Question

We did a lab with Copper Chloride (II) where we dehydrated a sample for 30 minutes, weighed it, heated it up for another 10 minutes, and then put it over boiling water and rehydrated the sample, Here's out numbers:

First weigh (before dehydration):.589 g
Second weigh (30 min in the oven): 17.501 g
third (after an extra 10 min in the oven): 17.499
and after re-hyradtion: 1.256 g

I need help finding the ratio of water to copper chloride in the sample.

Answer 1

and it's the mole ratio I need help with

Answer 2

Is the after rehydration weight 1.256kg

Answer 3

yeah that was are final number

Answer 4

My partner got back to me saying it was a 243.9 : 1 ratio, but no idea how he would get that number

Answer 5

k ...u wrote 1.256g in your question :P

Answer 6

you can safely assume that the weight of given amount of CuCl2 (completely dehydrated) is around 17.500g

Answer 7

yes

Answer 8

you can see this because after putting the sample in the oven for additional time - its weight does not reduce right??

Answer 9

Increase in weight after rehydration is -> (1256 - 17.5)g
So this is the weight of the water that combines with the CuCl2

Answer 10

it reduced very slightly...taking the excess water that was left out

Answer 11

yeah it reduced very slightly because all the water was (almost) already taken out :P

Answer 12

1238.5 g water (H20) for 17.5 g of CuCl2

Answer 13

Can you find how many moles of water will be there in 1238.5g of H20?

Answer 14

1 mole of water = 18g

Answer 15

68.8 mol?

Answer 16

what do I do with this number?

Answer 17

right!!.......sry I was away

Answer 18

now find the number of CuCl2 moles in 17.5g of CuCl2

Answer 19

what is the number of CuCl2? Look up the atomic mass?

Answer 20

yeah u can do that
atomic mass of Cu + 2* atomic mass of Cl

Answer 21

so 63.546 + 2 =127.092* 35.45 = 4,505.4114? right?

Answer 22

Nope

Answer 23

it seemed wronged

Answer 24

M(Cu) = 63.546
M(Cl) = 35.45
M(CuCl2) = M(Cu) + 2M(Cl)

Answer 25

so 63.546 + 70.9 =134.446?

Answer 26

right!!

Answer 27

go on find the number of moles in 17.5g of CuCl2

Answer 28

is it 7.682 /18? so .426? and thanks for all the help, by the way.

Answer 29

Nope
1 mole of CuCl2 is equal to the atomic mass of CuCl2 you calculate -> 134.446g
So use simple unitary method to find how many moles will be there in 17.5g of CuCl2

Answer 30

134.46g of CuCl2 === 1mole
-> 1g of CuCl2 === (1/134.46)mole
so 17.5 g of CuCl2 === ??? moles

Answer 31

2,353.5 g?

Answer 32

134.46 * 17.5

Answer 33

nope

Answer 34

it is 17.5 *(1/134.46)

Answer 35

.00743

Answer 36

where do I go from here?

Answer 37

you still have your calculations wrong there!

Answer 38

anyway if you find the number of moles of water in the sample and then the number of moles of CuCl2 -> you can divide them both to get the mole ratio

Answer 39

hmm I keep getting that .000743 or .130

Answer 40

0.130 is right!!

Answer 41

Oh great! so divide .130 and 134.46?

Answer 42

I just observed that you have to find the mole ration of water and CuCl2 in the original sample..............SO wt of the sample b4 dehydration was - 589g
and after dehydration was 17,5
In dehydration all water was lost = 589g -17.5g =571.5g
so number of moles of water in ORIGINAL SAMPLE = 571.5/18 = 31.75

Answer 43

so divide 31.75 and 0.13

Answer 44

you have your answer there

Answer 45

244.2:1

Answer 46

Thanks for all the help!

Answer 47

right!!

Answer 48

you are welcome..........i hope u understood the concept

Answer 49

Yeah, itsdefinitely made more sense as I worked through it