Stoichiometry Mole Concept Problem

[mohnish khiani]

A sample of impure Magnesium is reacted with diluted Sulphuric Acid to
give the respective salt and Hydrogen.If 1 gram of impure sample gave
298.6 cc of Hydrogen at STP.Calculate the % purity of the sample
(MAgnesium = 24,Hydrogen = 1)

[John Cuthber]

How much hydrogen would you expect 1 gram of pure magnesium to produce?

[mohnish khiani]

I didn't get you.

 

Can you please post the complete solution and the answer.

 

Thanks in advance.

Mg(s) + H2SO4(aq) --> MgSO4(aq) + H2(g)

[pwagen]

Can you please post the complete solution and the answer.

He can't.

 

http://www.scienceforums.net/topic/75772-read-this-before-posting-in-homework-help/

 

How are you going to learn anything if you're spoon-fed the answer? I would suggest reading his question to you, think about how it applies to your question, then go from there.

[mohnish khiani]

I was posting this question on behalf of my mother,who is a teacher and had this doubt.I have no idea about this topic.Can someone please give me the solution,it's urgent I am sorry,

 

Also,I am just guessing that 1 gram of Magnesium would produce I gram of Hydrogen

Edited June 23, 2013 by mohnish khiani

[Amaton]

I was posting this question on behalf of my mother,who is a teacher and had this doubt.I have no idea about this topic.

 

I don't trust that claim, but I'm not willing to dismiss it entirely. Please post the work she's done so far and where specifically her doubt lies.

[hypervalent_iodine]

Are you familiar with the concept of moles? You may want to look this up if not. Your equation:

 

Mg(s) + H2SO4(aq) --> MgSO4(aq) + H2(g)

 

Is essentially telling you that for every mole of Mg metal that reacts, you will produce 1 mole of H₂ gas. You should be able to use that information to solve your problem.

[mohnish khiani]

Okay,let me try this one.

 

A pure sample of 1 mole of Magnesium would give 1 mole of Hydrogen. But since 1 mole of magnesium gives 0.2986 moles of hydrogen. The purity of Magnesium would be 29.86%. Am I right ??

[hypervalent_iodine]

Nope. You need to do a few conversions first and you need to know that the molar mass of H₂ is ~2 g/mol, not 1 g/mol. It is also useful / necessary for you to recognise that 298 cc is another way of expressing mL (so volume, not mass) and STP is an acronym for standard temperature and pressure (i.e. 298K, 1atm). For the purposes of this question, you can assume hydrogen to be an ideal gas, in which case there is a simple rule of thumb for how many litres a mole of gas will occupy at STP. It shouldn't be too hard to look up.

 

Also, moles =/= mass. You do not have 1 mole of Mg, you have 1 gram.

[daniton]

Let me make everything clear

- Change the cc to mass using PV = nRT

- Find the mole of Hydrogen

- Since mole of Hydrogen and magnesium is equal change that mole to mass of magnesium

- Use the mass to find the percentage