Question #cd3c6

By salt, I assume you mean common table salt, #NaCl#. You are given that you have .2 moles of salt, thus you have #.2" mol " Na^+ "and " .2 " mol " Cl^-#.

Molarity is defined as the moles of a substance per Liter, so the molarity of the solution for both #Na^+# and #Cl^-# is as follows:

#(.2" moles")/(2" Liters") = .1 ("mol")/("Liter") = .1 " M"#

All you need to know here is that molarity is defined as the number of moles of solute present for every #"1 L"# of the solution.

This means that in order to find the molarity of a given solution, you must determine how many moles of solute are present for every #"1 L"# of this solution.

In your case, you know that #0.2# moles of solute are dissolved in #"2 L"# of the solution. Your goal here is to figure out how many moles of solute must be present in #"1 L"# of this solution in order to have a solution of equal concentration to the one that contains #0.2# moles of solute in #"2 L"# of the solution.

#"? moles solute"/"1 L solution" = "0.2 moles solute"/"2 L solution"#

Rearrange to get

#? = (1 color(red)(cancel(color(black)("L solution"))))/(2color(red)(cancel(color(black)("L solution")))) * "0.2 moles solute"#

#? = color(darkgreen)(ul(color(black)("0.1 moles solute")))#

The answer is rounded to one significant figure.

So, you can say that this solution will have a molarity of #"0.1 mol L"^(-1)#, which implies that #"1 L"# of the solution will contain #0.1# moles of solute.

#"molarity"=("moles of solute")/("1 L of solution")#

There are #"0.2 mol of salt"# dissolved in #"2 liter of salt solution"#.

#"molarity"=("0.2 mol salt")/("2 L")="0.1 mol salt/L = 0.1 M salt"#