What is the mass of 4.0 moles of sodium, Na? – previous question: “how many atoms are present in 4.0mol of sodium?” = 2.4 x 10^24 atoms of Na in 4.0 moles.
need an explanation of how to figure this out (& info on how to do this in other problems as well, thank you) <3

91.60 grams

Explanation:

For this specific problem, you are asked to find the weight of an element, when given moles. Other problems could give you a compound. In each case, you need to find the molar mass of the element or compound, that is, the weight (in grams) of 1 mole of the element or compound. Now that you know the molar mass of the element/compound, you can multiply by the amount of moles the equation the equation gives you to find the total weight.

In this problem, you are asked to find the mass of Sodium (Na). First, we need to look on the Periodic Table to find the Atomic Mass of Sodium. If we look, we find this to be 22.990 amu. Side note - when we find molar mass, amu and grams are interchangeable - you'll see here. This 22.990 amu is also the molar mass in GRAMS of 1 mole of sodium. The equation asks us to find the mass of 4 moles of sodium, so now we simply multiply by 4. 22.990 * 4 = 91.60 grams.

In summary, find the molar mass (1 mole) of the substance, by adding the amu's of each element (keeping mind the amount of each). Then, multiply this total number by the amount of moles that is given, and put your answer in moles.

Hope this helps

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)