[Tobes]

Both Sodium Hydride and Calcium Carbide react with water to produce a gaseous product:
 NaH(s)+H₂O(l) ---> H₂(g)+NaOH(s)
CaC₂(s)+2H₂O(l) ---> C₂H₂(g) + Ca(OH)₂(s)

A mixture of NaH and CaC₂ weighing 0.7514g is mixed with excess H₂O. The resulting gas mixture occupies 413mL at 22 degree Celsius and 746 torr. What is the mass % of the cpd in the original mixture of NaH and CaC₂.

So I started solving the equation: Let x= mass of NaH and 0.7514g-x=CaC₂
      After calculating everything I came to this;
          0.8685g-1.1559x+1.6618x= y      y = the mass of the residue from the mixture
      From that I knew that I had to figure out how much residue was produced by this reaction so I did this:
   n=PV/RT= (0.982atm)(0.413L)/ (0.08206Latm/molK)(295.15K)
               = 0.01675 mol of C₂H₂ + H₂ (gases)
 0.01675 mol of C₂H₂ + H₂ (28.05376g/1molC₂H₂ + H₂)= 0.4699g of C₂H₂ + H₂ gases

Now I'm stuck because I don't know how to obtain the mass of the residue not the gas. I can't subtract it from the original mass of the mixture because H₂O is incorporated in the mass of 0.4699g. What am I to do??

[Borek]

Write down equation expressing gas volume as function of x and y. You will have two equations in two unknowns.

[Tobes]

I'm a little confused after i find the mass of the two gases then what do I do?
I tried using those answers to find the moles of the solid ppt but when i incorporate that into the "y" (mass of residue) it doesn't add up.

[Borek]

I'm a little confused after i find the mass of the two gases then what do I do?

First - no idea how you have calculated mass of both gases - but you did it wrong.

Second - you don't need mass of these gases. Express number of moles of NaH and CaC₂ using compounds masses (x and 0.7514g-x). Using these numbers of moles write equation for the number of moles of gases - and you have already calculated how much gases there is!

I was wrong in my previous post - you will have one equation in one unknown. Even simpler to do

[Tobes]

oh i see, i did calculte it wrong. thanks!