March 28, 2024, 07:14:06 PM
Forum Rules: Read This Before Posting


Topic: Calculating mass of element in compound?  (Read 3173 times)

0 Members and 1 Guest are viewing this topic.

Offline otter

  • New Member
  • **
  • Posts: 4
  • Mole Snacks: +0/-0
Calculating mass of element in compound?
« on: December 07, 2014, 04:30:13 PM »
I have the following question on homework:

Calculate the mass of P in a sample of CaHPO4 (Dicalcium phosphate).

This seems like a trick question. Would the Phosphorus mass be just as it is in the Periodic table? That is, the answer would be: 30.9g?

I could see if it would be a mass % of the compound, but the question isn't asking for that. So what is there to calculate? What am I missing?

thanks,

Otter

Offline sjb

  • Global Moderator
  • Sr. Member
  • ***
  • Posts: 3652
  • Mole Snacks: +222/-42
  • Gender: Male
Re: Calculating mass of element in compound?
« Reply #1 on: December 07, 2014, 05:23:31 PM »
I have the following question on homework:

Calculate the mass of P in a sample of CaHPO4 (Dicalcium phosphate).

This seems like a trick question. Would the Phosphorus mass be just as it is in the Periodic table? That is, the answer would be: 30.9g?

I could see if it would be a mass % of the compound, but the question isn't asking for that. So what is there to calculate? What am I missing?

thanks,

Otter

What are the units of the mass in the periodic table?

Offline otter

  • New Member
  • **
  • Posts: 4
  • Mole Snacks: +0/-0
Re: Calculating mass of element in compound?
« Reply #2 on: December 07, 2014, 06:02:08 PM »

What are the units of the mass in the periodic table?

As I mentioned above, 30.973

Offline otter

  • New Member
  • **
  • Posts: 4
  • Mole Snacks: +0/-0
Re: Calculating mass of element in compound?
« Reply #3 on: December 07, 2014, 06:15:11 PM »
UPDATE!!! - I'm sorry, I missed a previous part to this question and took it out of context of the greater problem.

See answer below

again, my apologies.

otter
« Last Edit: December 07, 2014, 07:09:42 PM by otter »

Offline billnotgatez

  • Global Moderator
  • Sr. Member
  • ***
  • Posts: 4399
  • Mole Snacks: +223/-62
  • Gender: Male
Re: Calculating mass of element in compound?
« Reply #4 on: December 07, 2014, 06:20:57 PM »
@otter
Want to share your insight or answer to the question and how you got it?

Offline otter

  • New Member
  • **
  • Posts: 4
  • Mole Snacks: +0/-0
Re: Calculating mass of element in compound?
« Reply #5 on: December 07, 2014, 06:59:12 PM »
Sorry, yes, it is probably best I clarify.

My intial question was PART B, of a series of questions that started with this assumption:

You have 0.479 g CHPO4

So therefore, the P mass I am looking for in...

Calculate the mass of P in a sample of CaHPO4 (Dicalcium phosphate).

...is based on having an initial amount of 0.479 g of CHPO4.

Answer to initial question. 0.109g of P.

work: 0.479g CHPO4 x 30.97 g P (atomic mass of P) / 136.06 (mass of CHPO4 ) = 0.109g of P


Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27633
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Calculating mass of element in compound?
« Reply #6 on: December 08, 2014, 03:22:19 AM »

What are the units of the mass in the periodic table?

As I mentioned above, 30.973

Not that it still matters if you have solved the question, but 30.973 is a value, not units.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Sponsored Links