Acids, Bases, Indicators & pH
Indicators
Indicators are dyes that will change color in the presence of an acid or base. Some indicators only show the presence of acid or base but do not indicate the strength. (For example, Litmus is red in acid & blue in base, regardless of the strength of the acid or base.) Universal indicator is a mixture of indicators and gives a range of colors depending on the strength of the acid or base.
Analysis Questions
Analysis Questions: (answer in sentences) 1. Give the definition of an indicator: A compound that changes color to indicate (tell) if a substance is an acid or a base 2. Did any of the indicators you tested give very different colors for different strengths of acids/bases? If so, which one? Universal indicator 3. If you were testing an unknown and could only use one indicator, which one would you use? EXPLAIN WHY. Universal - gives a range of colors to tell more accurately how strong or weak the acid or base is. 4. Is your unknown an acid or a base? Is it strong or weak? How do you know? Skip this - we did not test an unknown. 5. Explain two ways in which universal indicator is different from other indicators. ➢ Gives a range of colors for different strengths of acids & bases ➢ Made of a mixture of indicators.
Strengths of Acids and Bases (Dissociation = separating into ions)
STRONG ACIDS produce large numbers of hydrogen ions in water WEAK ACIDS produce few hydrogen ions in water. STRONG BASES produce large numbers of hydroxide ions in water. WEAK BASES produce few hydroxide ions in water.
Neutralization
double displacement reaction between an acid and a base. The H+ (or H3O+) ions from the acid react with the OH- ions of the base to form water: H+ + OH- => H2O
Bases
• Produce hydroxide ions (0H-) in solution • Feel slippery • Taste bitter • Strong bases are corrosive • Bases dissolved in water conduct electricity • Bases react with acids to produce a salt and water
pH Scale
• The pH Scale measures the strengths of both acids and bases. • This scale is based on the numbers 0-14 • The more H+ ions it produces in water, the more acidic a substance is. • The more OH- ions it produces, the more basic a substance is. • pH 0 - 6 indicates an acid: 1-3 strong acids, 4-6 weak acids • pH 8-14 indicates a base: 8-11 weak bases, 12-14 strong bases • pH 7 indicates a neutral compound such as distilled water - Neither H+ nor OH- ions are present in a solution that is neutral.
Acids
• When dissolved in water, produce H+ ions • Sour taste • Acids dissolved in water conduct electricity • Acids are corrosive • Acids react with bases to produce a salt and water
