Yatayyat
Badges: 14
Rep:
?
#1
Report Thread starter 1 year ago
#1
Name:  Screenshot 2018-12-26 at 17.46.37.png
Views: 173
Size:  245.4 KBI've tried combing the two equations together giving:

2Cu2 + 4I- + 2S2O3 2- ----> 2CuI + 2I- + S4O6 2- (where the I2 on both sides of the equation cancel out)

I've also found moles of the sodium thiosulfate from using mol = conc * vol so (24.5/1000) * (0.100) = 0.00245 moles

Not entirely sure what to do next now?
0
reply
BobbJo
Badges: 12
Rep:
?
#2
Report 1 year ago
#2
Use the mole ratio to find the number of moles and hence mass of copper

Find %
0
reply
Yatayyat
Badges: 14
Rep:
?
#3
Report Thread starter 1 year ago
#3
(Original post by BobbJo)
Use the mole ratio to find the number of moles and hence mass of copper

Find %
So from the combined equation I got, I know the molar ratio to be 1:1 between sodium thiosulfate and copper iodide.

And 1 mole of CuI has 1 mole of copper

So mass of copper is '0.00245 * 63.5 = 0.155575 g'

Hence to find percentage purity for copper, it's just 0.305/0.155575 * 100 = 51%

Does this seem okay?
0
reply
BobbJo
Badges: 12
Rep:
?
#4
Report 1 year ago
#4
(Original post by Yatayyat)
So from the combined equation I got, I know the molar ratio to be 1:1 between sodium thiosulfate and copper iodide.

And 1 mole of CuI has 1 mole of copper

So mass of copper is '0.00245 * 63.5 = 0.155575 g'

Hence to find percentage purity for copper, it's just 0.305/0.155575 * 100 = 51%

Does this seem okay?
Yes but wrong logic. (correct answer though)

We have Cu2+

It reacts with the iodide from potassium iodide to give CuI and I2

From the first equation, 2 moles of Cu2+ give 1 mole of I2

then the I2 liberated is titrated with thio.

2 mole of thio reacts with 1 moles of I2

Then overall it's 2 moles of Cu2+ reacting with 2 moles of thio and that is the 1:1 ratio

It is not the moles of CuI that should be considered, but moles of Cu2+. (which are equal so the answer is the same)
0
reply
Yatayyat
Badges: 14
Rep:
?
#5
Report Thread starter 1 year ago
#5
(Original post by BobbJo)
Yes but wrong logic. (correct answer though)

We have Cu2+

It reacts with the iodide from potassium iodide to give CuI and I2

From the first equation, 2 moles of Cu2+ give 1 mole of I2

then the I2 liberated is titrated with thio.

2 mole of thio reacts with 1 moles of I2

Then overall it's 2 moles of Cu2+ reacting with 2 moles of thio and that is the 1:1 ratio

It is not the moles of CuI that should be considered, but moles of Cu2+. (which are equal so the answer is the same)
I'm sort of getting it, but where are you getting the 2 moles of I2 from?
0
reply
BobbJo
Badges: 12
Rep:
?
#6
Report 1 year ago
#6
(Original post by Yatayyat)
I'm sort of getting it, but where are you getting the 2 moles of I2 from?
You must have misread it.

Try reading it again

I did not write 2 moles of I2
0
reply
Yatayyat
Badges: 14
Rep:
?
#7
Report Thread starter 1 year ago
#7
(Original post by BobbJo)
You must have misread it.

Try reading it again

I did not write 2 moles of I2
Sorry, yeah I did accidentally misread it, I understand it now. Thank you for clearing up my misconception.
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Current uni students - are you thinking of dropping out of university?

Yes, I'm seriously considering dropping out (84)
14.43%
I'm not sure (26)
4.47%
No, I'm going to stick it out for now (182)
31.27%
I have already dropped out (12)
2.06%
I'm not a current university student (278)
47.77%

Watched Threads

View All