Pleas help! Chemistry calculations

[Aka]

the folowing reaction proceeds with a 70% yeild

 

C6H6 + HNO3 = C6H5NO2 + H2O

 

calculate the mass of C6H5NO2 expected if 12.8g of C6H5 reacts with excess HNO3

 

How do you do this problem?

 

 

and

 

If 3.45 x 10^23 formula units of Hg(NO3)2 are reacted with excess of Na2S, what mass of HgS can be expected if this process occurs with 97% yield?

 

 

What are fomula units?

[hybrid04]

Basically you have to look at the forumulas. Since HNO3 is in excess the amount of product produced is dependant on the other reagent. The mole ratio given from the reaction is 1mol C6H6 produces 1 mol C6H5NO2. Remember it is a mole not a mass ratio. So 1g doesnt make one g. Figure out how many moles of starting material that equals the number of moles of product and then multiply by the molar weight. This gives you 100% yield (or theoretical yield). Multiply that by .71 and you have 71% yield.

 

For the second one im not sure exactly what 'formula units' are but you could still use the same process and get formula units in the end. You need to find the balanced formula for the reaction and then just match the coefficients. 1 for 1 or 1 for 2 etc and then mulitply out the forumla units.

[Aka]

^ Thanks i got it now