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FORMAL LAB: IDENTIFY THE SOLUTION: ACID, BASE OR WATER (100 PTS)
Introduction:
Acids and bases are useful reagents in the chemistry lab and play an important role in
biology and nature. Can you use your knowledge of the properties of acids and bases to
indentify the 5 unknown solutions?
Background:
Acids and bases make up two groups of substances that can be categorized by their
physical and chemical properties. Let's take a look at the distinguishing properties:
1. Taste: Acids, such as lemons or oranges, taste sour. Bases, such as soap, taste bitter.
Note: Taste should never be used to identify a lab chemical or unknown substance.
2. Feel: Acid solutions do not feel much different than water; however, they sting if they
contact broken skin. Base solutions have a slippery feeling. Note: Lab chemicals or
unknown substances should never be touched with the bare skin.
3. Indicators: An indicator is a chemical compound, either on a test paper or in a solution,
that changes color depending on the acidity or basicity (concentration of H+ ions) of a
solution and, thus, is used to test for the presence of acids or bases. There are many
different kinds of indicators.
 Blue litmus paper turns red when dipped in an acid solution of pH 1-6.
 Red litmus paper turns blue when dipped in a basic solution of pH 8-14.
 In a neutral solution with pH 7, each paper retains its original color.
 Approximate pH can be estimated using universal pH paper or universal indicator.
The container includes a color chart.
 Phenolphthalein indicator solution remains colorless in an acid solution, but has a
distinct pink color in a basic solution.
4. Reaction with metals and carbonates: While most bases show no reaction with metals,
acids react with active metals to release hydrogen gas. For example
Fe + 2HCI  H2+ FeCl2
Similarly, most bases show no reaction with carbonates, while acids react with carbonates
to release carbon dioxide gas. This is also a neutralization reaction. For example:
BaCO3+ 2HCl  BaCl2+ CO2+ H2O5.
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5. Electrical conductivity: Strong acids and strong bases split fully into their positive and
negative ions and therefore both conduct an electrical current quite well. Weak acids
and weak bases remain, for the most part, together and in molecular form (with fewer
ions in solution) and thus do not conduct an electrical current well.
Problem: Can you use your knowledge of acids and bases and identify the five unknown
solutions as:
 Hydrochloric Acid (HCl) – a strong acid
 Acetic Acid (CH3COOH) – a weak acid
 Distilled water
 Ammonium hydroxide (NH4OH ) weak base
 Sodium hydroxide (NaOH) – a strong base
Material available to you:
Unknown A
Unknown B
Unknown E
Microwell plate
Blue litmus paper
pH paper
Sodium Bicarbonate Forceps
(baking soda)
Distilled water
Paper towels
Unknown C
Micropipettes
Universal Indicator
Magnesium ribbon
Unknown D
Red litmus paper
Phenolphthalein
White paper
Conductivity testers
pH meters
Conserve resources: Please conserve your resources, for each test you should only need
to fill each well about ½ way for each test. Also, please rip papers in half for testing. Be
sure to use care and avoid cross contamination!
Safety Precautions:
All of the acids and bases used in this lab are very corrosive to eyes, skin, and other body
tissues. They are toxic by ingestion. Avoid all body tissue contact. Acetic acid, hydrochloric
acid, and ammonium hydroxide are also toxic by inhalation. Avoid breathing the vapors.
Wear chemical splash goggles and wash hands thoroughly with soap and water before
leaving the laboratory
Clean up/ Disposal:
When using test papers, please place them on your white paper. When done, throw the
paper and all litmus paper in the garbage can. Do NOT dispose of the litmus paper in the
sink! Use the forceps to remove the magnesium ribbon and place it into the trash. The rest
of the microwell plate may be rinsed under the water and left in the sink.
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For this lab, you must develop your own procedure and data table(s) to determine the
identity of the unknowns. Tests to be performed:
You should include in your planning a procedure flow chart and have it checked by the
teacher before you begin.
Row 1: Conductivity test, Red and Blue Litmus paper test, then Phenolphthalein test
Row 2: pH paper, pH meter, then liquid Universal Indicator test
Row 3: Neutralization test with sodium bicarbonate (retest with pH paper)
Row 4: Reaction test with magnesium metal
Data and Observation Table:
Test Property
Unknown
A
R Conductivity Test
o
w
Red Litmus Test
1
Unknown
B
Unknown
C
Unknown
D
Unknown
E
Blue Litmus Test
Phenolphthalein
test
R pH paper test
o (include pH value)
w
pH meter
(include pH value)
2
Universal
Indicator
(include color)
R Sodium
o Bicarbonate
w neutralization
test (observations
3 plus retest with pH
paper)
4 Magnesium
reaction test
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Discussion & Conclusions:
Answer the following questions:
1. How can litmus paper and phenolphthalein be used to tell whether a solution is an
acid or base?
2. What would be some benefits of using pH paper or universal indicator rather than
phenolphthalein?
3. What signs of change were observed when metals and carbonates were placed in
acids? In bases?
4. Which solutions reacted with magnesium? Write the balanced chemical equation for
one of the reactions. Classify this type of reaction.
5. What were the bubbles in the solution when the metals reacted? How do you think
we could test to see what kind of gas was being produced in that reaction?
6. Make a table that summarizes the general properties of acids and bases.
You will now put your investigations to the test and see if you can identify the unknowns. In
your conclusion, be sure to:
 Identify each unknown and explain what test or procedure you did to reveal its
identity.
 Include any problems you had during the lab or any thing you would do differently if
you were to do the lab again.
UNKNOWN ACIDS AND BASES LAB
GRADING RUBRIC
10
Pre-lab flowchart
2
1. Cover page
3
2. Purpose
3
3. Hypothesis
5
4. Materials List
2
5. Safety
25
6. Procedure
20
7. Data and observation tables
0
8. Calculations & Results (if applicable)
30
9. Discussion & Conclusions
/ 100
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