NO3)2, white ppt
3. add AgNO3, white ppt

Question 8

how do we know is Cl- anion is in it?

Answer 8

1. add HNO3, no reaction
2. add Ba(NO3)2, no reaction
3. add AgNO3, white curdy ppt

Question 9

how do we know if Br- is present?

Answer 9

1. HNO3 no reaction
2. Ba(NO3)2 no reaction
3. add AgNO3, cream colored ppt

Question 10

formula for CO3 formation

Answer 10

H+ + CO3 2- = CO2 + H2O

Question 11

formula for SO4 formation

Answer 11

SO4 2- + Ba 2+ = BaSO4 (s)

Question 12

formula for Cl- formation

Answer 12

Cl- + Ag + = AgCl (s)

Question 13

formula for Br- formation

Answer 13

Br- + Ag + = AgBr (s)

Question 14

how do we find mass of anhydrate?

Answer 14

mass of hydrate sample - mass h20 lost

Question 15

how do we find mass H2O lost?

Answer 15

mass of sample + test tube - mass of test tube of sample after first heating

Question 16

how do we find mass % of h20

Answer 16

mass h20 / mass hydrate x 100%

Question 17

how do we find n for the empirical formula?

Answer 17

moles h2o / moles hydrate

ex na2co3 x WHOLE NUMBER Nh20

Question 18

evidence of water?

Answer 18

condensation

Question 19

how do we know if dehydration is reversible?

Answer 19

had liquid and ppt at bottom

Question 20

evidence of carbon

Answer 20

black or brown residue

Question 21

CdCl closed vs open

Answer 21

lumpy clumps

fine powder

Question 22

CaCl2 closed vs open

Answer 22

large spheres

clear liquid

Question 23

how would empirical formula differ if it was not heated to a constant mass?

Answer 23

would still contain water, mass of h2o lost would be lower making mols lower, and n lower.

Question 24

how would empirical formula differ if overheated to decomp?

Answer 24

less mass of sample resulting in less mols of anhydrate. mol h2o is higher, n is too high

Question 25

heating copper sulfate vs heating sugar

Answer 25

CuSO4 is reversible bc water is removed from crystal lattice. add h2o to reverse
sugar: water is irreversibly lost due to decomp.

Question 26

which hydrate is hygroscopic?

Answer 26

CdCl2