Question

Question 1: Titrations

Answer 1

Copper metal is easily oxidized to Cu2+ by nitric acid according to the following equation: 3Cu(s) + 8HNO3(aq) → 3Cu(NO3)2(aq) + 2NO(g) + 4H2O(l)
A copper penny with a mass of 3.067 g is dissolved in 100.0 mL of 1.000 M nitric acid.
a. How many moles of copper are in the penny assuming it is pure copper? (5 points)
b. When the reaction stops, the undissolved penny is removed. What is the mass of the undissolved penny? (6 points)
c. The solution prepared in step B is transferred quantitatively to a 250.00 mL volumetric and diluted to the line. What is the molarity of the Cu2+ ion in this solution? (4 points)

Answer 2

First calculate amount of substance of nitric acid

Answer 3

I think you manageri a) easily :)

Answer 4

so what would the answers for a b and c? i want to see if they line up with my answers

Answer 5

just let me know what you get and i'll see if they match up with mine :)

Answer 6

@Hoslos can U continue?

Answer 7

You can also first find the moles of copper using the formula n=m/Mr, where n is moles, m is mass and Mr is given mass. So n= 3.067/64= 0.047 moles.

Answer 8

Yes, I can.

Answer 9

B) I wonder is there enough acid to dissolve all copper or
Is acid limiting reactant?

Answer 10

Thank you @Hoslos

Answer 11

I see that there is not enough acid from equation and number @Hoslos got.

Have to go now, bye for the next time and sorry

Answer 12

Ok, for that, you have to back to the question and check the molar ration of Cu as to HNO3. It is 3:8, but for this exercise you have 0.047, which is as to x. Making x subject of the formula is x= 0.047*8/3= 0.125mol of HNO3. This is the molarity of the acid expected. But according to the question, there is undissolved penny, meaning the acid must be limiting, so basing from its given volume and concentration, let us find the moles contained. For liquids, moles=CV/1000, where C id concentration, V volume in cm^3. Hence n= 1*100/1000= 0.1mol. So this is the moarity of acid available.
To know the reacted penny's amount, we need to find the molar basing from this available moles of the limiting acid, being 3:8 again and x:0.1 then x=0.1*3/8=0.037 mol of penny reacted fully.
Thereore the unreacted moles are 0.047-0.037= 0.010mol.

Answer 13

No problem @Gebooors .

Answer 14

ok great. and for b) and c) ?

Answer 15

What I explained now, Vera was b).

Answer 16

Are you ok up to this point?

Answer 17

And what about a) and c) ?

Answer 18

I answered a), when Geboors first mentioned my name in this chat, can you see?

Answer 19

oh yes i see. thanks. now just c)

Answer 20

Ok. Let me carry on then.

Answer 21

ok

Answer 22

Well, I am not familir with those words, but from what I understood, when something is transfered quantitatively, it means that have made the ratio of moles as to the ration of volume. For instance, previously, the volume of acid was 100mL and then changed to 250mL, meaning it multiplied by 2.5, hence the moles of penny should also multiply in this ration, being 0.037 * 2.5 = 0.009 moles.

Answer 23

so is that the answer for c) ?

Answer 24

Yes.

Answer 25

thanks so much! :)

Answer 26

Again, it is My pleasure.

Answer 27

@Hoslos, good work!

Answer 28

Thanks @Gebooors .