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Grade 10 Science — Chemical reactions and equations

Balance a skeletal equation by counting atoms, name the five kinds of reaction the chapter sets out, and say which substance has been oxidised and which reduced.

Name: ________________________

  1. 1.In 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂, how many oxygen atoms stand on the right-hand side? Answer with a number.

  2. 2.Two clear solutions are mixed and a white solid that will not dissolve appears in the tube. What is that solid called? Answer with one word.

  3. 3.Sort each reaction by the kind of reaction it is.

    Groups: Combination · Decomposition · Displacement · Double displacement

    • Sodium sulfate solution mixed with barium chloride solution
    • Carbon burning in oxygen to give carbon dioxide
    • Calcium oxide and water make slaked lime
    • An iron nail left in copper sulfate solution
    • Limestone heated in a kiln
    • Ferrous sulfate crystals heated in a boiling tube

  4. 4.Put the chapter's balancing procedure back into the order it gives, starting with "Draw a box round each formula, and change nothing inside a box".

    • Draw a box round each formula, and change nothing inside a box
    • Write in the physical states of the reactants and products
    • Start with the compound that has the most atoms, and balance its commonest element
    • Balance the elements that are still unequal, one at a time
    • List how many atoms of each element sit on the two sides
    • Count the atoms on both sides again to check the equation

  5. 5.Butter kept too long smells and tastes different, because the fat in it has been oxidised. What is this change called? Answer with one word.

  6. 6.Sort each of these by whether energy comes out of the reaction or goes into it.

    Groups: Heat given out · Energy taken in

    • Quick lime added to water
    • Water split by an electric current
    • Natural gas burning
    • Green crystals heated until they give off a sharp smell
    • Silver chloride left in sunlight
    • Respiration in our cells

  7. 7.Sodium reacts with water: __ Na + 2H₂O → 2NaOH + H₂. Which coefficient belongs in the gap?

    • a) 3
    • b) 1
    • c) 4
    • d) 2

  8. 8.Iron nails are left in blue copper sulfate solution for twenty minutes. What do you see when they come out?

    • a) The nails have turned brownish and the blue has faded
    • b) The nails are unchanged and the blue is deeper
    • c) The nails have turned black and the solution is clear
    • d) The nails have dissolved and the solution is green

Answer key — Grade 10 Science — Chemical reactions and equations

  1. 1. 12
  2. 2. precipitate
  3. 3. Calcium oxide and water make slaked lime → Combination; Carbon burning in oxygen to give carbon dioxide → Combination; Ferrous sulfate crystals heated in a boiling tube → Decomposition; Limestone heated in a kiln → Decomposition; An iron nail left in copper sulfate solution → Displacement; Sodium sulfate solution mixed with barium chloride solution → Double displacement
  4. 4. 1. Draw a box round each formula, and change nothing inside a box 2. List how many atoms of each element sit on the two sides 3. Start with the compound that has the most atoms, and balance its commonest element 4. Balance the elements that are still unequal, one at a time 5. Count the atoms on both sides again to check the equation 6. Write in the physical states of the reactants and products
  5. 5. rancidity
  6. 6. Quick lime added to water → Heat given out; Respiration in our cells → Heat given out; Natural gas burning → Heat given out; Silver chloride left in sunlight → Energy taken in; Water split by an electric current → Energy taken in; Green crystals heated until they give off a sharp smell → Energy taken in
  7. 7. d) 2
  8. 8. a) The nails have turned brownish and the blue has faded