Acids + Alkalis

• What does the pH scale measure?

  How acidic or alkaline a substance is
• What is the pH range of the scale?

  0 to 14
• What pH value indicates a neutral substance?

  7
• What does a pH value less than 7 indicate?

  The substance is acidic
• What does a pH value greater than 7 indicate?

  The substance is alkaline
• What color does stomach acid turn universal indicator paper?

  Strong red
• What color does toothpaste turn universal indicator paper?

  Blue
• What is used to find the pH of substances?

  A universal indicator
• How does a universal indicator work?

  It changes color at different pH values
• What is the pH of pure water?

  7
• Why might tap water have a different pH than pure water?

  It contains other dissolved substances
• What is an aqueous solution?

  A solution made by dissolving in water
• What happens to copper sulfate when dissolved in water?

  It becomes slightly acidic with pH 6
• What is the main solute in sea water?

  Sodium chloride
• How is a substance classified based on its pH?

  As acidic, alkaline, or neutral
• What pH value indicates an alkali?

  Above 7
• What is the pH of a substance with a pH of 8?

  It is classified as an alkali
• What are the two methods for testing pH?

  Using a pH meter or an indicator
• What does a pH meter provide?

  A numerical value of pH
• What is litmus?

  An indicator that shows acidity or alkalinity
• What color does litmus turn in acidic solutions?

  Red
• What color does litmus turn in alkaline solutions?

  Blue
• What is special about universal indicator compared to litmus?

  It shows strength of acidity or alkalinity
• What color indicates a neutral pH with universal indicator?

  Green
• What happens when lemon juice is added to water with universal indicator?

  It changes from green to yellow/orange
• How can you make your own universal indicator?

  • Use red cabbage or other colored vegetables
  • Mash in hot water to extract color
  • Compare with color charts for pH
• What should you do if your experiment with red cabbage does not show expected color changes?

  Check each step and repeat the experiment
• What are the characteristics of a good indicator?

  • Changes color at different pH levels
  • Provides a clear range of colors
  • Easy to use and interpret
• What do an acid and an alkali produce when they neutralise each other?

  A salt and water
• What is a neutralisation reaction?

  It is when an acid reacts with an alkali.
• How can the name of the salt produced in a neutralisation reaction be determined?

  From the names of the acid and alkali.
• What pH value indicates a neutral solution?

  A pH of 7
• What happens to the pH of a solution when an acid is added to an alkali?

  The pH moves towards 7, becoming neutral.
• What is the pH range for acids?

  0 to 6
• What is the pH range for alkalis?

  8 to 14
• What are the products of an acid-alkali reaction?

  Water and a salt
• What is sodium nitrate used for?

  Fertilisers and food preservatives
• How does the name of the salt change when an acid reacts?

  The acid's name changes to a specific ion.
• What does hydrochloric acid become when it forms a salt?

  Chloride
• What does nitric acid become when it forms a salt?

  Nitrate