HU Chemistry II final (CHEM004)

What is the mass percent of a methanol solution that contains 25.0 g of CH3OH (methanol) in 125 grams of water?

16.7% explanation: mass percent=mass of solute/total mass of solution X 100 =25g/150g X 100 =16.7%

In fcc cubic lattice, an atom lying at the center of a side of the unit cell is shared equally by how many unit cells?

2 explanation: The faces of an fcc cubic lattice are parallel to each other, and since there are 6 atoms on each face, there are 3 atoms (½ X 6) that are shared by each unit cell (1 atom per 2 unit cells)

What is the concentration of As ion in a solution that contains 25.0 micro grams the As ion in 100 grams of water? [1 micro gm =10-6 gm]

250 ppb explanation: 25.0mg X 10^-6g=2.5 X 10^-5g ppb=mass of solute/total mass of solution X 10^9 =2.5 X 10^-5g As/100.000025g total mass of solution X 10^9 =250 ppb

In a face-centered cubic lattice, how many atoms are present in a unit cell?

4

What is the packing efficiency of a bcc unit cell?

68%

What is the packing efficiency of a fcc unit cell?

74%

What is the coordination number of a bcc unit cell?

8

Rank the following liquids in order of increasing boiling points, from lowest to highest: He , NH3 , Ar , N2

He < N2< Ar < NH3 explanation: NH3 is a hydrogen bond, which in this case, has the highest boiling point. For the other compounds, look into the molecular weight to see for dispersion, which is the next strongest force to determine the boiling point.

Which of the following aqueous solutions would have the highest vapor pressure? (Hint: Which solute in aqueous solution produces the greatest/lowest number of particles?) a. 0.1 M KCl b. 0.4 M NaCl c. 0.2 M NaCl d. 0.1 M CaCl2

a. 0.1 M KCl explanation: Solutes decrease vapor pressure-Higher concentration=lower vapor pressure, solutes increase boiling point,- igher concentration=higher boiling point, and solutes lower freezing point-higher concentration=lower freezing point. To determine which solution will have the highest vapor pressure, determine which solution has the least amount of particles, which in this case, is KCl.

What is the equilibrium constant for the following reaction, if [HBr] = 0.5 M, [H2] = 0.1 M and [Br2] = 0.1 M at equilibrium? H2(g) + Br2(g) -----> 2HBr(g) a. 25 b. 0.04 c. 0.02 d. 50

a. 25 explanation: In order to find the equilibrium constant for the following reaction, substitute the given concentrations into the Kc equation, Kc=[products]/[reactants] Kc=[0.5]^2/[0.1][0.1] =25

What percentage of a material will persist after 120 minutes if its half-life is 60 minutes? a. 25% b. 12.5% c. 50% d. 33%

a. 25% explanation: 120/60=2 120=100% 60=x% 120x=6000 x=50 50/2=25%

The reaction A + 2B -----> C is an elementary reaction. The overall order of the reaction is: a. 3 b. 1 c. 2 d. 0

a. 3 explanation: In order to determine the overall order of the reaction, add up the coefficients of the reaction, which in this case, is 1+2=3.

Which of the following has the highest boiling point? a. 4M CaCl2 b. 2M NaCl c. 4M NaCl d. Pure H2O

a. 4M CaCl2 explanation: Solutes decrease vapor pressure-Higher concentration=lower vapor pressure, solutes increase boiling point,- higher concentration=higher boiling point, and solutes lower freezing point-higher concentration=lower freezing point. To determine which solution will have the highest boiling point, determine which solution has the highest concentration , which in this case is 4M CaCl2.

If a solution has a [H+]=1 x 10 -9 M, what is the pOH of that solution? a. 5 b. -9 c. 9 d. -5

a. 5 explanation: POH= 14-PH POH= 14-9 POH= 5

The solubility of CaCO3 in water is 15mg/L. Which of the following masses of CaCO3 will form a 5 L supersaturated solution? a. 85 mg b. 3 mg c. 65 mg d. 75 mg

a. 85 mg Correct explanation: 15mg X 5L=75mg/L to figure out which solution will form a supersaturated solution, look for the solution with more than 75mg, which in this case, is 85mg.

Which response has the following substances arranged in order of INCREASING boiling point? Ar, NaClO3, H2O, H2Se a. Ar < H2Se < H2O < NaClO3 b. Ar < H2O < H2Se < NaClO3 c. Ar < NaClO3 < H2Se < H2O d. NaClO3 < H2Se < H2O < Ar e. NaClO3< H2O < H2Se < Ar

a. Ar < H2Se < H2O < NaClO3 explanation: NaClO3 is an ion-dipole (Na being an ion and ClO3 being a polar molecule), which has the highest boiling point. The second-highest boiling point is H2O due to it being a hydrogen bond. With Ar and H2Se left, the third highest boiling point is dispersion, in that whichever compound has the highest molecular weight will have the highest boiling point.

Which of the following substances would have the lowest solubility in water? a. CH3CH2CH2CH2OH b. Na2SO4 c. CH3OH d. NaCl

a. CH3CH2CH2CH2OH explanation: Alcohols with longer chains will dissolve more in CCl4, which is a nonpolar solvent, and less in water (which is a polar solvent) due to the decrease in hydrogen bonds following the increase in molecular weight and dispersion.

Which of the following gaseous substances would have the highest solubility in water? a. CO2 b. NH3 c. O2 d. H2

a. CO2 explanation: When determining the solubility of gaseous substances in water, look at molecular weight. The higher the molecular weight, the higher the solubility. Hence, CO2 has the highest molecular weight. Also, water is a polar solvent, meaning the solutes must also be polar.

Which of the following has the most delocalized/mobile electron? a. Cu b. NaCl c. Diamond d. Graphite

a. Cu explanation: Cu is a metallic solid, which conducts electricity as a result of being held together by an electron sea. The free electrons within this sea allows Cu to conduct electricity. Diamond and Graphite are covalent-network solids (held by a network of covalent bonds) and NaCl is an ionic solid (held by electrostatic attractions)

Which of the following has the lowest band gap? a. Cu b. Graphite c. Si d. H2O

a. Cu explanation: When looking at band gap, insulators have the highest band gap (ex. C) as a result of the band gap going up due to a decrease in molecular weight, followed by semiconductors (ex. Graphite and Si) and lastly, conductors (ex. Cu). Because Cu is a conductor, it will have the lowest band gap.

What is the nature of the dominating intermolecular attractive forces between solute and solvent for a solution of CH3OH in hexane (C6H14)? a. London dispersion force b. Dipole-dipole attractions c. Ion-dipole attractions d. Hydrogen bonding

a. London dispersion force explanation: although CH3OH has hydrogen bonds, it is being dissolved in a nonpolar solvent, and the result of this would be dispersion. However, when dissolving a solute in a polar solvent, the dominating force will be dipole-dipole.

What is the nature of the dominating intermolecular attractive forces between solute and solvent for a solution of CH3CH2CH2CH2CH2OH in water? a. London dispersion force b. Dipole-dipole attractions c. Ion-dipole attractions d. Hydrogen bonding

a. London dispersion force explanation: since CH3CH2CH2CH2CH2OH has long alcohol chains it will dissolve in water, whereas shorter alcohol chains are needed for it to be dissolved in hexane. It is being dissolved in a polar solvent so the result of this would be dispersion.

Which of the following intermolecular forces is INCORRECTLY assigned as the principal force in the compound given? a. NH3, London b. CH3OH, H-bonding c. HF, H-bonding d. CCl4, London

a. NH3, London explanation: NH3 is held together by a hydrogen bond. A requirement for a compound to be considered a hydrogen bond is if hydrogen is bonded to either fluorine, oxygen, or nitrogen.

Which of the following salt will have a neutral solution? a. NaCl a. Fe(NO3)3 a. Al(NO3)3 a. NH4Cl

a. NaCl explanation: A salt will have a neutral solution, if it has the a strong acid and a strong base. A salt will have an acidic solution if it has a strong acid and a weak base. A salt will have a basic solution if it has a weak acid and a strong base. Na+ will bond to OH- and Cl- will bond to H+. Determine if the formed molecules are strong or weak acids/bases. NaOH is a strong base and HCl is a strong base, so NaCl will have a neutral solution.

Consider the following table of Ksp values. Compound Ksp PbCO3 7.4 x 10-14 ZnCO3 1.4 x 10-11 CePO4 6.3 x 10-16 PbS 8.0 x 10-28 Which one of the compounds shown in the table is the least soluble? a. PbS b. CePO4 c. ZnCO3 d. PbCO3

a. PbS explanation: The lower the KsP value, the lower the solubility. The higher the KsP value, the higher the solubility. Since PbS has the lowest solubility, it is the least soluble.

Which of the following has the highest freezing point? a. Pure H2O b. 4M CaCl2 c. 4M NaCl d. 2M NaCl

a. Pure H2O Correct explanation: Solutes decrease vapor pressure-Higher concentration=lower vapor pressure, solutes increase boiling point,- higher concentration=higher boiling point, and solutes lower freezing point-higher concentration=lower freezing point. To determine which solution will have the highest freezing point, determine which solution has the lowest concentration, which in this case, is pure H2O.

Which of the following is the correct Kc expression for the reaction CaCO3 (s) -----> CaO(s) + CO2(g) ? a. [CaO][CO2] b. [CO2] c. [CaO][CO2]/[CaCO3]2 d. [CaO][CO2]/[CaCO3]

a. [CO2] explanation: Kc=[products]/[reactants] *not including liquids and solids Kc=[CO2]

For the reaction 2 A + 2B ---> 3 C, how does the rate of disappearance of A compare to the rate of production of C? a. the rate of disappearance of A is 2/3 the rate of appearance of C b. the rate of disappearance of A is 3/2 the rate of appearance of C c. the rate of disappearance of A is 1/2 the rate of appearance of C d. the rate of disappearance of A is 1/3 the rate of appearance of C

a. the rate of disappearance of A is 2/3 the rate of appearance of C explanation: The reason why the rate of disappearance of A is 2/3 the rate of appearance of C is the correct answer is that the coefficient of A is ½ and the coefficient of C is 1/3. You would multiply both A and C by 2, canceling out the coefficient of reactant A and reactant C would be multiplied by 2. As a result, the disappearance of A (with A being the only variable left over) is equal to 2/3 the rate of appearance of C.

If the reaction quotient Q has a larger value than the related equilibrium constant, K, which of the following is true? a. the reaction is not at equilibrium and will make more reactants at the expense of products b. the reaction is not at equilibrium and will make more products at the expense of reactants c. the reaction is at equilibrium

a. the reaction is not at equilibrium and will make more reactants at the expense of products explanation: When Q>K the reaction is not at equilibrium and has too many products, so it will proceed toward the reactants. If Q=K the reaction is at equilibrium.

If a solution has a pH of 5, what is the [H+] of that solution? a. 1 x 10 -6 b. 1 x 10 -5 c. 1 x 10 -9 d. 1 x 10 -14

b. 1 x 10 -5 explanation: [H+]= 10^-PH [H+]= 10^-5 [H+]= 1.0 X 10^-5 M

What volume of 0.2 M NaOH will be required to neutralize 50 mL of 0.1 M of HCl ? a. 45 mL b. 25 mL c. 100 mL d. 50 mL

b. 25 mL explanation:

What is the most likely value of the pH of the equivalence point of a titration curve of a strong acid and a weak base? a. 7 b. 5 c. 14 d. 9

b. 5 explanation: strong acid + strong base= equivalence 7 Weak acid + strong base= equivalence > 7 Strong acid + weak base= equivalence < 7 Weak acid + weak base= equivalence 7

What is the most likely value of the pH of the equivalence point of a titration curve of a strong acid and a strong base? a. 5 b. 7 c. 9 d. 14

b. 7 explanation: strong acid + strong base= equivalence 7 Weak acid + strong base= equivalence > 7 Strong acid + weak base= equivalence < 7 Weak acid + weak base= equivalence 7

Which of the following substances would have the highest solubility in benzene, C6H6? a. H2O b. CCL4 c. CH3OH d.HCL

b. CCL4 explanation: When determining the solubility of nonpolar substances, look into molecular weight. The higher the molecular weight, the higher the solubility. Also, Benzene is a nonpolar solvent, meaning the solutes must also be nonpolar.

For the reaction CH3COOH+ NH3 ---> CH3COO- + NH4+, which of the following is the conjugate base of the reactant acid CH3COOH? a. NH4+ b. CH3COO- c. H+ d. NH3

b. CH3COO- explanation: CH3COOH is the acid because it is a proton donor. It becomes more negative and its conjugate base is CH3COO-. On the contrary, NH3 is the base because it is a proton acceptor. It becomes more positive and its conjugate acid is NH4+.

Which one of the following is not a conjugate acid-base pair? a. NH3 and NH2- b. H3O+ and OH- c. NH4+ and NH3 d. H2PO4 - and HPO4 2-

b. H3O+ and OH- explanation: When looking for a conjugate acid-base pair, the conjugate has to 1 be proton less, and since the conjugate in this case is 2 protons less, its not a true conjugate acid-base pair.

Which of the following can be mixed together in water to produce a buffer solution? a. HNO3 and NaNO3 b. H3PO4 and NaH2PO4 c. HCl and NaCl d. H2SO4 and NaHSO4

b. H3PO4 and NaH2PO4 explanation: For acid-base buffers, a weak acid must be paired to its strong conjugate base or a weak base must be paired to its strong conjugate acid. H3PO4 is a weak acid and NaH2PO4 is its strong conjugate base so it can be mixed together in water to produce a buffer solution.

Use the following acid ionization constants to identify the correct order of acid strengths. HF Ka = 7.2 × 10-4 HNO2 Ka = 4.5 × 10-4 HCN Ka = 6.2 × 10-10 a. HF < HNO2 < HCN b. HF > HNO2 > HCN c. HCN > HF > HNO2 d. HF > HCN > HNO2

b. HF > HNO2 > HCN explanation: Increase in Ka = Increase in strength of acid Decrease in Ka= Decrease in strength of acid To compare the numbers easier, find the pKa of the Ka values. pKa= -log (Ka), and increase in pKa=decrease in strength of acid decrease in pKa=increase in strength of acid HF pKa = 3.14 HNO2 pKa = 3.35 HCN pKa = 9.21 since HCN has the highest pKa, it's has the lowest acid strength, followed by HNO2, then HF.

Which response lists inter-particle forces (between molecules of comparable size) in order of increasing strength? a. London< ionic < H-bonds < dipole b. London < dipole < H-bond < ionic c. H-bond < ionic < dipole < London d. dipole < London < H-bond < ionic

b. London < dipole < H-bond < ionic explanation: since molecules of comparable size are being looked at, that means that the dipole-dipole interaction will be stronger than the London force, followed by hydrogen bonds then ionic bonds having the greatest strength.

Which of the following pure substances exhibits hydrogen bonding? a. CH4 b. NH3 c. H2S d. HCl

b. NH3 explanation: Hydrogen is bonded to Nitrogen which is one of the three elements it needs to be bonded to in order to exhibit hydrogen bonding (O,N, or F)

Which of the following conduct electricity only in a molten state? a. Cu b. Na2CO3 c. C5H12 d. F2

b. Na2CO3 explanation: Na2CO3 is an ionic solid, which is held together by electrostatic attraction. Though they cannot conduct electricity in their solid form, they are able to conduct electricity only in a molten state due to these types of solids being brittle.

GaAs is a semiconductor. If As is replaced by P, which of the following is a correct statement? a. The band gap will be decreased b. The band gap will be increased c. The band gap will not change

b. The band gap will be increased explanation: because GaAs is a compound semiconductor, the band gap will increase when the change in electronegativity increases, therefore, since P is more electronegative than As, the band gap will be increased.

A chemical reaction has an equilibrium constant, Kc= 0.002. Which of the following is true? a. The reaction is spontaneous and the products will be more in the equilibrium mixture b. The reaction is not spontaneous and the reactants will be more in the equilibrium mixture

b. The reaction is not spontaneous and the reactants will be more in the equilibrium mixture explanation: When Kc<1 the reaction is not spontaneous and it will move toward the reactants.

A chemical reaction has an equilibrium constant, Kc= 2000. Which of the following is true? a. The reaction is not spontaneous and the reactants will be more in the equilibrium mixture b. The reaction is spontaneous and the products will be more in the equilibrium mixture

b. The reaction is spontaneous and the products will be more in the equilibrium mixture explanation: when Kc>1 the reaction is spontaneous and it will move toward the products.

Which of the following substances will have the highest boiling point? a. methane[CH4] (MW=16) b. ethyl alcohol [CH3CH2OH] (MW=46) c. butane [C3H8] (MW=58) d. methyl alcohol [CH3OH] (MW=32)

b. ethyl alcohol [CH3CH2OH] (MW=46) explanation: butane and methane can be turned by looking into molecular weight (hence dispersion). When looking at alcohol compounds (methyl alcohol and ethyl alcohol), both compounds have an H-bond, which gets canceled out. You then look into molecular weight and whichever has the higher molecular weight will have the highest boiling point.

Which of the following substances will have the lowest boiling point? a. Water [H2O] b. helium [He] c. neon [Ne] d. ammonia [NH3]

b. helium [He] explanation: Water and Ammonia are hydrogen bonds (in which hydrogen needs to be bonded with either F, O, or N). Look into the molecular weight of neon and helium and whichever has the lowest molecular weight will have the lowest boiling point. In this case, it's helium [He].

A stepwise reaction (2A+2B ----> 2D) has the following elementary steps: 2A+B ------> C (slow step) B+C-------> 2D What is the rate law for this reaction? a. rate = K [B] [C] b. rate = K [A]^2 [B] c. rate = K [A] [B] d. rate = K [A]^2 [B]^2

b. rate = K [A]^2 [B] explanation: In order to determine the rate law for the reaction, identify the slowest step and use those coefficients to set up a rate law formula.

The interaction responsible for the cohesive intermolecular forces of liquid nitrogen is: a. hydrogen bonding b. the London dispersion force c. dipole-dipole interaction d. covalent bonding

b. the London dispersion force explanation: both Nitrogen atoms (N2) have the same degree of electronegativity, making them non polar and diatomic. These atoms stick together to form a liquid due to London dispersion forces.

For the reaction 2A + B -----> C + 2D, the rate law is: rate =k [A]^2 [B]^2 Which of the following statements is false? a. the reaction is second order in [B] b. the reaction is an elementary reaction c. the reaction is a step-wise reaction d. the reaction is second order in [A]

b. the reaction is an elementary reaction explanation: The reaction is second order in [B] and [A], and the reaction is a step-wise reaction because the coefficients of the reaction don't match the exponents in the rate law. In order for the reaction to be an elementary reaction, the coefficients of the reaction would have to match the exponents in the rate law.

If a solution has a [H+]=1 x 10 -9 M, what is the pH of that solution? a. 5 b. -9 c. 9 d. -5

c. 9 explanation: PH= -log [H+] PH= -log[1 x 10 -9] PH= 9

Which of the following substances would have the highest solubility in CCl4? a. NaCl b. Na2SO4 c. CH3CH2CH2CH2OH d. CH3OH

c. CH3CH2CH2CH2OH explanation: Alcohols with longer chains will dissolve more in CCl4, which is a nonpolar solvent, and less in water (which is a polar solvent) due to the decrease in hydrogen bonds following the increase in molecular weight and dispersion.

For the reaction CH3COOH+ NH3 ---> CH3COO- + NH4+, if CH3COOH is a weak acid and NH3 is a weak base, which of the following is a true statement? a. CH3COO- is a weak acid, NH4+ is a weak base b. CH3COO- is a weak base, NH4+ is a weak acid c. CH3COO- is a strong base, NH4+ is a strong acid d. CH3COO- is a strong acid, NH4+ is a strong base

c. CH3COO- is a strong base, NH4+ is a strong acid explanation: Because CH3COOH is a weak acid, its conjugate base has to be strong, and because NH4+ is a weak base, its conjugate acid must be strong. Vice versa for strong base, strong acid.

Which of the following has the lowest melting points? a. Graphite b. NaCl c. CO2 d. Mg

c. CO2 explanation: CO2 is a molecular solid, which is held together by intermolecular forces and as a result of that, they are generally soft and do not conduct electricity. Hence, they will have the lowest melting point.

Which of the following has the highest melting points? a. H2O b. CO2 c. CaCl2 d. C4H10

c. CaCl2 explanation: CaCl2 is an ionic solid, and due to the ions within it which are electrostatic interactions requiring a great amount of energy to overcome and conduct electricity when in the molten state, compared to H2O liquid and the other options.

Use the following acid ionization constants to identify the correct order of the conjugate base strengths. HF Ka = 7.2 × 10-4 HNO2 Ka = 4.5 × 10-4 HCN Ka = 6.2 × 10-10 a. CN- > F- > NO2- b. F- > CN- > NO2- c. F- < NO2- < CN- d. F- > NO2- > CN-

c. F- < NO2- < CN- explanation: Since the following are the conjugate bases of the previous acids, the strengths will be reversed. Since HF has the highest acid strength, F- will have the lowest base strength, Followed by NO2-, then CN- which would have the highest base strength since it's the conjugate base of the weakest acid HCN.

GaAs is a semiconductor. If As is replaced by another element, which of the following element will make a p-type semiconductor? a. P b. Se c. Sn d. Sb

c. Sn explanation: P-doping is when there are electron vacancies (fewer electrons in the valence band called holes. In this case, when we go to the left of As, the element with fewer electrons than As is Sn.

For the reaction CH3COOH+ NH3 ⟺ CH3COO- + NH4+, if CH3COOH is a weak acid and NH3 is a weak base, which of the following is a true statement? a. The forward reaction is spontaneous b. Both forward and backward reactions are spontaneous c. The backward reaction is spontaneous

c. The backward reaction is spontaneous explanation: Spontaneous reactions occur in the direction of the weak acids and bases. Since CH3COOH is a weak acid and NH3 is a weak base and they are to the left, the backward reaction is spontaneous.

GaAs is a semiconductor. If As is replaced by Sb, which of the following is a correct statement? a. The band gap will be decreased b. The band gap will not change c. The band gap will be increased

c. The band gap will be increased explanation: because GaAs is a compound semiconductor, the band gap will increase when as molecular weight increases going down the group, therefore, since Sb has a higher molecular weight than As, the band gap will be increased.

The reaction A+ B ---> C has the following rate law: Rate = k[A]^2 [B]. If the concentration of A is increased by a factor of 4 while the concentration of B is increased by a factor of 2, the rate will a. increase by a factor of 8 b. decrease by a factor of 32 c. increase by a factor of 32 d. increase by a factor of 16

c. increase by a factor of 32 explanation: In order to find the change in the rate, write the rate law, then substitute 4 into A, and substitute 2 into B. 4A squared will equal 16A and 2B multiplied by 16A will equal 32AB. The rate will increase by a factor of 32.

If the reaction quotient Q has a smaller value than the related equilibrium constant, K, which of the following is true? a. the reaction is at equilibrium b. the reaction is not at equilibrium and will make more reactants at the expense of products c. the reaction is not at equilibrium and will make more products at the expense of reactants

c. the reaction is not at equilibrium and will make more products at the expense of reactants explanation: When Q<K the reaction is not at equilibrium and has too many reactants, so it will proceed toward the products. If Q=K the reaction is at equilibrium.

If the rate of formation of ammonia is 0.500 M/s, what is the rate of disappearance of H2? N2 (g) + 3 H2 (g) ------> 2 NH3 (g) a. 0.250 M b. 0.333 M c. 0.500 M d. 0.750 M

d. 0.750 M explanation:

If a solution has a pH of 5, what is the [OH-] of that solution? a. 1 x 10 -5 b. 1 x 10 -6 c. 1 x 10 -14 d. 1 x 10 -9

d. 1 x 10 -9 explanation: POH= 14-PH POH= 14-5 POH= 9 [OH-]= 10^-9 [OH-]= 1.0 X 10^-9 M

Chlorine has a critical temperature of 144°C and critical pressure of 77 atm. Under which of the following conditions would Cl2 most likely be a liquid? a. 150°C, 30 atm b. 125°C, 30 atm c. 150°C, 70 atm d. 125°C, 70 atm

d. 125°C, 70 atm

What volume of 0.1 M NaOH will be required to neutralize 50 mL of 0.1 M of HCl ? a. 100 mL b. 25 mL c. 45 mL d. 50 mL

d. 50 mL explanation:

What percentage of a material will persist after 60 minutes if its half-life is 60 minutes? a. 12.5% b. 33% c. 25% d. 50%

d. 50% explanation: 60/60=1 60=100% 50=x% 60x=600 x=100 100/2=50%

Which of the following change will shift the equilibrium to the right for the following reaction? NH4CO2NH2(s) ------> 2NH3(g) + CO2(g) a. Increasing NH3 (g) b. Increasing CO2 (g) c. Increasing NH4CO2NH2(s) d. Decreasing the pressure

d. Decreasing the pressure explanation: increasing NH3(g) will cause a shift to the left increasing CO2(g) will cause a shift to the left Increasing NH4CO2NH2(s) will have no change on the equilibrium Decreasing the pressure will cause a shift to the right because reducing the volume of a gaseous equilibrium mixture causes the system to shift in the direction that reduces the number of moles. number of moles increases, pressure decreases. Forward direction number of moles decreases, pressure increases. Backward direction

Which of the following is the right order of the acid strength of HF, HCl, HBr and HI? a. HF > HCl> HBr > HI b. HCl< HBr < HI< HF c. HCl> HBr > HI > HF d. HF < HCl< HBr < HI

d. HF < HCl< HBr < HI explanation: Acid strength is determined by either electronegativity or bond strength. For electronegativity, which increase left to right of the periodic table, increase in electronegativity=increase in acid strength For bond strength, which decreases going down a group, decrease in bond strength=increase in acid strength. Since HF has the greatest bond strength, its the weakest acid followed by HCl, HBr, then HI, which has the smallest bond strength, so it's the strongest acid.

The intermolecular forces that are most significant in accounting for the high boiling point of liquid water relative to other substances of similar molecular weight are the: a. London Dispersion Forces b. Ion-ion attractions c. Dipole-Dipole attractions d. Hydrogen bonding forces

d. Hydrogen bonding forces explanation: the molecules in water are pulled together, and more energy is required to separate their attraction compared to a compound that only has London dispersion forces.

Which of the following change will shift the equilibrium to the left for the following reaction? NH4CO2NH2(s) ------> 2NH3(g) + CO2(g) a. Increasing NH4CO2NH2(s) b. Decreasing NH4CO2NH2(s) c. Decreasing CO2 (g) d. Increasing NH3 (g)

d. Increasing NH3 (g) explanation: Increasing NH4CO2NH2(s) has no change on the equilibrium Decreasing NH4CO2NH2(s) has no change on the equilibrium Decreasing CO2 (g) will cause a shift right Increasing NH3 (g) will cause a shift left

Which of the following ionic compounds has the highest melting points? a. CaCO3 b. RbCl c. CsCl d. MgCO3

d. MgCO3 explanation: MgCO3 has the highest melting point because whenever metallic and ionic solids have the same charges, you look into their molecular weight. If the molecular weight is small, then that compound has the highest melting point.

Which is the weakest intermolecular force among a group of molecules of non-comparable molecular weight (molar mass)? a. ionic bonding b. hydrogen bonding c. London d. dipole-dipole

d. dipole-dipole explanation: non-comparable molecular weight are looked at, meaning that the traditional trend for the attraction of these forces is present which is Dipole < London< H-bond < ionic

Which of the following has the highest band gap? a. Mg b. Cu c. Si d. Graphite

d. graphite explanation: The reason why graphite has the highest band gap is that graphite is an elemental semiconductor (essentially carbon), which is the first element in its group. Elements that have a higher polarity (or electronegativity) will have a higher band gap and following graphite would be Si, Cu, and Mg. Si would have the second-highest band gap as it is also a semiconductor. Cu and Mg would have a low band gap because they are metals (or conductors) while diamond is an insulator.

What is the pH of a buffer solution where [HA] = [A-]? a. pH=7 b. pH=14 c. pH=1 d. pH=pKa

d. pH=pKa explanation:

GaAs is a semiconductor. If As is replaced by another element, which of the following element will make a n-type semiconductor ? a. Sn b. P c. Sb d. Se

d. se explanation: n-type semiconductors add more electrons to impure a substance, so since Se has 6 valence electrons while As has 5 valence electrons, if replaced, it will make a n-type semiconductor.

Which of the following semiconductor has the highest band gap? a. Pb b. Sn c. Ge d. Si

d. si explanation: Si has the highest band gap because when looking at elemental semiconductors, the band gap is determined by a decrease in size (molecular weight) and is determined by polarity. The more polar the element, the more it has a higher band gap.

Some solids can be converted directly to the vapor phase by heating. The process is called:

sublimation

The property that makes a water droplet to be a sphere is:

surface tension

The term used to describe resistance to flow of a liquid is:

viscosity