Answers – Homework – 1

  1. a) Completing the table:

    For each particle, charge = number of protons – number of electrons

    Particle Protons Electrons Neutrons Charge
    A 20 18 18 +2
    B 17 17 20 0
    C 9 9 10 0
    D 17 17 18 0
    E 13 10 14 +3
    F 16 18 19 -2

    b) Nucleon number of E

    = number of protons + number of neutrons

    = 13 + 14 = 27

    c) Particles B and D are isotopes because they:

    • Have same number of protons (17)
    • Have different number of neutrons (20 and 18)

    d) F has 16 protons, which corresponds to Sulfur (S) in the periodic table

  2. Completing the table:

    Particle Protons Electrons Electronic configuration Charge
    A 20 18 2,8,8 +2
    B 9 10 2,8 -1
    C 10 10 2,8 0
    D 8 10 2,8 -2

  3. Identifying structures:

    • a) B – atoms with full outer shell of electrons = Ne (neon)
    • b) E – giant covalent structure
    • c) D – particles formed by loss and gain of electrons (ionic compound KF)
    • d) A – conducts electricity when solid (metallic structure)
    • e) D – conducts electricity when molten/dissolved
    • f) C – lowest melting point (simple molecular)

  4. Dot-and-cross diagrams for:

    Draw your diagrams in the spaces below:

    a) Hydrogen fluoride, HF:

    Space for HF diagram

    b) Fluorine, F2:

    Space for F2 diagram

    c) Silicon tetrachloride, SiCl4:

    Space for SiCl4 diagram

    d) Hydrogen sulfide, H2S:

    Space for H2S diagram

  5. Complete the dot-and-cross diagrams:

    a) Ethanol, C2H5OH:

    Space for ethanol diagram

    b) Hydrogen cyanide, HCN:

    Space for HCN diagram

    c) Phosphine, PH3:

    Space for PH3 diagram

    d) Carbonyl chloride, COCl2:

    Space for COCl2 diagram

  6. Ionic compound formulae:

    • a) Calcium hydroxide = Ca(OH)2
    • b) Magnesium chloride = MgCl2
    • c) Ammonium phosphate = (NH4)3PO4
    • d) Lithium sulfide = Li2S
    • e) Lead(II) nitrate = Pb(NO3)2
    • f) Calcium carbonate = CaCO3
    • g) Aluminium nitrate = Al(NO3)3
    • h) Potassium sulfite = K2SO3
    • i) Zinc sulfate = ZnSO4
    • j) Ammonium sulfate = (NH4)2SO4

  7. Balanced equations:

    a) CaC2 + 2H2O → Ca(OH)2 + C2H2

    b) 2KOH + H2SO4 → K2SO4 + 2H2O

    c) TiCl4 + 4Na → Ti + 4NaCl

    d) 2KO2 + 2CO2 → 2K2CO3 + O2

    e) 2Al + 6HCl → 2AlCl3 + 3H2

  8. Concentration calculations:

    a) For NaOH:

    • Volume in dm³ = 500/1000 = 0.5 dm³
    • Concentration = 20.0/0.5 = 40.0 g/dm³

    b) For K2SO4:

    • Volume already in dm³ = 2 dm³
    • Concentration = 17.4/2 = 8.7 g/dm³

  9. For carbon atoms:

    • Number of moles = mass/Ar
    • = 6.0/12
    • = 0.5 moles

  10. For H2 molecules:

    • Mr of H2 = 2
    • Number of moles = 3.0/2 = 1.5 moles
    • Number of molecules = 1.5 × 6.022 × 1023
    • = 9.033 × 1023 molecules
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