Moles help (2 Viewers)

[findsome1]

Aye

Im confused about moles if you have 4g of 2HCL

would you find the amount of moles by:

n = 4/(1.008+35.45) or n= 4/2(1.008+35.45) im confused which one to use.

 

[mirakon]

Um, what? 4g of 2HCl? are you sure it's not 4g of HCl. Please quote entire question as something doesn't look right....

 

[findsome1]

oh im just giving an example. like do we take the mole number into account in the molar mass when we are trying to find the number of moles?

 

[mirakon]

No, i don't think so. The '2' in HCl simply indicates that that's how many moles participate in the reaction. If you're given 4g of hydrochloric acid, to calculate the number of moles you simply use n= m/M where M (in this case) = 4/(1.008+ whatever chlorine is can't remember off top of my head)

 

[Blushii]

It depends on what you're given. If you're given the mass in grams, then simply use the formula n=m/MM

get it? so for HCL it would be (n) moles= 4g/"molar mass of HCL"

but sometimes when you're not given enough info to use this, you might be required to use the other formula where you use the Avogadro number then rearrange the formula and etc.

 

[kiniki]

4g x 1mole/(35.45 + 1.008) = answer

 

[mirakon]

avogadro's number is used to determine the amount of atoms in a mole of a given substance.

 

[mirakon]

Well think of it this way. If you're looking for the no. of moles of 2HCL then you're essentially looking for 4g of 2x. Approach it like a normal math eqn..

so it's

4g x 1mole/2(35.45 + 1.008) = answer

I'm quite sure you're given 4g of HCl. How exactly do you get 4g of 2HCl? Doesn't the prefix just indicate the ratio of moles that take place in the reaction?

 

[kiniki]

ah! sorry re-read over the question. yes you're right, it's just 4g x 1mole/(35.45+1.008)

you only write the whole 2x thing and multiply it by 1/2 if it's something like O2 or Na2CO3.

 

[hscishard]

Um, what? 4g of 2HCl? are you sure it's not 4g of HCl. Please quote entire question as something doesn't look right....

Woudn't it cancel down to 2g of HCL.

 

[Omnipotence]

How does that work? 2HCL?

Did you get this by balancing an eq/n? If so it is only a co-efficient and disregard it.

In that case its n=m/M, where m = 4g and M = 1.008+35.45

n = 4/36.458
n = 0.1097152888 mols

 

[mdmm92]

the coefficient represents the stoichiometric ratio of moles in a given reaction
n(HCl) = mass/molar mass
= 4/36.46