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# What is the relative formula mass of: NaBr, CO2, H2S, BaSO4, Cu(NO3)2, FeCL3?

Relative formula mass Relative atomic masses can be used to find the relative formula mass of a compound. To find the relative formula mass (Mr) of a compound, you add together the relative atomic mass values (Ar values) for all the atoms in its formula. Here is one example: Find the Mr of carbon monoxide, CO. The Ar of carbon is 12 and the Ar of oxygen is 16. The Mr of carbon monoxide is 12 + 16 = 28. Example 2: Find the Mr of Copper Nitrate Cu(NO3)2 Ar of Cu = 63.5. Ar of N = 14 x 2. Ar of O = 6 x 16. Remember that the nitrate ion contains 3 oxygen atoms. But there are are 2 nitrate ions in copper nitrate, so there are 2 lots of 3 oxygen atoms. THAT IS WHY YOU MULTIPLY 6 BY 16. There is only one nitrogen atom in a nitrate ion, but there are 2 nitrate ions in copper nitrate. SO YOU MULTIPLY 2 X 14. Add up all of the relative atomic masses = 63.5+(14x2) + (16x6) = 187.5  ·

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NaBr: 23 + 79.9 = 102.9 CO2: 12 + 16 + 16 = 44 H2S: 1 + 1 + 32.1 = 34.1 BaSO4: 137.3 + 32.1 + 16 + 16 + 16 + 16 = 233.4 Cu(NO3)2: 63.5 + 14 + 16 + 16 + 16 + 14 + 16 + 16 + 16 = 187.5 FeCl3: 55.8 + 35.5 + 35.5 + 35.5 = 162.3  Josh Prince
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