[Supremacy]

I have to do these for hw and im not sure how to do it, can some1 tell me step by step how to do these?

1.KI+Pb(NO3)2-->KNO3+PbI2
What mass of PbI2 is produced from 30.0 g KI and excess Pb(NO3)2?

What is the mass of the other product, potassium nitrate?


2.AICI3+AgNO3-->AgCI+AI(NO3)3
Calculate the mass of AgCI made from 200.0 g of AICI3 and excess AgNO3

3.How many grams of AuCI3 can be made from 100.0 grams of chlorine by this reaction:2 Au+3 Cl2-->2 AuCI3

4.Na+CL2-->NaCI
How many grams of sodium metal are required to react completely with 75.0 grams of chlorine to make sodium chloride?

[joie.de.vivre]

note/warning/disclaimer: i took AP chem back in 10th grade, so i may be a bit rusty...

in general [i'll use the third example because the numbers are easier]

1) balance the chemical rxn equation first...i.e. 2Na+Cl2-->2NaCl
2) use periodic table to find molar mass of the substances [how to find molar mass: i.e. for chlorine gas (Cl2)..it's molar mass is approximately 35.45 x 2 grams= 70.9 grams...i got that number from the atomic mass unit given for chlorine in the periodic table and multiplied it by two...and 1 atomic mass unit = 1 gram]
3) do multiplication to get all the numbers given in the questions from grams to moles [i.e. 75.0 grams of Cl2 x (1 mole of Cl2/ 70.9 grams of Cl2) = 1.06 moles of Cl2]
4) do multiplication to find out how much of the other reactants you need for the rxn to be completed [i.e. 1.06 moles of Cl2 x (2 moles of Na/1 mole of Cl2)= 2.12 moles of needed Na]
5) do multiplication to convert moles back to grams using molar masses

* when it says 'excess' it means the reactants react completely with each other and that the rxn goes through

i hope this is pretty much right :\

[Vivskies]

^ Mmm. You're right i think.
I'm taking AP Chem this year, so hope I'm right,