Acids, Bases and salts

• What does the pH scale measure?

  How acidic or alkaline a solution is (0-14 scale)
• What ion do acids release in solution?

  H ⁺ (hydrogen ions)
• What ion do alkalis release in solution?

  OH ⁻ (hydroxide ions)
• What is a strong acid?

  An acid that fully ionises in water
• What is a weak acid?

  An acid that partially ionises in water
• What is the reaction of an acid with a metal?

  Acid + Metal → Salt + Hydrogen
• How does metal reactivity affect acid reactions?

  More reactive metals react more vigorously with acids
• What is the general equation for neutralisation with a base?

  Acid + Base → Salt + Water
• What is the general equation for acid with a carbonate?

  Acid + Carbonate → Salt + Water + Carbon Dioxide
• What is the ionic equation for neutralisation?

  H ⁺(aq) + OH ⁻(aq) → H2O(l)
• What is observed when an acid reacts with a carbonate?

  Effervescence (CO2 gas released)
• How can you test for carbonate ions?

  Add acid – if CO2 is produced, carbonate ions are present
• How do you make soluble salts from insoluble bases?

  React with warm acid, filter excess base, evaporate to crystallise
• What salt is formed by hydrochloric acid?

  Chloride
• What salt is formed by nitric acid?

  Nitrate
• What salt is formed by sulfuric acid?

  Sulfate
• What is the test for sulfate ions (SO₄²⁻)?

  Add barium chloride – a white precipitate of barium sulfate forms
• What is titration used for?

  To find concentrations of acids/alkalis or make pure salts
• What is the formula for concentration?

  Concentration (mol/dm³) = moles ÷ volume (dm³)
• What are the key steps in a titration?

  Add alkali to acid with indicator, find end point, repeat for accuracy
• What does 'dilute acid' mean?

  Low amount of substance in given volume
• What does 'strong acid' mean?

  Fully ionises in water
• How does a strong acid compare to a weak acid in reactions?

  Reacts faster and more completely
• How are insoluble salts made?

  Mix two soluble salts to form a precipitate, then filter and dry it
• $HCl$


  Hydrochloric acid
• $H_2SO_4$


  Sulfuric acid
• $HNO_3^{ }$


  Nitric acid
• Signs of reactions

  • Change in temperature: Endothermic and Exothermic
  • Releasing gas: Fizzing
  • Precipitation: Solid appears
  • Partical collision
  • Change in colour
• Reactions with hydrochloric acid

  • Copper: No observation
  • Iron: Small, few bubbles
  • Zinc: Small, lots of bubbles
  • Magnesium: Hot, lots of fizzing
• pH scales

  • Strong acid: 0-2
  • Weak acid: 3-6
  • Neutral: 7
  • Weak alkali: 8-11
  • Strong alkali: 12-14
• Titration steps

  1. Measure exactly 25 cm3 of alkali into a clean conical flask.
  2. Add a few drops of indicator to the flask.
  3. Place the flask onto a white tile.
  4. Fill the burette with acid.
  5. Slowly add the acid from the burette to the alkali until the indicator changes colour*. This is the endpoint of the reaction
  6. Record the volume of acid added to the flask.
  7. Repeat steps 1-6 without using the indicator and adding the same volume of acid from the burette.
• What are metals, bases and certain carbonates in water?

  Insoluble
• Steps to make a salt from an metal or insoluble base/carbonate

  1. Add excess metal/base/carbonate to the acid and make sure that all the substance has reacted with the acid. Heating and stiring help. Fizzing stops when reaction has stopped for metals and metal carbonates.
  2. Filter the mixture through a filter funnel using filter paper. Salt passes through, excess solid remains in the paper.
  3. The salt crystals are formed by evaporation. The solution is heated to evaporate water
• What to do with large crystals

  Evaporate slowly near a radiator or window
• What to do with small crystals

  Use a bunsen burner to evaporate 2/3 of water quickly, allow rest to evaporate naturally