Question #81d94

1 Answer
Aug 21, 2017

Here's what I got.


The problem provides you with Avogadro's constant, which is the definition of a mole, so your goal here will be to use the molarity and the volume of the solution to find the number of moles of sulfuric acid present in the sample.

Once you know the number of moles of sulfuric acid, you can use Avogadro's constant to determine how many molecules of sulfuric acid you have.

So, you know that molarity is defined as the number of moles of solute present in #"1 L" = 10^3# #"mL"# of solution.

This means that your sample will contain

#100 color(red)(cancel(color(black)("mL solution"))) * overbrace(("0.02 moles H"_2"SO"_4)/(10^3color(red)(cancel(color(black)("mL solution")))))^(color(blue)("= 0.02 M H"_2"SO"_4color(white)(.)"solution")) = "0.002 moles H"_2"SO"_4#

To find the number of molecules of sulfuric acid that would be needed in order to have #0.02# moles of sulfuric acid, simply use Avogadro's constant as a conversion factor

#0.002 color(red)(cancel(color(black)("moles H"_2"SO"_4))) * overbrace((6.022 * 10^(23)color(white)(.)"molecules H"_2"SO"_4)/(1color(red)(cancel(color(black)("mole H"_2"SO"_4)))))^(color(blue)("Avogadro's constant"))#

# = color(darkgreen)(ul(color(black)(1.2 * 10^(21)color(white)(.)"molecules H"_2"SO"_4)))#

I'll leave the answer rounded to two sig figs, but keep in mind that you only have one significant figure for your values.

SIDE NOTE This question is poorly thought out because sulfuric acid is a strong acid, so you can say for a fact that the solution will not contain any sulfuric acid molecules.

However, I assumed that the question was about using Avogadro's constant to convert the number of moles of a substance to molecules.

That said, you should always keep in mind that a sulfuric acid solution does not contain any sulfuric acid molecules because the acid will ionize completely in its first ionization.