Measuring pH and Understanding Acids and Bases
This page covers methods for measuring pH, the nature of acids and bases, and the pH scale. It provides detailed information on experimental procedures and key concepts in acid-base chemistry.
pH Measurement Techniques
Two primary methods for measuring pH are described:
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Using universal indicator paper:
- Place indicator paper on a white tile
- Dip a glass rod into the liquid and tap onto the paper
- Wait 30 seconds and match the color to a pH chart
- Rinse the glass rod with water between measurements
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Using a pH probe data logger:
- Provides a numerical pH value
- More accurate than visual color matching
Highlight: Using a pH probe data logger improves accuracy compared to visual color matching with indicator paper.
Experimental Variables
The page outlines key variables in pH experiments:
- Independent variable: Amount of base added
- Dependent variable: pH of the liquid
- Controlled variables: Factors kept constant during the experiment
Definition: Independent variable is the factor changed by the experimenter, while the dependent variable is the measured outcome.
Acids and Bases
The document explains the fundamental properties of acids and bases:
- Acids form hydrogen (H+) ions in water
- Bases form hydroxide (OH-) ions in water
- pH scale ranges from 0 to 14, with 7 being neutral
Vocabulary: Ionization refers to the process of an acid or base breaking apart to form ions in solution.
Strong vs. Weak Acids
The text distinguishes between strong and weak acids:
- Strong acids fully ionize in water (e.g., hydrochloric acid)
- Weak acids only partially ionize (e.g., ethanoic acid in vinegar)
Example: Hydrochloric acid (HCl) completely dissociates into H+ and Cl- ions in water, making it a strong acid.
pH Scale and Indicators
The page describes the pH scale and various indicators:
- pH measures the concentration of H+ ions
- Each pH unit represents a tenfold change in H+ concentration
- Indicators like litmus, universal indicator, and phenolphthalein change color at different pH levels
Quote: "Every increase of 1 in pH, the concentration of H+ ions get divided by 10."
Concentration vs. Strength
The document clarifies the difference between acid concentration and strength:
- Concentration refers to the amount of solute in a given volume
- Strength relates to the degree of ionization in water
Highlight: The strength of an acid is determined by how much it ionizes in water, not by its concentration.
