How do we calculate the percent composition? Here are the steps:

- Calculate the molar mass of the compound.

2.Divide the molar mass of each element by the molar mass of the compound and multiply by 100%.

For example, here is how you calculate the percent by mass of Na in NaCl:

1. Add the molar mass of Na (23 grams) to the molar mass of Cl (35.5 grams). Therefore, the molar mass of Na Cl is 58. 5 grams.

2. To calculate the percent by mass of Na, divide the 23 grams by the 58. 5 grams and multiply by 100%.

Answer: the percent by mass of N a in NaCl is 39%. A similar procedure is followed to find the mass percent by Cl in Na Cl.

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