Chapter 13-A
Ch 13 Is this an oxidation or a reduction or neither one? Fe --> Fe3+ + 3e-
What is an oxidation?
OIL RIG of e's. Oxidation is loss. Reduction is gain.
Is this a redox reaction?
CaO + CO2 --> CaCO3
+2 -2 +4 -2 each --> +2 __ __
HINT: Ask yourself if there is a change in oxidation number for any element?
No. It is not a redox.
HINT: If you see an uncombined element, it is a redox. This is one way to assure that a change will occur in the oxidation number of that element. Example:
2Nao + Cl2o --> 2Na1+Cl1-
Ch 13 Two types of electrochemical cells are the galvanic/voltaic and the electrolytic cells. Which is spontaneous and which is nonspontaneous?
Galvanic cells are spontaneous redox reactions that generate direct current. Electrolytic cells consume direct current to drive nonspontaneous redox reactions, including charging a battery or electroplating with a metal.
Ch 1 Leading zeroes versus trailing zeroes, one is never a SF, but the other can be if it comes _______ the decimal. Which is which? What is the missing term also.
What are leading zeroes are never SFs, but trailing zeroes are if AFTER the decimal point?
This number, 0.08020, has 4 SFs.
Ch 6 What are the four quantum numbers for the one electron in the hydrogen atom? n = __, l = ____, and ml = ___ and ms = ____
HINT: 1s1
What are 1,0,0 and 1/2?
But n = 2 and l = 1 for a 2px electron.
A favorite question: how many electrons can be in a 5fxyz atomic orbital?
It it is a orbital, not a subshell, it has only 2 e's.
Ch 13 In electrochemistry what is the SHE?
The standard hydrogen electrode has a Pt electrode in 1 M HCl with 1 atm H2 gas bubbled over it. It is assigned an SRP value of 0 volts by convention.
SRP is standard reduction potential.
Ch 13 one metal has an SRP value of 1.34 V and another has a value of -0.56 V. Calculate the cell potential for the galvanic cell made with these.
What is 1.84 volt?
One has to run backward and be the oxidation half of the process, changing its sign, before its voltage is added. Ecell = SRPred - SRPox
Ch 13 The electrode where reduction occurs in spontaneous cells as well as electrolytic cells is called the __________.
What is the cathode?
Ch 2 Isotopes of the same element have the same number of _____ but a different number of ____.
What are protons, the atomic number, and neutrons?
Chlorine-37 has 17 protons and 20 neutrons.
The mass no. is 37. the atomic no. is 17.
Ch 7 Hydrogen selenide (H2Se) is highly toxic and smells like decayed horseradish, rotting garlic, or leaking gas at low concentrations, and rotten eggs at high concentrations. How many lone pairs are on the Se atom?
What are two lone pairs of electrons?
It resembles H2O in that respect, along with H2S and H2Te, which is extemely toxic, unstable and smelly. It smells like rotting garlic at very low concentrations and decaying or rotting leeks or onions at higher concentrations.
Ch 13 If you were an electron in a galvanic cell, which electrode needs you to accomplish its task?
What is the cathode, where electrons are needed to cause the reduction? Reduction is the gain of electrons.
Ch 13 In the wire, electrons carry the current. But in solution the current has to be carried by _______.
What are ions?
Cations go to the cathode to be reduced.
Anions go toward the anode.
Ch 13 This is shorthand way to illustrate a galvanic cell.
Fe(s)|Fe3+(aq)||Cu2+(aq)|Cu(s)
What happens on the left side of the || symbol?
What is the iron is oxidized at the anode?
A-B-C for Anode - Bridge - Cathode
The bridge is ||
Anode: Fe(s) --> Fe3+ + 3e-
Cathode Cu2+ + 2e- --> Cu(s)
Ch 3 Molarity gives the number of _____ of _____ per _______ of ________.
What is the no. of MOLES of SOLUTE per LITER of SOLUTION?
% by mass = 100 x mass of solute/(mass of solution)
Two ways of expressing concentration.
Ch 8 Which of the IMFs, HB, DD or LDF, are present and dominant between the two molecules in this example? Think in 3D. CH2Cl2--CH2Cl2
HINT: the Cl--C--Cl bond angle is not 180o.
What are Dipole-Dipole attractive forces?
For HB you must see O-H, N-H or H-F in the molecule.
LDF is ever present, but only dominant for nonpolar molecules like CO2, CH4, F2, He, etc.
What is the cell potential if one metal, X, has the SRP of -0.76 V and the other, Y, has a potential of -1.02 V?
The cell potential is +0.26 V.
Why? ∆G = - nFEcell
Galvanic cells are spontaneous. Hence, ∆G must be (-) and Ecell must be (+). Reversing the wrong half-cell gives -0.26 V.
Ch 13 If a current of 35.0 A is applied to Al2O3 for 3.00 h what mass of liquid Al will be deposited at the cathode? Q = I x t and Al3+ + 3e- --> Al(l)
What is a mere 35.3 g of liquid Al metal?
No wonder it is cheaper to recycle it? The recycling energy cost is 5% of the method of Hall that we use today.
Ch 13 On February 23, 1886, in his woodshed laboratory at the family home on East College Street in Oberlin, OH, Charles Martin Hall succeeded in producing this metal by passing an electric current through a solution of the metal oxide in molten cryolite.
What is aluminum?
It was a semi-precious metal worth as much as silver at that time. Imagine the millions of miles of electrical cables globally being made of silver.
Ch 4 When given the masses of 2 different reactants and asked to calculate the theoretical yield of product, which of the two different answers is correct?
What is trust the smaller value? It's the limiting reactant, the one not present in excess.
Cheap reactants can be used in excess if they are easily separated from the product(s). This can speed the reaction and ensure complete conversion.
Ch 9 What is the heat of reaction for Equation 3 below?
1. A + B ---> C ∆H = 250 kJ
2. C --> E + G ∆H = -455 kJ
3. A + B --> E + G
What is -205 kJ?
This is applying Hess's law of constant heat summation. It only works because H is a state function. Changes in these state functions (E,S,H,G,T, P,V) depend only on initial and final states, not on path. Work, w, is not a state function.
Ch 13 How many coulombs of charge are associated with a 25.1 ampere current flowing for 2.00 hours?
What is 181,000 C (to 3 SFs)?
Q = I x t = 15.1 C/s x 2.00 h x 3600 s/h = 180,720 C
1 A = 1 C/s
Ch 13 If you wanted to plate out iron metal from a solution of Fe2(SO4)3, you'd be expected to write a half-equation involving how many moles of electrons equal to one mole of the metal?
What is 3 moles of electrons per mole of iron?
Yes, iron metal can be electroplated, but pure iron electroplating is rare commercially, whereas Nickel-Iron Alloy Plating is widely used as a cost-effective alternative to plating pure nickel. Plated from FeSO4, the pure iron tends to rust rapidly & has little eye appeal.
Fe3+ + 3e- --> Fe(s)
Ch 13 Is any of these a redox reaction? If so which?
A. NaOH + HCl --> NaCl + H2O(l)
B. AgNO3 + KBr --> AgBr(s) + KNO3
C. Mg(s) + 2HCl --> MgCl2 + H2(g)
What is option C?
Note that it has uncombined elements, Mg and H2.
There was a change in oxidation state for Mg from 0 to +2 and for H from +1 to zero.
All single replacement rxns are redox rxns. No double replacements are. Pptns & acid-base rxns.
Ch 5 If 34 liters of H2 react with excess nitrogen at some 400oC and 25 atm, what could be the maximum volume of ammonia produced? All are gases.
N2 + H2 --> NH3 (not balanced)
Gay-Lussac's law of combining volumes of gases.
What are 23 liters of NH3 (to 2 SFs)?
If the volume of H2 had been given, this would be a limiting reactant problem.
The Haber process uses an iron catalyst with KOH.
N2 + 3H2 --> 2NH3
Ch 10 Which one or more of these has a positive entropy change?Hint: ∆S = Sfinal -Sinitial
A. H2(g) + Cl2(g) --> 2HCl(g)
B. 2NH3(g) --> N2(g) + 3H2(g)
C. Mg(s) + 2HCl(aq) --> MgCl2(aq) + 2H2(g)
What are both B and C?
Not the increase in gases. Gases have vast disorder. The particles are in "constant, random motion" acc. to the kinetic molecular theory.