CHEM1212 Final exam (EXP 9 - EXP 20)

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

11.88

What is the pH of a 1.8 x 10-2 M NaOH solution?

12.26

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

2.12

Overall Reaction Rate

Rate of the slowest step

You have one test tube which contains a solution that is either Cr+3(aq) or Fe+3(aq). Select a reagent that will allow you to differentiate between the two chemical species. If the solution is Cr+3(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 Cr+3(aq), the indigo solution will turn green after adding the NaOH. If it is Fe+3(aq), a gold-brown precipitate will form after adding the NaOH.

Match the correct inference to the description of the reactions from the Group 1 & 2 Qualitative Analysis Experiment. In step 2-C after adding NaOH and SnCl2, the white precipitate turned into a black solid.

Bi+3 is confirmed as present

Select the step(s) that will compose a rationale for the cation Fe+3 being present in an unknown.

-A precipitate formed when 6 M NaOH was added to the unknown solution in step 3-A. -The precipitate from step 3-A dissolved in 6 M HNO3. -A blood red solution formed when KSCN was added in step 3-D.

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

-A precipitate formed when 6 M NaOH was added to the unknown solution in step 3-A. -The precipitate from step 3-A dissolved in 6 M HNO3. -A strawberry red precipitate formed in step 3-F

A 75.0 mg sample of Red 40 dye was dissolved and diluted to a final volume of 1.25 L with deionized water. What is the concentration of the Red 40 dye solution in ppm? parts per milliion (ppm) refers to 1 mg of solute in 1.0 L of solution (mg/L)

60 ppm

A reaction mixture was formed by adding 55 mL H2O, 5.0 mL of 0.88 M H2O2, and 10.0 mL of 0.50 M KI. 1. What is the molarity of the H2 O2 in the reaction mixture? 2. What is the molarity of the KI in the reaction mixture?

1. 0.063 M 2. 0.071 M

What is the pH of a 1.8 x 10-2 M HCl solution?

1.74

What is the pH of a solution that has 0.25 M CH3COOH and 0.20 M NaCH3COO present? Ka for acetic acid = 1.80 x 10-5

4.65 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+]

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 375.0 g of CCl4 and 88.40 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

464.63

Brønsted-Lowry acid

Any substance that donates a proton

Match the correct inference to the descriptions of the reactions from the Group 3 Qualitative Analysis Experiment, After adding the 6 M NaOH to the starting solution, a precipitate formed.

At least one of Fe+3, Ni+2, and Mn+2 is indicated as present.

CrO4-2 (aq) and [Zn(OH)4]-2 (aq)

Box 3-B

Confirmed absent

Box 3-J

Match the correct inference to the descriptions of the reactions from the Group 3 Qualitative Analysis Experiment, A yellow-tan precipitate formed in step 3-H when BaCl2 was added.

Cr+3 is confirmed as present

Match the correct inference to the descriptions of the reactions from the Group 3 Qualitative Analysis Experiment, After the NaOH is added in step 3-A, the decantate solution is green.

Cr+3 is indicated as possible

Match the correct inference to the descriptions of the reactions from the Group 3 Qualitative Analysis Experiment, After the NaOH is added in step 3-A to the starting solution, the decantate solution is green.

Cr+3 is indicated as possible.

Select the appropriate word that matches the definition below. To carefully pour a liquid into another container.

Decant

The process of molecules escaping the liquid phase to go into the gas phase.

Evaporation

What is the formula for hydrogen peroxide?

H2O2

Match the correct inference to the descriptions of the reactions from the Group 3 Qualitative Analysis Experiment, A light sky blue solution formed after adding 6 M NH3 in step 3-E

Ni+2 is indicated as present

One of the chemicals used in this experiment is K2CrO4 (aq). What is its name?

Potassium chromate

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 the reaction is exothermic and it is placed in cold water bath. 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 to generate heat (a product) that was lost.

You have two test tubes. One test tube contains AgCl(s), a white precipitate, and the other test tube contains PbCl2(s), also a white precipitate. Predict what will happen when hot water is added to both test tubes. If a reaction occurs, what is the new chemical fomula?

AgCl(s) will remain unchanged. PbCl2(s) will dissolve and form a colorless solution of Pb+2(aq).

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

All of the white precipitate from step 1-A dissolved in hot water.

You have two test tubes. One test tube contains Fe+3(aq) solution and the other test tube contains Ni+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?

Fe+3(aq) will form a brown precipitate, Fe(OH)3 (s). Ni+2(aq) will form a green precipitate, Ni(OH)2 (s)

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

Consider the benzoic acid dissociation reaction below which is at equilibrium. C6H5COOH (aq) + H2O(ℓ) ⇋ C6H5COO-aq) + H3O+(aq) If some strong base is added (the hydroxide ion which removes H3O+) 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 increase. -The concentration of C6H5COOH will decrease.

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 -A reddish brown precipitate formed after adding K4Fe(CN)6 in step 2-E.

A reaction mixture was formed by adding 35 mL H2O, 10.0 mL of 0.75 M H2O2, and 5.0 mL of 0.55 M KI. 1. What is the molarity of the H2 O2 in the reaction mixture? 2. What is the molarity of the KI in the reaction mixture?

1. 0.15 M 2. 0.055 M

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 Cu+2 and Bi+3 to separate the two species?

NH3

Using the sample data below, answer the questions below. E + D → B + A (picture of graph on definition side) 1. What is the reaction order of D? 2. What is the reaction order of E?

1. 1 2. 3

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 1. How many electrons are transferred in the oxidation half-reaction? 2. How many electrons are transferred in the reduction half-reaction? 3. How many electrons are transferred in the overall reaction?

1. 2 2. 3 3. 6

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

A pale yellow-tan solid

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

A purple solution

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.

Match the correct inference to the description of the reactions from the Group 1 & 2 Qualitative Analysis Experiment. 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: One aluminum rod is not totally submerged in the calorimeter after it was transferred from the hot water.

Decreases the value of final temperature

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

What is the name of C2H8N2O2 ?

Dimethlyglyoxime

Match the correct inference to the descriptions of the reactions from the Group 3 Qualitative Analysis Experiment, After the addition of KSCN in 3-D, no change was observed.

Fe+3 is confirmed as absent.

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

Piers & Ida performed this experiment. Both started with the exact same volume of hydrogen peroxide. However, some gas escaped out of the test tube because the rubber stopper wasn't tight in Ida's set-up. Piers did not have any errors with his experiment. Which of the following statement(s) are TRUE concerning Ida's results? I. Ida's experiment will give a lower volume of O2(g) than Piers. II. Ida's experiment will give a lower partial pressure of O2(g) than Piers. III. Ida's calculations will give a smaller molarity of H2O2 than Piers.

I and III are true

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

If they calculated moles fraction of solute (moles of solute/total moles present); then as mole fraction of solute increased, 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

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. (graph is on definition side)

0.0843

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. (graph is on definition side)

0.121

Ferris & Mona used the ORP sensor to titrate a ferrous ammonium sulfate solution, (NH4)2Fe(SO4)2 with KMnO4 titrant. They titrated a 10.00 mL aliquot of the Fe+2 solution with 0.0207 M MnO4- solution and determined that the equivalence point was at 17.4 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

0.180 M

What is the average value of k (rate constant) for the data set below. Previously it was determined that the reaction was 3rd order in E and 1st order in D. Enter your value of k with 3 digits past the decimal. (graph is on definition side)

0.2797 or 0.28

What is the mole fraction (Χ) of CH3OH, methanol, in a solution of 9.00 mL of CH3OH and 6.79 g of C6H5COOH, benzoic acid ? Density of methanol is 0.792 g/mL Molar mass of CH3OH is 32.04 g/mol Molar mass of C6H5COOH is 122.12 g/mol

0.800 Mole fraction is simply the moles of interest divided by total moles present and is represented by the symbol Chi (Χ). mol of CH3OH (methanol) = mLmethanol x Densitymethanol x (1/Molar mass of methanol) mol of C6H5COOH (benzoic acid) = massbenzoic acid / (Molar mass of benzoic acid) Χ of methanol = (moles of CH3OH)/ (moles of CH3OH + moles of C6H5COOH)

What is the vapor pressure (in kPa) of CH3OH, methanol, over a solution which is composed of 7.50 mL of methanol and 3.23 g of C6H5COOH, benzoic acid, at 25ºC ? Pº methanol at 25ºC = 16.915 kPa Density of methanol is 0.792 g/mL Molar mass of benzoic acid is 122.12 g/mol

14.80 kPa

In a similar Exp. 9 experiment, a calibration plot of absorbance vs. concentration of Red 40 dye (ppm) was obtained with the slope of the best-fit straight line as 0.038 ppm-1 The diluted unknown sports drink solution had an absorbance of 0.86. What is the concentration (ppm) of the Red 40 dye in the dilute unknown sports drink?

22.6 Absorbance = Slope × Concentration Concentration = Absorbance / slope

Match the confirmation test with a description of the positive results. Confirmation test for Bi+3

A black solid

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

A greyish white solid

Acidic buffer

A mixture of a weak acid and the salt of its conjugate base.

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

A red-pink precipitate

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

A red-pink solid did not form after the addition of H2DMG in step 3-F.

Match the confirmation test with a description of the positive results. Confirmation test for Pb+2

A yellow precipitate

Match the correct inference to the description of the reactions from the Group 1 & 2 Qualitative Analysis Experiment. In step 1-A after adding the 6 M HCl, no white precipitate formed and the colorless solution remained unchanged.

Ag+ and Pb+2 are confirmed as absent.

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

Match the correct inference to the description of the reactions from the Group 1 & 2 Qualitative Analysis Experiment. In step 2-B, after adding the 15 M NH3 (the solution tested as basic), a white precipitate had formed and the solution remained colorless.

Bi+3 is indicated as possibly present.

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

A property of a solution that is dependent on the number of solute molecules in solution.

Colligative property

Match the correct inference to the description of the reactions from the Group 1 & 2 Qualitative Analysis Experiment. 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

Match the correct inference to the description of the reactions from the Group 1 & 2 Qualitative Analysis Experiment. In step 2-D, after adding the CH3COOH, the solution tested as acidic and the colorless solution remained unchanged. Then after adding K4Fe(CN)6 in step 2-E, the colorless solution turned yellow, but no precipitate formed.

Cu+2 is confirmed as absent.

Buffering capacity

The amount of acid or base that can be added before the pH changes by 1 pH unit

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.

You have two test tubes. One test tube contains Mn+2(aq) solution and the other test tube contains Ni+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). Ni+2(aq) will form a green precipitate,Ni(OH)2 (s)

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 Fe+3(aq) and Cr+3(aq) to separate the two species?

NaOH

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 Fe+3(aq) and Zn+2(aq) to separate the two species?

NaOH

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?

NaOH If it is Ni+2(aq), a green precipitate will form after adding the NaOH. If it is Fe+3 (aq), a gold-brown precipitate will form after adding the NaOH.

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.

In the generic reaction below, experimental data indicate the reaction is third order in A, first order in C and rate constant is 5.4 x 10 -3 M -1sec -1. Which is the correct rate constant expression? A(aq) + 3 C(aq) → AC3(aq)

Rate = (5.4 x 10^-3 M^-1 sec^-1) [A]^3 [C]

In the generic reaction below, experimental data indicate the reaction is second order in A, first order in C and rate constant is 5.4 x 10 -3 M -2sec -1. Which is the correct rate constant expression? A(aq) + 2 C(aq) → AC2(aq)

Rate = (5.4 x 10^-3 M^-2 sec^-1) [A]^2 [C]

Rate

Change in concentration of A per change in time, Δ[A]/Δtime.

The partial pressure of solvent molecules in the gas phase at equilibrium.

Vapor pressure

Rate determining step

Step in the reaction mechanism that has the slowest rate

Select all that apply to an endothermic reaction.

-Heat is a reactant. -The reaction absorbs heat from the surroundings.

Select all that apply to an endothermic reaction.

-Adding heat (hot water bath) will cause the equilibrium to shift towards products. -Heat is a reactant

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

-As an acidic solution is diluted the pH increases. -The greater the concentrations of the buffer components, the greater its buffering capacity.

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.

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, 1st order in E, and the average rate constant, k is equal to 0.03404 kPa/(sec · M2). Enter your Initial Rate with 3 significant figures. (graph is on definition side)

0.00511

When 5.73 g of CaCl2 dissolved in 50.00 mL of water in a coffee cup calorimeter, the temperature of the solution rose from 23.4°C to 28.6°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 1. What is qsolution? 2. What is qreaction? 3. What is ΔHrxn in kJ/mol of CaCl2?

1. +1210 J 2. -1210 J 3. -23.5 kJ/mol

Match the confirmation test with a description of the positive results. Confirmation test for Fe+3

A blood red solution

Confirmation test for Zn+2

A greyish white solid

Match the confirmation test with a description of the positive results. Confirmation test for Cu+2

A maroon precipitate

Basic buffer

A mixture of a weak base and the salt of its conjugate acid

Neutral solution

A solution that has a pH of 7.

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 Ag+ and Bi+3 to separate the two species?

HCl

What is the name for H2O2 ?

Hydrogen peroxide

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

Select the appropriate word that matches the definition below. A solid compound that forms as a result of mixing reagents together in a solution.

Precipitate

Select the appropriate word that matches the definition below. The liquid above the solid in a mixture of solid and solution.

Supernate

Which statement about the spectrophotometric analysis of Red 40 dye is TRUE?

The calibration plot is a graph of Absorbance (y-axis) versus Concentration of Red 40 dye (x-axis).

Which statement about the spectrophotometric analysis of Red 40 dye is TRUE?

The intensity of the color of the solution is directly proportional to concentration of the Red 40 dye

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

The larger Tinitial would produce a smaller ΔT, which would result in a smaller q.

What is the correct definition of ΔH?

The quantity of heat of reaction measured at constant pressure.

One of the chemicals used in this experiment is SnCl2 (aq). What is its name?

Tin(II) chloride

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

A coffee cup calorimeter contained 50.0 mL of a 1.33 M KOH solution at an initial temperature of 24.0 ºC. A student quickly add 50.0 mL of 1.04 M HNO3 to the calorimeter. The maximum temperature reached during the neutralization reaction was 29.8ºC. 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.

-46.63 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

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

-No white precipitate formed when 6 M HCl was added to the unknown solution in step 1-A.

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

-The greater the concentrations of the buffer components, the greater its buffering capacity. -A buffer works when either acids or bases are added.

What is the vapor pressure (in kPa) of ethanol, CH3CH2OH, over a solution which is composed of 30.00 mL of ethanol and 11.07 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

11.64

What is the mole fraction (Χ) of CH3OH, methanol, in a solution of 8.50 mL of CH3OH and 4.53 g of C6H5COOH, benzoic acid ? Density of CH3OH is 0.792 g/mL Molar mass of CH3OH is 32.04 g/mol Molar mass of C6H5COOH is 122.12 g/mol

0.850 Mole fraction is simply the moles of interest divided by total moles present and is represented by the symbol Chi (Χ). mol of CH3OH (methanol) = mLmethanol x Densitymethanol x (1/Molar mass of methanol) mol of C6H5COOH (benzoic acid) = massbenzoic acid / (Molar mass of benzoic acid) Χ of methanol = (moles of CH3OH)/ (moles of CH3OH + moles of C6H5COOH)

When 5.86 g of CaCl2 dissolved in 50.00 mL of water in a coffee cup calorimeter, the temperature of the solution rose from 24.3°C to 29.7°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 1. What is qsolution? 2. What is qreaction? 3. What is ΔHrxn in kJ/mol of CaCl2?

1. +1260 J 2. -1260 3. -23.9 kJ/mol

Using the sample data below, answer the questions below. E + D → B + A (picture of graph on definition side) 1. What is the reaction order of D? 2. What is the reaction order of E?

1. 1 2. 1

Consider the half-reactions below and determine the overall reaction. Pt(s) → Pt+2(aq) + 2 e - Cr2O7 -2(aq) + 14 H+(aq) + 6 e - → 2 Cr+3(aq) + 7 H2O 1. How many electrons are transferred in the oxidation half-reaction? 2. How many electrons are transferred in the reduction half-reaction? 3. How many electrons are transferred in the overall reaction?

1. 2 2. 6 3. 6

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. 1. Adding a small amount of white NaBr(s). 2. Adding a few drops of Ag+(aq) solution (Ag+ reacts with Cl- ions).

1. Brown solution 2. Brown solution

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. 1. Placing the system in an ice-bath for 10 minutes. 2. Adding a small amount of white NaBr(s).

1. Brown solution 2. Brown solution

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 1. The reaction is defined as the __________. 2. The surroundings ________ heat. 3. qsystem has a ___________ value.. 4. The reaction is an ______________ reaction.

1. System 2. Gained 3. Negative 4. Exothermic 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.

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) 1. Increasing the overall temperature of the equilibrium system. 2. Increasing the overall volume (decreasing the overall pressure) of the equilibrium system.

1. Will shift the equilibrium towards the products. 2. Will shift the equilibrium towards the products.

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) 1. Increasing the partial pressure of methane, CH4. 2. Decreasing the overall total pressure of the equilibrium system.

1. Will shift the equilibrium towards the products. 2. Will shift the equilibrium towards the products.

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) 1. Decreasing the overall pressure of the equilibrium system. 2. Decreasing the overall temperature of the equilibrium system.

1. Will shift the equilibrium towards the products. 2. 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) 1. Increasing the overall pressure of the equilibrium system. 2. Increasing the overall temperature of the equilibrium system

1. Will shift the equilibrium towards the reactants. 2. Will shift the equilibrium towards the products.

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. 1. The water is defined as the _____. 2. The system _____ heat. 3. qsystem has a _____ value. 4. The reaction is an _____ reaction.

1. surroundings 2. lost 3. negative 4. exothermic 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.

What is the vapor pressure (in kPa) of ethanol, CH3CH2OH, over a solution which is composed of 27.50 mL of ethanol and 14.38 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

10.95

A calibration plot of absorbance vs. concentration (ppm) was obtained with standard known Red 40 dye solutions. The slope of the best-fit straight line of the plot is 0.043 ppm- 1 The absorbance of the dilute unknown sports drink was 0.48 What is the concentration of this dilute unknown sports drink ?

11.2 ppm

A red sports drink contains Red 40 dye. A 3.5 mL aliquot of this sports drink was diluted to 25.0 mL with deionized water in a volumetric flask to form a dilute drink solution. The concentration of Red 40 dye in the dilute solution was determined to be 19.6 ppm from the calibration plot. What is the concentration of Red 40 dye (ppm) in the original sports drink?

140 Concstock × Volumestock = Concdilute × Volumedilute Concstock= (Concdilute x Volumedilute) / Volumestock The aliquot of concentrated solution = Volumestock The diluted final volume of sample solution = Volumedilute

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

15 M NH3 If it is Cu+2, a dark blue solution will form after adding the 15 M NH3. If it is Bi+3, a white precipitate will form after adding the 15 M NH3.

An 3.00 mL aliquot of a 125 ppm stock Red 40 dye solution was diluted to a final volume of 25.0 mL with deionized water. What is the concentration of the dilute Red 40 dye solution (in ppm)?

15.0 ppm

What is the vapor pressure (in kPa) of CH3OH, methanol, over a solution which is composed of 5.00 mL of methanol and 1.68 g of C6H5COOH, benzoic acid, at 25ºC? Pº methanol at 25ºC = 16.915 kPa Density of methanol is 0.792 g/mL Molar mass of benzoic acid is 122.12 g/mol

15.22 kPa

Ozzie wanted to do another experiment with a stronger H2O2 solution to check the accuracy of the experiment by calculating the theoretical volume of O2(g) it would produce. Then he could compare his experimental volume of O2(g) to the theoretical volume of O2(g). He used 5.20 mL of 2.21 M H2O2 and the partial pressure of O2 was 0.9341 atm and the temperature was 298.35 K. What volume of O2(g) could he theoretically produce (in mL)? Enter your answer to 3 significant figures.

150 This question is just working the calculations in reverse from the lab. There are three parts to the calculations. Using Molarity and mL of H2O2 find moles of H2 O2 By stoichiometry find moles of O2 (g) By Ideal Gas Law find Volume of O2 Part 1. Find moles of H2O2 Molarity H2O2 x mL H2O2 x 1L/1000 mL = mol of H2O2 Part 2. Find moles of O2(g) moles H2O2 (from above) x 1 mol O2/2 mol H2O2 = mol O2 (from the balanced reaction) Now that you have moles of O2 gas you can use the Ideal Gas Law. The H2O2 data is aqueous, so you can't use gas law calculations for solutions! Part 3. Find Volume of O2(g) Use R = 0.08206 L atm/K mol and the PV=nRT ; Rearrange PV=nRT to solve for V since you have R, PO2 ,T, mol of gas (which is n) V = (nRT/P) Finally convert to mL of O2

In a similar Exp. 9 experiment, a calibration plot of absorbance vs. concentration of Red 40 dye (ppm) was obtained with the slope of the best-fit straight line as 0.046 ppm-1 The diluted unknown sports drink solution had an absorbance of 0.83. What is the concentration (ppm) of the Red 40 dye in the dilute unknown sports drink?

18.04 Absorbance = Slope × Concentration Concentration = Absorbance / slope

Ozzie wanted to do another experiment with a stronger H2O2 solution to check the accuracy of the experiment by calculating the theoretical volume of O2(g) it would produce. Then he could compare his experimental volume of O2(g) to the theoretical volume of O2(g). He used 5.20 mL of 3.18 M H2O2 and the partial pressure of O2 was 0.9959 atm and the temperature was 291.25 K. What volume of O2(g) could he theoretically produce (in mL)? Enter your answer to 3 significant figures.

198 This question is just working the calculations in reverse from the lab. There are three parts to the calculations. Using Molarity and mL of H2O2 find moles of H2 O2 By stoichiometry find moles of O2 (g) By Ideal Gas Law find Volume of O2 Part 1. Find moles of H2O2 Molarity H2O2 x mL H2O2 x 1L/1000 mL = mol of H2O2 Part 2. Find moles of O2(g) moles H2O2 (from above) x 1 mol O2/2 mol H2O2 = mol O2 (from the balanced reaction) Now that you have moles of O2 gas you can use the Ideal Gas Law. The H2O2 data is aqueous, so you can't use gas law calculations for solutions! Part 3. Find Volume of O2(g) Use R = 0.08206 L atm/K mol and the PV=nRT ; Rearrange PV=nRT to solve for V since you have R, PO2 ,T, mol of gas (which is n) V = (nRT/P) Finally convert to mL of O2.

A 2.50 mL aliquot of a 0.10 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 8.00 mL of the first dilution and diluting it to 50.00 mL. What is the molarity of this second dilution?

1st Dilution = 0.0100 M 2nd Dilution = 1.60 x 10-3 M

A 7.50 mL aliquot of a 0.48 M HCl solution is diluted to a final volume of 100.00 mL. What is the molarity of this first dilution solution? Then a second dilution was made by taking 8.00 mL of the first dilution and diluting it to 50.00 mL. What is the molarity of this second dilution?

1st Dilution = 0.0360 M 2nd Dilution = 5.76 x 10-3 M

A calibration plot of absorbance vs. concentration (ppm) was obtained with standard known Red 40 dye solutions. The slope of the best-fit straight line of the plot is 0.032 ppm- 1 The absorbance of the dilute unknown sports drink was 0.91 What is the concentration of this dilute unknown sports drink ?

28.4 ppm

What is the pH of a buffer in which the concentration of benzoic acid, C6H5COOH, is 0.066 M and the concentration of sodium benzoate, NaC6H5COO, is 0.035 M ? Enter your answer with 2 digits past the decimal. Ka of C6H5COOH is 6.30 x 10-5

3.93 [H3O+] = 1.19 x 10-4 and pH = 3.93 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+]

What is the pH of a buffer in which the concentration of benzoic acid, C6H5COOH, is 0.25 M and the concentration of sodium benzoate, NaC6H5COO, is 0.15 M ? Enter your answer with 2 digits past the decimal. Ka of C6H5COOH is 6.30 x 10-5

3.98 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+]

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 325.0 g of CCl4 and 203.4 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

384.98

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

4.57 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+]

Ozzie wanted to do another experiment using 20.0% (by mass) H2O2. What is the Molarity of this H2O2 solution ?

5.88 M For this problem, we need to work it in the reverse. % (by mass) = Molarity H2O2 x Molar Mass × (1 / (Density) × (1 L/1000 mL) × 100% However, this time start with the % and convert it to Molarity by rearranging the equation above. Molarity = % (by mass) / 100 x Density × (1/Molar mass) x (1000 mL/1L) Now substitution the definition of % (by mass) into the equation above. % (by mass) = (mass of H2O2/ mass of solution) Molarity = [(g of H2O2/g of soln) / 100)] x (1.0 g soln/mL soln) x ( 1 mol H2O2/ 34.01 g H2O2) × (1000 mL/1L)

An 10.0 mL aliquot of a 125 ppm stock Red 40 dye solution was diluted to a final volume of 25.0 mL with deionized water. What is the concentration of the dilute Red 40 dye solution (in ppm)?

50 ppm

A red sports drink contains Red 40 dye. A 7.0 mL aliquot of this sports drink was diluted to 25.0 mL with deionized water in a volumetric flask to form a dilute drink solution. The concentration of Red 40 dye in the dilute solution was determined to be 17.8 ppm from the calibration plot. What is the concentration of Red 40 dye (ppm) in the original sports drink?

63.6 Concstock × Volumestock = Concdilute × Volumedilute Concstock= (Concdilute x Volumedilute) / Volumestock The aliquot of concentrated solution = Volumestock The diluted final volume of sample solution = Volumedilute The correct answer is: 63.6

A 97.0 mg sample of Red 40 dye was dissolved and diluted to a final volume of 1.50 L with deionized water. What is the concentration of the Red 40 dye solution in ppm? parts per milliion (ppm) refers to 1 mg of solute in 1.0 L of solution; (mg/L)

64.7 ppm

From the observations for a Qualitative Groups 1 & 2 Unknown D, (see below) match the physical observation to the indicated box in the modified flowchart below. The inference lines were omitted for clarity. Some descriptions may be used more than once. Unknown "D" was initially a colorless solution. After the addition of HCl, a white precipitate and colorless decantate was obtained. (The decantate was saved for step 2-A.) When the white solid had hot water added, there was still some solid present and a colorless solution was decanted for the next step. After adding K2CrO4, a yellow precipitate formed. The white solid dissolved when the 6 M NH3 was added to form a colorless solution, but the white precipitate reformed after adding the HNO3. To the saved decantate from step 1-A, it remained unchanged after adding the 6 M H2SO4. To this colorless solution, no change was observed after adding 15 M NH3. After adding CH3COOH to the colorless solution, no apparent reaction occurred. Finally, the addition of K4Fe(CN)6 turned the colorless solution light yellow, but not no precipitate formed.

Box 2e: yellow solution Box 2c: no observation; step was omitted Box 1c: yellow precipitate Box 2b-2: colorless solution

Ana Elyse filled in the flowchart below with the observations from her Group 3 Unknown "B". Assign the correct formulas to the boxes indicated. The Inference boxes are not shown to simplify the flowchart. Remember all cations are listed until confirmed absent. CrO4-2 (aq) and [Zn(OH)4]-2 (aq)

Box 3-B

Ana Elyse filled in the flowchart below with the observations from her Group 3 Unknown "A". Assign the correct formulas to the boxes indicated. The Inference boxes are not shown for ease of viewing. Remember all cations are listed until confirmed absent. Fe+3 (aq), Ni+2 (aq), Mn+2 (aq)

Box 3-C

Ana Elyse filled in the flowchart below with the observations from her Group 3 Unknown "B". Assign the correct formulas to the boxes indicated. The Inference boxes are not shown to simplify the flowchart. Remember all cations are listed until confirmed absent. Fe+3 (aq), Ni+2 (aq), Mn+2 (aq)

Box 3-C

Ana Elyse filled in the flowchart below with the observations from her Group 3 Unknown "A". Assign the correct formulas to the boxes indicated. The Inference boxes are not shown for ease of viewing. Remember all cations are listed until confirmed absent. [Fe(SCN)6] -3(aq)

Box 3-D

Ana Elyse filled in the flowchart below with the observations from her Group 3 Unknown "B". Assign the correct formulas to the boxes indicated. The Inference boxes are not shown to simplify the flowchart. Remember all cations are listed until confirmed absent. Confirmed Absent

Box 3-D

Ana Elyse filled in the flowchart below with the observations from her Group 3 Unknown "B". Assign the correct formulas to the boxes indicated. The Inference boxes are not shown to simplify the flowchart. Remember all cations are listed until confirmed absent. Ni(HDMG)2

Box 3-F

If an error caused the mass of the solution to be larger, how does this affect the calculations?

The larger mass would result a larger qsolution

Match the correct inference to the descriptions of the reactions from the Group 3 Qualitative Analysis Experiment, When the yellow K4Fe(CN)6 solution was added in step 3-J, no precipitate formed.

Zn+2 is confirmed as absent

Match the correct inference to the descriptions of the reactions from the Group 3 Qualitative Analysis Experiment, A greyish-white precipitate formed with K4Fe(CN)6 was added in step 3-J.

Zn+2 is confirmed as present.

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.