You have 2.5L of .14M salt solution, how many grams of salt would be needed to make this solution?

1 Answer
Stefan V.
Mar 9, 2018

#"20. g"#

Explanation:

The thing to recognize here is that the molarity of the solution tells you the number of moles of solute present in exactly #"1 L"# of this solution.

In your case, the solution is said to have a molarity of #"0.14 M"#, which implies that every #"1 L"# of this solution contains #0.14# moles of salt, the solute.

Now, in order to have #"2.5 L"# of #"0.14 M"# salt solution, you need the solution to contain

#2.5 color(red)(cancel(color(black)("L solution"))) * "0.14 moles salt"/(1color(red)(cancel(color(black)("L solution")))) = "0.35 moles salt"#

In order to find the number of grams needed to have #0.35# moles of salt, you need to use the compound's molar mass. Assuming that the salt is table salt, or sodium chloride, #"NaCl"#, you will have

#0.35 color(red)(cancel(color(black)("moles NaCl"))) * "58.4 g"/(1color(red)(cancel(color(black)("mole NaCl")))) = color(darkgreen)(ul(color(black)("20. g")))#

The answer must be rounded to two sig figs, the number of sig figs you have for your values.

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