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Unit 15

Acids & Bases

Common Acids & Bases to Memorize

Acids

Hydrochloric Acid HCl

Sulfuric Acid H2SO4

Nitric Acid HNO3

Acetic Acid HC2H3O2

Bases

Sodium hydroxide NaOH

Calcium hydroxide Ca(OH)2

Ammonia NH3

or NH4OH

Potassium hydroxide KOH

Properties of Acids

1. Taste sour

2. React with metals to release H2 (g)

3. React with bases to form salts and water

4. Cause a color change in pH indicators (example : litmus turns red in acids)

Properties of Bases • Taste bitter

• Feel slippery

• React with acids to form salts and water

• Cause a color change in pH indicators (example :

turn litmus blue)

Arrhenius Theory of Acids & Bases Acids release H+1 example: HCl H+1 + Cl-1

Bases release OH-1 example : NaOH Na+1 + OH-1

Bronsted – Lowry Theory of Acids & Bases Acids donate a proton (H+1) example : HNO3 H+1 + NO3

-1

Bases accept a proton example : NH3 + H

+1 NH4+1

It is hard to see the base in the ammonia NH4OH NH3 + H2O NH4

+1 + OH-1

Indicators

pH indicators are chemicals which undergo a change in color when there is a change in the pH of a solution. Each pH indicator

provides a color over a specific pH range.

Example:

Phenolphthalein in acid is clear,

in base is magenta (pink).

Useful pH ranges for several common indicators.

Two factors are involved in determining whether an acid or a base is strong or weak:

1. Original molarity

Example: 0.001 M is very weak

0.1 M is much stronger

2. Equilibrium constant for the acid or base dissolving in water (the value of Kc)

K > 1000 mostly products

K = 1 equal amount of reactants and products

K < .001 mostly reactants

Strong Acids: Sulfuric acid Ka is very large H2SO4 (aq) 2 H+1

(aq) + SO4-2

(aq)

Hydrochloric acid Ka is very large HCl (aq) H+1

(aq) + Cl-1(aq)

Weak Acid: Acetic Acid Ka = 1.8 x 10-5

HC2H3O2 (aq) H+1(aq) + C2H3O2

-1(aq)

Strong Bases Sodium hydroxide K is very large NaOH(aq) Na+1

(aq) + OH-1(aq)

Weak Bases Ammonia Kb = 1.8 x 10-5 NH4OH(aq) NH4

+1(aq) + OH-1

(aq)

Calcium hydroxide Kb = 1.3 x 10-6

Ca(OH)2 (aq) Ca+2 (aq) + 2 OH-1

(aq)

Versions of formula

MA VA = MB VB

MA = (MB) (VB)

VA

MB = (MA) (VA) VB

A student uses 25 mL of 0.100 M NaOH to titrate with 50 mL of HNO3 of unknown concentration. What is the concentration of the acid?

Microscopic picture of the solutions

in the titration of unknown M HNO3

with 0.100 M NaOH. (the problem on the 4th page

back)

Phenolphthalein pH indicator added to flask

The pH curve for the titration of 50.0 mL of unknown M HNO3 with 0.100 M NaOH.

Titration is a method used to determine the molarity of a solution. A measured volume of

the solution with unknown molarity is placed into a flask. A solution with known molarity is slowly poured into the solution until the neutralization point (end point) is reached. The point when :

Acid + Base H2O + salt

Moles of Acid = Moles of Base MA VA = MB VB

Remember : Moles = (Molarity) (volume in liters)

Titration Procedure 1. Label 4 beakers: acid, base, H2O, waste 2. Place liquid of known concentration in the burette. A burette is a glass tube that delivers a varied amount of liquid with an accuracy of +0.10 mL. Run some liquid out of the burette until the air bubbles are out of the tip of the burette. 3. Pipet 10 mL of unknown concentration solution into an Erlenmeyer flask. A pipet is a glass tube calibrated to deliver an exact amount of liquid. Accuracy is + 0.05 mL. Touch the last drop to the side of the flask. 4. Add a few drops of a pH indicator to the flask. Phenolphthalein is often used. 5. Run a rapid titration first to obtain a rough estimate of the amount of solution needed to reach the neutralization point. Be sure to record an initial reading and final reading of the solution in the burette.

6. Run 2 (or more) slow titrations to obtain accurate data to

calculate the molarity of the unknown solution.

Acids Crossword

Across

21. Yellow

30. Hydrogen

34. Hydronium

37. Oxidizing

Down

3. Corrosive

20. Dehydration

22. Oxyacids

pH is a measure of the amount of acid in solution. It is defined as: pH = -log 10 [H+1] Any H2O solution must follow: H2O(L) H+1

(aq) + OH-1(aq)

Kw = [H+1] [OH-1] = 1.0 x 10-14 [H+1] = 1.0 x 10-7 pH of pure H2O = -log10(1.0 x 10-7) = 7

The pH scale.

A change from 1 pH unit to the next, the [H+1] changes by a

factor of 10!

Calculate the pH of a solution that has the [H+1] of 0.45 M. Calculate the pH of a solution that has the [OH-1] of 0.31 M. Calculate the pH of a solution that is made with 0.84 g KOH mixed in 600 mL of H2O.

Calculating the pH is done using pH = -log10 [H+] If you know the pH, you can calculate the [H+] using

10-pH = [H+] Calculate the [H+] if the pH = 5.26 Calculate the Molarity of an HCl solution if the pH = 8.22 Calculate the Molarity of a NaOH solution if the pH =12.55

pH data table [H+1] [OH-1] pH examples

1 x 100 1 x 10-14 0 Strong acid

1 x 10-1 1 x 10-13 1

1 x 10-2 1 x 10-12 2 Stomach acid

1 x 10-3 1 x 10-11 3 vinegar

1 x 10-4 1 x 10-10 4 tomato

1 x 10-5 1 x 10-9 5 coffee

1 x 10-6 1 x 10-8 6

1 x 10-7 1 x 10-7 7 Pure H2O

1 x 10-8 1 x 10-6 8 Sea H2O

1 x 10-9 1 x 10-5 9 Milk of magnesia

1 x 10-10 1 x 10-4 10

1 x 10-11 1 x 10-3 11 ammonia

1 x 10-12 1 x 10-2 12

1 x 10-13 1 x 10-1 13

1 x 10-14 1 x 100 14 Strong base

Review 1. Just memorize the 8 from your notes

2. Taste sour, release H+, donate protons, acid + base = salt + water,

3. Taste bitter, release OH-, accept protons, acid + base = salt + water

4. Hydrogen, H+1

5. Hydroxide, OH-1

6. Salt + water

7. HCl + NaOH H2O + NaCl

8. HCl H+1 + Cl-1 if HCl is .1 M, then H+1 is also .1 M , -log .1 = pH of 1

9. NaOH Na+1 + OH-1 if NaOH is .01 M, then OH-1 is .01 M, you need to use the formula Kw = [H+1][OH-1] = 1 x 10-14 1 x 10-14 / .01 = 1 x 10-12 which is the [H+1] -log1x10-12 = pH of 12

10. 0.78 M

Matching

1. K 5. M 9. F 13. N 17. L

2. O 6.. P 10. H 14. A 18. Q

3. J 7. D 11. E 15. B

4. G 8. R 12. I 16. C

Bases Crossword

Down 2. Autoprotolysis

11. Atomic number 49

19. Normal

25. Amphiprotism

38. Methyl

Across 10. Alizarin

13. Nonmetals

20. Molality

24. Conjugate

27. Anhydrous

42. Equivalent