General Chemistry Flashcards
A compound is found to contain 64% silver, 8% nitrogen and 28% Oxygen by mass. What is the empirical formula?
AgNO3
Ag: 64/108=.6
N: 8/14=.6
O: 28/16=1.8
Ag:N:O = 1:1:3
Magnesium metal burns in air with a brilliant white flame. Why?
Magnesium metal burns in air with a brilliant white flame because magnesium is undergoing several different electronic transitions at the same time.
no such thing as a white photon.
“Oxygen atoms always emit UV light during combustion” is partially true, but invisible UV light has nothing to do with white light.
x-rays are not produced by heated magnesium, and even if they were, they would also be invisible. (In fact, if you actually looked at a strong source of x-rays, the world would begin to look darker and darker as the x-rays obliterated your cones and rods.)
Which one of the following molecules is a free radical?
BrO3
N2O
Correct Answer
BrO3
Explanation
Of the molecules listed, BrO3 is the free radical.
A radical has an odd number of electrons. Bromine trioxide, having 7 + 6 + 6 + 6 = 25 valence electrons, is a radical.
Given that the electron configuration of nickel is [Ar] 4s2,3d8, what would be the electron configuration of the Ni- ion?
[Ar] 4s1, 3d10
Given that the electron configuration of nickel is [Ar] 4s2 3d8, [Ar] 4s1 3d10 would be the electron configuration of the Ni- ion.
One might expect that the extra electron would be accommodated into the partially filled 3d orbital, such that the Ni- ion would have a configuration of [Ar] 4s2 3d9. This line of thought is correct but incomplete. Just like the copper atom, the Ni- ion will immediately take a 4s electron and use it to close the 3d subshell.
If the ground state (n = 1) energy for a hydrogen atom is -13.6 eV, the first excited state (n = 2) is -3.4 eV and the second excited state (n = 3) is -1.5 eV, what photon energies would be emitted from one mole of excited (n = 3) hydrogen atoms?
12.1 eV, 10.2 eV, and 1.9 eV
First of all, photons can never have negative energy
Now, the energy of the photon released from an excited atom always equals the difference between the excited energy level and the lower energy level. There are three possible drops an electron originally in level n = 3 can make:
n = 3 to n = 1: E = -1.5 - (-13.6) = 12.1 eV,
n = 2 to n = 1: E = -3.4 - (-13.6) = 10.2 eV,
n = 3 to n = 2: E = -1.5 - (-3.4) = 1.9 eV.
Does changing concentration or pressure change the reaction’s Keq value?
No, changing concentration or pressure only changes the reaction quotient “Q”, but does not change a reactions Keq value.
Only Temperature can change a reactions Keq value, since every reaction involves an endothermic & exothermic (forward or reverse) reaction.
Adding or removing heat will change the reaction kinetics allowing it to reach an equilibrium faster, but once at equilibrium, adding or removing heat will change the Keq.
Will a change in temperature affect the reaction’s Keq?
Yes, but only if the reaction was already at equilibrium and heat was added or removed.
If heat is added prior to equilibrium, equilibrium will be reached faster since all reactions proceed faster when the temperature is increased (even for an exothermic reaction)
Does adding Helium to a reaction change the partial pressure or concentration of the products or reactants?
No, adding an inert (or non-reactive) gas doesn’t participate in the reaction (no reactions at all for the mcat) so it will NOT change the partial pressure nor the concentrations of the products or reactants. If neither of these values change, then there is no change in equilibrium.
What are the 6 common strong acids that you should memorize for the MCAT?
Hyrdoiodic acid HI Hydrobromic acid HBr Hydrochloric acid HCl Perchloric acid HClO4 Sulfuric acid H2SO4 Nitric acid HNO3
Is HClO3 considered a strong acid?
No, its pKa is -1, could be considered strong, but it is definitely one of the weaker strong acids and is not likely to appear on the MCAT. However HClO4 (Perchloric acid), with an extra oxygen atom, is a strong acid and considered a strong acid on the MCAT.
A 1M aq solution of boric acid (H3BO3, Ka=5.8x10^10) which species will be present in solution in the greatest quantity?
Since Boric acic is not a strong acid, its Ka is less than one, which means more reactants than products, hence there will be more of the original H3BO3 boric acid in solution at equilibrium.
What are the 4 broad categories of strong bases used in aqeous solutions that may be used on the MCAT, and give an example of each?
Group 1 Hydroxides: NaOH
Group 1 Oxides: Li2O
Group 2 Hydroxides: Ba(OH)2, Sr(OH)2, Ca(OH)2
Metal Amides: NaNH2
Characterize Ammonia, (NH3), as a strong, weak, or moderate Acid/Base?
Ammonia NH3 is a weak base
Characterize Amines, as a strong, weak, or moderate Acid/Base?
Amines are weak bases
Characterize the conjugate bases of weak acids, as a strong, weak, or moderate Acid/Base?
The conjugate base of a weak acid is a weak base
