Chemistry Can the amount of moles in a mixture be determined using mass and molar mass?

[fk378]

General question:

If given the mass (15.0 g) of a mixture of two solids (NaCl + C12H22O11), can I find the amount of moles in the mixture by multiplying (15.0 g)*(mol / mass NaCl + mass C12H22O11)? I don't think this is valid, but I don't know why not...

 

[erjkism]

i don't think you can really do that... mainly because you don't know what fraction of the mixture is NaCl or C12H22O11.

 

[fk378]

Well what if you're just trying to find the moles of solution present? Then would it matter the fraction of each?

 

[erjkism]

well.. that is sort of impossible to say the total moles of "solution present". for example, try making up your own values for a solution... like 20% A (molar mass 20) and 80% B (molar mass 5). you could then find find moles A and moles B and add them up together to find total moles.
now try doing it again except with like 50% A and 50% B. You should get a different number of moles.. at least i hope so lol

 

[mgb_phys]

Suppose I told you there was 1000tons of vehicles in the car park and they were a mixture of 0.5t Smart Cars and 10t Buses - you couldn't work out how many vehicles were present.