4.2.4.3 Using indicators and pH meters to measure

• What are indicators?

  Substances that change color in solutions
• What color does litmus paper turn in acidic solutions?

  Red
• What color does litmus paper turn in alkaline solutions?

  Blue
• What is an indicator in chemistry?

  A substance that changes color based on pH
• What color does the universal indicator show at pH 1-3?

  Red
• What color does methyl orange turn in acids?

  Red
• What color does litmus turn in alkalis?

  Blue
• What color is phenolphthalein in acids?

  Colorless
• How does the universal indicator function?

  It shows a range of colors across pH levels
• What color does the universal indicator show at pH 12-14?

  Purple
• What color is phenolphthalein in alkalis?

  Pink
• How does litmus paper indicate acidity or alkalinity?

  • Red in acidic solutions
  • Blue in alkaline solutions
• What are the color changes of different indicators at various pH levels?

  • Universal indicator:
  • Red (pH 1-3)
  • Purple (pH 12-14)
  • Litmus:
  • Red in acids
  • Blue in alkalis
  • Phenolphthalein:
  • Colorless in acids
  • Pink in alkalis
  • Methyl orange:
  • Red in acids
  • Yellow in alkalis
• What is the name of the dye labeled "Crystal violet"?

  Crystal violet
• What is the relationship between the pH and the color of the dyes shown in the image?

  • The color of the dyes changes as the pH changes, indicating they are pH indicators.
  • The image shows the color range of each dye across different pH values.
• What is the name of the dye labeled "Erythrosin B"?


  Erythrosin B
• What color does methyl orange turn in alkalis?

  Yellow
• What is the purpose of a titration?

  To determine the concentration of an acid or base
• What is the name of the dye labeled "Thymol blue"?

  Thymol blue
• What is the name of the dye labeled "Cresol red"?

  Cresol red
• What does the image accompanying the text show?

  How different indicators change color at different pH levels
• If a solution has a pH of 7, which dye from the image would appear blue?

  Thymol blue
• What is filled in the burette during a titration?

  Acid or base solution
• What are the main components of an electrode head?

  • Lead to meter
  • Electrode head
  • Filler opening
  • Reference electrolyte
  • Internal buffer
  • Reference electrode
  • Internal reference electrode
  • Diaphragm (separator)
  • Glass membrane
• What should you measure before starting a titration?

  A known volume of solution in a flask
• Why is it important to choose the right indicator for a titration?

  Different indicators change color at different pH levels
• What is the purpose of the reference electrolyte in an electrode head?

  To provide a stable reference potential
• How do indicators function in acid-base titrations?

  • Indicators change color at specific pH levels
  • Help determine the end point of titration
  • Selection of the right indicator is crucial
• Why is the diaphragm (separator) included in the electrode head?

  To allow ions to pass through while keeping the internal and external solutions separate
• What indicates the end point of a titration?

  Distinct color change of the indicator
• If the glass membrane of the electrode head is damaged, how would this affect the measurements?

  It would lead to inaccurate and unstable readings
• What is added to the solution in the flask during a titration?

  Indicator
• How can the image be used to determine the pH range of each dye?

  • The x-axis shows the pH values from 0 to 13.
  • The colored bars for each dye indicate the pH range over which the dye changes color.
  • By looking at the position and extent of the colored bars, you can determine the pH range for each dye.
• What does the glass membrane in a pH meter do?

  Selectively binds hydrogen ions
• What role does the reference electrode play in a pH meter?

  It provides a stable baseline
• What are the main components of a pH meter's operation?

  1. Submerging the glass membrane
  2. Reference electrode provides a stable baseline
  3. Meter calculates pH from voltage difference
  4. Result is displayed digitally
• How does a pH meter detect pH?

  By measuring potential difference between electrodes
• What is the name of the device shown in the image?

  High Impedance Voltmeter
• What should be recorded during a titration?

  Volume of solution used
• How is the pH result displayed in a pH meter?

  Digitally