Symbol/picture cards

Question 1

What is Charle’s law of gases concerning volume and temperature?

Answer 1

The volume (V) of a gas is directly proportional to the absolute temperature (expressed in Kelvins) when P and N are kept constant.

V₁/V₂ = T₁/T₂

Question 2

What is Boyle’s law of gases concerning pressure and volume?

Answer 2

The volume (V) of a fixed weight of gas, held at constant temperature (T) varies inversely with the pressure (P)

V = (constant)(1/P)

Question 3

What is the combined gas law?

Answer 3

Question 4

What is Dalton’s law? Give the formula for Dalton’s law and for the mole fraction (X_i)

What does the sum of all mole fractions equal?

Answer 4

Dalton’s Law states that the total pressure observed for a mixture of gases is equal to the sum of the pressures that each individual component would exert were it alone in the container

P_T = P₁ + P₂ + … + P_i

Where P_T is the total pressure and P_i is the partial pressure of any component. The ideal gas law applies to any component of a mixture!

The mole fraction of any one gas: (X_i) = n_i/n_(total)

where n_i is moles of one gas, and n_total is moles of all gas

The sum of all mole fractions must equal 1

Question 5

The partial pressure (Pi) of a component of a gas mixture is equal to: (formula)

Answer 5

P_i = X_iP_T

Where X_i = mole fraction = n_i/n_total

Question 6

Give the formula for the kinetic energy of particles in a gas

Answer 6

KE = ½mv²

Question 7

Describe a phase diagram

Answer 7

• At any point on the three curves the phases are in equilibrium
• The diagram is split into three areas (solid, liquid, vapour)
• The boiling point is at the transition liquid-vapour at 760 mmHg
• The diagram extends only to the critical point (C) where liquid and vapour are indistinguishable
• AE represents metastable equilibrium (supercooled water and its vapor)
• Line AD shows that increase pressure linearly decreaes melting point (unique property of water, line slants to right for almost all other substances)
• The triple point is the pressure/temperature where solid, liquid and vapour are in equilibrium. Ice and water have the same fixed vapour pressure at this temperature.

Question 8

What is Raoult’s law (vapour-pressure lowering)?

Answer 8

The vapour pressure of the components of an ideal solution behave as followed:

p_i = X_i(p_i)_pure

Where: p_i= vapour pressure of component in equilibrium

(p_i)_pure= vapour pressure of pure component at the same T

X_imole fraction of component in the liquid

Raoult’s law states that the vapour pressure of any component of a mixture is lowered by the presence of other component. Experimentally it can be observed that when dissolving a solute which cannot evaporate (nonvolatile), the pressure of the resulting solution is lower than that of the pure solvent. The extent depends on the mole fraction of solvent in solution:

P = P^o X

wgere P = vapour pressure of solution

P^o= vapour pressure of pure solvent (at T)

When arranged this way, Raoult’s law states that the lowering of the vapour pressure of the solvent is proportional to the mole fractio nof solvent and is independent of the chemical nature of the solute

Question 9

How does the addition of a solute to a solvent effect the solutions boiling point and freezing point?

Give the formulas that can predict the change in boiling point temperature (ΔT_B) and freezing temperature (ΔT_F)

Answer 9

Boiling point is increased

Freezing point is decreased

ΔT_{<strong>B</strong>} = K_B‘X_B = K_Bm

ΔT_{<strong>F</strong>} = K_F‘X_B = K_Fm

Where: K_B/F’ = boiling/freezing point elevation/depression constant for solvent

K_B/F = mole fraction of solute

m = molality (moles solute per kg solvent)

For molecules with strong dissociative properties (eg. NaCL), which gives strong negative and positive ions) the righ thand side is multiplied by a factor ‘n’ equal to number of ionic species generated per mole of solute (eg. NaCl = 2, MgCl₂ = 3) because this is an colligative property (depends on # of particles)

Question 10

Define the equilibrium constant for the solubility product (K_sp) of a substance

Answer 10

K_sp= [X⁺][X^-]

eg. Ag₂S: K_sp= [Ag⁺]²[S^2-]

low K_sp indicates low solubility

Question 11

List 8 strong acids and 8 weak acids

Answer 11

Question 12

Give the formula for the acid/base equilibrium constant (K_a) and examples of ionization of: HCl, HF and HCN

Answer 12

Question 13

How is the equilibrium constant for bases calculated?

Answer 13

Question 14

Describe water dissociation and the ion product constant for water

Answer 14

Water can ionize itself

2H₂O ⇋ H3O⁺ + OH^-

At STP, Kw = [H⁺][OH^-] = 10^-14 M

In a neutral solution: [H⁺] = [OH^-] = 10^-7 M

K_w increases with temperature

Question 15

What does the pH scale represent? What is it defined as? (formula)

Why is the pH of a neutral solution of pure water 7?

Answer 15

The concentration of hydrogen ions in solution.

pH = -log₁₀[H⁺]

[H+] = -log₁₀(10^-7) = 7

Question 16

What is the formula for pK_wand what is this at pH = 7?

Answer 16

pK_w = pH + pOH

At 25°C, pH + pOH = 14

Question 17

To determine pH values, it is important to remember certain logarithmic properties. Define the following:

• log_aa =
• log_aM^k=
• log_a(MN) =
• log_a(M/N) =
• 10^log₁₀M =

Answer 17

log_aa = 1

log_aM^k = (k)(log_aM)

log_a(MN) = log_aM + log_aN

log_a(M/N) = log_aM - log_aN

10^log₁₀M = M

Question 18

How can the pH of weak acids and bases be calculated?

Answer 18

Question 19

What is the salt of a weak acid?

Answer 19

The salt of a weak acid is a Bronsted base, which will accept protons.

eg. Na⁺OAc^- + H₂O ⇋ HOAc + Na⁺OH^-

The HOAc here is undissociated and therefore does not contribute to the pH. This ionization isknown as hydrolysis of teh salt ion. Because it hydrolyzes, sodium acetate is a weak base (the conjugate base of acetic acid). The ionization constant is equal to the basicity constant of the salt. The weaker the conjugate acid, the stronger the conjugate base, that is, the more strongly the salt will combine with a proton.

Question 20

What is the hydrolysis constant of a salt and how is it calculated?

Describe the relationship between salts and the dissociation constants of acids and bases (as well as the water dissociation constant)

Answer 20

eg. Na⁺OAc^- + H₂O ⇋ HOAc + Na⁺OH^-

K_H = K_b = [HOAc][OH^-]/[OAc^-]

K_H is the hydrolysis constant of a salt

The product of K_a of any weak acid and K_b of its conjugate base is always equal to K_w

(K_a)(K_b) = K_w

Question 21

Describe a titration curve between a strong acid and a strong base. Where is the equivalence point?

Answer 21

Question 22

Describe the titration curve of a weak acid versus a strong base. Where is the equivalence point?

Answer 22

Question 23

What is Hess’s law and how is it applied to determining net change in enthalpy for multi component reactions?

Answer 23

Application of the fact that H is a state function. By knowing the changes of enthalpy for a system in one reaction, the change in enthalpy in other reactions (or the net reaction) can be determined.

ΔH_OVERALL = ΔH₁ + ΔH₂

1. Start by writing the overall reaction that you want to obtain through a series of reaction additions. (keep reactants on left and products on left)
2. Number reactions
3. Circle or underline first reactant, find reaction in list that involves this reactant (as reactant or product), and rewrite so that reactant is on left (may need to switch H sign). Multiply by stoichiometric coefficient
4. Continue until all reaction component H’s are summed

Question 24

Give the two calorimetric formulas for measuring the amount of heat (Q) released or absorbed during a chemical reaction

Answer 24

Q = mC(T₂-T₁)

Q = nc(T₂-T₁)

m: mass of sample
n: number of moles of sample

C: Specigic heat capacity in J/kg/K

c: heat capacity in J/mol/K

Question 25

Give the formula for the rate of a chemical reaction (given in moles/litre/second)

Answer 25

rate = k[A]^m[B]ⁿ

Where [] is the concentration of the corresponding reactance in moles/litre

k: the rate constant
m: the order of teh reaction with respect to A
n: the order of the reaction with respect to B

m+n is the overall reaction order

According to the rate law above, the reaction is said to be an (m+n)th order reaction

Question 26

How can the order of a chemical reaction be determined?

Answer 26

It can be determined experimentally. By measuring the initial rate of reaction and the initial concentrations.

Method: Find a pair of experimental runs that the concentration of only one reactant changes. This is called the method of isolation and a good experimental design always has one such pair of experimetal runs. We can see that in runs 1 and 2, only the initial concentration of B has been varied. In fact, [B] has doubled from run 1 to run 2 and the reaction rate has also doubled. Therefore the reaction must be First Order in B.

Question 27

What is the reaction order for A and B?

Give the formula for determining the rate constant (k)

Answer 27

A: 1

B: 2

Rate increases by factor of (change in initial concentration eg. 2x)^order

k = (rate)/([A]¹[B]]²)

Question 28

Contrast a potential energy diagram for an exothermic and endothermic chemical reaction

Answer 28

Question 29

Contrast the potential energy diagrams of chemical reactions with and without a catalyst.

Answer 29

Question 30

Give the formula for calculating the equilibrium constant (K_eq)

What is the law of mass action?

Answer 30

Question 31

Recall the procedure for determining redox half-reactions

Answer 31

Question 32

From the following half reactions, describe what would happen if Zn came in contact with a solution containing Cu²⁺

What about the opposite (Cu in Zn²⁺ ions)?

Answer 32

• A spontaneous redox reaction would occur (known because of the positive E° value, which predicts spontaneity)
• If you put Cu directly in contact with a solution containing Zn²⁺ ions, no reaction takes place spontaneously.

Question 33

If the concentration of all the ions in a galvanic cell is 1, how do you calculated the electromotive force (emf)?

Answer 33

emf = n x E°_{(reduction half reaction)} - m x E°_{(oxidation half reaction)}

Where n and m are the stoichiometric factors by which each half reaction needs to be multiplied by to yield a balanced overall reaction.

Voltage can be measured by a voltmetre.

Question 34

Recall a galvanic cell

Answer 34

Question 35

Concentrated H₂SO₄ is 98% H₂SO₄ and 2% water by mass. The density of concentrated H₂SO₄ is 1.84 g/mL.

How can the number of moles of water in 1 mL of concentrated H₂SO₄ be determined? (just give equation)

Answer 35

(1. 84 g conc. H₂SO₄)/(1 mL solution) x (2 g H₂0)/(100 g conc. H₂SO₄) x (1 mol H₂0)/(18 g H₂0) =
(1. 84)(0.02)/18

AKA: Multiply the density of the compound in solution by the percent water (.02) to get grams of water. Divide by molar mass of water to get moles water.

Question 36

Which of the following species has the smallest concentration in 98% H2SO4?

1. SO₄^2-
2. H₂SO₄
3. H30⁺
4. HSO₄^-

Answer 36

1. SO₄^2-

The first ionization of sulfuric acid (H₂SO₄) is normally 100% in water. However, under conditions of low water content (only 2% is water in this example), not all of the H₂SO₄ can ionize. And qualitatively, the only source of SO₄^2- is HSO₄^-

The Ka for the second ionization step of a parent acid is a few orders of magnitude smaller than that of the first step, therefore SO₄^2- must be the least abundant species because it is only formed in the second ionization step.

Question 37

Suppose that CH₄(g) reacts completely with O₂ (g) to form CO2 (g) and H₂O (g), with a total pressure of 1.2 torr. What is the partial pressure of H₂O (g)?

Answer 37

The pressure of the gaseous products is 1.2 torr, for every three product molecules, two are water. Therefore, the partial pressure of water is 2/3 the total pressure, because the total pressure is a function of the total number, but not kind, of molecules.

2/3(1.8) = .8 torr

Question 38

A sparingly soluble metal hydroxide, M(OH)₂ has a molar solubility of S mol/L at 25 degrees celsius. Its K_sp value is:

Answer 38

4S³

The Ksp for a substance AaBb, equals [A]^a[B]^b. The K_sp for M(OH)₂ = [M][OH^-]₂. If the solubility of M(OH)₂ is S mol/L, then [M] = S mol/L and [OH^-] = 2S mol/L. The K_sp = S(2S)² = 4S³

Question 39

The atomic number of nitrogen is 7. What is the most stable electron configuration?

Answer 39

1s² 2s² 2p³

The electrons will begin to fill the lower energy levels first, consequently the 1s level will fill first with two electrons, followed by 2s with two electrons, and then the 2p level with the last three electrons.

Question 40

From reactions 3-5, what can be determined about the relative concentrations of CFCs and O₂?

A. One equivalent of CFC is required to produce two equivalents of O₂

B. One equivelent of CFC is required to produce two equivalents of O₂

C. A catalytic amount of CFC can produce much O₂

D. The CFC is produced by a catalytic amount of O₂

Answer 40

C. A catalytic amount of CFC can produce much O₂

After the initial step of breaking the bond in the chlorofluorocarbon CF3Cl, the Cl* and ClO* radical are recycled. In other words, these two species act as catalysts: they react with the substrate (O3 and O) and are reformed. The re-formed chlorine free radical can participate in another cycle of reactions 4 and 5. Thus, a small amount of the CFC can produce much O2 by catalyzing the decomposition of ozone.

Question 41

Consider the above unbalanced equation. For this reaction, how many mL of a 2 M solution of Na₂CO₃ are required to produce 11.2 L of CO₂ at STP?

Answer 41

• The equation must be balanced first
• You must know that one mole of an ideal gas at STP will occupy a volume of 22.4 L.
  
  • Therefore 11.2 L of CO2 gas, at STP, must represent .5 mole of CO2 (virtually all gases can be approximated as ideal gases at common temperatures and pressures).
  • One mole of CO2 is produced when one mole of Na2CO3 reacts, therefore, the amount of Na2CO3 required to produce .5 mole of CO2 gase must also be .5 moles.
• To find the volume of 2 M Na2CO3 solution, which contains the required .5 moles of reactant we follow the equation shown
  
  • Essentially, find dilution by cancelling out common units (eg. mol)
• The answer is 250 mL

Question 42

What are the oxidation numbers for the following:

• F
• Group 1 metals
• Group 2 metals
• Elemental form
• H
• O
• Cl, Br, I

Answer 42

Note the variation among the halogens (Cl, Br and I vs. F)

Question 43

Give the equation that you would use if you were asked to find the initial ratio of an acid and its conjugate base in a buffer solution.

Answer 43

You would use the Henderson-Hasselbalch equation.

pH = pK_a + log([conj base]/[conj acid])

or

pOH = pK_b + log[conj acid]/[conj base])

To find the ratio, you would take the antilog

Question 44

How many metres is 450 nm?

Answer 44

450 x 10^-9m

Question 45

When a strip of Cu is placed into H₂O (l), no change is observed. However, when a strip of Cu is placed into a solution of HNO₃ (aq), a gas evolves. What is the most likely identity of the gas?

Answer 45

NO (g)

Nitrogen monoxide is one gas evolved when copper metal is placed in a nitric acid (HNO3) solution. This reaction is an oxidation reduction reaction, where copper is oxidized (loses electrons) and nitrogen is reduced (gains electrons). Nitric acid is an oxidizing acid, and nitrate salts can be oxidizing agents as well, under the proper conditions.

Question 46

What is the orbital hybridization of O in THF?

Answer 46

sp³

The oxygen atom in THF is in the same bonding situation as the oxygen atom in water. O has eight electrons around it, four of these are bonding electrons, representing the two bonds to neighboring carbons shown in the structure. THe other four electrons comprise two lone pairs on oxygen.

An atom with four charge clouds around it would be expected to utilize sp³ hybrid orbitals, since these will provide the correct number of orbitals and the observed geometry.

Question 47

Give the equation that describes the effect on boiling point, when a nonvolatile solute is added to a liquid.

Answer 47

ΔT_<em>b</em> = K_<em>b</em>m

This is the boiling point elevation equation for a solid solute (molality/m, rather than molarity/M).

K_b is the molal boiling point elevation constant, therefore molality (moles/kg solvent) MUST be used!

Question 48

When an electron fall from n = 3 to n = 2 in a hydrogen atom, what is the value of the energy released, given that A is the energy needed to remove an electron from the ground state of a hydrogen atom to an infinite distance from the atom.

Answer 48

0.14 A

Bohr equation: E = -A x (1/n_i² - 1/n_f²)

n_i = first quantum number of the electron in its initial state

n_f = first quantum number of the electron in its final state.

E = -A x (1/9 - 1/4) = -A x (-5/36) = 0.14 A

A is the amount of energy needed to remove an electron from the lowest energy level of a hydrogen atom to a pont at an inifinite distance away. BE CAREFUL OF SIGNS! If the electron is falling towards the nucleus it is giving off energy and A is negative. If it is moved to a higher orbital, it requires energy and A is positive.

Question 49

Give the formula for determining energy of combustion (ΔEcomb)

Answer 49

ΔE_comb = ΔE_f,CO2 + ΔE_f,H2O - ΔE_f,reactant

Question 50

How many pi electrons are in pyrrole? How do you know?

Answer 50

Hückel’s Rule (4n+2 rule)

n = 0, 1, 2, 3 etc. (usually 1)

4(1) + 2 = 6 pi electrons

• 4 pi electrons in the double bonds
• 2 pi electrons as a lone pair

Question 51

which of the following is the product of a Claisen rearrangement of the following allyl vinyl ether?

Answer 51

In this case, there are three pairs of electrons being transferred among the atoms shown. An aldehyde is formed and the reaction stops there prior to enolization, as the carbonyl form is more stable than its corresponding enol (beware, this isn’t always the case!)

Question 52

Define an enol

Answer 52

Enols (also known as alkenols) are alkenes with a hydroxyl group affixed to one of the carbon atoms composing the double bond. Alkenes with a hydroxyl group on both sides of the double bond are called enediols.

Question 53

Answer 53

Only I and II have reactants which are in their most thermodynamically stable state (a requirement for the overall H to be H_formation)

Question 54

This is the Van der Waals equation, a descriptor of non-ideal gases (and hence, modified ideal gas equation).

How has P and V been modified in the Van der Waals equation and why?

Answer 54

Pressure: Pressure has been modified by adding n²a/V², this is to account for the fact that gas molecules exert intermolecular attractive forces. As density of molecules increases, so will intermolecular attractive forces, and hence.

Volume: By subtracting nb, you are substracting the volume of space occupied by the gas molecules. This is to account for the fact that gas molecules have finite (non-negligible) volume.

Question 55

How do you determine the acceleration of m₂?

The surface between m1 and m2 is frictionless, yet the force F does not cause m3 to rise or fall. What is the acceleration of m1?

Answer 55

a2 = (m₃/m₂)g

This is derived from the fact that the equation of motin for m2 is m₂a₂ = T and T = m₃g

m2a2 = m3g

a₂ = (m₃/m₂)g

Because m₃ isn’t moving up or down, m₂ isn’t moving and therefore must have the same acceleration as m₁ (m₃/m₂)g

Question 56

Using the VSEPR theory, what is the shape of SF₄

Answer 56

Seesaw-like

SF4 has 5 valence shell electron pairs. These would normally arrange themselves in a trigonal bipyramidal fashion to maximize repulsion among electron pairs. However, one of the electron pairs is a lone pair that repels more than other pairs. It therefore resides in the middle plane and the molecule consequently has a seesaw shape.

Question 57

Using VSEPR theory, what is the shape of BrF₅?

Answer 57

Square pyramidal

BrF5 has 6 valence shell electron pairs. These would normally arrange themselves in an octahedral fashion. However, since one of the electron pairs is a lone pair, the molecule consequently has a square pyramidal shape.

Question 58

Using VSEPR theory, what is the shape of PCl₅?

Answer 58

Trigonal bipyramidal

PCl5 has 5 valence shell electron pairs. These will arrange themselves in a trigonal bipyramidal shape.

Question 59

Using the VSEPR theory, the shape of SF₆ is?

Answer 59

SF6 has 6 valence shell electron pairs. These will arrange themselves in an octahedral shape.

Question 60

Using VSEPR theory, the shape of PCl₃ is?

Answer 60

Trigonal pyramidal

PCl3 has 4 valence shell electron pairs. These would normally arrange themselves in an tetrahedral fashion. However, since one of the electron pairs is a lone pair, the molecule has consequently a trigonal pyramidal shape.

Question 61

VSEPR ClF₃

Answer 61

T-shaped