[madscientist]

Hi peoples,

I know this must seem like a very easy question but im stumped for some reason.

can anyone please tell me how i can calculate  
(what formula do i use) how many moles there are in
1.00 litre of Methanol ( CH3OH).

the question im trying to answer is:

Methanol, CH3OH, is added to some automobile fuels to improve burning and reduce pollution.  What volume of O2 is consumed in the combustion of 1.00 L of methanol at 25°C and 1.00 atm?  The density of methanol is 0.791 g mL-1.
            
2CH3OH(l) + 3O2(g) ––> 2CO2(g) + 4H2O(l)

ive figured out all the other info i need but am stuck on the volume to moles part.

cheers,

Madscientist

[Borek]

What is mass of 1L of methanol?

[madscientist]

Would i be right to say that the answer to the questin posted would be that:

907L of oxygen (g) is consumed in the combustion of 1.0L of methanol?

hope this is right

cheers,

madscientist

[Borek]

Seems OK to me.

[xiankai]

according to my calculations, the figure appears to be 890L, (3 sig. fig.)

i hope u managed to calculate the correct mass of methanol...

[Borek]

Show your math, I got 907 like madscientist did.

[ksr985]

Answer's 907.14 litres.

[Borek]

Where did you get so many significant digits from?

[xiankai]

mass of CH3OH = 0.791*1000
                       = 791g

mol of CH3OH = 791/(12+4+16)
                     = 791/32
                     = 24.71875
                     = 24.7 mol (3 sig. fig.)

mol of O2 = 24.7 * (3/2)
               = 37.05 mol
               = 37.1 mol (3 sig. fig.)

vol. of O2 = 37.1 * 24
               = 890.4
               = 890L (3 sig fig.)

is anything wrong? :/

[Borek]

vol. of O2 = 37.1 * 24

What is 24?

[xiankai]

the volume of 1 mol of gas at r.t.p.

according to my syllabus that is...

checked wikipedia, and calculated the constant at r.t.p. seems to be 24.45 to me, which gives the correct answer.

i guess my textbooks are wrong :/

sorry!

[Borek]

Put 24.45 instead of 24 into calculations and you will get 907.

At STP 1 mole of gas has 22.4L.

At 25 deg C its volume is

(273+25)/273*22.4 = 24.45

(to be exact 24.5 - due to significant digits).

[madscientist]

thanks for the reasurance,

cheers,

madscientist