I am trying to find th e# of moles of NaCl but I am not sure of the units.
3.914g NaCl / mm=58.44 so is it
3.914g/mol divided by 58.44g/mol = 0.0669moles.
I am not sure how many significant figues to use.
If we rearrange your first equation to
3.914 g NaCl x (1 mol NaCl/58.44 g) = ? mol NaCl. Note g unit cancels and you are left with moles.
You have 4 s.f. in 3.914 and 4 s.f. in 58.44; you are allowed 4 s.f. in the answer.
for my answer I get 0.0669. Should I leave it like this or do 6.69e-2?
I wouldn't do either.
3.914/58.44 = 0.06697. Why did you throw the 7 away? You're allowed 4 s.f. You kept only 3. (Besides that you didn't round the 7. To 3 s.f. you should have written 0.0670.)
To find the number of moles of a substance, you need to divide the given mass of the substance by its molar mass. It seems like you have correctly identified the molar mass of NaCl as 58.44 g/mol.
To determine the number of significant figures to use in the final answer, you should consider the number of significant figures in the given mass of NaCl (3.914 g). In this case, 3.914 g has four significant figures.
When performing division, the general rule for significant figures is that the result should have the same number of significant figures as the least precise measurement involved in the calculation. In this case, the least precise measurement is the given mass of NaCl (3.914 g) with four significant figures.
Therefore, you should round your final answer to 0.0669 moles to four significant figures, matching the least precise measurement in the question.
In conclusion, the number of moles of NaCl is approximately 0.0669, rounded to four significant figures.