March 29, 2024, 04:38:06 AM
Forum Rules: Read This Before Posting


Topic: Help with decomposition of sodium chlorate (ideal gas law)  (Read 9162 times)

0 Members and 1 Guest are viewing this topic.

Offline Jennifer Anderson

  • New Member
  • **
  • Posts: 7
  • Mole Snacks: +0/-0
Hi everyone.  :)I'm really having trouble with this section and was hoping someone could show me how to solve one of these problems.  :)

The O2 gas produced in the decomposition of sodium chlorate was collected into a 475-mL container over water at a temperature of 16 degrees celcius. At this temperature, the vapor pressure of water is 14mm Hg. If the total pressure in the container was 730 mm Hg, calculate the mass of NaCl that the reaction produced.

thank you  :)

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27633
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Help with decomposition of sodium chlorate (ideal gas law)
« Reply #1 on: May 08, 2010, 04:19:07 AM »
Anyone?

Please read forum rules.

You have to show your attempts at solving the question to receive help. This is a forum policy.

Start with the reaction equation. What was partial pressure of oxygen? Moles of oxygen?
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline Jennifer Anderson

  • New Member
  • **
  • Posts: 7
  • Mole Snacks: +0/-0
Re: Help with decomposition of sodium chlorate (ideal gas law)
« Reply #2 on: May 08, 2010, 04:06:44 PM »
Hi, sorry about that.

heres the balanced reaction equation that i got

NaClO3 -->  NaCl + 3/2 O2                   

and as far as i know the partial pressure of O2 is 160

can you show me how to set up the rest of the problem?

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27633
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Help with decomposition of sodium chlorate (ideal gas law)
« Reply #3 on: May 08, 2010, 05:04:11 PM »
Partial pressure of oxygen in the container is not 160 mm Hg.

What two gases are present in the container?
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline Jennifer Anderson

  • New Member
  • **
  • Posts: 7
  • Mole Snacks: +0/-0
Re: Help with decomposition of sodium chlorate (ideal gas law)
« Reply #4 on: May 08, 2010, 09:53:39 PM »
oh sorry! so we have O2 and H20 (water vapor) in the container

i know that the total pressure is the sum of the partial pressures but i don't know how to find them.

isn't the partial pressure of H20 given as 14mm hG? how do i find the P of o2?


once i get the values figured out don't i just plug them into PV = nRT and solve for n?

thanks for being patient i'm really bad at this

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27633
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Help with decomposition of sodium chlorate (ideal gas law)
« Reply #5 on: May 09, 2010, 03:45:16 AM »
i know that the total pressure is the sum of the partial pressures but i don't know how to find them.

isn't the partial pressure of H20 given as 14mm hG? how do i find the P of o2?

You have properly listed almost all information needed to calculate partial pressure of oxygen. What is the total pressure in the container?

Quote
once i get the values figured out don't i just plug them into PV = nRT and solve for n?

Yes.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline Jennifer Anderson

  • New Member
  • **
  • Posts: 7
  • Mole Snacks: +0/-0
Re: Help with decomposition of sodium chlorate (ideal gas law)
« Reply #6 on: May 09, 2010, 01:26:11 PM »
730 mm Hg - 14 mm Hg = 716 mm Hg (partial pressure of O2)

arranging the formula i got n = PV/RT

so

(716 mm Hg)(0.475 L)
--------------------- =   1197185.14
    (0.0821)(289 K)


that doesn't seem right what am i doing wrong?

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27633
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Help with decomposition of sodium chlorate (ideal gas law)
« Reply #7 on: May 09, 2010, 05:26:23 PM »
Check your units and units of the ideal gas constant you used.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline Jennifer Anderson

  • New Member
  • **
  • Posts: 7
  • Mole Snacks: +0/-0
Re: Help with decomposition of sodium chlorate (ideal gas law)
« Reply #8 on: May 09, 2010, 07:03:41 PM »
hmm...i'm not entirely sure what you mean... like this?


(716 mm Hg)(0.475 L)
--------------------- =          .09  g NaCl
(62.4 mm Hg per mol)(289 K)

Offline Jennifer Anderson

  • New Member
  • **
  • Posts: 7
  • Mole Snacks: +0/-0
Re: Help with decomposition of sodium chlorate (ideal gas law)
« Reply #9 on: May 09, 2010, 07:32:16 PM »
no wait wouldn't that be mol NaCl which i then convert to grams?

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27633
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Help with decomposition of sodium chlorate (ideal gas law)
« Reply #10 on: May 10, 2010, 02:58:51 AM »
Take a look at the table on the right:

http://en.wikipedia.org/wiki/Ideal_gas_constant

You were doing OK, but the value you have used for R was the one fit for pressure in atm, while you have pressure in mmHg, hence your result was off.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline Jennifer Anderson

  • New Member
  • **
  • Posts: 7
  • Mole Snacks: +0/-0
Re: Help with decomposition of sodium chlorate (ideal gas law)
« Reply #11 on: May 10, 2010, 01:03:31 PM »
62.4 is the value for mmHg, did you see the updated version i did?

(716 mm Hg)(0.475 L)
--------------------- =          .09  mol/L  NaCl
(62.4 mm Hg per mol . K)(289 K)


i know i would need that in three significant figures, i just wanted you to check an see if that is the correct formula before i go ahead.
i'm worried because the question wants the mass of NaCl produced and it looks like i am left with the molarity

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27633
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Help with decomposition of sodium chlorate (ideal gas law)
« Reply #12 on: May 10, 2010, 04:10:42 PM »
(716 mm Hg)(0.475 L)
--------------------- =          .09  mol/L  NaCl
(62.4 mm Hg per mol . K)(289 K)

Units, units, units. 62.4 - value is OK, but units are not, you ate L. Even then using units you have listed it should be mol*L, not mol/L.

Besides, you are not calculating number of moles of NaCl, but number of moles of gas (do you still remember which one?)
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Sponsored Links