Lesson
Purpose of the work:
- To study the general chemical properties of acids
Expected results:
After completing the work, students can:
- develop teamwork skills
- be able to analyze and summarize the information received
- draw logical conclusions
Teacher’s Guide:
- The task is performed in groups of 2-3 people
- Before starting laboratory work, please read the safety rules by following the link:
- To download the worksheet, follow the link:
Theoretical part
What is an acid?
Acids are substances capable of donating hydrogen cations (H⁺) in aqueous solutions. These ions give acids their characteristic properties: sour taste, the ability to change the color of indicators, and interact with various substances.
Acids can be classified according to various criteria:
By strength:
- Strong acids: completely dissociate in aqueous solutions, forming a large number of hydrogen ions (e.g., hydrochloric acid HCl, sulfuric acid H₂SO₄).
- Weak acids: do not completely dissociate in aqueous solutions, forming a small amount of hydrogen ions (e.g., acetic acid CH₃COOH, carbonic acid H₂CO₃).
By the presence of oxygen:
- Oxygen-containing acids: the molecule contains oxygen atoms (e.g., sulfuric acid, nitric acid HNO₃).
- Oxygen-free acids: the molecule does not contain oxygen (e.g., hydrochloric acid, hydrogen sulfide H₂S).
By basicity:
- Monobasic acids: the molecule contains one hydrogen atom that can be replaced by a metal (e.g., hydrochloric acid).
- Dibasic acids: the molecule contains two hydrogen atoms that can be replaced by a metal (e.g., sulfuric acid).
- Tribasic acids: the molecule contains three hydrogen atoms that can be replaced by a metal (e.g., phosphoric acid H₃PO₄).
Properties of Acids
- Sour taste: Acids have a sour taste (but it is strictly forbidden to taste them!).
- Color change of indicators: Acids change the color of indicators (e.g., litmus paper).
- Interaction with metals: Many acids react with metals, forming a salt and hydrogen.
- Interaction with bases: Acids neutralize bases, forming salt and water.
- Interaction with salts: Acids can interact with salts, forming a new salt and a new acid.
Applications of Acids
- Acids are widely used in various fields of human activity:
- Industry: production of fertilizers, explosives, dyes, and medicines.
- Food industry: production of beverages, canned food, and fermented milk products.
- Household chemicals: part of detergents and cleaning powders.
Important! Many acids are corrosive and hazardous substances. When working with acids, it is necessary to follow safety precautions.
Practical part
Experiment #1: Interaction with indicators
Step 1: Pour a small amount of each acid into separate test tubes. In the photo below: No. 1 – acetic acid; No. 2 – citric acid; No. 3 – ascorbic acid.
Step 2: Dip a strip of litmus paper into each test tube. Record the color change.
Step 3: Repeat the experiment with the natural indicator anthocyanin. Compare the results and draw conclusions. Lesson 1 – experimentum.kz
Experiment #2: Interaction with metals
Step 4: Now in the same sequence, pour the acids into Petri dishes.
Step 5: Place coins into Petri dishes and add a pinch of salt.
Step 6: Observe the changes after a few hours or a day. Record your observations in the Worksheets. Make conclusions.
Conclusion
During the experiment, students conducted qualitative reactions for acids. Students observed the color change of indicators under the action of acids and the interaction of acids with metals. As a result of the experiment, they were convinced that acids have characteristic chemical properties.