Qualitative Properties of Acids and Bases
Pre-Lab
1. What is the qualitative data? Give an example.
2. Write three things that you know about acids and bases.
a.
b.
c.
3. Name each of the following
KOH
H2SO4
HF
Purpose: The purpose of this lab is to determine what physical properties make acids and
bases different. To do this, you will feel, taste and observe seven common household acids
and bases. You will also use two indicators (litmus paper, red cabbage juice). Indicators
change color in the presence of acids and bases.
Materials:
Vinegar, lemon juice, orange juice, water
Yoghurt, baking soda, toothpaste – dissolve each in water
Red cabbage juice, red and blue litmus paper
Paper cups, pipette
Safety
You will taste different substances in this lab. This is an exception to never tasting things
in the chemistry laboratory. Only use appropriate cups, utensils when tasting each
substance.
Part 1: Qualitative Analysis
1. Taste each substance. Record results
2. Feel each substance. Record results.
3. Smell each substance. Record results.
4. Add 5ml of each substance to a test tube. Add 10 drops of red cabbage juice. Record
results.
5. Dip a small piece of red and blue litmus paper in each substance. Record results.
Taste
Feel
Smell
Red Cabbage
Juice
Vinegar
Baking Soda
Lemon Juice
Toothpaste
Orange Juice
Yoghurt
Orange Juice
Water
Post-Lab Questions
1. Which substances are similar to each other?
2. What are the common characteristics among the similar groups?
3. Are there any substances that don't fit into either group? Explain
Red Litmus
Blue Litmus
Quantitative Properties of Acids and Bases
Pre-Lab
1.What is quantitative data? Give an example
2. The pH of an unknown solution is 7.35. What is the hydrogen ion concentration of the
solution? Show all of your work
3. What is the hydroxide ion concentration of the unknown solution in question 2? Show
all of your work.
Purpose: The purpose of this lab is to determine the pH, of different household acids and
bases using pH paper and a pH probe. From this information you will calculate the
hydrogen ion concentration and hydroxide ion concentration of each household acids and
bases.
Materials
Detergent dissolved in water, ammonia, orange juice milk, pure water, vinegar, pH paper,
pH probe
Part 2: Quantitative Analysis
1. Test each substance using the pH paper. Record the color and estimated pH
2. Use the pH verneir probe to test the pH of each substance. Record in the data table.
Rinse the probe with distilled water and dry between substances.
3. Use the pH from the pH probe to calculate the hydrogen ion and hydroxide ion
concentration present in each substance.
pH paper
color
pH paper
value
Probe pH
H+
concentration
OHconcentration
Acid or
Base?
Detergent
Ammonia
Orange Juice
Milk
Pure Water
Vinegar
Post-Lab
1. Explain the difference between the pH paper value and the pH probe value.
2. In terms of hydrogen ion concentration and hydroxide ion concentration, what patterns do you see
with acids?
3. In terms of hydrogen ion concentration and hydroxide ion concentration, what patterns do you see
with bases?
Titration with and Acid and a Base
Pre-Lab
1. Balance the reaction: _____NaOH+_____H2SO4_____Na2SO4+_____H2O
2. If it takes 54mL of 0.05 M NaOH to neutralize 55mL of an H2SO4 solution, what is the
concentration of the H2SO4?
Purpose
Titration is a process in which you determine the concentration of a solution. The process
consists of the gradual addition of a known concentration to a measured quantity of the
unknown concentration until there is an equal numbers of moles of acid and base. This is
known as the equivalence point. An indicator is used to signal when the equivalence point
is reached. Phenolphthalein will be used as the indicator in this lab. In acidic solution,
Phenolphthalein is colorless, and in basic solution, it is pink.
Objectives
Use burets to accurately measure volumes of solution.
Recognize the end point of a titration.
Describe the procedure for performing an acid-base titration.
Determine the molarity of a base.
Materials
• H2SO4-unknown concentration
• 50 mL burets, 2
• 100 mL beakers, 3
• 125 mL Erlenmeyer flask
• double buret clamp
• 0.1 M NaOH
• phenolphthalein indicator
• ring stand
• wash bottle filled with deionized water
Safety
Always wear safety goggles, gloves, and a lab apron to protect your eyes and clothing.
Do not touch any chemicals.
Call your teacher in the event of a spill.
Never put broken glass into a regular waste container.
Procedure
1. Set up the apparatus as shown
2. Label the burette NaOH and the flask H2SO4
3. Rinse the burette with 20ml of NaOH and
allow it to run through the stopcock.
4. Repeat two more times with new NaOH.
5. Fill the burette with NaOH. Allow some
solution to run through the burette to remove
any air bubbles.
6. Record the initial reading of the burette.
7. Add 10ml of H2SO4 to the Erlenmeyer flask.
8. Add 2-3 drops of phenolphthalein to the
Erlenmeyer flask.
9. Place the flask under the buret. Slowly add
NaOH until the color in the flask begins to turn
pink.
10. Add a drop at a time until a light pink color
persists for more than 30 seconds.
11. Record the final NaOH reading.
12. Repeat steps 6-12 until the difference in
volume is no more than 1mL.
13. Calculate the unknown concentration of H2SO4.
Stopcock
Data Sheet
Concentration of sodium hydroxide: ____________________________M
Trial 1
Initial Volume NaOH
(mL)
Final Volume NaOH
(mL)
Volume NaOH Used
(mL)
H2SO4 concentration
(M)
Show your H2SO4 concentration calculations here:
Trial 2
Trial 3
Post Lab
1. What was the average concentration of H2SO4?
2. What may have caused error between your trials?
3. Sketch the graph in the teacher demo.
4. Identify the equivalence point on your graph
5. What is the pH of the equivalence point?
How Much Citric Acid is in Drinks?
Pre-Lab
1.Balance ____C6H8O7+____NaOH ____Na3C6H5O7+ ____H2O
2. If it takes 5 mL of 0.1 M NaOH to neutralize 10 mL of citric acid, what is the
concentration of the citric acid? (USE YOUR BALANCED EQUATION)
3. Make a prediction ranking the drink with the most citric acid to the least citric acid.
Background: Titration isn’t just an experiment you need to perform to pass chemistry in
school. It has many important applications in everyday life. For example, food-processing
companies can use titrations to calculate the amount of salt and vitamins in food.
Titrations are also used in water treatment processes, monitoring blood glucose levels,
analyzing urine samples and deciding if wine and cheese are ready for consumption.
The acid content of many foods and beverages contributes significantly to their taste. Soft
drinks often contain varying quantities of several acids, which give sodas their tart flavor.
In cola products, these acids are predominantly carbonic acid (from the carbonated water)
and phosphoric acid. In sodas such as Squirt and 7-Up, the acids are carbonic acid and
citric acid.
In this experiment you will be performing a titration to determine the concentration of
citric acid in a drink. Prior to the titration, the majority of the carbonic acid was removed
by allowing the soft drink to go flat so we do not have to take it into consideration.
Purpose: To use titrations to determine how much citric acid is in drinks.
Materials: Sierra Mist, Mountain Dew, Lemon Lime Gatorade, Lemonade, Squirt, lemon
juice 0.1M NaOH, phenolphthalein, burette, Erlenmeyer flask
Procedure:
1. Read through the procedure; make an appropriate data table(s). Each group will test
two different beverages, and get results for other beverages from other groups.
2. Pipette 10 mL of the soft drink into a clean 250 mL Erlenmeyer and add 2 to 3 drops of
phenolphthalein.
3. Rinse and fill your buret with the standardized NaOH.
4. Carry out titration (The citric acid content in many soft drinks is quite low, so good
technique is critical.)
5. Calculate the molarity of the citric acid in the soft drink. Show all of your work
6. Repeat this procedure two more times and calculate the average molarity.
Post-Lab
1. Rank the beverages from most acidic to least acidic.
2. Why is it necessary to use flat soda?
Data Tables
Calculations
Acid Dissociation Constant (Ka)
Background
The ionization constant of a weak acid can be calculated using the equation:
[𝐻+ ][𝐴− ]
𝐾𝑎 =
[𝐻𝐴]
This can be rewritten as:
𝐾𝑎 = [𝐻+ ]
[𝐴− ]
[𝐻𝐴]
= 10-pH
[𝐴− ]
[𝐻𝐴]
If you know the pH and the ratio of HA and A, you can calculate the Ka without using an ICE
table
Example
Suppose it was found that 24.00mL of NaOH was required to reach the endpoint. Now, let’s
say we take an identical acid sample but only add 6.00 mL of NaOH and measure a pH of 4.51.
6 mL will be neutralized leaving 18 ml unreacted.
HA = H + A(24ml-6ml)=18
𝐾𝑎 = [𝐻+ ]
[𝐴− ]
[𝐻𝐴]
6ml
= 10-4.51
[6]
= 1.03*10-5
[18]
Pre-Lab
20mL of a weak acid was titrated with 0.1M NaOH solution and it was found that 10mL of
NaOH was required to reach the endpoint. In a separate experiment, 2mL of 0.1 M NaOH was
added to a second 20mL aliquot of the same weak acid solution. Using a pH electrode, the pH
is found to be 5.18. Calculate the Ka.
Purpose: The purpose of this lab is to take pH measurements of different concentrations and
to experimentally determine the dissociation constant (Ka) and the unknown acid.
Materials
pH probe
0.1 NaOH
unknown acid
pipettes
10mL beaker
Safety
Unknown acids are used during this lab. If the acid gets on your skin or eyes, flush with water
for at least 15 minutes. Immediately alert the teacher.
Procedure
1. Perform a titration to determine how much NaOH is needed to neutralize 5mL of the
unknown acid. Record the data in table 1
2. Repeat the titration two more times
3. Average the amount of NaOH needed for the neutralization
4. Calculate ¼. ½ and ¾ of the neutralization amount. Record in Table 2 for NaOH required
5. Calculate the acid required, ratio, pH and Ka. Show all calculation on calculation sheet.
Table 1
Trial 1
Trial 2
Trial 3
Initial Buret Reading
Final Buret Reading
Volume of NaOH
Average NaOH needed:_____________________________________________
Table 2
NaOH required Unknown Acid
required
𝐻𝐴
𝐴
pH
Ka
1/4
1/2
3/4
Average Ka:________________________Acid Identity_______________________________