Acids, bases, and salts are fundamental categories of chemical compounds, each characterized by unique properties and behaviors. Acids are substances that increase the concentration of hydrogen ions (H⁺) in solution, typically with a pH below 7. Bases reduce hydrogen ion concentration, often increasing hydroxide ions (OH⁻), and generally have a pH above 7. Salts, on the other hand, are neutral ionic compounds that form as products of acid-base reactions and have a pH close to 7.
This laboratory activity aims to examine the properties of acids, bases, and salts through tests such as electrical conductivity, reactions with magnesium, and pH measurements. In addition, students will explore the relationship between the concentration of an acid and its pH, observing how changes in concentration affect acidity. By performing these experiments, students will develop a deeper understanding of chemical properties, bonding, and the importance of acids, bases, and salts in various applications.
Educational Goals
- Understanding Properties of Acids, Bases, and Salts: Students will differentiate between acids, bases, and salts based on their chemical and physical properties, including pH, conductivity, and reactivity with magnesium.
- Exploring pH and Concentration Relationships: Students will study the exponential relationship between pH and the concentration of hydrogen ions in acidic solutions, gaining insights into chemical equilibrium.
- Hands-On Experimental Skills: This activity will enhance students’ ability to conduct experiments, use pH meters and conductivity detectors, and handle chemical reagents safely and effectively.
- Analyzing Experimental Data: By recording observations and analyzing results, students will develop critical thinking and data interpretation skills.
- Application of Theory to Practice: Students will connect theoretical concepts of acid-base chemistry to practical applications, such as industrial processes and biological systems.
- Promoting Collaboration and Teamwork: Working in small groups, students will collaborate to perform experiments, collect data, and discuss their findings.
- Encouraging Safety Awareness: Students will follow strict safety protocols, including wearing protective equipment and properly handling acids, bases, and magnesium strips.
By the conclusion of this laboratory activity, students will have a comprehensive understanding of acids, bases, and salts, and the skills necessary to apply these concepts in real-world contexts.
Protocol
Part A: The properties of acids, bases, and salts
- Turn on the Electrical Conductivity Detector (ECD).
- Pour 10 ml of the 0.1M NaCl solution into beaker A.
- Clean the ECD electrodes with distilled water and wipe them with absorbent paper. Dip the electrodes into solution A. Observe whether the bulb lights up or not and note the result.
- Dip the electrodes into solution A. Observe whether the bulb lights up or not and record the result in the results table.
- Repeat steps 2 to 4 with the 0.1M HCl and 0.1M NaOH solutions; with beakers B and C.
- Dip a piece of blue litmus paper and a piece of red litmus paper into solution A. Note the colors obtained in the results table.
- Dip a piece of pH paper into solution A and evaluate the pH using the colorimetric scale. Record the pH in the results table.
- Repeat steps 6 and 7 with solutions B and C.
- Place a strip of magnesium in solution A and record the observations in the results table.
- Repeat step 9 with solutions B and C.
Part B: The concentration of an acidic solution and its pH
- Pour 10 ml of 1M HCl solution into the 100 ml graduated cylinder.
- Add distilled water up to the 30 ml mark.
- Pour the contents of the cylinder into the 100 ml beaker identified by the number 1.
- Pour 10 ml of 1M HCl solution into the 100 ml graduated cylinder.
- Add distilled water up to the 60 ml mark.
- Pour the contents of the cylinder into the 100 ml beaker identified by the number 2.
- Pour 10 ml of 1M HCL solution into the 100 ml graduated cylinder.
- Add distilled water up to the 100 ml mark.
- Pour the contents of the cylinder into the 100 ml beaker identified by the number 3.
- Pour 1 ml of 1M HCl solution into the 100 ml graduated cylinder.
- Add distilled water up to the 100 ml mark.
- Pour the contents of the cylinder into the 100 ml beaker identified by the number 4.
- Measure the pH of the 1M HCl solution and that of solutions 1 to 4 using the pH meter (if no pH meter is available; use pH paper). Record the results in the results table.
Anticipated Outcomes
Properties of acids, bases and salts
|
Solution | Electrical conductivity | Colour of litmus paper |
pH | Reaction to magnesium | |
| Red | Blue | ||||
|
A | Yes | Red | Blue | 7 | No reaction |
|
B | Yes | Red | Red | Between 1 and 2 | Effervescence |
|
C | Yes | Blue | Blue | Between 12 and 13 | No reaction |
Relationship between concentration and pH
| Solution | pH | Concentration (calculations) | Effect of the decrease pH concentration |
|
d |
1 |
35.5 g/L (reference solution) | |
| 1 | 1.5 | CdVd= C1V1 = C1=CdVd/V1 C1 = 35g/L*10mL/30mL C1 = 11.7 g/L | The concentration is 3 times lower than that of the initial solution. |
| 2 | 1.7 | CdVd= C2V2 = C2=CdVd/V2 C2 = 35g/L*10mL/60mL C2 = 5.8 g/L | The concentration is 6 times lower than that of the initial solution. |
| 3 | 2 | CdVd= C3V3 = C3=CdVd/V3 C3 = 35g/L*10mL/100mL C3 = 3.5 g/L | The concentration is 10 times lower than that of the initial solution. |
| 4 | 3 | CdVd= C4V4 = C4=CdVd/V4 C4 = 35g/L*1mL/100mL C4 = 0.35 g/L | The concentration is 100 times lower than that of the initial solution. |
- Acids, bases, and salts conduct the electric current.
- Only acids produce a gas when in contact with magnesium.
- When the pH increases by one unit on the pH scale, the concentration of H+ ions is 10 times lower.
-
Classification of Solutions: Students will classify solutions (NaCl, HCl, and NaOH) as acidic, basic, or neutral based on pH, conductivity, and litmus paper tests.
-
Observing Chemical Reactions: The reaction of magnesium with acids will produce effervescence (gas formation), confirming the presence of hydrogen ions, while no reaction will occur with bases or salts.
-
Understanding pH and Concentration: Students will measure the pH of solutions with varying concentrations of HCl and observe that pH increases logarithmically as concentration decreases.
-
Skill Development: Students will improve their proficiency in using pH meters, conductivity detectors, and other laboratory tools.
-
Data Analysis and Interpretation: By analyzing their results, students will learn to draw conclusions about chemical properties and the relationships between pH and concentration.
-
Connecting Theory to Applications: Students will relate their findings to broader concepts in chemistry, including acid-base reactions, buffer systems, and the role of pH in biological and industrial processes.
Summary of Assignment by Grade Range
Grades 6-8
Focus: Introduction to acids, bases, and salts and their properties.
-
Students will conduct simple tests to identify acids, bases, and salts using litmus paper, pH paper, and conductivity.
Expected Outcomes:
-
Basic understanding of chemical classifications.
-
Development of observation and recording skills.
-
Introduction to safety practices in the lab.
Grades 9-10
Focus: Intermediate exploration of pH and concentration relationships.
-
Students will measure pH and conductivity and analyze the effect of dilution on acidic solutions.
Expected Outcomes:
-
Enhanced understanding of acid-base chemistry and exponential relationships.
-
Development of analytical and data interpretation skills.
-
Greater proficiency in handling laboratory tools and reagents.
Grades 11-12
Focus: Advanced analysis and synthesis of chemical properties.
-
Students will conduct comprehensive experiments, calculate hydrogen ion concentrations, and evaluate their results in detailed lab reports.
Expected Outcomes:
-
Mastery of acid-base and salt properties, pH measurement techniques, and data analysis.
-
Ability to critically evaluate experimental results and identify potential sources of error.
-
Production of professional-grade scientific reports demonstrating a clear understanding of acid-base chemistry.
This structured approach ensures that students at all grade levels can engage with the material at an appropriate depth, building a solid foundation for further study in chemistry and related sciences.
Laboratory essentials
Instruments
Electrical conductivity detector (DCE)
pH meter
Tweezers
Paper towel
100mL graduated cylinder
50mL beakers x3
100mL beakers x4
Blue & Red Litmus paper
Universal pH strips
Products
NaCl 0.1M
HCl 0.1M
NaOH 0.1M
HCl 1M
Magnesium ribbons