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beryllium (Z=4) and its cation formed when losing two
electrons.
2.83 g of a sample of haematite iron ore [iron (III) oxide, Fe2O3] were dissolved in concentrated hydrochloric acid and the solution diluted to 250 cm3. 25.0 cm3 of this solution was reduced with tin(II) chloride (which is oxidised to Sn4+ in the process) to form a solution of iron(II) ions. This solution of iron(II) ions required 26.4 cm3 of a 0.0200 mol/dm3 potassium dichromate(VI) solution for complete oxidation back to iron(III) ions.
(a) given the half–cell reactions
(i) Sn4+(aq) + 2e– ==> Sn2+(aq)
and (ii) Cr2O72–(aq) + 14H+(aq) + 6e– ==> 2Cr3+(aq) + 7H2O(l)
deduce the fully balanced redox equations for the reactions
(i) the reduction of iron(III) ions by tin(II) ions
(ii) the oxidation of iron(II) ions by the dichromate(VI) ion
(b) Calculate the percentage of iron(III) oxide in the ore.
Balance the reactions below using the change in oxidation number method.
- PbO2+HBr-PbBr2+O2+H2O
- PbO+NH3-Pb+N2+H2O
- KBr+KCIO2+H2SO4-Br2+KCI+K2SO4+H20
- BR^- +CIO^- +H^+ - Br2+CI^- +H20
- SN^2+ +VO4^3- +H^+-- SN^4+ +V^2+ + H20
Initially, a mixture of 0.200 M NO, 0.100 M H_{2} , 0.200 M H_{2}*O was permitted to reach equilibrium (initially there was no*N_{2} ). At equilibrium, the concentration of NO was discovered to be 0.062 M. Determine the value of the equilibrium constant, Ke, for the reaction:
2NO(g) + 2H_{2}(g) N_{2}(g) + 2H_{2}*O(g)
The reaction of bromine gas with chlorine gas has a Kc value of 7.20 at 200°C. If a closed 2.50 L vessel were charged with the two reactants, with the former weighing 9.65 g while the latter is 5.70 g, what would be the equilibrium concentration of the two reactants and BrCl(g)? Determine whether the forward or the reverse reaction will be favored. Explain your answer.
Which substance in each pair has the higher entropy, JUSTIFY YOUR ANSWER
A. 2 mol of He(g) at 100 K and 1 atm or 2 mol of He(g) at 150 °C and 0.2 atm
B. a mixture of 4 mol of H2 (g) and 1.5 mol of N2(g) at 25 °C and 1 atm or, sample of 3 mol of NH3 (g) at 25°C and 1 atm
Which of the following is TRUE about the law of conservation of energy? *
a. ∆E_sys = ∆E_surr
b. ∆E_sys = -∆E_surr
c. ∆E_sys - ∆E_surr = 0
d. none of the above
What is the ∆E for a gas that releases 43 J of heat and has 120 J of work done on it. *
a. 55 J
b. 77 J
c. 99 J
d. 110 J
Colligative property depends on the amount of ___________. *
a. Solvent
b. Solute
c. Ions
Which of the following is a characteristic of a non-electrolyte? *
a. Dissolves in water and conducts electricity
b. Dissolves in water but does not conduct electricity
c. A substance made up of ionic bonds
d. A substance formed by transfer electrons
