Use the unit canceling method to determine the grams of NiCl2 required:

I have. 4248 mol NiCl2 x 129 g NiClc / 1 mol NiCl2 = 54.799 g NiCl2

Is this correct?

The final result must be rounded to four significant figures and reported as 55.05 g NiCl₂.

Explanation:

The molar mass of NiCl₂ is 129.5994 g/mol but you are using 129 g/mol, which is not quite accurate,

That means 129.5994 g NiCl₂ / 1 mol NiCl₂.

Thus, since you are starting with 0.4248 mol of NiCl₂ you can use the unit cancelation method to convert 0.4248 mol of NiCl₂ to grams.

The expression is:

0.4248 mol NiCl₂ * 129.5994g NiCl₂ / 1 mol NiCl₂

Notice that the unit mol NiCl₂ appears on the numerator of the first factor and on the denominator of the second factor, thus they cancel out, leaving only g NiCl₂ which is grams of NiCl₂.

The result of the operation is: 0.4248 * 129.5994 / 1 = 55.0538 and the units is gNiCl₂.

The other thing that you must take into account is the number of significant figure. You must consider that the 129.5994 gNiCl₂ is a constant; this is, an exact value that does not affect the number of significant figures.

Then, the result mus contain the same number of significant figures as the factor that is a measure. That is 0.4248 which has four significant figures.

Then, the final result must be rounded to four significant figures and reported as 55.05 gNiCl₂ instead of 55.0538 gNiCl₂.