An aqueous solution of lead (II) nitrate Pb(NO3)2 is mixed with aqueous sodium phosphate Na3PO4 to produce solid lead (II) phosphate Pb3(PO4)2 and aqueous sodium nitrate NaNO3

3Pb(NO3)2 + 2 Na3PO4
—> Pb3(PO4)2 + NaNO3

a) How many moles of sodium nitrate are produced from 12.3 moles of Na3PO4?
b) Calculate the grams of Pb(NO3) needed to react with 8.5 moles of Na3PO4
c) How many moles of NaNO3 are produced from 152.3 g of Na3PO4
d) Calculate the amount of Pb(NO3)2 in grams needed to react with 108 g of Na3PO4

answer : third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol

explanation :

let us write down the given equations

equation 1 :

equation 2 :

equation 3 :

let us use hess's law to find out which 2 equations can be added to get the third equation.

let us reverse equation 2 and multiply it by 2. the new equation that we get is,

equation 4 :

let us add equation 1 & 4

the above equation is similar to equation 3 but has different value for dhrxn.

therefore third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol