Chemistry help

the questions are :

-1.)how many moles of calcium nitrate are there in 82.0 g of compound

-2.)what is the total number of oxygen atoms that is contained in 42.6g of sodium sulphate?

-3)A ballon was filled with nitrogen gas under stp.what is the mass of of the gas if the volume at stp was determined to be 16.8L

 

-4.)zn+2hcl–>zncl2+h2

if you were provided with 1.3g of zinc and 50.0ml of 0.60M HCL WHAT IS THE MAXIMUM volume of hydrogen gas that you produced (measured at stp)?

  

5.)97.5g sodium chloride were dissolved in distilled water in 500ml volumeristic flask.the mixture was stirred to form a colourless solution.More distilled water was added until the total volume of the solution was 500ml.What is the molarity of this sodium chloride solution?