Asidi alkalimetri

Summary

An engaging, clear lecture introduces acid–base titration (acidimetry and alkalimetry), explaining pH, acids and bases, and the roles of primary and secondary standard solutions, titrant, and titrate. It describes laboratory equipment (burette, pipette, stand) and indicators (litmus, phenolphthalein, methyl orange) and how colour changes mark the titration endpoint. The talk covers titration curves for strong/weak acid–base pairs, factors influencing endpoint selection (concentration, Ka/Kb), equivalent weight, and the calculations that translate titrant volume into compound concentration. Practical examples and step-by-step procedure prepare students for hands-on lab titrations.

Takeaways

• 😀 pH is a measure of the acidity or alkalinity of a substance, ranging from 0 to 14. Acids have a pH of 0-6, neutral substances like water have a pH of 7, and bases have a pH of 8-14.
• 😀 Titration is a quantitative method used to determine the concentration of an unknown solution by reacting it with a solution of known concentration.
• 😀 In titration, a **standard solution** has a known concentration, and the **titrant** is the solution added from the burette. The **titrate** is the solution being analyzed.
• 😀 Acidimetry and alkalimetry are types of titration: acidimetry involves using acids to measure basic compounds, while alkalimetry uses bases to measure acidic compounds.
• 😀 Indicators are chemicals that change color at specific pH levels, signaling the end of the titration process when the equivalence point is reached.
• 😀 Common titration equipment includes a **burette** for holding the titrant, an **Erlenmeyer flask** for the analyte, and a **pipette** to transfer measured amounts of solution.
• 😀 Titration curves represent the pH change during titration. For example, a strong acid and a strong base will have a neutral equivalence point (pH 7), while weak acids and strong bases will have a higher equivalence point (pH > 7).
• 😀 The concentration of the analyte and titrant influences the pH change at the equivalence point, making it important to use the correct indicator.
• 😀 The **equivalent weight** is used in titration calculations to determine the concentration of substances. This is based on the number of hydrogen ions (H+) exchanged in the reaction.
• 😀 Proper indicator selection is crucial for accurate titration results. The indicator’s color change must occur in the pH range of the equivalence point of the titration.

Q & A

What is the main purpose of acid–base titration in quantitative analysis?

The main purpose is to determine the concentration or content of an unknown solution by reacting it with a standard solution of known concentration until the equivalence point is reached.

What does pH represent, and how is it used in titration?

pH represents the degree of acidity or alkalinity of a substance, expressed as the power of hydrogen (H⁺). In titration, pH helps identify the nature of the analyte and determine appropriate indicators and endpoints.

What distinguishes an acid from a base in this context?

An acid donates hydrogen ions (H⁺), while a base accepts hydronium ions (H₃O⁺) or provides hydroxide ions (OH⁻) when dissolved in water.

What is a primary standard solution?

A primary standard solution is a highly pure substance whose concentration is known accurately because it is determined through gravimetric weighing and dissolution in a precise volume of solvent.

What is a secondary standard solution (titrant)?

It is a solution whose concentration is determined through standardization using a primary standard. It is typically placed in a burette and used to titrate the analyte.

What is the role of an indicator in acid–base titration?

An indicator signals the endpoint of titration by changing color when the pH shifts into a specific range, indicating that the equivalence point has been reached or approached.

Why must the acid–base indicator be weaker than the acids and bases being titrated?

The indicator must be weaker so it does not influence or alter the titration reaction itself and only reacts near the equivalence point to show a visible color change.

What is meant by the equivalence point in titration?

The equivalence point is when the amount of titrant added chemically matches the amount of analyte present, meaning they have reacted in stoichiometrically equivalent proportions.

How does phenolphthalein behave as an indicator during titration?

Phenolphthalein is colorless in acidic solutions and turns pink in basic solutions, making it suitable for titrations where the endpoint occurs in the pH range of approximately 8–10.

What factors influence the accuracy of titration?

Key factors include the concentration of the analyte and titrant, the strength of the acid and base (Ka and Kb values), the appropriate selection of the indicator, and the sharpness of the pH change near the equivalence point.

What is equivalent weight, and how is it calculated?

Equivalent weight is the mass of a substance that supplies or reacts with one mole of H⁺ ions (or other univalent ions). It is calculated as the molecular weight divided by the substance’s equivalence value.

How is the concentration of a sample determined after titration?

The concentration is calculated using the relationship: gram-equivalent of titrant = gram-equivalent of titrate, typically expressed as (volume of titrant × normality × equivalent weight) adjusted for sample volume.