mole- help!!?

Question

I need help setting up these problems:

For 7 x 10^33 atoms of Al, how many grams are present?

For 235.1 grams of sodium hydroxide, how many formula units are present?

What is the mass (in amu or in grams) of 5 molecules of carbon dioxide?

Thanks for the help!!

Answer 1

Change 7 x 10^33 atoms of Al to moles of Al by dividing by 6.022 x 10^23 atoms/mole. Then change moles of Al to grams by multiplying by the atomic mass of Al (found on the periodic chart.

Change 235.1 g of sodium hydroxide by moles by dividing by the formula mass of NaOH (add up the individual atomic masses) then multiply by 6.022 x 10^23 to change it to formula units.

Determine the molar mass of carbon dioxide (add up the individual atomic masses); divide by 6.022 x 10^23 to get the number of grams per molecule; multiply by 5

Answer 2

The most important thing to remember for moles is that Avogardro's number is:

6.022 x 10^23

Therefore, that many molecules (or atoms) will have the molecule's (or atom's) fromula weight.

In other words:

1mole of hydrogen = 1 gram
1mole of oxygen = 16 grams.

Thus, 7 X 10^33 divided by Avogadro's number = 1.16 x 10^10 moles.

Since Al has an atomic weight of 26.98, that means there is a total of 1.16 X 10^10 X 26.98 = 3.13 X 10^11 grams = 3.13 X 10^8 kilograms, etc.

Try the rest.

Answer 3

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Answer 4

1)
1 mole = 6.02x10^23 = avogadro's number = A

#atoms / A = #moles

#moles * atomic mass of Al = # grams

2) exact opposite calculation as above

3) same calculation as #1