When a solute is dissolved in a solvent, it expresses a #"concentration"#.
Typically, #"concentration"# #=# #"Amount of solute in moles"/"Volume of solution in litres"#.
And thus, typically, #"concentration"# has units of #mol*L^-1#; this is typically called the #"molarity"# of the solution.
Depending on whether you are in 1st year university or not, #"concentration"# can be expressed in terms of #"molality"#, where #"molality"="Moles of solute"/"Mass of solvent in kg"#.
#"Molality"# is thus a temperature invariant term (because volume can alter with temperature), but at low to moderate concentrations in aqueous solutions, #"molality "-=" molarity"#.
And thus for solutes, we write #C=n/V# #"(C = concentration; n = amount of moles; V = volume in litres)"#; given 2 terms we can find the third.
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