Solvent determines whether the solution exists as a solid, liquid, or a gas. However, for learning
purposes, the aqueous (aq) solution will be used as a solvent.
Solute is the material being dissolved by the solvent.
Aqueous reactions can be grouped into three general categories: Precipitation reactions, acid-base
neutralization reactions and oxidation-reduction (red ox) reactions.
Molarity is a solution property defined as the number of moles solute per liter of solution
Molarity (M) = (amount of solute, in moles / volume of solution, in liters)
The term M stands for the term molar or mol/L.
Problem: A solution is prepared by dissolving 25.0 mL ethanol, C H OH (d= 0.789 g/mL), in enough water
to produce 250.0mL solution. What is the molarity of ethanol in the solution?
Solution: To determine the molarity, we must first find how many moles of ethanol exists in a 25.0 mL
? mol C H2OH5= [25.0 mL C H OH x2( 5.789g C H OH/ 1 mL 2 H5OH) x ( 1 mol 2 5 OH/ 46.07 g C H O2)]5 2 5
= 0.428 mol C H O2 5
Now apply the definition of molarity to this answer. Thus divide the moles of C H OH by the solution
Molarity = (0.428 mol C H OH 2 5.2500 L soln) = 1.71M C H OH 2 5
Preparation of a Solution
1. Weigh the solid sample.
2. Dissolve it in a volumetric flask partially filled with solvent.
3. Carefully fill to the mark.
M i V = i x V f f
Problem: A particular analytical chemistry procedure requires 0.0100 M K CrO . What volume2of 04250
M K C2O mu4t be diluted with water to prepare 0.250L of 0.0100 M K CrO ? 2 4
? mol K C2O = [4.250 L soln x (0.0100 mol K CrO /1L s2ln)] 4 0.00250 mol K CrO 2 4
? L soln = [0.00250 L soln x ( 1L soln / 0.250 K CrO ] 2 0.0400 L soln
V i V xfM/M =f[25i.0mL x (0.0100 M/ 0.250 M)] = 10.0 mL Determining Limiting Reactant
The reactant that is completely consumed is called the limiting reactant. The reactant that remains after
a reaction is done is said to be in excess.
Problem: Phosphorus trichloride, PCl , is a3commercially important compound used in the manufacture
of pesticides, gasoline additives, and a number of other products. It is made by the direct combination of
phosphorus and chlorine. P + 6 Cl → 4 PCl
4(s) 2(g) 3(l)
What mass of PCl 3 (l)orms in the reaction of 125g P with4323g Cl ? 2