UWorld Gen Chem Missed

Suppose 0.80 L of 3.0 M aqueous K2MnO4 is combined with 0.20 L of 2.0 M aqueous KMnO4 to make a solution. What is the concentration of potassium ions in the solution?

0.8L x 3M x 2 mol K/K2Mn)4 = 4.8 mol K 0.2L x 2M = 1mol K/K2MnO4 = 0.4 mol K 0.2L + 0.8L = 1.0L, 5.2 mol/1L = 5.2M

Which elements are radioactive

All ones that have 83 protons or above

pOH and [OH-]

As [OH-] increases, [H+] decreases, so pH increases and pOH decreases

Exception to electron affinity trends increasing down a group

Atoms with small radii (oxygen, 1st/2nd period) have increased electron electron repulsion

Change in [H+] as bicarbonate ions acting on HCl

Bicarbonate neutralize gastric acid, decreasing [H+] and increasing pH Also would increase [OH-], decrease pOH

Boiling point and freezing point upon addition of solute

Boiling point increases, freezing point decreases Triple point happens at lower temp and pressure (down left diagonal shift)

pH of solution of CH3COONa

CH3COONa is made of weak acid CH3COOH and strong base NaOH, so would make a basic salt pH>7

If free energy change is ∆G = kRTlog(Final[]/Initial[]), how to calculate

Can't use pH, must use [H+]. If final pH = 1 and initial = 7, ∆G = kRTlog(10e-1/10e-7) = kRT(6)

Heterogenous catalyst

Catalyst is in different phase than reactant Like in catalytic converter, catalyst is in solid phase while reactant is gas

Ionic radius and charge

Cation have lowest radius, while anion have largest Losing e- to make cation causes greater Zeff, causing e- to become closer to eachother

Oxidizing agents

Cause oxidation in another compound

What could be changed that would not affect the reaction?

Could change the cation in a catalyst, like from NaI to KI Since the I is what is colliding with the reactant, not a big deal

Density as you increase T

D = M/V, T is proportional to V, so increasing T increases V, decreasing D

Beta - decay

Emits e-, increases atomic # by 1

How to calculate mmol of acid from ml

Find pH, [H+] = 10^-pH. [H+] = mol/L

Why would you not test corrosion rates by titrating the beaker with HCl

HCl could throw off the reaction equilibrium and it could cause more corrosion due to its acidic properties

Lewis acidity of alkali earth metals (Ca+2 and Mg+2)

Have large cationic radius and low charge, making them weak lewis acids

Type of catalyst and what do they affect

Homogeneous or heterogenous, affects rate of reaction

[] of electrode at cathode/anode depending on ∆Ecell

If +∆E, then greater [electrode] at cathode If -∆E, then greater [electrode] at anode

Finding [] given Ksp

If CuF2(s) ⇄Ksp Cu2+(aq)+2 F−(aq), Ksp = [Cu][F-]^2

If given Ksp for molecule with 2 ions, how to calculate one ion concentration

If NaOH, NaOH -> Na+ + OH- Ksp = [X][X], so square root of Ksp = [X]

vibrational modes from IR analysis and dipole moment

If dipole moment is cancelled out (symmetric stretch 180º from each other), there will be no IR signal

Coordinate bonds formed from a divalent ion

If ion such as oxalate C2O4-2, since charge of -2 one molecule will form 2 coordinate covalent bonds So if only forming 2 coordinate bonds, only should add one molecule of C2O4-2, not two

Ksp and responsivenesss to changes in ion concentration

If small Ksp, then changes to [A+] or [X-] have a larger impact than if Ksp is large

What forces does freezing point depend on

Intermolecular forces

How to tell what atom has smallest ionic radius

Ionic radii decrease with increasing atomic number More protons cause greater Zeff, pulling e- closer to nucleus

Energy to remove an e-

Ionization energy Decreases down group - easier to remove e- from Cl than from F Increases across row - easier to remove e- from F than Ne

Ksp of M(OH)2 ⇄M+2 + 2OH−, when pH = 10

Ksp = [M][2 OH-]^2, if pH = 10, pOH = 4, [OH-] = 10e-4 M is 1/2 of OH-, so [M] = 10e-4/2 = 5e-5 5e-5 x (10e-4)^2 = 5e-13 Based on equilibrium expression, we know there are twice as much OH as M

What law explains increase in reaction rate upon change of reactant ratios?

Law of mass action

How to determine what to dissolve molecule in and then titrate with

Look at structure, must make molecule soluble. After molecule is soluble, use opposite thing to titrate

Beta + decay

Lose a positron, product decreases atomic #, mass number is the same Proton converts to a neutron

Effect of very low solubility (Ksp) and le chatlier's principle

Low solubility means that by adding another species (like NaOH) to the solution, the precipitate won't form since it is insoluble If normally would affect equilibrium, no longer would

Metalloids

Make diagonal line done from Boron. Brittle, but conductive Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium

What to catch out for when determining oxidation number

Make sure molecule doesn't have charge on it. In Cu(C2H3O2)2, Copper has +2 charge meaning acetate has -1. Must take into account -1 charge when finding formal charge

How to find mass percent of compound

Mass (in GRAMS) of compound/total Must use mass, not volume. Can find mass if given volume and density

What does it mean if reaction mixture increases in temp

Mixture is releasing heat, so exothermic (-∆H)

Can H move when forming a resonance structure?

No

Can molecule be oxidizing/reducing agent if it is not oxidized/reduced?

No

Do catalysts affect heat of a reaction?

No, catalysts only change ∆G. Heat (∆H) is not affected

Are SO3 and SO3-2 the same compound?

No, since they have different numbers of e- and a different bonding configuration

Electrolysis

Nonspontaneous electrochemical decomposition of a compound

Between different groups of molecules with sigma bonds, what molecule would have longest bond length

One with largest atomic radius, which increases down a column and decreases across a row

Oxidizing agent

Oxidize something by taking e- away from something, getting reduced themselves Electron acceptor

Why does O have lowest e- affinity in group 6A

Oxygen has a small nucleus, resulting in more electron electron repulsion

Alpha decay

Release of He atom Decreases atomic number by 2, mass number by 4

Bonds involving H

Since H has small radii, makes short and strong bond Only reason that redox reactions can break X-H bond is because they form a new bond to H, providing the energy

∆G and pH

Since ∆G = -RTlnKeq, ∆G = -RTln([H+][A-]/[HA]) As pH decreases [H+] increases, causing a decrease in ∆G

∆H and energy of products and reactnats

Since ∆H = ∆Hproducts - ∆Hreactants +∆H = products>reactants -∆H = reactants>products

Moles present in solution in Ksp

Smaller Ksp means less soluble, meaning less moles will be present

What should be the reference electrode

Something that is not used up in a reaction

Lone pairs on strong lewis base

Strong Lewis base will replace weaker Lewis base. Stronger base has more lone pairs of e-

Calculating ∆G for reaction with different stteps

To find ∆G for step 2 product, must add ∆G of step 1 AND step 2

How would you titrate acid with hydrocarbon and carboxyl groups

Use base to dissolve, as it would make carboxylate ions that are soluble. Can then use acid to titrate

Reference electrode

Used in conjunction with a recording electrode to measure the difference in charge between the two. Reference electrodes are placed where the electrical signal remains constant, so any change in charge shows stuff is happening

Why is Hb red when it binds O2

When in a coordination sphere, atomic orbitals are not degenerate, so they have different energies. Energy of orbitals determines how which wavelengths of light are absorbed, so can change visible spectrum

Does [] of indicator in battery change?

Yes, if using H2SO4 as indicator, water will be produced when battery is discharged, diluting the []

How to calculate Zeff

Zeff = Charge - Core For N, 7-2 = 5

Homogenous catalyst

a catalyst that is in the same phase as all the reactants A catalyst that is in a solution

Concentration cell

a galvanic cell in which both compartments contain the same components, but at different concentrations

What type of bond has smaller dissociation energy, sigma or pi

pi bond is smaller

Disproportionation reaction

the same element is simultaneously oxidized and reduced 3 K2MnO4 + 4 HCl → 2 KMnO4 + MnO2 + 2 H2O + 4 KCl Mn goes from +6 charge to +7 charge and +4 charge

How to calculate ∆H given bond enthalpy values

∆H = sum(∆H bonds broken - bonds formed)

How to find ∆H given ∆H of each product/reactant

∆H products - ∆H reactants If coefficient, must multiply ∆H by that