March 28, 2024, 08:46:24 AM
Forum Rules: Read This Before Posting


Topic: Finding Weight Percent in a Compound (check)  (Read 9027 times)

0 Members and 1 Guest are viewing this topic.

Offline Hemidol

  • Regular Member
  • ***
  • Posts: 68
  • Mole Snacks: +2/-2
  • Rune of Punishment
Finding Weight Percent in a Compound (check)
« on: October 08, 2009, 12:19:22 AM »
A mixture of Zn3(PO4)2 and its hydrate Zn3(PO4)2•4H2O has a mass of 1.9497 g. After heating to drive
off all the water, the mass is only 1.8311 g. What is the weight percentage of Zn3(PO4)2•4H2O in the original
mixture? Report your answer to 4 significant figures.
Molar masses: Zn3(PO4)2 386.11 g/mol; Zn3(PO4)2•4H2O 458.17 g/mol.


Here is my work...

1.9497g - 1.8311g = 0.1186g


(386.11/72.06) x 0.1186 g = 0.635479406


Then:

0.1186g + 0.635479406g = 0.7541g

0.7541g * 100% = 75.41 %

Is this the correct technique?

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27637
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Finding Weight Percent in a Compound (check)
« Reply #1 on: October 08, 2009, 03:41:24 AM »
You have correctly found mass of hydrate, but 75% is not the correct result.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline Hemidol

  • Regular Member
  • ***
  • Posts: 68
  • Mole Snacks: +2/-2
  • Rune of Punishment
Re: Finding Weight Percent in a Compound (check)
« Reply #2 on: October 08, 2009, 10:27:25 AM »
You have correctly found mass of hydrate, but 75% is not the correct result.
Where did I go wrong? What will the correct perrcent be?


Thanks for finding this correction.

Offline AWK

  • Retired Staff
  • Sr. Member
  • *
  • Posts: 7981
  • Mole Snacks: +555/-93
  • Gender: Male
Re: Finding Weight Percent in a Compound (check)
« Reply #3 on: October 08, 2009, 10:37:35 AM »
Quote
0.7541g * 100% = 75.41 %
this step is wrong
AWK

Offline Hemidol

  • Regular Member
  • ***
  • Posts: 68
  • Mole Snacks: +2/-2
  • Rune of Punishment
Re: Finding Weight Percent in a Compound (check)
« Reply #4 on: October 08, 2009, 10:51:19 AM »
Quote
0.7541g * 100% = 75.41 %
this step is wrong
Ah, so:

0.635479406 / 0.7541g * 100 = 84.27

Better? :)

Offline DrCMS

  • Chemist
  • Sr. Member
  • *
  • Posts: 1296
  • Mole Snacks: +210/-81
  • Gender: Male
Re: Finding Weight Percent in a Compound (check)
« Reply #5 on: October 08, 2009, 11:45:44 AM »
Quote
0.7541g * 100% = 75.41 %
this step is wrong
Ah, so:

0.635479406 / 0.7541g * 100 = 84.27

Better? :)

No worse.

You have correctly calculated the weight of hydrate in the sample as 0.7541g.

What was the weight of the sample?

So what is the % of hydrate in the sample?

Offline Hemidol

  • Regular Member
  • ***
  • Posts: 68
  • Mole Snacks: +2/-2
  • Rune of Punishment
Re: Finding Weight Percent in a Compound (check)
« Reply #6 on: October 08, 2009, 12:14:59 PM »
Weight of sample = 1.9497 g

% of hydrate = 0.7541g * 1.9497 ?

Sorry this question really is boggling me.  ???

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27637
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Finding Weight Percent in a Compound (check)
« Reply #7 on: October 08, 2009, 12:40:40 PM »
Edit: oops.  :-[
« Last Edit: October 08, 2009, 01:59:10 PM by Borek »
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline DrCMS

  • Chemist
  • Sr. Member
  • *
  • Posts: 1296
  • Mole Snacks: +210/-81
  • Gender: Male
Re: Finding Weight Percent in a Compound (check)
« Reply #8 on: October 08, 2009, 01:39:45 PM »
Weight of sample = 1.9497 g

% of hydrate = 0.7541g * 1.9497 ?

No the % of hydrate = 0.7541 / 1.9497

Your maths teacher should be shot.

Offline Hemidol

  • Regular Member
  • ***
  • Posts: 68
  • Mole Snacks: +2/-2
  • Rune of Punishment
Re: Finding Weight Percent in a Compound (check)
« Reply #9 on: October 08, 2009, 02:25:16 PM »
Weight of sample = 1.9497 g

% of hydrate = 0.7541g * 1.9497 ?

No the % of hydrate = 0.7541 / 1.9497

Your maths teacher should be shot.
This gives a percent of 0.3867... that doesn't seem correct. That tiny?

I'm assuming I'll then times this value by 100% :P?
« Last Edit: October 08, 2009, 02:41:10 PM by Hemidol »

Offline DrCMS

  • Chemist
  • Sr. Member
  • *
  • Posts: 1296
  • Mole Snacks: +210/-81
  • Gender: Male
Re: Finding Weight Percent in a Compound (check)
« Reply #10 on: October 08, 2009, 04:14:36 PM »
Weight of sample = 1.9497 g

% of hydrate = 0.7541g * 1.9497 ?

No the % of hydrate = 0.7541 / 1.9497

Your maths teacher should be shot.
This gives a percent of 0.3867... that doesn't seem correct. That tiny?

I'm assuming I'll then times this value by 100% :P?

Yes the correct answer is 38.67% and I was wrong actually your maths teacher should commit suicide in shame.

Sponsored Links