September 23, 2019, 03:55:23 AM
Forum Rules: Read This Before Posting


Topic: Olympiad question #2 (Salts)  (Read 9001 times)

0 Members and 1 Guest are viewing this topic.

Offline Evaldas

  • Full Member
  • ****
  • Posts: 127
  • Mole Snacks: +1/-3
  • Gender: Male
Olympiad question #2 (Salts)
« on: December 30, 2010, 01:30:52 PM »
10 g iron plate was submerged into 200 g 8% copper(II) sulfate solution. After some time the plate was taken out and it got heavier by 0,8 g. Find out:
a) did all the copper(II) sulfate react?
Reaction:
CuSO4(aq) + Fe(s)  :rarrow: FeSO4(aq) + Cu(s)
m(CuSO4) = 16 g.
What's next?
n(Fe)=0.17857 mol; n(CuSO4)=0.1 mol?
All the copper sulfate reacted because there was excess of iron?

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 25198
  • Mole Snacks: +1656/-397
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Olympiad question #2 (Salts)
« Reply #1 on: December 30, 2010, 02:58:31 PM »
How does mass of the plate change when 1 mol of iron reacts?
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline Evaldas

  • Full Member
  • ****
  • Posts: 127
  • Mole Snacks: +1/-3
  • Gender: Male
Re: Olympiad question #2 (Salts)
« Reply #2 on: December 30, 2010, 03:08:19 PM »
How does mass of the plate change when 1 mol of iron reacts?
Gets replaced with 1 mol of copper?

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 25198
  • Mole Snacks: +1656/-397
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Olympiad question #2 (Salts)
« Reply #3 on: December 30, 2010, 07:00:21 PM »
Mass of the plate gets replaced with 1 mole of copper?

Think again. This time start by reading the question I asked.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline Evaldas

  • Full Member
  • ****
  • Posts: 127
  • Mole Snacks: +1/-3
  • Gender: Male
Re: Olympiad question #2 (Salts)
« Reply #4 on: December 31, 2010, 04:26:17 AM »
Gets heavier because copper is heavier than iron?

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 25198
  • Mole Snacks: +1656/-397
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Olympiad question #2 (Salts)
« Reply #5 on: December 31, 2010, 06:08:40 AM »
By how much?
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline Evaldas

  • Full Member
  • ****
  • Posts: 127
  • Mole Snacks: +1/-3
  • Gender: Male
Re: Olympiad question #2 (Salts)
« Reply #6 on: December 31, 2010, 06:25:40 AM »
If we're speaking about 1 mol of each then the difference between M(Fe) and M(Cu), 64g/mol-56g/mol=8g/mol.
Right?

Offline Schrödinger

  • Chemist
  • Sr. Member
  • *
  • Posts: 1161
  • Mole Snacks: +138/-98
  • Gender: Male
Re: Olympiad question #2 (Salts)
« Reply #7 on: December 31, 2010, 06:46:14 AM »
Yes. Correct :)
"Destiny is not a matter of chance; but a matter of choice. It is not a thing to be waited for; it is a thing to be achieved."
- William Jennings Bryan

Offline Evaldas

  • Full Member
  • ****
  • Posts: 127
  • Mole Snacks: +1/-3
  • Gender: Male
Re: Olympiad question #2 (Salts)
« Reply #8 on: December 31, 2010, 07:36:53 AM »
This is what solution they suggest (saying that it is one of the many possible):
               CuSO4 + Fe  :rarrow: FeSO4 + Cu
Reacted:    x mol    x mol
Formed:                          x mol   x mol
Reacted iron mass: 56x, formed copper mass 64x
:delta: m = -56x + 64x = +0,80
from here x = 0,1 mol. That means 0,1 mol of CuSO4 reacted (which is 16 g) and 0,1 mol of FeSO4 formed (which is 15,2 g)
There were 16 g of CuSO4 in the solution so it means all the CuSO4 reacted.

What do you think about this solution?
Do you think this exercise is too easy/difficult for students who are in the last two years of high school chemistry?

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 25198
  • Mole Snacks: +1656/-397
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Olympiad question #2 (Salts)
« Reply #9 on: December 31, 2010, 11:41:23 AM »
You have checked that 8g mass difference means 1 mole reacted, next step is to answer the question - if 8g change in mass means 1 mole reacted, how many moles reacted if mass changed by 0.8g?

That's the same approach they used, they too combined mass difference with number of moles.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline Evaldas

  • Full Member
  • ****
  • Posts: 127
  • Mole Snacks: +1/-3
  • Gender: Male
Re: Olympiad question #2 (Salts)
« Reply #10 on: December 31, 2010, 12:12:09 PM »
You have checked that 8g mass difference means 1 mole reacted, next step is to answer the question - if 8g change in mass means 1 mole reacted, how many moles reacted if mass changed by 0.8g?

That's the same approach they used, they too combined mass difference with number of moles.
0,1 mol

Sponsored Links