[ChennistryNewbie]

From that I got the formula PV = nRT

[mikasaur]

ChennistryNewbie, I feel like you're being very defeatist through this whole process. We're hand-feeding you the process to solve these problems and you're doing very little of the work yourself. As a general guideline for school and for life, try to take a little more initiative. I understand that the concepts in chemistry can be difficult for some people, but you have to at least try.

So you know Pv = nRT.

Do you know what each of those variables mean? If you have 3.25dm³ of H₂ at STP you could pretty easily calculate the number of moles, right?

[ChennistryNewbie]

P - Pressure

V - Volume

n - number of moles

R - Gas Constant

T - Tempreture

It just because in school I didn't learn this fomula so I don't know how it works .. I learnt the 22.4dm³⁺ and Avogado Constant

[mikasaur]

You keep mentioning learning 22.4dm³.

Why is this volume so special? What does it mean?

[ChennistryNewbie]

1 mole of anything will occupy 22.4dm³⁺

[mikasaur]

Yes! (Well, if by anything you mean any ideal gas at standard temperature and pressure)

Now c'mon ChennistryNewbie I know you can put it all together from here!

You have 3.25dm³ of H₂. How many moles do you have? How many moles of Zn did you need to make that many moles of H₂? What's the mass of those moles of Zn?

[ChennistryNewbie]

1 mole of H₂ = 1 mole of Zn
22.4dm          =     ?
3.25              =      65g

like that?

[mikasaur]

The way you set up equations for solving is very strange. Maybe it's some new way that schools are teaching but I'm unfamiliar with it.

Another suggestion for you. You should actually learn the science and principles behind the equations and heuristics the teachers give you. If you understood what the equations actually meant you wouldn't be so confused as to what values to plug in where. You wouldn't even think of problems as things to plug values into.

Back to it. You've told us that you know 1 mole of anything (at STP) will occupy 22.4dm³ of volume. And you have 3.25dm³ of H₂.

I asked the questions that I did because that's the order in which you should be thinking through this problem. It's a simple problem but it can be broken down into even smaller steps. So...

• How many moles of H₂ do you have if you have 3.25dm³ at STP? (Hint, use your 22.4dm³/mol constant)
• How many moles of Zn did you need to make that many moles of H₂? (Hint, use your balanced chemical equation Zn + 2 HCl ZnCl₂ + H₂
• What's the mass of that many moles of Zn? (Hint, the molar mass of Zn is 65.38g/mol).

I don't think it's possible for me to help you any more without actually telling you the answer. Please, please consider going back into your notes to find examples from your teacher. And you should probably reach out to your teacher for more assistance. He or she will hopefully be able to solidify some of these concepts for you.

[ChennistryNewbie]

1 mole of Zn as there isn't any number infront of it in the equation

1 mole of Zn is the RMM in grams? 65g ?

We use rounded units not with point for the RMM

[mikasaur]

I'm sorry but I can't provide you any more information without actually answering it for you. So here's the last post you'll get from me.

Answer the questions I asked in the order I asked them. Get a definitive answer for each one.

• Your answer should be in units of moles of H₂ and you will need to use your Molar Volume of 22.4dm³.
• Your answer should be in units of moles of Zn and you will need to use your balanced equation.
• Your answer should be in units of grams of Zn and you will need to use your molar mass of Zn of ~65g/mol.

Go through the three problems methodically and intelligently. Use the correct units in your equations. Cancel units where needed to help you.

Good luck.

[Borek]

The way you set up equations for solving is very strange. Maybe it's some new way that schools are teaching but I'm unfamiliar with it.

It looks like the approach described here: http://www.chembuddy.com/?left=balancing-stoichiometry&right=ratio-proportions

[mikasaur]

Well that looks like it could be a faster way of solving these stoichiometry problems, but I feel like it also obfuscates what's going on. Students look for numbers to plug into a heuristic and as soon as some thought is involved they get confused. At least that's what seems to be going on here.

[Borek]

Well that looks like it could be a faster way of solving these stoichiometry problems, but I feel like it also obfuscates what's going on.

For some it obfuscates, for some it helps

I believe for those that feel confident with the proportions this approach fits like a second skin. Unfortunately, most students don't understand proportions at all.