Chem igcse

• Define acid in terms of pH

  A substance with a pH of less than 7
• Define acids in terms of ions

  A substance which releases H⁺ ions in solution
• What does (aq) stand for?

  Aqueous: when something is dissolved in water. E.g. NaCl(aq) is salt water
• State the three common acids and give their formulae

  Hydrochloric acid, HCl(aq), Sulfuric acid, H₂SO₄(aq), Nitric acid, HNO₃
• Which ions do the common acids form in solution?

  HCl forms H⁺ and Cl⁻, H₂SO₄ forms 2H⁺ and SO₄²⁻, HNO₃ forms H⁺ and NO₃⁻
• What is a neutral solution?


  A solution with a pH of 7. Water is an example.
• How do you measure pH?

  With an indicator or pH probe.
• What is a base?

  A metal oxide, hydroxide or carbonate that will react with an acid. E.g. copper oxide
• What is an alkali?

  A soluble base. E.g. sodium hydroxide
• Which ions are always present in a solution of an alkali?

  OH⁻
• What is a salt?

  A compound formed when some or all of the hydrogen from an acid is replaced by a metal. E.g. CuSO₄, copper sulfate, where copper has replaced H from H₂SO₄
• What type of salts are formed by the three main acids?

  Hydrochloric acid produces chlorides, sulfuric acid = sulfates, nitric acid = nitrates
• What is a neutralisation reaction?


  A reaction involving an acid that results in a neutral solution
• Which ions always react together in a neutralization reactions between acids and alkalis?

  H⁺ and OH⁻
• Write the equation showing the reaction between H⁺ and OH⁻ ions

  H⁺ + OH⁻ → H₂O
• metal + acid →

  → salt + hydrogen gas
• metal hydroxide + acid →

  → salt + water
• metal oxide + acid →

  → salt + water
• metal carbonate + acid →

  → salt + water + carbon dioxide
• How do you make a soluble salt from an acid?


  React the acid with a base. E.g. to make copper sulphate react copper oxide with sulphuric acid
• If a salt is in solution, how do you extract it as a solid?

  Allow the water to evaporate off and it will leave the salt behind as a solid.
• What is a strong acid?

  An acid which completely splits up into its ions in water. E.g. when HCl is in water all the HCl molecules split up into H⁺ and Cl⁻
• What is a weak acid?

  An acid which will have some molecules which do not split up into their ions. E.g. in ethanoic acid only some of the molecules will have split up into the ethanoate ion and H⁺ ions.
• What is the relationship between the strength of an acid and its pH?

  As an acid increases in strength the pH decreases.
• What is a concentrated acid?

  An acid where there are lots of acid particles in the water.
• What is a dilute acid?

  An acid where there are fewer acid particles in the water.
• How is pH measured?

  pH is related to the concentration of H⁺ in a solution.
• Particle


  The tiny things that materials are made from.

  
• Pure Substance


  A material made of one type of particle

  
• Matter


  Anything that has mass and takes up space

  
• Solid


  State of Matter that is made of closely packed particles that vibrate in place.

  
• Liquid


  State of matter in which particles are loosely attached and flow and tumble over each other.

  
• Gas


  A state of matter in which the particles spread out to fill their container.

  
• Fixed Volume

  A volume that remains the same, and does not change based on the container.

  
• Boiling

  rapid change from liguid to gas

  
• Melting


  change from a solid into a liquid

  
• Freezing


  change from a liquid into a solid

  
• Evaporation


  change from liquid to gas

  
• Condensation


  Change gas to liquid

  
• Sublimation


  Change solid to gas