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This is the complete lecture note for CHM 207 General Chemistry Practical III. You can read it online below, open it in the full viewer, or download the PDF for offline study. It pairs with the course's video lectures, so you can read and watch together.
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Course code: CHM 207 Course title: General Chemistry Practical III Course unit: 1 Unit Series 1: Measurement of pH Part 1 Fundamentals of pH 1.1.1 Definition of pH 1.1.2 Importance of pH in chemistry and everyday applications 1.1.3 pH scale and interpretation Part 2 Methods of measuring pH 1.2.1 Indicators and colour change methods 1.2.2 pH meters: principle and operation 1.2.3 Good laboratory practice in pH measurement Part 3 Applications and calculations involving pH 1.3.1 pH in acid–base chemistry 1.3.2 pH in environmental and biological systems 1.3.3 Simple calculations involving hydrogen ion concentration and pH Introduction In everyday life, the acidity or alkalinity of substances plays a crucial role, from the food we eat to the medicines we take and the water we drink. Chemists use the concept of pH to express this property in a precise and measurable way. Learning how to measure pH is therefore fundamental in chemistry, as it provides insight into chemical reactions, environmental conditions, and biological processes. This Series will help you appreciate the importance of pH measurement and prepare you to carry it out accurately in the laboratory. The aim of this Series is to introduce you to the concept of pH, equip you with practical methods for measuring it, and enable you to apply pH values in chemical calculations and real-world contexts. We shall commence this Series by exploring the fundamentals of pH, including its definition, importance, and the pH scale. Next, we will move on to methods of measuring pH, ranging from simple indicators to the use of pH meters, together with good laboratory practices. Finally, we will wrap up by considering applications and calculations involving pH in acid–base chemistry, environmental systems, and biological contexts. In conclusion, this Series will provide you with both theoretical understanding and practical competence in measuring and applying pH.
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Series Learning Outcomes Upon completing this Series, you should be able to: define pH and explain its significance in chemistry, describe the pH scale and interpret values in terms of acidity and alkalinity, demonstrate how to measure pH using indicators, operate a pH meter and explain its principle of measurement, apply good laboratory practices when measuring pH, calculate pH from hydrogen ion concentration, analyse the role of pH in acid–base chemistry, evaluate the importance of pH in environmental and biological systems. 1.1 Fundamentals Of pH 1.1.1 Definition of pH pH is defined as the negative logarithm of the hydrogen ion concentration in a solution. It provides a numerical scale to express the acidity or alkalinity of a substance. A solution with a high concentration of hydrogen ions has a low pH, indicating acidity, while a solution with a low concentration of hydrogen ions has a high pH, indicating alkalinity. Fill in the blank: A solution with a high concentration of hydrogen ions has a __________ pH. 1.1.2 Importance of pH in chemistry and everyday applications pH is important because it influences chemical reactions, biological processes, and environmental conditions. In chemistry, pH determines the rate and extent of acid–base reactions. In biology, enzymes function optimally within specific pH ranges. In everyday life, pH affects food preservation, water quality, and even skin care products. Fill in the blank: Enzymes function optimally within specific __________ ranges. 1.1.3 pH scale and interpretation The pH scale ranges from 0 to 14, with 7 representing neutrality. Values below 7 indicate acidity, while values above 7 indicate alkalinity. Strong acids typically have pH values close to 0, and strong bases have values close to 14. The scale is logarithmic, meaning each unit change represents a tenfold difference in hydrogen ion concentration.
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Fill in the blank: The pH scale is __________, meaning each unit change represents a tenfold difference in hydrogen ion concentration. pH range Classification Example substance Notes 0 – 6 Acidic Lemon juice Contains citric acid, giving it a sharp sour taste 7 Neutral Pure water Neither acidic nor alkaline, serves as the reference point 8 – 14 Alkaline Soap Contains alkaline compounds, useful for cleaning and removing grease Table 1.1 pH ranges with examples Figure 1.1 – The pH Scale Pilot questions 1.1 Define pH. What does a low pH value indicate? State one importance of pH in biology. What is the range of the pH scale? What does each unit change on the pH scale represent?
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS 1.2 Methods Of Measuring pH 1.2.1 Indicators and colour change methods Indicators are substances that change colour depending on the pH of the solution they are placed in. They provide a simple and inexpensive way of estimating pH. Common examples include litmus, phenolphthalein, and methyl orange. Each indicator has a specific pH transition range, which is the range of pH values over which it changes colour. Fill in the blank: Litmus is an indicator that turns red in acidic solutions and __________ in alkaline solutions. Figure 1.2 Colour changes of indicators at different pH values 1.2.2 pH meters: principle and operation A pH meter is an electronic device that measures pH more accurately than indicators. It works by detecting the voltage difference between a glass electrode, sensitive to hydrogen ions, and a reference electrode. This voltage is converted into a pH reading displayed on the meter. Proper calibration with standard buffer solutions is essential before use to ensure accuracy. Fill in the blank: A pH meter must be calibrated using standard __________ solutions before measurement.
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Plate 1.1 Digital pH meter in use 1.2.3 Good laboratory practice in pH measurement Accurate pH measurement requires careful attention to laboratory practice. Electrodes should be rinsed with distilled water between measurements to avoid contamination. Buffers should be fresh and properly prepared. Instruments must be calibrated regularly, and readings should be taken promptly to avoid drift. By following these practices, reliable and reproducible results can be obtained. Fill in the blank: Electrodes should be rinsed with __________ water between measurements to avoid contamination. Pilot questions 1.2 What is an indicator in pH measurement? State the colour change of litmus in acidic and alkaline solutions. What principle does a pH meter operate on? Why is calibration necessary before using a pH meter? Mention one good laboratory practice in pH measurement.
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS 1.3 Applications And Calculations Involving pH 1.3.1 pH in acid–base chemistry In acid–base chemistry, pH plays a central role in determining the strength of acids and bases, as well as the direction of chemical reactions. Strong acids such as hydrochloric acid have very low pH values, while strong bases such as sodium hydroxide have very high pH values. The neutralisation of an acid by a base results in a solution with a pH closer to 7. Fill in the blank: Neutralisation of an acid by a base results in a solution with a pH closer to __________. 1.3.2 pH in environmental and biological systems pH is critical in both environmental and biological contexts. In environmental science, pH determines water quality, influencing the survival of aquatic organisms. Acid rain, for example, lowers the pH of lakes and rivers, harming fish and plants. In biological systems, pH affects enzyme activity and metabolic processes. Human blood, for instance, must maintain a pH around 7.4 for proper physiological function. Fill in the blank: Human blood must maintain a pH around __________ for proper physiological function. 1.3.3 Simple calculations involving hydrogen ion concentration and pH pH of a Solution The pH of a solution can be calculated using the formula: pH = −log₁₀[H⁺] Where: • [H⁺] is the hydrogen ion concentration in moles per litre. Example: If the hydrogen ion concentration is 1 × 10⁻³ mol/L, then: pH = −log₁₀(1 × 10⁻³) = 3 This logarithmic relationship means that small changes in hydrogen ion concentration lead to significant changes in pH. Fill in the blank: A solution with [H⁺] = 1 × 10⁻³ mol/L has a pH of __________. Table 1.3 Hydrogen ion concentrations and pH values
LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Hydrogen ion concentration [H⁺] (mol/L) pH value Classification Example substance 1 × 10⁻¹ 1 Strongly acidic Gastric acid 1 × 10⁻³ 3 Moderately acidic Vinegar 1 × 10⁻⁷ 7 Neutral Pure water 1 × 10⁻¹² 12 Strongly alkaline Household ammonia Pilot questions 1.3 What does pH indicate in acid–base chemistry? What is the pH of a neutral solution? State one environmental application of pH. What is the approximate pH of human blood? Write the formula used to calculate pH from hydrogen ion concentration. Series Summary This Series has guided you through the concept and measurement of pH, a fundamental aspect of chemistry with wide-ranging
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