CHEM 1212 Final
What is the oxidation number of Cu in Cu2O?
+1
What is the oxidation number of C in C2O4−2 ?
+3
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.
-46.6 kJ/mol
Predict the initial rate (in kPa/sec) for Trial D using the data below.It was previously determined that the reaction is 2nd order in D, 1st order in E, and the average rate constant, k is equal to 0.0843 kPa/(sec · M3). [E] M = 0.600 [D] M = 0.200
0.00202 KPa/sec
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?
0.036 0.00576
Ferris & Mona used the ORP sensor to titrate a ferrous ammonium sulfate solution, (NH4)2Fe(SO4)2 with KMnO4 titrant. They titrated a 15.00 mL aliquot of the Fe+2 solution with 0.0250 M MnO4- solution and determined that the equivalence point was at 20.2 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
0.168
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.
0.28
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 0.156 M Br2 using an ORP probe. The equivalence point of the titration curve was determined to be 15.5 mL. What is the mass (in grams) of Vitamin C, C6H8O6, in the tablet.
0.426 g
Piers & Aida added 1.00 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 16.80 mL of 0.0207 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?
0.9
What is the pH of a 3.3 x 10-3 M NaOH solution?
11.52
What is the pH of a 4.5 x 10-3 M HCl solution?
2.35
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-1The 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?
23 ppm
A standard solution of 252 ppm Blue 2 dye was prepared. A 23.9 mL aliquot of the stock Blue 2 dye was diluted to 250 mL in a volumetric flask. What is the concentration (in ppm) of this dilute Blue 2 dye?
24 ppm
What is the pH of a buffer in which the concentration of benzoic acid, C6H5COOH, is 0.075 M and the concentration of sodium benzoate, NaC6H5COO, is 0.050 M ? Ka of C6H5COOH is 6.30 x 10-5
4.02
How many total electrons are transferred in this reaction? Pt(s) → Pt+2(aq) + 2 e - Cr2O7 -2(aq) + 14 H+(aq) + 6 e - → 2 Cr+3(aq) + 7 H2O
6
A red sports drink contains Red 40 dye. A 5.4 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 18.1 ppm from the calibration plot. What is the concentration of Red 40 dye (ppm) in the original sports drink?
83.8 ppm
Which statement about the spectrophotometric analysis of Red 40 dye is TRUE? Select one: A.) The intensity of the color of the solution is directly proportional to concentration of the Red 40 dye. B.) The calibration plot is a graph of Concentration of Red 40 dye (y-axis) versus Absorbance (x-axis). C.) If there is no Red 40 dye present in the solution, the absorbance will be one. D.) Absorbance = slope / concentration.
A - this statement is true B - concentration = x, absorbance = y C - absorbance will be 0 D - slope = absorbance / concentration
Select the steps that will compose a rationale for the cation Fe+3 being absent in an unknown.
A blood red solution did not form when KSCN was added in step 3-D.
The Alizarin pH indicator has two pH ranges: 5.4 - 7.2 (yellow to red) 11.0 - 12.4 (red to purple) After adding Alizarin indicator to a solution, it turned yellow. Predict the expected pH range of the solution.
A pH of below 5.4
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.
A reaction mixture was formed by adding 40 mL H2O, 8.00 mL of 0.44 M H2O2, and 7.0 mL of 0.70 M KI. A.) What is the molarity of the H2 O2 in the reaction mixture? B.) What is the molarity of the KI in the reaction mixture?
A.) 0.064 M B.) 0.089 M
Match the correct inference to the description of the reactions from the Group 1 & 2 Qualitative Analysis Experiment. A.) In step 1-B, when hot water was added to the white precipitate, the white precipitate remained even after stirring the solution. The decantate was a colorless solution. B.) In step 1-C, after adding the 6 M CH3COOH and K2CrO4 to the colorless solution, the solution turned light yellow, but no solid was observed. C.) In step 1-A after adding the 6 M HCl to an unknown, a white precipitate formed with a light blue decantate.
A.) Ag+ is indicated as possibly present. B.) Pb2+ is confirmed absent. C.) Ag+ and Pb2+ are indicated as possibly present.
Match the correct inference to the descriptions of the reactions from the Group 3 Qualitative Analysis Experiment, A.) After adding NaBiO3 and centrifuging in step 3-G, a purple supernate is observed over the excess NaBiO3. B.) After adding H2DMG in step 3-F, a strawberry red precipitate formed. C.) After adding the K4Fe(CN)6 in step 3-J, no precipitate formed. D.) After the H2O2 is added in step 3-B, the solution turns yellow.
A.) Mn2+ is confirmed as present B.) Ni 2+ is confirmed as present C.) Zn2+ is confirmed as absent D.) Cr3+ is indicated as possibly present
A substance that is often used as food colorant or food dye is chlorophyll. It is sometimes referred to as a "natural" dye, as it is derived from plants. One component is chlorophyll a, which has two peaks in the visible spectrum. There is one peak at an observed λmax of 430 nm. Using the visible spectrum and the color star, predict... A.) the color absorbed B.) then color observed
A.) blue violet B.) yellow-orange
Indie, Cate, & Ora tested a new indicator to determine its pH range and color changes. The solution used in the experiment was colorless and acidic at pH 1. They added 2 drops of erythrosine indicator to the solution, which turned orange. This is the initial observation for the pH and color. Next, they added NaOH to increase the pH, and recorded the pH and color data below. pH 1 - orange (initial observation) pH 2- orange pH 4 - red pH 6 - red pH 8 - red Use the data set above to answer the following questions. A.) What is the pH range of the indicator? B.) What is the first color change for this indicator? C.) What is the second color change for this indicator?
A.) pH 2-4 B.) orange to red-orange C.) red-orange to red
The meta-cresol purple pH indicator has the following pH ranges: 1.2 - 2.8 (red to yellow) 7.4 - 9.0 (yellow to purple) For each of the pH values below, what color do you expect to see? A.) 1.0 B.) 2.0
A.) red B.) orange
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 change after the equilibrium has been re-established: - Adding a few drops of colorless HCl to the solution
Adding HCl increases the Cl- ions in the products. An increase in products creates a shift to the left, increasing the reactants. This causes an increase in CuCl4 which causes the color to be light green.
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. Predit 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).
What is the confirmation for Ag+ being absent?
All of the white precipitate from step 1-A dissolved in hot water.
Select all that apply to an endothermic reaction. Select one or more: A.)The reaction releases heat to the surroundings. B.) Heat is a reactant. C.) Heat is a product. D.) Adding heat (hot water bath) will cause the equilibrium to shift towards products. E.) Removing heat (cold water bath) will cause the equilibrium to shift toward products.
B, D
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
What is the formula for barium chloride?
BaCl2
define rate
Change in concentration of A per change in time, Δ[A]/Δtime
You have two test tubes. One test tube contains Cr+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?
Cr+3(aq) will form a green solution, [Cr(OH)4]- (aq). Ni+2(aq) will form a green precipitate,Ni(OH)2 (s).
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) Decreasing the overall pressure of the equilibrium system.
Decreasing the overall pressure of the equilibrium system will cause a shift to the side with the most moles. The products have the most moles, so this equation will shift to the products, to the right.
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) Decreasing the overall total pressure of the equilibrium system.
Decreasing the overall pressure of the system will cause a shift to the side with the most moles. The products have the most moles, so the equilibrium will shift right.
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) Decreasing the overall temperature of the equilibrium system.
Decreasing the overall temperature of the equilibrium system will cause a shift to the left because this is an endothermic reaction, so heat is a reactant. Removing a reactant will cause a shift to the reactants (left)
concerning pH and buffers, is this statement true? - A buffer only works when acids are added and not when bases are added.
False. A buffer works for acids and bases.
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).
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
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?
HCl or Hot water
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 HCl is added. Then explain what will occur in terms of Le Châtelier's principle.
HCl reacts with NH3, so adding HCl will cause a removal of the reactant, NH3. Removing a reactant causes a shift to the left, which causes an increase in reactants. Therefore the color of the solution will be a light blue.
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: Added 50 mL of 1.0 M NaOH solution and 50 mL (instead of 40 mL) of 1.0 M HCl into the calorimeter.
Increases the value of final Temperature.
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 carbon monoxide gas.
Increasing the partial pressure of a product causes a shift to the left. This increases the reactants.
How does Bi3+ react with HCl?
It remains a colorless 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 change after the equilibrium has been re-established: Adding a few drops of Ag+(aq) solution (Ag+ reacts with Cl- ions)
It says that Ag+ reacts with Cl- ions so an addition of Ag decreases the product Cl-. A decrease in products creates a shift to the right, increasing the products to reach equilibrium. Therefore CuBr4 is increased causing the solution to have a dark brown color.
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 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.
You have two test tubes. One test tube contains Pb+2 (aq) solution and the other test tube contains Cu+2(aq). Predit what will happen when HCl (aq) is added to both test tubes. If a reaction occurs, what is the new chemical formula?
Pb+2 (aq) will form a white precipitate, PbCl2 (s).Cu+2 (aq) will remain unchanged.
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. What is the correct rate constant expression? A(aq) + 3 C(aq) → AC3(aq)
Rate = (5.4 x 10 -3 M -1sec -1) [A]3 [C]
define overall reaction rate
Rate of the slowest step.
In Experiment 4, the starting material of NiCl2 was observed to be a lime green solid. Using the Figure 10-2 Color Star, what color of wavelengths are being absorbed? Select one: red red-orange orange yellow-orange yellow yellow-green green blue-green blue blue-violet violet red-violet
Red-violet. This is the opposite color on the color wheel.
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 first turned brown, which was a smaller 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 lower than the other two students. Since the volume of MnO4- is in the numerator for the calculation of M of Fe+2, the lower volume of MnO4- results in lower M of Fe+2.
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? What will happen to C6H5COOH? What will happen to C6H5COO- ?
The concentration of C6H5COOH will decrease. - because decreasing the reactants will cause a shift to the left which causes reactants to decrease. The concentration of C6H5COO- will increase. - the shift to the left due to the removal of H3O will cause the other product to increase
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.
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 T(initial) would produce a smaller ΔT, which would result in a smaller q.
In a certain reaction, a solid chemical dissolved in water. The temperature of the water sample rose from 22.4°C to 27.3°C. What is true about this experiment?
The water is defined as the surroundings Heat was lost by the system The reaction is exothermic
concerning pH and buffers, is this statement true? - The greater the concentrations of the buffer components, the greater its buffering capacity.
True. Because the more buffer there is the more buffer that is available to consume the acid/base added.
When 5.22 g of CaCl2 dissolved in 50.00 mL of water in a coffee cup calorimeter, the temperature of the solution rose from 25.3°C to 28.9°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 q(solution)? + 831 J What is q(reaction)? -831 J What is ΔHrxn in kJ/mol of CaCl2 ? - 17.7 kJ/mol
define pH buffer
a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid
Confirmation test for Cr3+
a pale yellow-tan solid
Confirmation test for Ni2+
a red-pink percipitate
does a base donate or accept a proton
accept
Define Brønstead-Lowry Acid
any substance that donates a proton
Define Brønstead-Lowry Base
any substance that takes a proton
NH3 (aq) and NH4OH (aq) are different ways of writing the chemical formula of the which chemical ?
aqueous ammonia
What color is Bi (s)
black solid
Consider the equilibrium reaction below. At high concentrations of HA the solution will be yellow; but at low concentrations of HA the solution will be blue. Initially the equilibrium mixture below is green (combination of yellow & blue). What color is expected after adding some colorless OH-(aq) to the equilibrium solution? A-(aq) + H2O(ℓ) ⇋ HA(aq) + OH-(aq)
blue. Adding a product will cause a shift to the left (reactants) and lowers the other products (HA) so there is a low concentration of HA, therefore it is blue.
What color is Cu2+ (aq)
colorless
What is a liquid that is carefully poured into a new container after being separated from the solid?
decantate
does an acid donate or accept a proton
donate
oxidizing agent
electron acceptor
reducing agent
electron donor
concerning pH and buffers, is this statement true? - As a basic solution is diluted the pH increases.
false. As basic solutions are diluted, the pH decreases. If the pH is increasing, the solution is becoming more basic.
What is the name for H2O2 ?
hydrogen peroxide
What is a supernate?
liquid above the precipitate
Cole & Lars pour their unknown solution into two test tubes and label them A & B. ProcedureTest tube A: added a few drops of bromocresol green indicator, which has a pH range of 3.8 - 5.4 (yellow to blue) Test tube B: added a few drops of phenolphthalein indicator, which has a pH range of 8.2 - 10.0 (colorless to pink) ObservationTest tube A is yellow and test tube B is colorless. What is the approximate pH range that matches the observation above?
pH < 3.8
What is the pH for a buffer that is a mixture of 0.25 M HC2H3O2 and 0.20 M NaC2H3O2? Ka for HC2H3O2 = 1.3 x 10 ^(-5)
pH = 4.65
What is the pH of a solution that has 0.040 M CH3COOH and 0.060M NaCH3COO present? Ka for acetic acid = 1.80 x 10-5
pH = 4.92
equation to determine pH
pH= -log[H+]
equation to determine pOH
pOH = -log[OH-]
What is a solid compound that forms as a result of mixing reagents together in a solution.
percipitate
rate law equation
rate = k [A]^x [B]^y
the slowest step is called the
rate determining step
define buffering capacity
the amount of acid/base that can be added before the pH changes by 1 pH unit
what does it mean for a species to be reduced?
to gain electrons
what does it mean for a species to be oxidized?
to lose electrons
concerning pH and buffers, is this statement true? - As an acidic solution is diluted the pH increases.
true
what is the confirmation test for Ag+
white perciptate
What color is AgCl (s)
white solid
What color is Bi(OH)3 (s)
white solid
What color is PbCl2 (s)
white solid
What is the confirmation test for Pb 2+
yellow percipitate
