And how did we get that figure? Well, we took a Periodic Table, and summed the molar masses of each atomic constituent:

#"Molar mass of lead sulfate"# #=# #{207.2(Pb)+2xx32.06(S)+8xx15.99(O)}*g*mol^-1=??g*mol^-1#

Note that you are not expected to know these atomic masses, even tho you quickly learn the masses of the more common elements, i.e. hydrogen, carbon, oxygen, and nitrogen. You are expected to use a Periodic Table to calculate molar masses for any given compound.

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Note that #Pb(SO_4)_2#, #"plumbic sulfate"#, would be a very unusual salt. #"Plumbous sulfate"#, #PbSO_4#, is much more common.

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Nov 28, 2016

399 g/mol


#Pb(SO_4)_2# contains 1 atom of Pb, 2 atoms of S and 8 atoms of O.Atomic masses of these elements are:Lead - 207 uSulphur - 32 uOxygen - 16 uSo, atomic mass of #Pb(SO_4)_2# is 207 + 64 + 128 = 399 u.Therefore, molar mass of #Pb(SO_4)_2# is 399 g/mol.

Note that these values are approximate values.

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Jacob C.
Nov 28, 2016

The molar mass is approximately 399.3352 g/mol.


To find the molar mass of any compound, you determine the constituent elements and how many of them there are. In this case, there is on 1Pb (lead), 2S (sulfur) and 8O (oxygen).

1 atom of lead, 2 atoms of sulfur and 8 atoms of oxygen.

Then you have to use the periodic table of elements (in a classroom situation, one is usually given to you) to find the molar mass of each individual element. For example,

The molar mass of lead is 207.2- there is only one atom so you leave this number as it is.

The molar mass of sulfur is 32.07- since there are two atoms, you multiply this number by 2.

The molar mass of oxygen is 15.9994- since there are 8 atoms, you multiply this number by 8.

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The calculation would be: 207.2+(32.07x2)+(15.9994x8)=399.3352

Keep in mind that different versions of the period table of elements will use different molar masses for each element, so the answer may be off by a 0.01, or 0.001, etc, etc.

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