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### Topic: Please calculate the number of mols of oxygen gas produced per second  (Read 67801 times)

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#### Frederick95

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##### Re: Please calculate the number of mols of oxygen gas produced per second
« Reply #60 on: March 18, 2008, 05:37:04 PM »
Cp(msol) = (msol)(msubst)(100%)

Sir, algebra is not my strong point.

Is there any other method or formula I could use?

Here is what I have in mind:
The only thing I know about the rate is the oxygen production: 93.0 mL / 60 s

The reaction that gives the oxygen is:

2 H2O2 --> 2 H2O + O2

So, I need to calculate the amount of moles of oxygen produced. Then I know the amount of moles of peroxide that are reacting away... which is the answer I need.

n = 93 g / 32g per mol

= 2.90635 mol

= 2.90635 mol / 60 seconds

= 0.0484375 mol / sec of O2 are created in reaction 2

Since there is twice the amount of H2O2, multiply 0.0484375 mol / sec by 2 to get
0.096875 mol/L s of H2o2

Therefore the rate is 0.096875 mol/L s ?

#### Borek

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##### Re: Please calculate the number of mols of oxygen gas produced per second
« Reply #61 on: March 18, 2008, 05:57:13 PM »
Cp(msol) = (msol)(msubst)(100%)

No.

Cp = msubst/msol x 100%

If you multiply BOTH sides by msol you get

msol x Cp = msol x msubst/msol x 100%

Can you cancel something?

Quote
Sir, algebra is not my strong point.

Don't sir me. And I already know you struggle.

Quote
Is there any other method or formula I could use?

Any other approach needs separate approach to each question, which doesn't make sense. Once you know how to rearrange formula and solve for particular unknown you have a tool to solve each question. Well, almost each question.

Quote
The only thing I know about the rate is the oxygen production: 93.0 mL / 60 s

The reaction that gives the oxygen is:

2 H2O2 --> 2 H2O + O2

So, I need to calculate the amount of moles of oxygen produced. Then I know the amount of moles of peroxide that are reacting away... which is the answer I need.

n = 93 g / 32g per mol

= 2.90635 mol

= 2.90635 mol / 60 seconds

= 0.0484375 mol / sec of O2 are created in reaction 2

Since there is twice the amount of H2O2, multiply 0.0484375 mol / sec by 2 to get
0.096875 mol/L s of H2o2

Therefore the rate is 0.096875 mol/L s ?

Could be you are on the right track, but you have started with 93 mL of gaseous oxygen and then it miraculously became 93 g of oxygen.
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#### Frederick95

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##### Re: Please calculate the number of mols of oxygen gas produced per second
« Reply #62 on: March 18, 2008, 06:07:38 PM »
Regarding your quote

msol x Cp = msol x msubst/msol x 100%

Can you cancel something?

I can cancel msol on both sides to get Cp = msubst x 100%

Regarding your quote

Could be you are on the right track, but you have started with 93 mL of gaseous oxygen and then it miraculously became 93 g of oxygen.

#### Frederick95

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##### Re: Please calculate the number of mols of oxygen gas produced per second
« Reply #63 on: March 18, 2008, 06:08:50 PM »
hmm.. oxygen gas is not water so 1 g cannot equal 1 mL.

Could 93 mL be converted to 0.093 L? Could volume be accepted as mass?

#### Frederick95

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##### Re: Please calculate the number of mols of oxygen gas produced per second
« Reply #64 on: March 18, 2008, 06:13:45 PM »
Sorry I misread

Cp = msubst/msol x 100%

#### Borek

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##### Re: Please calculate the number of mols of oxygen gas produced per second
« Reply #65 on: March 18, 2008, 06:16:23 PM »
Quote
msol x Cp = msol x msubst/msol x 100%

Can you cancel something?

I can cancel msol on both sides to get Cp = msubst x 100%

No. Grouping msl on the right:

msol x Cp = msol/msol x msubst x 100%

as

msol/msol = 1

so

msol x Cp = msubst x 100%

and msol was mobed to the LHS. Now, try to do the same to 100% (hint: divide both sides).

Quote
hmm.. oxygen gas is not water so 1 g cannot equal 1 mL.

Could 93 mL be converted to 0.093 L? Could volume be accepted as mass?

No, it is gas, so PV = nRT. Marcus already got it right.
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#### Frederick95

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##### Re: Please calculate the number of mols of oxygen gas produced per second
« Reply #66 on: March 18, 2008, 06:29:37 PM »
Regarding Marcus's post

n = PV / RT

Thus,

=(102.6 kPa)(0.93 L) / (8.3145)(290 K)

= 95.418 / 2411. 205

= 0.0395727447 mol of O2

Since there exists twice the amount of hydrogen peroxide,

0.0791 mol of H2O2

#### Frederick95

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##### Re: Please calculate the number of mols of oxygen gas produced per second
« Reply #67 on: March 18, 2008, 06:47:41 PM »
msol x Cp = msubst x 100%

Dividing both sides:

msol x cP / msol = msubst x 100% / msol

msol cancels out on the LHS.

Thus,

cP = msubst x 100%

#### Borek

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##### Re: Please calculate the number of mols of oxygen gas produced per second
« Reply #68 on: March 18, 2008, 07:04:25 PM »
Regarding Marcus's post

n = PV / RT

Thus,

=(102.6 kPa)(0.93 L) / (8.3145)(290 K)

Almost OK. Almost, as you have forgot to subtract water vapor pressure. Marcus did.
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#### Borek

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##### Re: Please calculate the number of mols of oxygen gas produced per second
« Reply #69 on: March 18, 2008, 07:06:56 PM »
msol x Cp = msubst x 100%

Dividing both sides:

msol x cP / msol = msubst x 100% / msol

msol cancels out on the LHS.

Thus,

cP = msubst x 100%

Please, pay attention to what you are doing, reading and writing. I told you to move 100% to LHS, why do you divide by msol? But even then you have lost it on the RHS for no reason.
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#### Frederick95

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##### Re: Please calculate the number of mols of oxygen gas produced per second
« Reply #70 on: March 18, 2008, 07:09:24 PM »
102.6 kPa - 1.94 kPa = 100.7 kPa

n = PV / RT

Thus,

=(100.7 kPa)(0.93 L) / (8.3145)(290 K)

=  93.65 / 2411. 205

= 0.03884 mol of O2

#### Frederick95

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##### Re: Please calculate the number of mols of oxygen gas produced per second
« Reply #71 on: March 18, 2008, 07:14:06 PM »
Please, pay attention to what you are doing, reading and writing. I told you to move 100% to LHS, why do you divide by msol? But even then you have lost it on the RHS for no reason.

I divided 100% by msol by reading your hint (divide both sides). I lost msol on the RHS because one is the denominator, the other is numerator. They are both the same so I cancelled them out

On a second attempt,

100% x msol x Cp = msubstance

#### Borek

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##### Re: Please calculate the number of mols of oxygen gas produced per second
« Reply #72 on: March 18, 2008, 07:20:43 PM »
I divided 100% by msol by reading your hint (divide both sides). I lost msol on the RHS because one is the denominator, the other is numerator. They are both the same so I cancelled them out

On a second attempt,

100% x msol x Cp = msubstance

It is hopeless. You have to move 100%, so you should divide by 100%.

msol x Cp = msubst x 100%

Both sides divided by 100%:

msol x Cp / 100% = msubst x 100%/100%

canceling:

msol x Cp / 100% = msubst

Solved for msubst.
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#### Frederick95

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##### Re: Please calculate the number of mols of oxygen gas produced per second
« Reply #73 on: March 18, 2008, 07:29:55 PM »
honestly, I can't beleive I didn't realize this

msubstance = msolution x cP / 100%

= 10 g x 80% / 100%

= 8 g

Is this correct?

#### Borek

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##### Re: Please calculate the number of mols of oxygen gas produced per second
« Reply #74 on: March 18, 2008, 07:34:29 PM »
honestly, I can't beleive I didn't realize this

msubstance = msolution x cP / 100%

= 10 g x 80% / 100%

= 8 g

Is this correct?

As written - yes. If it fits the problem - I don't know, you have long lost me.
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