Acids and Bases

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Acids

• Substance that releases hydrogen ions (H+) into an aqueous solution (containing water)

Properties of Acids

• Corrosive
• Sour taste
• Turn blue litmus paper red
• React with some metals releasing hydrogen gas and leaving a salt behind
• Conduct electricity
• Neutralised by bases causing water and a salt

Strength of Acids

• Not pure substances
• Mixtures of acid with water
  • Why we commonly refer to a “concentration” of acid
  • How many acid molecules are there?
• When mixed with water some of the hydrogen atoms in the molecule are released to form hydrogen ions
• Strong acids release more hydrogen ions
• Strength means how many hydrogen ions are released?
• 3 common strong acids
  • Hydrochloric acid
  • Sulfuric Acid
  • Nitric Acid
• Acid is considered to be weak if the molecules only release a small amount of hydrogen ions
• Number of hydrogen atoms within a solution depends on
  • Strength of the acid
  • Concentration of the acid

IMPORTANT NOTE!!!!!!!!

• Strength of acid and the concentration if an acid are not the same thing
• Strong acid = completely ionise in water
• Weak acid = do not completely ionise in water
• Concentrated acid = more particles present in water
  • Not necessarily ions
• Dilute acid = less particles present in the water

Bases and alkalis

• Base is a substance that releases Hydroxide ions
• If a base can be dissolved in water, it is known as an alkali
• The solution it forms is known as an alkaline solution
• WE can have strong bases and weak bases
  • Depends on release of hydroxide ions
• Can burn you as bad as acids

Properties of bases and alkalis

• Caustic
  • Able to burn or corrode organic tissue by chemical action
• Soapy and slimy
• Turn red litmus paper blue
• Have bitter case (think coffee)
• Conduct electricity
• Neutralised by acids producing water and a salt

Common bases

• Sodium hydroxide
• Potassium Hydroxide
• Ammonium hydroxide
• Calcium hydroxide
• Magnesium hydroxide
• NOT ALL BASES ARE HYDROXIDES
• Sodium carbonate
• Potassium phosphate
• Ammonia

Strong and weak bases

• Strong bases completely ionise in water
  • All of the molecules disassociate into positive ions and negative hydroxide ions
  • The less hydroxide ions produced by a base the weaker it is

pH

• Concentration of hydrogen ions is measured using pH scale
• In an acidic solution, there are more hydrogen ions than hydroxide ions
• In an alkaline solution, there are more hydroxide ions than hydrogen ions

Measuring pH

• Indicators are chemicals that change colour to show whether a substance is acidic, neutral or basic
• Common indicator is litmus paper
• Turns red when dipped in acid
• Turns blue when dipped in base
• Litmus does not tell us the exact pH but other indicators do

Acid Reactions

Acid + Base → Salt + Water

Acid + Metal → Salt + H2

Acid + Metal Oxide → Salt + Water

Acid + Carbonate → Salt + Water + Carbon Dioxide

Neutralisation

• Acids release $H^{+}$
• Bases absorb $H^{+}$
• Resultant products are salts and water (H+ and OH- )
• Can also be written as metal hydroxide in some instances
• Acid + Base → Salt + Water

Metals

• Metals and acid react to produce hydrogen gas($H^{+}$ ions bond)
• Other product is metal salt
• Acid + metal  → salt + hydrogen

Metal oxides

• Similar to metal reactions
• Difference - oxygen from oxide bonds with $H^{+}$ ions
• Acid + Metal Oxide → Salt + Water

Carbonates

• Carbonates also react with acids
• Acid + Carbonate → Salt + Water + Carbon Dioxide