Question #268ae

1 Answer
Apr 11, 2016

Answer:

#"1.89e23"#

Explanation:

The first thing to do here is use hydrazine's molar mass to determine how many moles you get in that #"10.08-g"# sample.

Hydrazine has a molar mas of #"32.045 g mol"^(-1)#, which means that one mole of this compound has a mass of #"32.045 g"#. This means that your sample will contain

#10.08 color(red)(cancel(color(black)("g"))) * ("1 mole N"_2"H"_4)/(32.045color(red)(cancel(color(black)("g")))) = "0.3146 moles N"_2"H"_4#

To convert the number of moles of hydrazine to molecules, use the fact that one mole of any compound contains #6.022 * 10^(23)# molecules.

#color(blue)(|bar(ul(color(white)(a/a)"1 mole" = 6.022 * 10^(23)"molecules"color(white)(a/a)|))) -># Avogadro's number

In your case, #0.3146# moles of hydrazine will contain

#0.3146 color(red)(cancel(color(black)("moles N"_2"H"_4))) * overbrace((6.022 * 10^(23)"molec.")/(1color(red)(cancel(color(black)("mole N"_2"H"_4)))))^(color(purple)("Avogadro's number")) = 1.8945 * 10^(23)"molec."#

Rounded to three sig figs, the answer will be

#"no. of atoms of N"_2"H"_4 = color(green)(|bar(ul(color(white)(a/a)"1.89e23"color(white)(a/a)|)))#