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Offline motownmuscle

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Help with calculations...
« on: July 22, 2009, 04:41:59 PM »
I know how to do the calculations (volume to volume, volume to mass, mass to mass), but Im not sure how to set up the equation and the question is confusing me...

*They also ask the question with fractions which is not helping either, so if someone can help explain that too it would be great.

10a) How many grams of sulphuric acid will neutralize 10.0 g of sodium hydroxide?
b)What volume of water vapour at 100C and 110kPa would also be produced?

**The next questions have fractions, Im not sure how to do them or how the equation is balanced when fractions are there**

11) Calculate the mass of potassium chlorate needed to prepare 5.00L of oxygen gas at 24.0C and .950 ATM
-the eqation is KCLO3--->KCL+3/2O2

12) Consider the following reationc which takes place in an autoclave at 250C and 800atm.
NH3 + 7/4O2---> NO2 + 3/2H2O
Into the reaction vessel has been placed 200L of NH3 and 120L of O2. The reaction is allowed to go to completion. Determine the quantity, in moles, of hte gas that remains unreacted.

Offline cliverlong

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Re: Help with calculations...
« Reply #1 on: July 23, 2009, 03:24:17 AM »
I know how to do the calculations (volume to volume, volume to mass, mass to mass), but Im not sure how to set up the equation and the question is confusing me...

<< snip >>
Can you list the calculations you know so we can see what you know?
Quote
10a) How many grams of sulphuric acid will neutralize 10.0 g of sodium hydroxide?
b)What volume of water vapour at 100C and 110kPa would also be produced?
(Almost) always you must have a balanced chemical equation in order to attempt a chemical calculation.
So what are the formulae for:
sulphuric acid
sodium hydroxide
How do those two react? What are the products of this reaction? Can you write a chemical equation for this reaction?

Next: the general approach to chemical calculations about quantities of materials is to convert all the amounts into moles, use the balanced chemical equation you worked out above, work out the unknown moles , then convert back into masses or volumes or concentrations. Getting everything into moles is central.

Next: what equations do you know that relate:
moles, masses, volumes of gases etc. (the molar equations)
for gases: pressure, volume, temperature, number of moles etc.

Quote
**The next questions have fractions, Im not sure how to do them or how the equation is balanced when fractions are there**

<< snip rest >>
Why are fractions a problem?
Go back to the balanced equation you wrote for sulphuric acid and sodium hydroxide. Now multiply all the quantities by 10. What does this mean? Well in one sense nothing has changed, because what is important in the equation is the ratio between the quantities in the chemical equations. Similarly. If you multiply every term in the chemical equation by 1/2 or 1/3 or 1/10 all the quantities stay in the same ratio.

Clive

Offline motownmuscle

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Re: Help with calculations...
« Reply #2 on: July 23, 2009, 04:48:10 PM »
Im not really sure about a lot of it, can you just complete the first one for me (10a) so I can attempt the rest on my own and have some idea of how it works. The sample questions in the book are worded much differently, and they give the balanced forumla already without any fractions...

Offline UG

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Re: Help with calculations...
« Reply #3 on: July 23, 2009, 11:53:41 PM »
can you just complete the first one for me (10a) so I can attempt the rest on my own
Just this once...
Balanced reaction is
H2SO4 + 2NaOH :rarrow: Na2SO4 + 2H2O
Moles of NaOH = 10g / 40 g mol-1 = 0.4 moles. The ratio of NaOH to H2SO4 is 2:1 so you need how many moles of H2SO4? Once you have that, calculate the mass, by multiplying the number of moles by the molar mass.

Offline Borek

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Re: Help with calculations...
« Reply #4 on: July 24, 2009, 03:52:45 AM »
they give the balanced forumla already without any fractions...

As Clive wrote - don't worry about fractions. Coefficient is just a number. Doesn't matter if it is integer or fraction, you calculate the result exactly the same way.

By convention we write coefficients as integers, but that's only a convention. Good one, nonetheless convention only.
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