1.1

• What does the formula of a compound indicate?


  It shows which elements are present and the ratio of atoms of each element.
• How many aluminium atoms are in the formula Al2(SO4)3?


  There are two aluminium atoms.
• How many sulfur atoms are present in Al2(SO4)3?


  There are three sulfur atoms.
• How many oxygen atoms are in Al2(SO4)3?


  There are twelve oxygen atoms.
• What does the number outside the bracket in a chemical formula do?


  It multiplies everything in the bracket by that number.
• What are the formulas of some common substances?


  • Water: H2O
  • Hydrochloric acid: HCl
  • Oxygen: O2
  • Sulfuric acid: H2SO4
  • Hydrogen: H2
  • Nitric acid: HNO3
  • Nitrogen: N2
  • Sodium hydroxide: NaOH
  • Carbon dioxide: CO2
  • Sodium carbonate: Na2CO3
  • Sulfur dioxide: SO2
  • Ammonia: NH3
• How can the charge on some ions be deduced?


  From the element’s group in the Periodic Table.
• What is the charge of sodium ions (Na+)?


  +1
• What is the charge of magnesium ions (Mg2+)?


  +2
• What is the charge of oxide ions (O2–)?


  2–
• What is the charge of chloride ions (Cl–)?


  –
• What are some examples of cations and anions?

  Cations:

  • Hydrogen: H+
  • Silver: Ag+
  • Zinc: Zn2+
  • Ammonium: NH4+

  
  

  Anions:

  • Hydroxide: OH–
  • Nitrate: NO3–
  • Sulfate: SO4 2–
  • Carbonate: CO3 2–
• What is the process for constructing a formula from ions?


  1. Write the symbols for the ions required.
  2. If charges balance, write the formula without charges.
  3. If charges do not balance, choose the ratio of positive to negative ions needed.
  4. Use brackets for clarity when compound ions are involved.
• What is the formula for sodium chloride when combining Na+ and Cl– ions?


  NaCl
• What is the formula for potassium oxide when combining K+ and O2– ions?


  K2O
• What does the oxidation number of an element indicate?


  It indicates the number of electrons that need to be lost or gained to make the element neutral.
• What does an increase or decrease in oxidation numbers during a redox reaction indicate?


  It shows which species is oxidised and which is reduced.
• What is the sum of the oxidation numbers in a compound?


  It is 0.
• What is the sum of the oxidation numbers in an ion?


  It is equal to the overall charge on the ion.
• What is the oxidation number of uncombined elements?


  0
• What is the oxidation number of Group 1 metals?


  +1
• What is the oxidation number of Group 2 metals?


  +2
• What is the oxidation number of oxygen in most compounds?


  –2
• What is the oxidation number of hydrogen in most compounds?


  +1
• What is the oxidation number of fluorine in compounds?


  –1
• What is the oxidation number of calcium in CaCl2?


  +2
• What is the oxidation number of carbon in HCO3–?


  +4
• What do chemical equations show us?


  • They show what happens during a chemical reaction.
  • They must be balanced with the same number of atoms of each element on each side.
  • State symbols indicate the states of the species in the equation.
• What are the state symbols used in chemical equations?


  (s) for solid, (l) for liquid, (g) for gas, (aq) for solution in water.
• How do you balance the equation 4Na + O2 → Na2O?


  By having four units of Na and two units of Na2O.
• What are ionic equations?


  • They show only the ions that take part in a chemical reaction.
  • Spectator ions that do not change during the reaction are left out.
• What are the important ions in the reaction CuSO4(aq) + 2NaOH(aq) → Cu(OH)2(s) + Na2SO4(aq)?


  Cu2+ and OH– ions.
• What is the product formed from the reaction of Cu2+ and OH– ions?


  A pale blue precipitate of copper(II) hydroxide, Cu(OH)2.
• What is the formula for copper(II) hydroxide?


  Cu(OH)2
• What are the key components of balanced chemical and ionic equations?


  • Balanced chemical equations have the same number of atoms of each element on both sides.
  • Ionic equations show only the ions involved in the reaction.
  • State symbols indicate the physical states of the reactants and products.