1. Common Lab Methods and Calculations

2. Measuring Stuff Measuring Mass: most accurate
Measuring Volume: less accurate
Why??? (DEMOS)

3. Measuring Stuff
TIPS: Always weigh chemicals if possible (you can also weigh liquids in beakers) Use Volumetric glassware to measure volumes of liquids

4. Making Solutions of Specific Conc. (It’s all about UNITS)
Remember : ‘Dissolve a solute in a solvent to make a solution’
Common Types: Molarity (mol/L), % mass, g/L and ppm (mg/L) g/L = grams solute per Liter solution Molarity (mol/L or M) = moles solute per Liter solution % mass = (mass solute per mass solution) x 100% ppm = milligrams solute per kg solution

5. Stock Solutions: It is often necessary to make up a stock solution (a solution of known concentration) in lab. Walkthrough: Preparing a g/L (1.0 M) NaCl (aq) stock solution:

6. Calculations 1. Molarity:
Molarity* (M) = number moles of solute per Liter of solution
* The Molarity (mol/L conc.) is most often printed on lab reagent solution bottles, e.g. 9.0 M H2SO4 (aq)
i.e. Molarity = Moles Solute Units: mol/L or just M
Liters Solution
Example: What is the concentration (molarity, M) of a solution made by dissolving 25 g of NaCl in water and making the final volume of the solution equal to 750 mL?

7. More Calculations 2. % Mass % Mass = Mass Solute x 100 % (units of %)
Mass Solution
Example: What is the % mass concentration of an NaCl in a solution made by dissolving 25 g of NaCl in water and making the final volume of the solution equal to 750 mL? Assume the final solution has a density of 1.15 g/mL
How do we determine density (DEMO)?