Chemistry HP Unit 8 – Acids and Bases
Learning Targets (Your exam at the end of Unit 8 will assess the following:)
8. Acids and Bases
8-1. Define and give examples of acids and bases.
8-2. Give the common properties of acids and bases including colors seen when each is combined with indicators such as
phenolphthalein, bromothymol blue, and cabbage juice.
8-3. Calculate pH, pOH, [H+], and [OH‒] for acids and bases.
8-4. Classify a solution as acidic, basic, or neutral from the pH.
8-5. Perform stoichiometric calculations involving pH and pOH for a neutralization reaction
8-6. Use data from a titration experiment to perform stoichiometric calculations.
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8-1. Define and give examples of acids and bases.
8-2. Give the common properties of acids and bases including colors seen when each is combined with indicators such as
phenolphthalein, bromothymol blue, and cabbage juice.
Acid Base Definitions.
An acid is a substance that donates H+ ions to solution.
Example: HCl (aq)  H+ (aq) + Cl- (aq)
A base donates OH- ions to solution.
Example: NaOH (aq)  Na+ (aq) + OH- (aq)
Properties of acids and bases.
Acids
pH < 7.0
Taste sour
React with metals to produce H2 gas
Turns pH paper red
Phenolphthalein turns colorless
Bromothymol blue turns yellow
Cabbage juice turns pink
Strong acids are strong electrolytes (Acids in solution
conduct electricity)
Bases
pH > 7.0
Taste bitter
Feel slippery
Turns pH paper blue
Phenolphthalein turns pink
Bromothymol blue stays blue
Cabbage juice turns blue/green
Strong bases are strong electrolytes (Bases in
solution conduct electricity)
Sample pH Scale
pH
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Substance
1.0 M HCl
Stomach Acid, Battery Acid
Lemons, Limes, Plums
Grapes, Apples, Pickles, Oranges, Peaches
Vinegar, Cherries, Tomatoes
Bananas, Asparagus, Turnips, Pumpkins
Milk, Tuna, Peas, Salmon
Water
Eggs, Sea Water
Baking Soda
Soap, Antacid
Ammonia, Windex
Laundry Detergent
Drain Cleaner, Bleach
1.0 M NaOH
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8-3. Calculate pH, pOH, [H+], and [OH‒] for acids and bases.
8-4. Classify a solution as acidic, basic, or neutral from the pH.
pH
pH = Measure of acidity of a solution
[H+] = concentration of hydrogen ion in solution, in Molar (moles/liter).
𝑝𝐻 = −𝑙𝑜𝑔[𝐻+ ]
10−𝑝𝐻 = [𝐻+ ]
pH is a measure of the acidity of a solution: the lower the pH, the more acidic the solution is and the higher the pH, the
more basic the solution is.
A solution is acidic when pH < 7 and [H+] > [OH-].
A solution is basic when pH > 7 and [H+] < [OH-].
pOH is a measure of the basicity (or alkalinity) of a solution: the lower the pOH, the more basic the solution is and the
higher the pOH, the more acidic the solution is.
pH or pOH = 7.0 indicates a neutral solution.
The pH scale is a base-10 logarithmic scale, which means that every change of one unit on the pH scale represents a
change in the acidity by a factor of 10.
More specifically, every decrease of one unit on the pH scale is equivalent to a tenfold increase in the hydrogen ion
concentration.
ex. A solution with a pH of one is _________ times more acidic than a solution with a pH of two.
ex. A solution with a pH of one is _________ times more acidic than a solution with a pH of three.
pH and pOH Equations
𝑝𝐻 = −𝑙𝑜𝑔[𝐻+ ]
𝑝𝑂𝐻 = −𝑙𝑜𝑔[𝑂𝐻 − ]
[𝐻 + ] = 10−𝑝𝐻
[𝑂𝐻 − ] = 10−𝑝𝑂𝐻
𝑝𝐻 + 𝑝𝑂𝐻 = 14.00
[𝐻+ ][𝑂𝐻− ] = 1.0 × 10−14
pH and Significant Figures:
For pH and pOH, only the digits after the decimal place are significant. (ie, pH= 10.20 has two significant digits since
there are two numbers after the decimal place; pOH = 1.384 has three significant digits since there are three numbers
after the decimal place).
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8-3. Calculate pH, pOH, [H+], and [OH‒] for acids and bases.
8-4. Classify a solution as acidic, basic, or neutral from the pH.
ex. Calculate pH if [H+] = 0.015 M
ex. Calculate [H+] if pH = 11.22
ex. Calculate pOH if [OH–] = 3.8 x 10–4 M
ex. Calculate [OH–] if pOH = 5.76
ex. Calculate pOH if pH = 12.50
ex. Calculate [H+] if [OH–] = 2.0 x 10–10 M
ex. Calculate the [H+], pH, pOH, and [OH–] of 0.10 M HCl
ex. Calculate the [OH–], pOH, pH, and [H+] of 0.020 M Sr(OH)2
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Worksheet 8-1 (Learning Targets 8.1 to 8.4)
(1) Complete the following table. Give the equation used to solve each problem.
[H+]
pH
[OH-]
pOH
Acidic, basic or
neutral?
0.030
4.62
2.72
1.6 x 10-6 M
Neutral
8.0 x 10-5 M
12.50
13.10
8.7 x 10-3 M
(2) Classify the following substances as acidic or basic and determine [H+] and [OH–].
(a) Cola, pH = 3.50
________________
[H+ ] ________________
[OH– ] ________________
(d) Human blood, pOH = 6.60
______________
[H+ ] = ________________
[OH– ] = _______________
(b) Borax, pH = 8.85
________________
[H ] = ________________
[OH– ] = _______________
(e) Vinegar, pOH = 11.60
______________
[H ] = ________________
[OH– ] = _______________
+
(c) Stomach acid, pH = 1.45
________________
[H+ ] = ________________
[OH– ] = _______________
+
(f) Sea water, pOH = 5.40
______________
[H+ ] = ________________
[OH– ] = _______________
(3) Determine the pH and pOH of the following solutions.
(a) 0.34 M HBr
(c) 0.030 M H2SO4
pH = _________
pOH = ________
(b) 0.42 M KOH
pH = _________
pOH = _______
(d) 0.010 M Ba(OH)2
pH = _________
pOH = ________
pH = _________
pOH = _______
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8-5. Perform stoichiometric calculations involving pH and pOH for a neutralization reaction
8-6. Use data from a titration experiment to perform stoichiometric calculations.
Acid Base Stoichiometry and Titration Calculations
A reaction between an acid and base is a special type of double-replacement reaction which forms a salt and water. This
is called a neutralization reaction.
HCl + NaOH  NaCl + H2O
Titration: an analytical procedure in which the concentration of a known solution is used to determine the
concentration of an unknown solution (commonly used in experiments to find the concentration of an acid or base).
Acid base titrations involve neutralization reactions.
For an experiment, the objective is to determine the volume of a solution with known concentration (a standard
solution) that is required to titrate (i.e. neutralize) a given volume of solution with an unknown concentration.
The moles of the standard solution used in the experiment can be calculated from the concentration and volume. The
moles of the unknown solution can then be calculated from the mole ratio in the balanced chemical equation. The moles
and volume of unknown solution can therefore be used to determine the concentration.
Usually three “trials” are performed and the average volume of the standard solution is used for calculations. Chemical
indicators (i.e. phenolphthalein or bromothymol blue) can be used to monitor when the reaction is complete.
Sample Problem. A titration experiment is carried out between HCl and NaOH. In the experiment, an average volume
of 20.00 mL of 0.150 M NaOH is required to titrate 25.00 mL of HCl solution. Determine the concentration and pH of
the HCl solution. Determine the mass of salt produced in the reaction.
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8-5. Perform stoichiometric calculations involving pH and pOH for a neutralization reaction
8-6. Use data from a titration experiment to perform stoichiometric calculations.
Sample Problem. A titration experiment is carried out between strontium hydroxide and phosphoric acid. Give the
balanced chemical equation for this reaction. The following data is collected:
Volume of H3PO4 = 20.00 mL
Concentration of Sr(OH)2 = 2.00 M
Trial 1 Volume of Sr(OH)2 required = 15.06 mL
Trial 2 Volume of Sr(OH)2 required = 14.98 mL
Trial 3 Volume of Sr(OH)2 required = 14.96 mL
(a) Calculate the average volume of strontium hydroxide required in the titration experiment.
(b) Determine the concentration of the phosphoric acid solution.
(c) Determine the mass of phosphoric acid contained in the solution (mass solute).
(d) From the volume of phosphoric acid used and the density of phosphoric acid (1.06 g/mL), determine the mass of the
phosphoric acid solution (mass solution).
(e) Calculate the percent concentration of phosphoric acid in the solution. 100% mass solute percent concentration x
mass solution
𝑝𝑒𝑟𝑐𝑒𝑛𝑡 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 =
𝑚𝑎𝑠𝑠 𝑠𝑜𝑙𝑢𝑡𝑒
× 100
𝑚𝑎𝑠𝑠 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛
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Worksheet 8-2 (Learning Targets 8.5 and 8.6)
(1) A titration experiment is carried out between sodium hydroxide and hydrochloric acid. Give the balanced chemical
equation for this reaction. The experiment requires 15.00 mL of 0.20 M sodium hydroxide to titrate 10.00 mL of
hydrochloric acid. Determine the concentration and pH of the hydrochloric acid. What mass of salt will be produced in
the reaction?
(2) A solution is prepared by dissolving 1.80 g of oxalic acid in water. The solution is then titrated with 0.400 M sodium
hydroxide. Give the balanced chemical equation for this reaction. What volume of sodium hydroxide is required in the
experiment?
(3) A titration experiment is carried out between sulfuric acid and potassium hydroxide. Give the balanced chemical
equation for this reaction. The following data is collected:
Volume of H2SO4 = 5.00 mL
Concentration of KOH = 0.500 M
Trial 1 Volume of KOH required = 19.96 mL
Trial 2 Volume of KOH required = 20.05 mL
Trial 3 Volume of KOH required = 19.99 mL
(a) Calculate the average volume of potassium hydroxide required in the titration experiment.
(b) Determine the concentration of the sulfuric acid solution.
(c) Determine the mass of sulfuric acid contained in the solution (mass solute).
(d) From the volume of sulfuric acid used and the density of sulfuric acid (1.10 g/mL), determine the mass of the sulfuric
acid solution used (mass solution).
(e) Calculate the percent concentration of sulfuric acid in the solution.
𝑝𝑒𝑟𝑐𝑒𝑛𝑡 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 =
𝑚𝑎𝑠𝑠 𝑠𝑜𝑙𝑢𝑡𝑒
× 100
𝑚𝑎𝑠𝑠 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛
(4) A titration experiment is carried out between nitric acid and barium hydroxide. Give the balanced chemical equation
for this reaction. The following data is collected for a titration experiment:
Concentration of nitric acid = 0.200 M
Initial reading of buret (mL)
Final reading of buret (mL)
Volume of nitric acid used (mL)
Trial 1
0.15
15.75
Trial 2
15.75
31.40
Trial 3
1.20
16.75
Volume of barium hydroxide: 10.00 mL
(a) Determine the volume of nitric acid used in each of the trials. Calculate the average volume of nitric acid required in
the titration experiment.
(b) Determine the concentration of the barium hydroxide solution.
(c) Find the pOH and pH of the barium hydroxide solution.
(d) Calculate the mass of the salt produced in this reaction.
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Worksheet 8-3 (Learning Targets 8.5 and 8.6)
Titration Problems
(1) An unknown acid (HA) is titrated with a solution of sodium hydroxide. The balanced equation for the neutralization
reaction that takes place is given below:
HA + NaOH → NaA + H2O
A sample of the unknown acid is weighed and the mass is recorded. The acid is then dissolved in water to make a
solution. A few drops of phenolphthalein are added to the solution. The solution is titrated using sodium hydroxide and
the volume required for the reaction to be complete is recorded. The data collected for the experiment is shown below.
Concentration of NaOH = 0.100 M
Average Volume of NaOH used = 10.50 mL
Mass of Unknown Acid = 0.185 g
(a) What observation indicated that the reaction was complete?
(b) Determine the moles of sodium hydroxide used in the experiment.
(c) How many moles of the unknown acid are required in the experiment?
(d) From the moles and the mass of unknown acid, determine the molar mass of the unknown acid.
(e) The unknown acid is known to have the following percent composition: 40.91 % carbon, 4.58 % hydrogen, 54.51%
oxygen. Determine the empirical formula for the unknown acid.
(f) From the empirical formula and the molar mass of the unknown acid (the molecular weight), determine the
molecular formula.
(2) The unknown acid is also called “ascorbic acid” and is found in the compound vitamin C. A different titration
experiment is carried out to determine the percent content of ascorbic acid found in a vitamin C tablet. The mass of a
vitamin C tablet (that contains ascorbic acid as well as a variety of other compounds that do not react in the experiment)
is determined and recorded. The tablet is then dissolved in water and a few drops of phenolphthalein are added to the
solution. The solution is titrated using sodium hydroxide and the volume required for the reaction to be complete is
recorded. The data collected for the experiment is shown below.
Concentration of NaOH = 0.100 M
Average Volume of NaOH used = 28.70 mL
Mass of the Vitamin C Tablet = 0.620 g
(a) Determine the moles of sodium hydroxide used in the experiment.
(b) How many moles of ascorbic acid are required in the experiment?
(c) From the moles and the molar mass of ascorbic acid, determine the mass of the ascorbic acid found in the tablet.
(d) From the mass of ascorbic acid and the mass of the vitamin C tablet, determine the percent content of ascorbic acid
in a tablet.
(e) The actual content of ascorbic acid in a vitamin C tablet is 500 mg. Calculate the percent error for the experiment.
Answers (1) 0.00105 mol NaOH/HA, 176 g/mol, C3H4O3, C6H8O6 (2) 0.00287 mol NaOH/ascorbic acid, 0.505 g ascorbic acid, 81.5%, 1.00% error
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Worksheet 8-4 (Review)
(1) Classify each of the following properties as characteristic of an acid (A) or base (B).
(a) dissociates to produce H+ ions
(b) dissociates to produce OH–
ions
(c) tastes sour
(d) tastes bitter
(e) turns pH paper red
(f) turns pH paper blue
(g) feels slippery
(h) reacts with metals to produce
hydrogen gas
(i) turns pink with phenolphthalein
(j) turns yellow with bromothymol
blue
(k) turns cabbage juice blue/green
(l) turns cabbage juice pink
(2) Complete the following table.
[H+]
pH
pOH
[OH–]
acidic or basic?
2.25
0.050 M
(3) Classify the following substances as acidic or basic and determine the [H+ ] and [OH– ].
(a) Milk, pH = 6.40 ________________
[H+] = ________________
[OH–] = ________________
(b) Lye, pOH = 2.64 ________________
[H+] = ________________
[OH–] = ________________
(4) Determine the pH and pOH of the following solutions.
(b) 4.8x10–5 M Ba(OH)2
(a) 0.014 M HCl
pH = ________________
pOH = ________________
pH = ________________
pOH = ________________
(5) A titration is carried out between strontium hydroxide and nitric acid. Give the balanced chemical equation for this
reaction. A 15.00 mL of 0.20 M strontium hydroxide is used to titrate 10.00 mL of nitric acid. Determine the
concentration, pH, and pOH of the nitric acid solution. Calculate the mass of the salt produced in the reaction.
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Worksheet 8-4 (Con’t)
(6) An acid called “benzoic acid” (HA) is titrated with a solution of sodium hydroxide. The balanced equation for the
neutralization reaction can be written as follows: HA + NaOH → NaA + H2O
A sample of benzoic is weighed and the mass is recorded. The acid is then dissolved in water to make a solution. The
solution is titrated using sodium hydroxide and the volume required for the reaction to be complete is recorded. The
data collected for the experiment is shown below.
Concentration of NaOH = 0.500 M
Average Volume of NaOH used = 20.60 mL
Mass of Benzoic Acid = 1.30 g
(a) Determine the moles of sodium hydroxide used in the experiment.
(b) How many moles of benzoic acid are required in the reaction?
(c) From the moles and the mass of benzoic acid, determine the molar mass of benzoic acid.
(d) Benzoic acid has the following composition: 68.84 % carbon, 4.95 % hydrogen, 26.20% oxygen. Determine the
formula for benzoic acid.
(e) From the formula, calculate the actual molar mass for benzoic acid. Calculate the percent error for the experiment.
Answers: (1) (a) A (b) B (c) A (d) B (e) A (f) B (g) B (h) A (i) B (j) A (k) B (l) A
(2) [H+ ] pH pOH [OH– ] acidic or basic 1.8x10–12 M 11.75 2.25 5.6x10–3 M basic 0.050 M 1.30 12.70 2.0x10–13 M acidic
(3) (a) acidic, [H+ ] = 4.0x10–7 M, and [OH– ] = 2.5x10–8 M (b) basic, [H+ ] = 4.4x10–12 M, and [OH– ] = 2.3x10–3 M
(4) (a) pH = 1.85 and pOH = 12.15 (b) pH = 9.98 and pOH = 4.02
(5) Sr(OH)2 + 2HNO3 → Sr(NO3)2 + 2HOH [HNO3] = 0.60 M, pH = 0.22, pOH = 13.78, 0.63 g Sr(NO3)2
(6) (a) 0.0103 mol NaOH (b) 0.0103 mol benzoic acid (c) 126 g/mol (d) C7H6O2 (e) actual molar mass = 122.118 g/mol,
3.18%
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