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