How do you calculate the molar mass of a compound?

Calculate the molar mass of the ionic compound cobalt(II) bromide?

• Please show complete work of seperate Cation formula, Molar Mass number of Ions and mass of ion compounds. Also do the same with the Anion----thank you! and please show the original formula as well.:)

• Answer:

  First you have to look at your periodic table and find both cobalt and bromide to find out there molar masses. molar mass of cobalt= 58.93gmol-1 molar mass of bromide=79.9 gmol-1 The charge of cobalt(II) is 2+ you can get this by just looking at the roman numeral next to it. The charge of bromide is Br- because it is in group 17 only needing 1 electron to have a full outer shell so it wants to gain an electron so there will be 1 more electron then protons giving it -1 or - charge. For these to form a compound the charge must be neutral and for the charge to be neutral there has to be 2 Bromide atoms to balance out the cobalt(II) 2+ charge Co2+ + Br- = CoBr2 Then to work out the molar mass just add them up 58.93 + 2 x 79.9= 159.8 = 218.73 gmol-1 CoBr2 Hope this helps Edit: NJ Br is molar mass is not 35.453 thats is chlorines molar mass you have just mixed them up because Br is just under chlorine. The question is to work out the molar mass of Cobalt(II) Bromide not of Cobalt(II) chloride.