Iron (Fe) is the fourth most abundant element in the Earth’s crust and has been used for more than 5 — Physical Chemistry — Electrochemistry Chemistry Question
Iron
Iron (Fe) is the fourth most abundant element in the Earth’s crust and has been used for more than 5,000 years.
Part A.
Pure iron is easily oxidized, which limits its utilization. Element X is one of the alloying elements that is added to improve the oxidation resistance property of iron.
Below is some information about the element X:
(1) In first ionization, an electron with quantum numbers n1 = 4 – l1 is removed.
(2) In second ionization, an electron with quantum numbers n2 = 5 – l2 is removed.
Model Answer
Answer: Cr
...respectively. Can X and Fe form a complete substitutional solid solution?
Tick the relevant box YES NO.
Show your calculation. The volume of sphere is 4/3πr³.
Model Answer
The correct answer: YES (since ΔR ≤ 15)
Calculation
For Fe:
V = 2 (4/3)πr³ (the bcc unit cell contains 2 atoms of Fe)
r³ = (3 V/ (8 π) = (3 ×1.59×10-23 cm³) / (8π) = 1.90×10-24 cm³
r = 1.24×10-8 cm i. e. r = 0.124 nm
For X:
(less than 15)
RFe = 0.124 nm
RX = 0.127 nm
ΔR = 2.42
Part B.
Iron in natural water is in the form of Fe(HCO3)2, which ionizes to Fe2+ and HCO3-. To remove iron from water, Fe(HCO3)2 is oxidized to an insoluble complex Fe(OH)3, which can be filtered out of the water.
Fe2+ can be oxidized by KMnO4 in a basic solution to yield Fe(OH)3 and MnO2 precipitates. Write the balanced ionic equation for this reaction in a basic solution.
Model Answer
3 Fe2+ + MnO4- + 5 OH- + 2 H2O → 3 Fe(OH)3 + MnO2
Under this condition, HCO3- ions are converted to CO32-. Write the balanced ionic equation for this reaction in a basic solution.
Model Answer
HCO3- + OH- → CO32- + H2O
A covalent compound A which contains more than 2 atoms and, a potential oxidizing agent, can be prepared by the reaction between diatomic halogen molecule (X2) and NaQO2
X2 + x NaXO2 → y A + z NaX where x + y + z ≤ 7
where x, y and z are the coefficients for the balanced equation. Among the binary compounds between hydrogen and halogen, HX has the lowest boiling point.
Identify X and if A has an unpaired electron, draw a Lewis structure of compound A with zero formal charge on all atoms.
Model Answer
X = Cl
Lewis structure of compound A:
(All are correct answers. Student draws only one structure.)
The molecular geometry of compound A: The correct answer: bent
Compound D is an unstable oxidizing agent that can be used to remove Fe(HCO3)2 from natural water. It consists of elements G, Z and hydrogen and the oxidation number of Z is +1. In this compound, hydrogen is connected to the element having the higher electronegativity among them. Below is some information about the elements G and Z:
(1) G exists in its normal state as a diatomic molecule, G2.
(2) Z has one proton fewer than that of element E. E exists as a gas under standard conditions. Z2 is a volatile solid.
(3) The compound EG3 has a pyramidal shape.
Identify the elements G and Z and draw a molecular structure of compound D.
Model Answer
G = O Z = I
Molecular structure of compound D
Hydrogen is connected to the element having the highest electronegativity.
The oxidation number of Z in compound D is I (+1).
Part C.
59Fe is a radiopharmaceutical isotope which is used in the study of iron metabolism in the spleen. This isotope decays to 59Co as follows:
6.7 What are a and b in equation (1)? (Mark in the appropriate boxes.)
proton neutron beta positron alpha gamma
[ ] [ ] [ ] [ ] [ ] [ ]
Model Answer
proton neutron beta positron alpha gamma
[ ] [ ] [] [ ] [ ] []
Consider equation (1), if the 59Fe isotope is left for 178 days which is n times of its half-life (t1/2), the mole ratio of 59Co to 59Fe is 15 : 1. If n is an integer, what is the half-life of 59Fe in day(s)? Show your calculation.
Model Answer
t = 0 59Fe = N0 and 59Co = 0
t = 178 d 59Fe = Nt and 59Co = N0 – Nt
The ratio of 59Co to 59Fe at t = 178 d is 15 = (N0-Nt) / Nt
Thus, Nt = N0 / (15+1)