1. Making a solution

2. Solution Vocabulary
Solution: A mixture in which individual molecules or ions are dispersed in a liquid.
Solvent: The liquid that makes up the majority of the solution.
e.g., water (aqueous solution)
Solute: The minority component of the solution. Often a solid before mixing.

3. Solutions Chemists describe solutions in terms of concentration.
Concentrated Solution: solution with a large amount of solute
Dilute Solution: solution with a small amount of solute
These are qualitative characteristics of a solution but are not informative enough to use in a lab setting.

4. Molarity

5. Allows chemist to quantitatively (using numbers)describe a solution.
Molarity
Allows chemist to quantitatively (using numbers)describe a solution.
When doing a lab, it is important that the amount of solute is accurate.

6. The most commonly used expression of concentration is molarity (M).
Molarity is defined as the number of moles of solute dissolved in a liter of solution.

7. Molarity Molarity is calculated using the following equation:
What does this mean for you?
Set-up these problems using dimensional analysis
If you’re given grams, you have to convert grams to moles
If you’re given mL, you have to convert mL to L
M= molarity = moles of solute = mol
liters of solution = L

8. Molarity Example 1
5.7 g KNO3 dissolves in a 233 mL solution. What is molarity?
Convert grams to moles
Convert mL to L
Divide mol/L
5.7 g KNO3 1 mol KNO3 = mol KNO3
g KNO3
233 mL 1 L = L
1000 mL
0.056 mol KNO3
0.233 L = 0.24 M KNO3

9. Molarity Example 2
Calculate the molarity of a solution that has 11.5 g of NaOH dissolved in 1500 mL of solution
Convert grams to moles
Convert mL to L
Divide mol/L
11.5 g NaOH 1 mol NaOH = mol NaOH
40.0 g NaOH
1500 mL 1 L = 1.5 L
1000 mL
0.288 mol NaOH
1.5 L = 0.19 M NaOH

10. Working Backwards
You may be asked to solve for Liters of solution, moles of solute or grams of solute.
Use triangle …

11. Example 3
How many moles of AgNO3 are present in 25 mL of a 0.75 M solution?
Convert mL into L
Liters of solution x molarity = moles of solute
0.025 L x 0.75 M = mol AgNO3
25 mL 1 L = L
1000 mL

12. Example 4
How many liters of must be used to prepare 930gHCHO 12.3 M formalin HCHO ?
Convert moles to grams
L = mol = L M
930 g HCHO 1 mol HCHO = mol HCHO
30.03 gHCHO

13. Making a Dilution

14. Making a Dilution
How do you make a concentrated solution into a diluted solution?
Add Water …
but how much?
what container will I use?
I need a solution of 0.5M CuCl2 for a lab but all I can find in the stockroom is a solution of 2M CuCl2 – how do I make it?

15. M1= Molarity of concentrated solution
Dilution Equation
M1 x V1 = M2 x V2
M1= Molarity of concentrated solution
V1 = Volume of concentrated solution
M2 = Molarity of diluted solution
V2 = Volume of diluted solution

16. Practice
I need to make a solution of 0.5M CuCl2 (M2) I’m mixing it in a 250mL (V2) bottle. What volume of the 2M CuCl2 (M1) concentrated (stock) solution do I need to make it?
Solve for V1

17. Steps for making a solution
I need an 2M solution of CuCl2 for an experiment in the lab. How do I make it?
Obtain a bottle to hold the solution (I have a 500mL bottle)
Calculate how many moles of CuCl2 are needed to make the solution – then convert that into grams.
Use a balance to measure the grams needed and then add that to a volumetric flask or bottle.
Add some water to the CuCl2 & stir until completely dissolved
Fill the rest of the way with water until 500mL is reached.

18. Steps for making a solution
1. Identify the molarity of your concentrated solution (M1). 2M 2. Identify the molarity of your desired diluted solution (M2). 0.5M 3. Identify the volume of the container you are going to put the diluted solution in (V2). 250mL bottle 4. Use the dilution equation to calculated the volume of your concentrated solution (V1) you need to add water to. M1 x V1 = M2 x V2 5. Measure V1 with a graduated cylinder or volumetric flask, add to the 250mL bottle, then fill with water.