Name: ______Period: ______Date: ______
Concentration Packet
You have learned about the process of solvation and the factors that affectsolubility. The concentration of a solution is a measure of how much soluteis dissolved in a specific amount of solvent or solution. How would youdescribe the concentration of the solutions in the picture? Concentrationmay be described qualitatively using the words concentrated or dilute. In generala concentrated solution, as shown on the left in the picture, containsa large amount of solute. Conversely, a dilute solution contains a small amountof solute. How do you know that the tea on the right in the picture is a moredilute solution than the tea on the left?
- Concentration = amount of solute in a solution in relation to a particular amount of solvent
- Dilute solution = weak solution, contains a comparatively low amount of solute
- Concentrated solution = strong solution, contains a comparatively high amount of solute
In chemistry, we need more than a qualitative way to describe concentration. We need a way to specify, numerically what the concentration is. Most solutions are unsaturated, so we need a way to express the amount of solute and solvent they contain. For our course, we are going to have two ways to specify concentration: molarity and molality. Both base concentration on the moles of solute in a given amount of water.
Molaritydefinition / number of moles of solute dissolved perliter of solution
abbreviation / M
formula /
Molarity
General Relationship
Here is the general relationship that you will be using over and over again. The molarity is equal to the number of moles of solute divided by the volume of the solution measured in liters. If you like to think of numbers and units instead of quantities look at the second version of the equation. / molarity = / moles of soluteliter of solution
M = / n moles
v L
2 M = / 6 moles
3 L
Calculating Molarity from Moles and Volume
Here we are given something to figure out. To get the molarity we need to divide the number of moles of NaCl by the volume of the solution. In this case that is 0.32 moles NaCl divided by 3.4 L, and that gives 0.094 M NaCl. / What is the molarity of a solution containing 0.32 moles of NaCl in 3.4 liters?molarity = / 0.32 moles NaCl
3.4 L
= / 0.094 M NaCl
Calculating Molarity from Mass and Volume
- Calculating Molarity from Mass and Volume This one is a bit more difficult. To get molarity we still need to divide moles of solute by volume of solution. But this time we're not given the moles of solute. We have to calculate it from the mass of NaCl.
- We multiply 2.5 g NaCl by the conversion factor of 1 mole NaCl over the formula weight of NaCl, 58.5 g. That tells us that we have 0.0427 mole of NaCl.
- Now that we know the moles we can calculate the molarity. Moles of solute (0.0427) divided by the volume of the solution (0.125 L) gives us 0.34 M NaCl.
molarity = / moles of solute
liter of solution
2.5 g NaCl x / 1 mole NaCl
58.5 g NaCl / = 0.0427 mole
molarity = / 0.0427 mole NaCl
0.125 L
= / 0.34 M NaCl
For example:
Molarity Problems
- What is the molarity of an aqueous solution containing 40.0 g of glucose (C6H12O6) in 1.5 L of solution?
- What is the molarity of a bleach solution containing 9.5 g of NaOCl per liter of bleach?
- Calculate the molarity of 1.60 L of a solution containing 1.55 g of dissolved KBr.
Molarity Practice Problems
1. What is the molarity of the solution produced when 145 g of sodium chloride is dissolved in sufficient water to prepare 2.75 L of solution?
2. How many grams of potassium chloride are needed to prepare 0.750 L of a 1.50 M solution of potassium chloride in water?
3. What is the molarity of the solution produced when 85.6 g of hydrochloric acid is dissolved in sufficient water to prepare 0.385 L of solution?
4. To produce 3.00 L of a 1.90 M solution of sodium hydroxide, how many grams of sodium hydroxide must be dissolved?