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    1.3 Stoichiometry Q

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    1.3 Stoichiometry Q

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    1.3 Stoichiometry Q

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    ilhamuna

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    of 4

    Tutorial 1.

    3 – Stoichiometry Semester 1 22/23


    1.3 - Stoichiometry
    1. Determine the oxidation number of the underlined elements in the following compounds:
    a. KNO3 d. H2PO42-
    b. SnF4 e. CrO32-
    c. NaClO f. NO3 -

    2. Balance each of the following equations:


    a. C6H14(ℓ) + O2(g) CO2(g) + H2O(ℓ)
    b. Al(s) + H2SO4(aq) Al2(SO4)3(g) + H2(g)
    c. NH3(aq) + CuO(s) Cu(s) + N2(g) + H2O(ℓ)
    d. Al2O3(s) + NaOH(aq) + H2O(ℓ) NaAl(OH)4(aq)
    e. MnO4-(aq) + C2O42-(aq) Mn2+(aq) + CO2(g) (acidic medium)
    f. P4(s) HPO32–(aq) + PH3(s) (basic medium)

    3. When baking soda which contains sodium bicarbonate, NaHCO3 is heated, it releases carbon dioxide, CO2
    and sodium carbonate, Na2CO3.
    i. Write the equation for the reaction.
    ii. Calculate the mass of NaHCO3 required to produce 20.5 g of CO2.
    [78.29]
    4. Hydrogen peroxide, H2O2, decomposes to produce water and oxygen as in the following equation:
    2 H2 O2(l) ⎯→ 2H2O(l) + O2(g)
    What would be the volume of O2 released from the decomposition of 250 mL of 2.0 M H2O2 at STP.?
    [5.6]
    5. Methanol, CH3OH, completely burn in oxygen and is used as fuel. If 10.9 g of methanol are burnt in
    oxygen, calculate the mass and volume of CO2 gas produced at STP.
    [14.99, 7.63]
    6. The combustion of copper(I) sulphide produces copper (I) oxide and sulphur dioxide gas.
    a. Write the equation of the reaction
    b. If 14.0 g of Cu2S has reacted, calculate
    i. The number of molecules of oxygen gas reacted.
    ii. The mass of SO2 gas produced.
    [7.95 x 1022, 5.63]
    7. Mangan (iv) oxide reacts with hydrochloric acid gas according to the following reaction.
    MnO2 + 4HCl MnCl2 + Cl2 + 2H2O
    In one experiment, 75.0 g of mangan (iv) oxide and 50.0 g of HCl gas are allowed to react.
    i. Determine the limiting reactant.
    ii. Calculate the mass of Cl2 produced. [24.32]
    Tutorial 1.3 – Stoichiometry Semester 1 22/23
    8. A reaction between 20.0 g aluminium, Al and of 300.0 mL of 0.5 M sulphuric acid, H2SO4, produces
    aluminium (III) sulphate, Al2(SO4)3 and hydrogen gas.
    a. Define limiting reactant.
    b. Calculate the mass of excess reactant after the reaction
    c. Determine the percentage yield if the mass of aluminium (III) sulphate obtained from the reaction is
    16.5 g.
    [17.31,96.49]
    9. Vanadium metal, V, which is used in steel alloys can be obtained by reacting vanadium(V)oxide, V2O5,with
    calcium, Ca, at high temperature :

    5Ca(s) + V2O5(s) 5CaO(s) + 2V(s)

    When 1.71 x 103 g of an impure sample of calcium reacts with 1.01 x 102 g of vanadium(V) oxide, 50.0
    g of vanadium was yielded. [Ar V: 50.94 g mol-1]
    a. Calculate the number of moles of vanadium yielded.
    b. Determine the limiting reactant.
    c. Determine the percentage of calcium in the impure sample.
    [0.982, 5.76%]
    10. A sample of 1.55 g of iron ore is dissolved in an acid solution in which the iron is converted into Fe2+.
    The solution formed is then titrated with KMnO4 which oxidises Fe2+ to Fe3+ while the MnO4- ions are
    reduced to Mn2+ ions. 92.95 mL of 0.020 M KMnO4 is required for the titration to reach the equivalence
    point.
    a. Write the balanced equation for the titration.
    b. Calculate the percentage of iron in the sample.

    [33.52%]

    OBJECTIVE QUESTIONS

    1. Given the reaction for the nickel-cadmium battery:


    2NiO(OH) (s) + Cd(s) + 2H2O (ℓ) 2Ni(OH)2 (s) + Cd(OH)2 (s)
    What species is oxidized during the discharge of the battery?
    A. Ni3+
    B. Cd
    C. Ni2+
    D. Cd2+
    Tutorial 1.3 – Stoichiometry Semester 1 22/23
    2. Which statement correctly describes a redox reaction?
    A. The oxidation half-reaction and the reduction-half reaction occur simultaneously.
    B. The oxidation half-reaction occurs before the reduction half reaction
    C. The oxidation half-reaction occurs after the reduction half-reaction
    D. The oxidation half-reaction occurs spontaneously but the reduction half-reaction does not

    3. Given the balanced equation:


    2Al(s) + 6H+(aq) 2Al3+(aq) + 3H2 (g)
    When 2 moles of aluminium, Al, completely reacts, what is the total number of moles of electrons
    transferred from Al to hydrogen ion, H+(aq)?
    A. 5
    B. 6
    C. 3
    D. 4

    4. Given the redox reaction:


    2I- (aq) + Br2(ℓ) → 2Br- (aq) + I2(s)
    What occurs during this reaction?
    A. The I- ion is oxidized, and its oxidation number increases.
    B. The I- ion is oxidized, and its oxidation number decreases.
    C. The I- ion is reduced, and its oxidation number increases.
    D. The I- ion is reduced, and its oxidation number decreases.

    5. Aluminium, Al reacts with sulphuric acids, H2SO4 as follows:

    2 Al(s) + 3 H2SO4 (aq) Al2(SO4)3 (aq) + 3 H2 (g)


    heat

    If 1.00 g Al is placed in a solution containing 50.0 ml 0.1 M H2SO4 how many moles of H2 will be
    formed?
    A. 0.100 mol
    B. 0.010 mol
    C. 0.05 mol
    D. 0.005 mol

    For question 6 till 7, there is one or more possible answers. Choose the most appropriate answer from the options
    given below.
    Tutorial 1.3 – Stoichiometry Semester 1 22/23
    MULTIPLE CHOICE QUESTIONS

    A B C D
    I only I and II only II and III only I, II and III

    6. For the following reaction:


    C3H8 (g) + 5O2(g) 3CO2(g) + 4H2O(ℓ)
    Which of the following statement(s) is/are true if 2.56 g of C3H8 is combusted with 15.25 g of O2?
    I. C3H8 is the limiting reactant
    II. The maximum yield of CO2 is 7.68 g
    III. The amount of O2 reacted is 0.291 mole

    7. When 1.0 g of potassium chlorate(V) is heated, oxygen gas is evolved according to the equation:
    2KClO3(s) ⎯
    ⎯→

    2KCl(s) + 3O2(g)

    [Mr of KClO3 = 122.55]


    Choose the TRUE statement(s).
    I. The moles of KClO3 is 8.16 x 10−3.
    II. The moles of oxygen evolved is 2.45 x 10−2.
    III. The volume of oxygen gas evolved at STP is 0.55 dm3.

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