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Compounds and equations

Ten questions of mixed difficulty, covering Compounds and equations. Print it, or work through it on screen — the answer key starts on its own page.

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Compounds and equations

Science 10 · maddyhelps.com

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Circle the best answer for each question. Show your work in the space provided.

  1. Balanced, the equation ___H₂ + ___O₂ → ___H₂O is

    1. a) H₂ + O₂ → H₂O
    2. b) 2H₂ + O₂ → 2H₂O
    3. c) 2H₂ + 2O₂ → 2H₂O
    4. d) H₂ + 2O₂ → 2H₂O

  2. The name of N₂O₅ is

    1. a) nitrogen oxide
    2. b) nitrogen(V) oxide
    3. c) dinitrogen pentaoxide
    4. d) dinitrogen pentoxide

  3. Compared with molecular compounds, ionic compounds generally have

    1. a) higher melting points
    2. b) lower melting points
    3. c) the same melting points
    4. d) no melting point

  4. A molecular compound is held together by

    1. a) shared pairs of electrons
    2. b) transferred electrons
    3. c) metallic bonds
    4. d) gravity

  5. The name of FeCl₂ is

    1. a) iron(II) chloride
    2. b) diiron chloride
    3. c) iron(III) chloride
    4. d) iron chloride

  6. The law of conservation of mass says that in a chemical reaction

    1. a) mass depends on temperature
    2. b) mass increases
    3. c) mass is always lost as energy
    4. d) the total mass of the products equals the total mass of the reactants

  7. The formula for calcium nitrate is

    1. a) CaNO₃
    2. b) Ca(NO₃)₂
    3. c) Ca₂NO₃
    4. d) CaN₂O₆

  8. Balanced, the combustion of methane CH₄ + ___O₂ → ___CO₂ + ___H₂O needs

    1. a) 2 O₂, 1 CO₂ and 2 H₂O
    2. b) 1 O₂, 1 CO₂ and 1 H₂O
    3. c) 3 O₂, 1 CO₂ and 2 H₂O
    4. d) 2 O₂, 2 CO₂ and 1 H₂O

  9. The formula for magnesium chloride is

    1. a) MgCl₂
    2. b) Mg₂Cl₃
    3. c) MgCl
    4. d) Mg₂Cl

  10. Of these, the substance that conducts electricity when dissolved in water is

    1. a) NaCl
    2. b) wax
    3. c) sugar
    4. d) oil

Answer key · Compounds and equations

Science 10 · maddyhelps.com

  1. b) 2H₂ + O₂ → 2H₂O — Count each element on both sides: 4 hydrogens and 2 oxygens each way. Only the coefficients in front may be changed — altering a subscript would change the substance itself.
  2. d) dinitrogen pentoxide — Two non-metals means a molecular compound, which takes prefixes on both elements. The a of penta- drops before the vowel, giving pentoxide.
  3. a) higher melting points — Melting an ionic solid means breaking a whole lattice of attractions at once, which takes a great deal of energy. Melting a molecular solid only has to separate whole molecules from each other.
  4. a) shared pairs of electrons — Two non-metals both want to gain electrons, so neither can take them outright and sharing is the compromise. The shared pair counts towards both atoms' outer shells.
  5. a) iron(II) chloride — Iron is multivalent, so a Roman numeral is required. Two chlorides carry 2− in total, so the iron must be Fe²⁺. The numeral names the charge, not the number of chlorines.
  6. d) the total mass of the products equals the total mass of the reactants — Atoms are rearranged, not created or destroyed, so the mass has to balance. That is the entire reason chemical equations must be balanced.
  7. b) Ca(NO₃)₂ — Ca²⁺ with two NO₃⁻ balances the charge, and a polyatomic ion needed more than once goes in brackets so the subscript applies to the whole group. CaN₂O₆ has the right atoms and hides the ion, so it is not how the formula is written.
  8. a) 2 O₂, 1 CO₂ and 2 H₂O — One carbon gives one CO₂, and four hydrogens give two H₂O. That needs 2 + 2 = 4 oxygen atoms, which is 2 O₂. Balancing carbon and hydrogen first and leaving oxygen to last is the standard order for combustion.
  9. a) MgCl₂ — Mg²⁺ needs two Cl⁻ to balance the charge. The subscripts come from balancing charge, not from anything in the name — ionic names never carry prefixes.
  10. a) NaCl — Sodium chloride separates into free-moving ions in water, and moving charges are a current. Sugar dissolves without forming ions, so its solution does not conduct.