Homework Help: AP Chemistry

Posted by Jake on Sunday, September 23, 2007 at 1:08pm.

My objective is to find the molar mass of a gas.

Is this the correct balanced equation for magnesium ribbon reacting with hydrochloric acid to form hydrogen gas?

2Mg (s) + 2HCL (l) ----> H2 (g) + 2MgCl (aq)

Also, I'm required to find the mass of the magnesium ribbon in grams and the moles of the hydrogen gas collected.

Is it correct to multiply the mass per meter (1.702 g/m) by the m of ribbon in order to get the mass?

then once i have the grams do i change it to moles of Mg? how do i get moles of h2? use the mole ratio of the equation?

AP Chemistry - bobpursley, Sunday, September 23, 2007 at 1:42pm
No. Correct the formula for MgCl2 and then rebalance.

Yes, mass is m/l * length

Yes, then change that mass to moles. You get moles of H2 from the balanced equation coefficents and the moles of Mg.

I will be happy to critique your thinking.
- AP Chemistry - Jake, Monday, September 24, 2007 at 6:08pm
  Thanks, sir.
  
  This is what I did, could you tell me if its correct?
  
  given value 1.072 g/meter
  
  1.072 g/m X .02 m [the magnesium ribbon was 2.0 cm] = 0.02144 gMg
  
  Then to find the moles of H2:
  
  0.02144 g mg ( 1 mol Mg/24.31 g Mg) (2 mol H2/1 mol Mg) = 1.76 X 10^ -3

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