CHEM 1212 FINAL

CH3COOH and HC2H3O2 are different ways of writing the chemical formula of the which chemical ?

Acetic Acid

What is the oxidation number of S in SO4−2 ?

+6

What is the oxidation number of Mn in MnO4− ?

+7

A coffee cup calorimeter contained 50.0 mL of a 1.33 M KOH solution at an initial temperature of 22.8 ºC. A student quickly add 50.0 mL of 1.17 M HNO3 to the calorimeter. The maximum temperature reached during the neutralization reaction was 28.6ºC. Determine the ΔHrxn for this neutralization reaction in kJ/mol of HNO3. assume specific heat of solution is the same as specific heat of water = 4.18 J/gºC assume density of both KOH and HNO3 are the same as water = 1.00 g/mL if negative value, be sure to type in a minus sign. HINT: You will need to first find qsolution.

-41.4 masssoln = (mL HNO3 x 1.00 g/mL) + (mL KOH x 1.00 g/mL) ΔT = Tfinal - T initial qsoln = specific heat × masssoln × ΔT qrxn = (-) qsoln mol HNO3 = M HNO3 x L HNO3 ΔHrxn = qrxn / mol HNO3

What is the average value of k (rate constant) for the data set below. Previously it was determined that the reaction was 1st order in E and 2nd order in D. Enter your value of k with 4 digits past the decimal. Rate of reaction Ave. Init. Rate TRIAL [D] M [E] M (kPa/sec) A 0.400 0.400 5.40 x 10-3 B 0.400 0.200 2.64 x 10-3 C 0.800 0.400 2.20 x 10-2

0.0843

Ferris & Mona used the ORP sensor to titrate a ferrous ammonium sulfate solution, (NH4)2Fe(SO4)2 with KMnO4 titrant. They titrated a 12.50 mL aliquot of the Fe+2 solution with 0.0210 M MnO4- solution and determined that the equivalence point was at 12.3 mL. What is the molarity of the Fe+2 solution? 5 Fe+2(aq) + MnO4-(aq) + 8 H+(aq) → 5 Fe+3(aq) + Mn+2(aq) + 4 H2O

0.103 M

A reaction mixture was formed by adding 60 mL H2O, 10.0 mL of 0.88 M H2O2, and 10.0 mL of 0.50 M KI. What is the molarity of the H2 O2 in the reaction mixture? What is the molarity of the KI in the reaction mixture?

0.11 M 0.063 M

Predict the initial rate (in kPa/sec) for Trial D using the data below. It was previously determined that the reaction is 1st order in D, 2nd order in E, and the average rate constant, k is equal to 0.674 kPa/(sec · M3). Enter your Initial Rate with 3 significant figures. Rate of reaction Ave. Init. Rate TRIAL [D] M [E] M (kPa/sec) A 0.100 0.200 2.66 x 10-3 B 0.100 0.100 6.83 x 10-4 C 0.200 0.200 5.40 x 10-3 D 0.500 0.600

0.121

In Experiment 6, Vitamin C (ascorbic acid) was titrated with dichloroindophenol (DCP) in a redox titration. But ascorbic acid, C6H8O6, can also be titrated in a redox titration with Br2(aq) solution as seen in the two half reactions below. Determine the overall reaction. C6H8O6 → C6H6O6 + 2 H+ +2 e- Br2 + 2 e- → 2 Br- One vitamin C tablet was dissolved in a slightly acidic solution and titrated with 0.110 M Br2 using an ORP probe. The equivalence point of the titration curve was determined to be 20.7 mL. What is the mass (in grams) of Vitamin C, C6H8O6, in the tablet. (Enter your answer with 3 digits past the decimal) Molar Mass of C6H8O6 is 176.04 g/mol

0.401

What is the pH of a 0.20 M HCl solution?

0.70

Piers & Aida added 1.25 mL aliquot of H2O2 to a beaker containing 5.0 mL of 6 M H2SO4 and 90 mL of water. The hydrogen peroxide solution required 19.00 mL of 0.0225 M MnO4- to reach the equivalence point using the ORP probe. 5 H2O2(aq) + 2 MnO4-(aq) + 6 H+(aq) → 5 O2(g) + 2 Mn+2(aq) + 8 H2O(ℓ) What is the molarity of the original H2O2 solution?

0.855

What is the pH of a 7.5 x 10-3 M NaOH solution?

11.88

What is the vapor pressure (in kPa) of ethanol, CH3CH2OH, over a solution which is composed of 25.00 mL of ethanol and 7.47 g of benzoic acid, C6H5COOH, at 35ºC ? Enter your number with two digits past the decimal. Pºethanol at 35ºC = 13.693 kPa Density of ethanol = 0.789 g/mL, Molar mass of ethanol = 46.07 g/mol Molar mass of benzoic acid = 122.12 g/mol

11.98

A 4.00 mL aliquot of a 0.15 M HCl solution is diluted to a final volume of 25.00 mL. What is the molarity of this first dilution solution? Then a second dilution was made by taking 7.50 mL of the first dilution and diluting it to 50.00 mL. What is the molarity of this second dilution?

1st Dilution = 0.0240 M; 2nd Dilution = 3.60 x 10-3 M

Consider the half reactions below and determine the overall reaction. Cu(s) → Cu+2(aq) + 2 e - NO3-(aq) + 4 H+(aq) + 3 e - → NO(g) + 2 H2O How many electrons are transferred in the oxidation half-reaction? How many electrons are transferred in the reduction half-reaction? How many electrons are transferred in the overall reaction?

2 3 6

Raoult's Law works for other units of pressure, such as atm, mmHg, and torr. The only requirement is that both vapor pressures have the same units. Predict the vapor pressure (in torr) of carbon tetrachloride, CCl4, over a solution which is composed of 350.0 g of CCl4 and 247.5 g of I2 at 65ºC. Submit your answer with 1 digit past the decimal. PºCCl4 at 65ºC = 531 torr Molar mass of CCl4 is 153.81 g/mol Molar mass of I2 is 253.8 g/mol

371.7

Match the confirmation test with a description of the positive results. Confirmation test for Mn+2 Confirmation test for Zn+2 Confirmation test for Ni+2 Confirmation test for Cr+3

A purple solution A greyish white solid A red-pink precipitate A pale yellow-tan solid

Select the step(s) that will compose a rationale for the cation Pb+2 being absent in an unknown (but Ag+ is present).

A yellow precipitate did not form when K2CrO4 was added in step 1-C.

Select all the statements that are true concerning pH and buffers.

As an acidic solution is diluted the pH increases., A buffer works when either acids or bases are added.

Separation can be achieved when a reaction occurs in a mixture. The resulting mixture will have one chemical species in a solution and the other chemical species as a solid. The mixture is centrifuged and the supernate is decanted into a separate test tube. Now the two chemical species (solid and solution) are separated from each other. What reagent could you add to a mixture of [Zn(OH)4]-2(aq) and CrO4-2(aq) to separate the two species?

BaCl2

In step 2-C after adding NaOH and SnCl2, the white precipitate turned into a black solid.

Bi^3+ is confirmed as present

Confirmation test for Bi+3

Black solid

Consider the equilibrium reaction below. At high concentrations of HA the solution will be blue; but at low concentrations of HA the solution will be red. Initially the equilibrium mixture below is purple (combination of red & blue). What color is expected after adding some colorless A-(aq) to the equilibrium solution? A-(aq) + H2O(ℓ) ⇋ HA(aq) + OH-(aq)

Blue

Consider the exothermic equilibrium system below. The [CuCl4]-2(aq) ion is light green while the [CuBr4]2(aq) ion is dark brown. Originally the equilibrium below was a dark green. [CuCl4]-2(aq) + 4 Br-(aq) ⇋ [CuBr4]-2(aq) + 4 Cl-(aq) Predict the color of the solution after the system has re-established equilibrium. Placing the system in an ice-bath for 10 minutes. Adding a small amount of white NaBr(s).

Brown solution Brown solution

What is the pH of a solution that has 0.050 M CH3COOH and 0.075M NaCH3COO present? Ka of acetic acid = 1.80 x 10-5

Buffer calculations for an acidic buffer, are simply a weak acid calculation where you have both the concentration of the weak acid and the salt of its conjugate base. In this reaction, the acetic acid is your weak acid and the sodium acetate is the salt of the conjugate base. CH3COOH + H2O ↔ CH3COO- + H3O+ Init. conc. init. conc. x Write the equilibrium constant expression for the weak acid dissociation of acetic acid. Then rearrange and solve for [H3O+], which is x. Next you will take that value of [H3O+] and find the pH. Ka = [CH3COO-] x [H3O+] / [CH3COOH] Ka x [CH3COOH] = [CH3COO-] x [H3O+] Ka x [CH3COOH] / [CH3COO-] = [H3O+] (1.80 x 10-5) x [acetic acid conc.] / [acetate ion conc.] = [H3O+] pH = -log [H3O+] The correct answer is: 4.92

In the redox reaction below, identify and match each reactant to their function. 3 CH3CH2OH (aq) + 2 Cr2O7−2 (aq) + 16 H+(aq) → 3 CH3CO2H (aq) + 2 Cr+3(aq) + 11 H2O(aq)

Cr2O7−2 (aq) - Species being reduced, CH3CH2OH (aq) - Species being oxidized

In step 2-B, after adding the 15 M NH3 (the solution tested as basic), a white precipitate had formed and the solution turned dark blue.

Cu^2+ and Bi^3+ are both indicated as possibly present

In step 2-D, after adding the CH3COOH, the solution tested as acidic and turned light blue. Then after adding K4Fe(CN)6 in step 2-E, the blue solution turned yellow and a reddish-brown precipitate formed.

Cu^2+ is confirmed as present

For the following error, select the answer that correctly describes how it will affect the value of the final temperature of the water/solution in the calorimeter: Some of the NH4NO3 solid was spilled on the lab bench and not successfully added to the calorimeter.

Decreases the value of final Temperature

You have two test tubes. One test tube contains Fe+3(aq) solution and the other test tube contains Cr+3(aq). Predict what will happen when NaOH(aq) is added to both test tubes. If a reaction occurs, what is the new chemical formula?

Fe+3(aq) will form a brown precipitate, Fe(OH)3(s). Cr+3(aq) will form a green solution, [Cr(OH)4 ]-(aq).

What is the formula for hydrogen peroxide?

H2O2

Separation can be achieved when a reaction occurs in a mixture. The resulting mixture will have one chemical species in a solution and the other chemical species as a solid. The mixture is centrifuged and the supernate is decanted into a separate test tube. Now the solid and solution are separated from each other. What reagent could you add to a mixture of Pb+2 and Bi+3 to separate the two species?

HCl

Select all that apply to an exothermic reaction.

Heat is a product., Adding heat (hot water bath) will cause the equilibrium to shift towards reactants., Removing heat (cold water bath) will cause the equilibrium to shift toward products.

Separation can be achieved when a reaction occurs in a mixture. The resulting mixture will have one chemical species in a solution and the other chemical species as a solid. The mixture is centrifuged and the supernate is decanted into a separate test tube. Now the solid and solution are separated from each other. What reagent could you add to a mixture of PbCl2(s) and AgCl(s) to separate the two species?

Hot Water

Callie, Gay, & Steve were discussing the results of this experiment in terms of general trends. Which statement below is TRUE ?

If the volume of the solvent was constant, as more solute was added, the Psolvent decreased.

Which is a correct statement about the system in thermodynamic terms?

It is defined as the chemical species that are reacting in the studied reaction.

What is the formula for potassium ferrocyanide?

K4Fe(CN)6

You have one test tube which contains a solution that is either Ni+2(aq) or Fe+3(aq). Select a reagent that will allow you to differentiate between the two chemical species. If the solution is Ni+2(aq), what will happen when the reagent is added? If the solution is Fe+3(aq), what will happen when the reagent is added?

KSCN If it is Ni+2(aq), the green solution will stay the same after adding the KSCN. If it is Fe+3(aq), the blood red solution will form after adding the KSCN.

Rate Constant Expression

Mathematical expression showing the relationship between the measured rate and the concentration of the reactants

You have two test tubes. One test tube contains Mn+2(aq) solution and the other test tube contains Zn+2(aq). Predict what will happen when NaOH(aq) is added to both test tubes. If a reaction occurs, what is the new chemical formula?

Mn+2(aq) will form a very pale pink precipitate, Mn(OH)2 (s). Zn+2(aq) will form a colorless solution, [Zn(OH)4]-2 (aq).

Match the correct inference to the descriptions of the reactions from the Group 3 Qualitative Analysis Experiment, After adding NaBiO3 and centrifuging in step 3-G, a purple supernate is observed over the excess NaBiO3. After adding H2DMG in step 3-F, a strawberry red precipitate formed. After adding the K4Fe(CN)6 in step 3-J, no precipitate formed. After the H2O2 is added in step 3-B, the solution turns yellow.

Mn^2+ is confirmed present Ni^2+ is confirmed present Zn^2+ is confirmed present Cr^3+ is indicated as possible

Separation can be achieved when a reaction occurs in a mixture. The resulting mixture will have one chemical species in a solution and the other chemical species as a solid. The mixture is centrifuged and the supernate is decanted into a separate test tube. Now the two chemical species (solid and solution) are separated from each other. What reagent could you add to a mixture of Mn+2(aq) and Ni+2(aq) to separate the two species?

NH3

You have one test tube which contains a solution that is either Zn+2(aq) or Fe+3(aq). Select a reagent that will allow you to differentiate between the two chemical species. If the solution is Zn+2(aq), what will happen when the reagent is added? If the solution is Fe+3(aq), what will happen when the reagent is added?

NaOH If it is Zn+2(aq), the solution will stay colorless after adding the NaOH. If it is Fe+3(aq), the gold-brown precipitate will form after adding the NaOH.

A solid compound that forms as a result of mixing reagents together in a solution.

Precipitate

In the generic reaction below, experimental data indicate the reaction is second order in A, first order in B and rate constant is 3.5 x 10 -3 M -2sec -1. Which is the correct rate constant expression? A(aq) + 2 B(aq) → A2B(aq)

Rate = (3.5 x 10 -3 M -2sec -1) [A] 2 [B]

Using the sample data below, answer the questions below. E + D → B + A Rate of reaction Ave. Init. Rate TRIAL [D] M [E] M (kPa/sec) A 0.300 0.400 5.40 x 10-3 B 0.300 0.200 6.83 x 10-4 C 0.600 0.400 1.05 x 10-2

Reaction Order of D is... 1 Reaction Order of E is... 3

Select the redox term(s) that apply to Cu+2 in the half reaction below. Cu+2(aq) + e- → Cu+(aq)

Species being reduced, Oxidizing agent

Sully, Fay & Tia worked together on the redox titration of Fe+2 with MnO4- (Part I). Fay & Tia used the equivalence point volume of MnO4- as determined from titration graph. However, Sully used the volume of MnO4- when the solution turned brown, which was a larger volume than Fay & Tia's volume. Will Sully's calculations of the molarity of Fe+2 be different than Fay & Tia's calculation? How and why?

Sully's M of Fe+2 will be higher than the other two students. Since the volume of MnO4- is in the numerator for the calculation of M of Fe+2, the higher volume of MnO4- results in higher M of Fe+2.

The liquid above the solid in a mixture of solid and solution.

Supernate

Buffering capacity Neutral Solution Acidic Buffer

The amount of acid or base that can be added before the pH changes by 1 pH unit. A solution that has a pH of 7. A mixture of a weak acid and the salt of its conjugate base.

Select the step(s) that will compose a rationale for the cation Zn+2 being present in an unknown.

The colorless decantate was isolated in step 3-H when BaCl2 was added., A grey-white solid formed in step 3-J.

Consider the benzoic acid dissociation reaction below which is at equilibrium. C6H5COOH (aq) + H2O(ℓ) ⇋ C6H5COO-(aq) + H3O+(aq) If some strong acid is added (which donates H3O+, hydronium ion) is added to the system (stress), how will the system change in order to re-establish equilibrium? Select all that might apply.

The concentration of C6H5COO- will decrease., The concentration of C6H5COOH will increase.

You have two test tubes. One test tube contains Pb+2 (aq) solution and the other test tube contains Bi+3(aq). Predit what will happen when HCl (aq) is added to both test tubes. If a reaction occurs, what is the new chemical fomula?

The correct answer is: Pb+2 (aq) will form a white precipitate, PbCl2 (s). Bi+3 (aq) will remain unchanged.

Select the step(s) that will compose a rationale for the cation Cu+2 being present in an unknown.

The formation of a dark blue solution in step 2-B., Dark blue solution turned to light blue in step 2-D after the addition of CH3COOH and then , A reddish brown precipitate formed after adding K4Fe(CN)6 in step 2-E.

Select the steps that will compose a rationale for the cation Mn+2 being absent in an unknown.

The lack of a purple-grape supernate over excess NaBiO3 in 3-G.

If an error caused the final temperature to be larger, how does this affect the calculation of the heat of solution (qsolution)?

The larger Tfinal would produce a larger ΔT, which would result in a larger q

In a certain reaction, a solid chemical dissolved in water. The temperature of the water sample raised from 25.4 °C to 30.3 °C. From this description of the experiment, select the correct words to fill the blanks. Heat is abbreviated as q and is calculated as: q = specific heat × mass × ΔT. In the coffee cup calorimeter, we monitor the T of the water (surroundings). Then we calculate the qsurroundings using the equation above. Next we use the relationship that the heat lost (or gained) by the surroundings is the heat gained (or lost) by the system. The value of qsystem is the same as qsurroundings, but opposite in sign. Mathematically this is expressed as: qsurroundings = (-) qsystem If qsystem is a (+) value, then heat is entering into the system from the surroundings. The reaction is classified as an endothermic reaction. If qsystem is a (-) value, then heat is exiting from the system and going to the surroundings. The reaction is classified as an exothermic reaction. In this reaction, the chemical reaction is the system and the water is the surroundings. The temperature of the surroundings increases. So heat is leaving (exiting) the system and going into the surroundings. (The system loses heat and the surrounding gains heat.) So qsurroundings will be a (+) value, but qsystem will be a (-) value and thus it is an exothermic reaction.

The reaction is defined as the system The surroundings gained heat qsystem has a negative value The reaction is an exothermic reaction

Iggy, Lee & Brianne planned a new experiment based on two reactions involving Cu complexes they had previously observed in Exp. 11 & 12. [Cu(H2O)4]+2 (or simply as Cu+2) is a sky blue solution and [Cu(NH3)4]+2 is a dark royal blue solution. [Cu(H2O)4]+2(aq) + 4 NH3(aq) ⇋ [Cu(NH3)4]+2(aq) + 4 H2O(ℓ) Make a hypothesis on what will occur in the equilibrium system (initially a medium blue solution) if additional ammonia is added. Then explain what will occur in terms of Le Châtelier's principle.

The solution will become a darker blue solution. The system must shift towards products in order to lower the concentrations of NH3.

When 4.51 g of CaCl2 dissolved in 50.00 mL of water in a coffee cup calorimeter, the temperature of the solution rose from 22.6°C to 25.8°C. Specific heat of the solution is equal to the specific heat of water = 4.18 J/gºC Density of the solution is equal to the density of water = 1.00 g/mL

What is qsolution? (+) 729 J What is qreaction? (-) 729 J What is ΔHrxn in kJ/mol of CaCl2 ? (-) 17.9 kJ/mol

LeChâtelier's principle also extends to equilibria involving gas phase reactions. Partial pressures can be treated as concentration. However, if the total pressure is increased, then the system shifts to the equilibrium side that contains fewer moles of gas. Predict the equilibrium shifts that will occur in the endothermic equilibrium reaction below in order to re-establish equilibrium. CH4(g) + H2O(g) ⇋ CO(g) + 3 H2(g) Increasing the partial pressure of methane, CH4. Decreasing the overall temperature of the equilibrium system

Will shift the equilibrium towards the products Will shift the equilibrium towards the reactants.

LeChâtelier's principle also extends to equilibria involving gas phase reactions. Partial pressures can be treated as concentration. However, if the total pressure is increased, then the system shifts to the equilibrium side that contains fewer moles of gas. Predict the equilibrium shifts that will occur in the endothermic equilibrium reaction below in order to re-establish equilibrium. CH4(g) + H2O(g) ⇋ CO(g) + 3 H2(g) Increasing the partial pressure of methane, CH4. Increasing the overall total pressure of the equilibrium system.

Will shift the equilibrium towards the products. Will shift the equilibrium towards the reactants.

Confirmation test for Pb+2

Yellow precipitate

What is the pH of a buffer in which the concentration of benzoic acid, C6H5COOH, is 0.035 M and the concentration of sodium benzoate, NaC6H5COO, is 0.060 M ? Enter your answer with 2 digits past the decimal. Ka of C6H5COOH is 6.30 x 10-5

[H3O+] = 3.68 x 10-5 and pH = 4.43 Buffer calculations for an acidic buffer, are simply a weak acid calculation where you have both the concentration of the weak acid and the salt of its conjugate base. In this reaction, the benzoic acid is your weak acid and the sodium benzoate is the salt of the conjugate base. C6H5COOH + H2O ↔ C6H5COO- + H3O+ Init. conc. init. conc. of salt x Write the equilibrium constant expression for the weak acid dissociation of benzoic acid. Then rearrange and solve for [H3O+], which is x. Next you will take that value of [H3O+] and find the pH. Ka = [C6H5COO-] x [H3O+] / [C6H5COOH] Ka x [C6H5COOH] = [C6H5COO-] x [H3O+] Ka x [C6H5COOH] / [C6H5COO-] = [H3O+] (6.30 x 10-5) x [benzoic acid conc.] / [benzoate ion conc.] = [H3O+] pH = -log [H3O+] The correct answer is: 4.43

Confirmation test for Cu+2

a maroon precipitate

You have one test tube which contains a white solid that is either AgCl (s) or PbCl2 (s). Select a reagent that will allow you to differentiate between the two chemical species. If the solid is AgCl, what will happen when the reagent is added? If the solid is PbCl2, what will happen when the reagent is added?

hot water If it is AgCl, the white solid will remain the same after adding the hot water. If it is PbCl2, the solid will dissolve and form a colorless solution after adding the hot water.

rate determining step

the slowest step in a reaction mechanism