007 Acids: Reactions with Common Substances

Expt 007 -- Acids: Reactions with Common Substances

Description

Common substances react with solutions of acids.

Safety

Although the amounts used are very small, the acids are used in concentrations that can be very dangerous. All of the acids are corrosive. Nitric acid causes yellow stains on skin. Wear goggles and apron. Wash spills immediately using large amounts of water. Wash hands after the experiment. Be certain to perform the experiments involving nitric acid under the hood. NO₂ can be produced; this gas is toxic and noxious. If a hood is not available, OMIT the nitric acid tests.
Use care not to splash the acids.

Procedure

Use a 96-well plate or a 24-well plate.
Arrange the experiment as 4 rows of six columns. The acids will vary by row; the other reactants will be the same down the columns.
Note differences and similarities of the reaction of each substance with different acids. Also differences and similarities in how one one acid reacts with different metals.
Place the following in each well of the designated column.
- column 1 small piece of marble chip (CaCO₃)
- column 2 small piece of zinc
- column 3 small piece of copper
- column 4 small piece of wire paper clip (Fe)
- column 5 small piece of aluminum
- column 6 2 drops of egg white mixture (protein)
Work with column 1, marble, first. Add different acids to each piece of marble.
Add 3 drops of 6 M HCl to the first well of column 1. Add 3 drops of 6 M H₂SO₄ to the third well. Add 3 drops of 0.6 M H₂SO₄ to the fourth well. Note and record any evidence for reaction. Note similarities and differences.
Work under the hood. Omit this step if no hood is available. Add 3 drops of 6 M HNO₃ to the second well of column. Note and record any evidence for reaction.

!!!Click here to See Movie.
Repeat the addition of acids to each column. Make careful observations. Note rates relative to other columns (Compare Zn to Cu etc.).
- column 2 small piece of zinc
- Acids are in order: 6 M HCl,6 M HNO₃,6 M H₂SO₄,0.6 M H₂SO₄.
  
  !!!Click here to See Movie.
  !!!Click here to See Movie.
- column 3 small piece of copper
- Acids are in order: 6 M HCl,6 M HNO₃,6 M H₂SO₄,0.6 M H₂SO₄.
  
  !!!Click here to See Movie.
- column 4 small piece of wire paper clip (Fe)
- Acids are in order: 6 M HCl,6 M HNO₃,6 M H₂SO₄,0.6 M H₂SO₄.
  
  !!!Click here to See Movie.
- column 5 small piece of aluminum
- Acids are in order: 6 M HCl,6 M HNO₃,6 M H₂SO₄,0.6 M H₂SO₄.
  
  !!!Click here to See Picture.
  !!!Click here to See Movie.
- column 6 5 drops of egg white mixture (protein)
- Acids are in order: 6 M HCl,6 M HNO₃,6 M H₂SO₄,0.6 M H₂SO₄.
  
  !!!Click here to See Movie.
If hood space is limited, do all reactions with HNO₃ at once in the hood. Work on the other reactions at your desk around time you are assigned to the hood.
Wait until reaction ceases. Record colors of the final solutions and the amounts of solid remaining.

!!!Click here to See Picture.
Summarize your results.

!!!Click here to See Movie. Click |> to step through the slides.
Discard the contents of the plate into a large 1 L disposal jar or bucket half-filled with water.
Rinse the plate at the sink. Wash hands.

Questions

Identify the three gases that are produced in the experiment.
Several of the reactions produce the same product, hydrogen. Explain.
When nitric acid reacts with copper, there are two potential oxidizing agents in the solution, H⁺ and NO₃^-. Write balanced equations for each reaction. Cite evidence to decide which reaction occurs.
Why is aluminum resistant to HNO₃? The other substances tested all react most vigorously with nitric acid.
Acid rain contains dilute nitric and sulfuric acid. Rank the resistance of the following to acid rain. Most resistant rank as one.
- Marble
- Zn
- Cu
- Fe
- Al

Handout

Handout Makeup

Name ___________________________ Class _______

Teacher __________________________

SmallScale 007 Acids: Reactions with Common Substances

Watch the movies and carefully record your observations.

Marble
HCl
HNO₃
H₂SO₄
H₂SO₄(dil)
Zn
HCl
HNO₃
H₂SO₄
H₂SO₄(dil)
Cu
HCl
HNO₃
H₂SO₄
H₂SO₄(dil)
Fe
HCl
HNO₃
H₂SO₄
H₂SO₄(dil)
Al
HCl
HNO₃
H₂SO₄
H₂SO₄(dil)
egg
HCl
HNO₃
H₂SO₄
H₂SO₄(dil)

Curriculum-

The is an excellent experiment to introduce the topic of acids and bases. This is not the same as Experiment 005, Classifying Strong Acids and Bases By Reactions. That experiment is intended to show that strong acids produce H⁺ in water, and strong bases produce OH^-. In this experiment, a series of reactions, which display distinct differences between the strong acids, are observed.

Safety-

Although the amounts used are very small, the acids are used in concentrations that can be very dangerous. All of the acids are corrosive. Nitric acid causes yellow stains on skin. Wear goggles and apron. Wash spills immediately using large amounts of water. Wash hands after the experiment. Be certain to perform the experiments involving nitric acid under the hood. NO₂ can be produced; this gas is toxic and noxious.
Use care not to splash the acids.

Time-

Teacher Preparation: 20 minutes

Class Time: 40 minutes

Materials-

0.2 g copper -- (Use snips to cut small pieces from wire or foil.)
0.2 g zinc -- (Use small pieces from mossy zinc, or cut pieces from foil strips.)
1.5 mL 6 M HCl -- (Wear apron, goggles, and rubber gloves. Work under a hood. Add 50 mL of concentrated HCl to enough water to make 100 mL of solution.)
1.5 mL 6 M HNO₃ -- (Wear apron, goggles, and rubber gloves. Work under a hood. Add 38 mL of concentrated HNO₃ to enough water to make 100 mL of solution.)
1.5 mL 6 M H₂SO₄ -- (Wear apron, goggles, and rubber gloves. Work under a hood. Add 33 mL of concentrated H₂SO₄ to 50 mL cold distilled water. Stir. Allow to cool. Add enough distilled water to make 100 mL of solution.)
1.5 mL 0.6 M H₂SO₄ -- (Add 10.0 mL 6 M sulfuric acid (H₂SO₄) to enough water to make 100 mL solution.)
0.2 g marble chips -- (Cover with canvas on a durable hard surface and smash with a hammer to get small pieces.)
0.2 g aluminum -- (Use household foil or pieces from a beverage can cut to size with a snips.)
0.2 g paper clip -- (Use steel paper clip cut into small pieces with a snips or cutting pliers.)
egg white -- (Separate the yolk from the white. Beat the white as if to make a meringue. Allow to settle. Use liquid. 1 large egg white (about 30 mL) is enough for 15 groups of students.)
24-well or 96-well plate
4 plastic transfer pipets filled with the acid solutions.

Disposal-

Decant the liquid from the solids. Discard the solids with ordinary solid trash. Under the hood, wearing goggles and apron, add sodium bicarbonate in 5 g portions to neutralize the liquid. Discard the neutralized liquid at the sink.

Lab Hints-

If no hoods are available omit the HNO₃ experiments.
The video shown here does NOT reflect the exact recommended procedure. Since changing acids requires more time to record, the solids and the egg white were added to a plate containing the acids. Students may splash the acid when adding solid objects; consequently, students are instructed to add the acids to the metal or solid.

Answers-

Q1. Identify the three gases that are produced in the experiment. A1. Carbon dioxide, hydrogen, and nitrogen dioxide. (Nitric oxide may be the first product of the reaction, but it reacts immediately with oxygen in air to form NO₂.)
Q2. Several of the reactions produce the same product, hydrogen. Explain. A2. Each acid solution contains H±, so this is always available as an oxidizing agent in these solutions. The product when H⁺ reacts as the oxidizing agent is hydrogen.
Q3. When nitric acid is reacted with copper, there are two potential oxidizing agents in the solution, H⁺ and NO₃^-. Write balanced equations for each reaction. Cite evidence to decide which reaction occurs. A3. 2 H⁺ + Cu --> H₂ + Cu²⁺ 8 HNO₃ + 3 Cu --> 2 NO + 3 Cu(NO₃)₂ + 4 H₂O; 2 NO + O₂ --> 2 NO₂ Since a brown gas (NO₂) is produced, the second reaction takes place.
Q4. Why is aluminum resistant to HNO₃? The other substances tested all react most vigorously with nitric acid. A4. Nitric acid is an oxidizing agent as well as an acid. Al reacts with air to form an oxides which are network solids crosslinked with many -O-Al-O- bonds. Oxidizing acids make this oxide coating more complete and consequently more resistant to acid.
Q5. Acid rain contains dilute nitric and sulfuric acid. Rank the resistance of the following to acid rain. Most resistant rank as one. A5. Marble 3 Zn 5 Cu 2 Fe 4 Al 1 (Marble may be fit in above Cu. It is not a clear choice from these experiments.)

Handout Ans.-

Marble
- HCl Bubbles gently
- HNO₃ Bubbles gently
- H₂SO₄ Bubbles gently
- H₂SO₄(dil) Bubbles more slowly.
Zn
- HCl Bubbles rapidly.
- HNO₃ Red brown gas is produced rapidly and vigorously.
- H₂SO₄ Bubbles rapidly, but more slowly than HCl or HNO₃.
- H₂SO₄(dil) Bubbles slowly.
Cu
- HCl Bubbles gently - much slower than Zn.
- HNO₃ Red brown gas produced. Reaction is much slower than Zn, but much faster than Cu reactions with other acids. Blue solution forms.
- H₂SO₄ Bubbles gently much slower than Zn; reaction is slower then HNO₃.
- H₂SO₄(dil) Little reaction observed.
Fe
- HCl Bubbles slowly to form yellow solution.
- HNO₃ Reacts rapidly with the release of red brown gas. Orange solution forms.
- H₂SO₄ Reacts slowly.
- H₂SO₄(dil) A few bubbles noted in final slide.
Al
- HCl Reaction is slow initially, but once the reaction starts the entire sample reacts quickly.
- HNO₃ No reaction is observed.
- H₂SO₄ A few bubbles noted after 2 minutes.
- H₂SO₄(dil) No reaction is observed.
egg
- HCl White precipitate forms as soon as the egg enters the acid.
- HNO₃ White precipitate forms as soon as the egg enters the acid.
- H₂SO₄ White precipitate forms as soon as the egg enters the acid.
- H₂SO₄(dil) White precipitate forms slowly.

Reference-

This approach was suggested by Robert Silberman of Cortland, NY.

Key Words 1-

acid, base, precipitate, oxidation, reduction, redox, acid rain

Elements-

H O Cl S N Zn Cu Al Fe Ca C