1. PREPARING SOLUTIONS AND REAGENTS

2. Chemical Solutions (aqueous = water is the solvent)
Types of vessels (least to most precise):
Beaker
Erlennmeyer flask
Graduated cylinder
Volumetric flask

3. DEFINITIONS: SOLUTES -- substances that are dissolved
SOLVENTS -- substance in which solutes are dissolved (usually water)
AMOUNT -- how much

4. Goals Make solutions Dilute solutions
Convert between different concentrations of solutions

5. Facts of Life Mass is measured in Grams, mg, μg
1g = 1000mg = 1,000,000µg
Volume is measured in liters, mL, μL
1L = 1000mL = 1,000,000 μL
Density of water is 1 g / mL

6. Facts of life (cont’d)
Concentration means: amount of solute in a volume of solution
Expressed in many ways:
1. percent
2. mg/ mL
3. molar
4. “X” solution

7. ? = 0.63 mg, so the concentration is 0.63 mg/mL
Each star represents 1 mg of NaCl.
What is the total amount of NaCl in the tube? _____
What is the concentration of NaCl in the tube (in mg/mL)? _____
5 mg = ?
8 mL mL
? = 0.63 mg, so the concentration is
0.63 mg/mL
8 mL

8. Percent Solutions Per means “for every one” Cent means 100
Example: a 5% sugar solution has
5 grams of sugar for 100g of solution, or
5g g of water = 100 mL, and the
100mL solution is mostly water.

9. Make 250 mL of a 3% starch solution
3 g / 100 g = 3 g / 100 mL because density of water is 1 g / mL
Set up a ratio:
3 g / 100 mL = ?g / 250 mL
Use 7.5 g of starch and bring to a volume of (BTV) 250 mL with distilled water

10. mg / mL Solutions
5 mg/mL has 5 milligrams of solute in 1 milliliter of solution

11. Make a 250 mL of a 3 mg /mL starch solution
Set up a ratio:
3 mg / 1 mL = ?mg / 250 mL
Use 750 mg of starch and bring to a volume of (BTV) 250 mL with distilled water

12. Molar Solutions 1 mole is 6.02 x 1023 items
Molecular weight or Formula weight is really the mass of 1 mole of molecules (see periodic table)
Example: 1 mol of sodium chloride (NaCl) has a mass of g.

13. MOLARITY
Molarity is: number of moles of a solute that are dissolved per liter of total solution.
A 1 M solution contains 1 mole of solute per liter total volume.

14. MOLE
How much is a mole?

15. EXAMPLE: SULFURIC ACID
For a particular compound, add the atomic weights of the atoms that compose the compound.
H2SO4:
2 hydrogen atoms 2 X 1.00 g = g
1 sulfur atom X g = g
4 oxygen atoms 4 X g = g
98.06 g

16. EXAMPLE CONTINUED
A 1M solution of sulfuric acid contains g of sulfuric acid in 1 liter of total solution.
"mole" is an expression of amount
"molarity" is an expression of concentration.

17. DEFINITIONS "Millimolar", mM, millimole/L. "Micromolar", µM, µmole/L.
A millimole is 1/1000 of a mole.
"Micromolar", µM, µmole/L.
A µmole is 1/1,000,000 of a mole.

18. FORMULA
HOW MUCH SOLUTE IS NEEDED FOR A SOLUTION OF A PARTICULAR MOLARITY AND VOLUME?
(g solute ) X (mole) X (L) = g solute needed
1 mole L or
FW X molarity x volume = g solute needed

19. EXAMPLE
How much solute is required to make 300 mL of 0.8 M CaCl2?

20. ANSWER
(111.0 g) x (0.8 mole) x (0.3 L) = g
mole L

21. Make 250 mL of a 3 molar NaCl solution
58.44g x 3 moles x L = ? g
1 mole L
? = 43.8g of NaCl
BTV of 250 mL

22. “X” solutions X means times
A 40X buffer solution is 40 times more concentrated than the standard working solution
Stock solutions / concentrates
How much stock solution you need = total volume you need divided by the “X” number

23. Diluting Solutions Conc 1 x Vol. 1 = Conc 2 x Vol 2
Usually want 1 X solutions

24. Example: Frozen Orange Juice
Solution 1 is the frozen concentrate
Solution 2 is the 1X juice you drink
How concentrated is it?
C1 V1 = C2 V2
(? X) (250mL) = (1X) (1000 mL)

25. Answer: Frozen OJ is 4X because ¼ of the final volume is the concentrated oj

26. Example: bleach sterilant
Solution 1 is 100% bleach – stock solution
Solution 2 is 6% bleach – what you want
How do you make 350 mL of 6% bleach?
C1 V1 = C2 V2
(100%) (?) = (6%) (350 mL)

27. Answer: You need 21 mL of 100% bleach BTV 350 mL.