11/1/2016

1

ACIDS & BASES

SC STANDARD COVERED

• Standard PS-3.7

• Classify various solutions as acids or bases according to their physical properties,

chemical properties (including neutralization and reaction with metals), generalized

formulas, and pH (using pH meters, or pH paper, and litmus paper).

ACIDS produce H+ /H3O

+ (hydronium ion) in solution

Formulas start with H (except for H2O and H2O2)

PROPERTIES OF ACIDS

1. Sour to taste

2. React with some

metals to form H2 gas

(corrosive to metals)

PROPERTIES OF ACIDS

3. Turn litmus red

4. Phenolphthalein

stays colorless

PROPERTIES OF ACIDS5.Electrolytes (conduct)

6.pH < 7

7.Corrosive to body tissues

11/1/2016

2

COMMON ACIDS

Acetic Acid (Vinegar) -

HC2H3O2

Folic acid - orange juice

COMMON ACIDS

Phosphoric acid - H3PO4 - soda

Ascorbic acid -

vitamin C -

citrus fruits

COMMON ACIDSHydrochloric acid -

HCl - stomach acid

Battery acid – H2SO4 –

sulfuric acid

NAMING ACIDS

• HCl

• HNO3

• H2SO4

• H2SO3

• HBr

• HI

• H2S

• H3PO4

• H2CO3

NAMING ACIDS BASES produce OH- (hydroxide ions) in solution

Formulas end with OH (except for NH3)

11/1/2016

3

PROPERTIES OF BASES1. Bitter to taste

2. Slippery to touch

PROPERTIES OF BASES3. Turn litmus blue

4. Phenolphthalein

turns Magenta

PROPERTIES OF BASES5. Electrolytes

6. pH>7

7. Corrosive to skin

and body tissues

COMMON BASES

Mg(OH)2 Magnesium

hydroxide- antacids

NH3 – ammonia

cleaners, fertilizers

COMMON BASES

NaOH – Sodium

hydroxide- Drano

Al(OH)3 – aluminum

hydroxide- deodorant

NEUTRALIZATION REACTION

• A reaction where an acid reacts with a base.

• The products are water and a salt.

• Acid + Base water + salt

• HCl + NaOH H2O + NaCl

• An Acid is used to neutralize a base and vice versa.

• This is a double displacement reaction!!! Nothing new

11/1/2016

4

NEUTRALIZATION REACTION

• HCl + NaOH

• 2 HNO3 + Ba(OH)2

• H2SO4 + 2 LiOH

• 2 HClO4 + Ca(OH)2

NaCl + H2O

Ba(NO3)2 + 2 H2O

Li2SO4 + 2 H2O

Ca(ClO4)2 + 2 H2O

IDENTIFYING ACIDS AND BASES

• If a solution contains more H+ (H3O+) than OH- then it

is acidic.

• If a solution contains more OH- than H + then it is basic.

• If a solution contains equal amounts of H + and OH-

then it is neutral (HOH = H2O)

THE pH SCALE

pH - measurement of the hydrogen ion (H+) concentration (Molarity)

• measures how acidic or basic a solution is.

• pH scale goes from 0-14.

• 7 is neutral.

• Less than 7 is acid. Lower pH, the more

acidic

• Greater than 7 is base. Higher pH, the

more basic.

DETERMINING pH

• pH is tested for three ways:

• pH meter

• Litmus paper – red paper turns blue if it is a base

and blue paper turns red if it is an acid

• Indicator – compound which turns different colors

based on the pH of the solution it is in

CALCULATING pH• pH = measure of H3O

+, expressed in powers of 10

• ex: 10-14 to 10-1

• Formula for calculating pH:

pH = -log[H3O+]

[ ] means Molarity

CALCULATING pHExample: What is the pH of a 1.8 x10-5 M acidic solution?

pH = -log[H3O+]

pH = - log 1.8 X 10-5

pH = - (- 4.74)

pH = 4.7

11/1/2016

5

CALCULATING pHFind the pH of these:

1) A 0.15 M solution of Hydrochloric acid

2) A 3.00 X 10-7 M solution of Nitric acid

pH = -log[H3O+]

pH = - log 0.15

pH = 0.82

pH = - log (3.00 x 10-7)

pH = 6.52

pH AND pOH• pH measures [H3O

+] concentration, but not everything we

measure is an acid

• pOH measures [OH-] concentration

• Use this formula if the substance being tested is a base.

pOH = -log[OH-]

pOH• Find the pOH of a sodium hydroxide solution with a

concentration of 2.5 x 10-4 M.

pOH = -log[OH-]

pOH = -log[2.5 x 10-4]pOH = 3.6

Calculating pH from pOH

pH = 14 - pOH pOH = 14 - pH

pH + pOH = 14

Calculating pH from pOH• What is the pH of a 0.0035 M barium hydroxide solution?• Starting with a base means you have to find pOH……• pOH = -log [0.0035]• pOH = 2.4• pH = 14 – pOH• pH = 14 – (2) = 12

Calculating pH from pOHCalculate the pH and pOH for the following:

a. H3O+ = 4.25 x 10-10 M

b. OH- = 8.52 x 10-7 M

c. OH- = 2.79 x 10-3 M

pH = 9.37 pOH = 4.63

pOH = 6.07 pH = 7.93

pOH = 2.55 pH = 11.4

11/1/2016

6

STRENGTH OF ACIDS AND BASES

STRONG ACIDS/BASES• Dissociate completely in water (break up into ions)

• Are strong electrolytes

• Higher reaction rate

HCl(aq) + H2O(l) H3O+ + Cl- NaOH Na+ + OH-

WEAK ACIDS/BASES• Partially dissociates in solution

• Are weak electrolytes

• Lower reaction rate

HF + H2O H3O+ + F- NH3 + H2O NH4

+ + OH-

TITRATIONS• Determine the concentration of a solution (solution 1) by reacting a

known volume with another solution (solution 2) of known

concentration

• Use Dilution Formula

• Slowly add acid to base or vice versa

• Indicator placed in the beaker will change colors as the pH changes

TITRATIONS• Indicator changes colors quickly – known as the end point.

• When the indicator color changes, you have passed the equivalence point.

• Strong acid + strong base = neutral solution

• Weak acid + strong base = weak base

• Strong acid + weak base = weak acid

11/1/2016

7

CALCULATIONS

MaVa = MbVb

Where M is the molarity & V is the volume

• Used to determine final concentration vs original concentration

TITRATION PROBLEMS• 50.0 mL of 4.0 M HCl were titrated with 250.0 mL of LiOH. What is the

concentration of the lithium hydroxide?

Ma = 4.0 M HCl

Mb = ?

MaVa = MbVbMb = 0.80 M

Va = 50.0 mL

Vb = 250.0 mL LiOH

4.0 M ∙ 50.0 mL = Mb (250.0 mL)

Mb = 200 M×mL

250.0 mL

TITRATION PROBLEMS• 150.0 mL of a 1.5 M NaOH solution were used to titrate 250.0 mL of

acetic acid. What is the concentration of acetic acid?

Mb = 1.5 M NaOH

Ma = ?

MaVa = MbVbMa = 0.90 M

Vb = 150.0 mL

Va = 250.0 mL HC2H3O2

Ma (250.0 mL) = 1.5 M ∙ 150.0 mL

Ma = 225 M×mL

250.0 mL

TITRATION PROBLEMS• What is the concentration of 90.0 mL of KOH when it was used to titrate

50.0 mL of 2.0 M H2SO4?

Ma = 2.0 M H2SO4

Mb = ?

MaVa = MbVbMb = 1.1 M

Va = 50.0 mL

Vb = 250.0 mL KOH

2.0 M ∙ 50.0 mL = Mb (90.0 mL)

Mb = 100 M×mL

90.0 mL

BUFFER

• Solution that resists changes in pH when small amounts of

acid or base are added