How many moles of Si are in 78.0 grams of silicon

Explanation:

To convert from grams to moles, we must use the molar mass. This number can be found on the Periodic Table.

We can use number as a ratio.

Multiply by the given number of grams.

Flip the fraction so the grams of silicon cancel.

The original number of grams (78.0) has 3 significant figures, so our answer must have the same. For the number of moles calculated, that is the hundredth place. The 7 in the thousandth place tells us to round the 7 to a 8.

There are about 2.78 moles of silicon in 78.0 grams.

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