Lab Exam Review CHEM 132
A solution has a pH of 5.50. What is the hydronium ion, H3O+, concentration in this solution? 0.74 M 3.2 x 10-6 M 3.2 x 105 M
3.2 x 10-6 M
Consider the titration of a weak monoprotic acid with NaOH (aq). Suppose the pH at the half-equivalence point (halfway point) is 3.75. What is the pKa of this acid? 10.25 cannot determine from this information 3.75 1.88
3.75
Consider the reaction: Fe3+(aq)+SCN-(aq)yields FeSCN2+(aq) Initially, the reaction vessel contained 0.20 M iron(III) ions and 0.20 M SCN-(aq). Once equilibrium was reached, the FeSCN2+(aq) had a concentration of 0.15 M. What is the value of the equilibrium constant, K, for this reaction under these conditions? 60. 130 0.017 3.8
60
The following ions were studied in this lab: Group A (Fe3+, Mn2+, Al3+) Group B (Ba2+, Ca2+, Mg2+) Group C (Cu2+, Ni2+, Co2+) Which reagent would you use to separate Mn2+(aq) from Cu2+(aq)? 6M NaOH 6M NH3 and 2 drops HNO3
6M NH3 and 2 drops HNO3
You want to make an aqueous solution of 150.0 mL of 0.300 M sodium thiosulfate, K2S2O3. Calculate the mass in grams of sodium thiosulfate that would you need to make this solution? molar mass K2S2O3 190.3 g/mol molar mass H2O 18.02 g/mol 0.236 g K2S2O3 95.2 g K2S2O3 0.475 g K2S2O3 8.56 g K2S2O3
8.56 g K2S2O3
When all of the following are mixed together in a beaker, what is the molar concentration of the SCN- ion in the solution just after mixing but before any reaction takes place? 10.00 mL of 2.00 x 10-3 M Fe(NO3)3 4.00 mL of 2.00 x 10-3 M KSCN 4.00 mL of 0.50 M HNO3
Between 0.0004 and 0.0005
A solution is made by mixing equal amounts of 0.20 M acetic acid, HCH3CO2, and 0.20 M potassium acetate, KCH3CO2. If one drop of HCl (aq) is added to the solution, pH only changes slightly. What species in the solution does the HCl react with so that the pH remains relatively constant? K+ CH3CO2- H2O HCH3CO2
CH3CO2-
The glass volumetric pipets can be put directly into the reagent bottles of stock solution. True or False.
False.
You can leave a drinking water bottle on your bench while doing experiments as long as it is closed. True or False.
False.
The product of the reaction of Fe(NO3)3 and excess ammonia is _______. Fe(OH)3(s) Fe(NH3)63+(aq)
Fe(OH)3(s)
Given the data below, which reaction has the larger value for the rate of reaction? Reaction A took 5 minutes to complete. Reaction B took 10 minutes to complete. Reaction A Reaction B Reaction A & Reaction B have equal rates
Reaction A
To the following reaction at equilibrium, a huge excess of Fe(NO3)3 (aq) is added. What will happen to the concentration of FeSCN2+ as the reaction returns to equilibrium. Fe3+(aq)+SCN-(aq) yields FeSCN2+(aq) [FeSCN2+] will decrease [FeSCN2+] will increase [FeSCN2+] will remain unchanged
[FeSCN2+] will increase
In the following reaction, the reactants are colorless but FeSCN2+ is orange and absorbs light around 450 nm. Imagine that you put the reactants into the spectrophotometer before the reaction begins. You continue to monitor absorbance, and the reaction begins. What will happen to the absorbance as more product is made? Fe3+(aq)+SCN-(aq) yields FeSCN2+(aq) absorbance will remain constant absorbance will increase absorbance will decrease
absorbance will increase
Ammonium chloride, NH4Cl, is a/n _____________. neutral salt basic salt strong base Correct! acidic salt
acidic salt
The minimum energy needed for a reaction to occur is the ____________. reaction order catalytic energy activation energy reaction time
activation energy
In order to obtain accurate results when measuring the pH of solutions it is necessary to use good laboratory technique. List one thing that must be done to the pH probe before taking measurements in order to obtain accurate pH readings. Do not include "use clean glassware" or "measure volumes carefully" - that is a given.
calibrate the pH meter or rinse thoroughly before placing in the solution
According to Beer's law, the concentration of a substance that absorbs light is _____________ to the absorbance of light by that substance. logarithmically related inversely proportional not related directly proportional
directly proportional
You remove some reagent from the reagent bottle in lab and place it in a clean beaker. At the end of the experiment, you have not used all of this reagent. What do you do with the leftover reagent? pour back in reagent bottle dispose of as waste leave it on the bench for the next lab
dispose of as waste
Which one of the following pieces of glassware can be used to accurately measure liquid volumes? watchglass beaker Erlenmeyer flask graduated cylinder
graduated cylinder
If the equilibrium constant for the following reaction is 3.0 x 10 -6, at equilibrium the expected concentration of FeSCN2+will be relatively ___________. Fe3+(aq)+SCN-(aq) yields FeSCN2+(aq) large small cannot determine
small
If you spill on the lab bench some 1 M HNO3 , what is the proper way to clean up the spill? wipe up with a wet paper towel sprinkle with baking soda and wipe up with a paper towel put it in the glass waste container wipe up with a paper towel
sprinkle with baking soda and wipe up with a paper towel
A solution has a pH of 3.00. When it is diluted to half the concentration, the pH is 3.30. The solution is a _________ ___________.
strong acid.
For the following reaction, it was determined that the reaction is 1st order in PH3. 4PH3(g) yields P4(g)+6H2(g) Which of the following represents the correct way to write the rate law (rate equation) for this reaction? rate = k k [PH3] rate = k [PH3]4 rate = k [PH3]
rate = k [PH3]
The following reaction represents the acid ionization of the weak acid, ammonium ion. NH4+(aq) + H2O(l) NH3(aq) + H3O+(aq) Ka = 5.6 x 10-10 20.0 mL of 0.15 M ammonium chloride, NH4Cl, solution would have a pH of 5.04. If 15.0 mL of 0.15 M ammonia, NH3, solution were added to the above ammonium chloride solution, what would happen to the Ka value of the ammonium ion? remain the same decrease increase
remain the same
The value of the rate constant, k, for a reaction remains constant when the temperature of the reaction changes. True or False.
False
If you plot ln k vs 1/T, the slope of the line for this graph will be equal to _________. 1/T [reactant] -Ea/R -k
-Ea/R
If 25.00 mL of a standard iron solution (with a concentration of 0.050 mg Fe2+/mL) is diluted to a total volume of 250.00 mL, what is the final iron concentration in mg Fe2+/mL? 0.0050 mg/mL 0.050 mg/mL 0.50 mg/mL 0.0025 mg/mL
0.0050 mg/mL
Calculate the initial concentration of thiosulfate, S2O32-, in a solution when 1.50 mL of 0.100 M Na2S2O3 is added to 4.00 mL of potassium iodide, KI, aqueous solution. 0.367 M 0.0375 M 0.100 M 0.0273 M
0.0273 M
For this reaction (CH3)3CBr + H2O à HBr + (CH3)3COH the rate law is: rate = k [(CH3)3CBr ] [H2O]0 When the concentration of (CH3)3CBr is 0.20 M and the concentration of H2O is 0.30 M, the rate of reaction was measured to be 0.0082 M/s. What is the rate constant for this reaction? 0.041 s- 7.3 s- 0.14 s- 0.46 s-
0.041 s-
A solution has a pH of 1.25. What is the equilibrium hydronium ion concentration of this solution? 0.056 M 0.25 M 1.25 M 18 M
0.056 M
If you use a 1-mL volumetric pipet to deliver liquid, how many significant figures are recorded for that volume measurement? 3 1 2 4
3
Which of the following solutions would have the smallest pH? 0.10 M NH3 (aq) 0.10 M HCl(aq) 0.10 M HC2H3O2 (aq)
0.10 M HCl(aq)
You experimentally created a calibration curve with absorbance on the y-axis and concentration (in molarity) on the x-axis. The data had a linear relationship with this equation: y = 1.9 x + 0.1000. If you then measured a sample of unknown concentration and found the absorbance was 0.650, what is the concentration of the sample in molarity? 1.3 M 0.29 M 0.034 M 0.39 M
0.29 M
The pH of a 0.10 M solution of unknown weak acid HA is 3.50. Determine the value of the Ka for this acid. 1.0 x 10-6 3.2 x 10-3 3.2 x 104 2.9 x 10-2
1.0 x 10-6
A 0.20 M hydrofluoric acid, HF, solution will have an equilibrium hydronium ion concentration of 0.010 M. What is the percent ionization of this weak acid? 20.% 10.% 5.0% 0.50%
5.0%
Which one of the following is the correct equation for Beer's law? c = Ab A = ε c A = ε b c c = A ε b
A = ε b c
In the Beer's Law equation, what does A stand for? A = εbc
A is the measured absorbance of the solution
The product of the reaction of Co(NO3)2 and excess ammonia is ___________. Co(NH3)62+ (aq) Co(OH)2 (s)
Co(NH3)62+ (aq)
Which of the following ions in solution is blue? Cu2+ Ba2+ Fe3+
Cu2
If aqueous sodium hydroxide is added to an equimolar solution of nickel (II) nitrate and copper (II) nitrate, which ion will form a precipitate first? No calculation required! Refer to Table 1 of the background of your lab report, also in the instructions for this quiz. Ni2+ Cu2+
Cu2+
Type out the balanced equation for copper ions, Cu2+, reacting with ammonia solution. Include states. You can use the phrase "single arrow" or "double arrow" to indicate the arrow in the equation.
Cu2+(aq) + 4 NH3(aq) "single or double arrow" Cu(NH3)42+(aq)
If the temperature of a reaction is increased, the rate constant, k, of the reaction will decrease. True False
False
Most hydroxide salts are soluble in water.
False
The Ka of HCO3- is 4.8 x 10-11. Choose the correct chemical reaction that this Ka represents.
HCO3-(aq)+H2O(l)yields CO3^2-(aq)+OH-(aq)
Which of the following acids has a Ka value greater than 1? (there is only one correct answer) HCl HCH3CO2 HF HClO
HCl
Write the correct balanced equation for the reaction that you would use when calculating the Ka of hydrofluoric acid if you were given the pH of an aqueous solution of HF mixed with aqueous sodium fluoride, NaF(aq). Include the states. Since there is no arrow symbol, you can write the words "single arrow" or "double arrow" where you would put the arrow in the reaction.
HF(aq) + H2O(l) double arrow F-(aq) + H3O+(aq)
Which of the following correctly represents the acid ionization constant expression for the weak acid hydrogen sulfate ion, HSO4-?
Ka=[SO4^2-][H3O+]/[HSO4-]
Before taking absorbance measurements, a blank must be run to zero the spectrophotometer at a specific wavelength using the pure solvent in a cuvette. True or False.
True
Why do we run a solvent blank in the spectrophotometer before running samples?
Running a solvent blank zeros any absorbance that may happen due to the cuvette and solvent in the spectrophotometer. It is like taring a balance that has a weigh boat.
HCl(aq) when added in excess will dissolve solid Ba(OH)2. True False
True
If you have a "standardized" solution of potassium hydroxide, what does that tell you about the solution? All solutions that are part of titrations are called "standardized solutions." The solution is a buffered solution. The concentration of the solution has been precisely determined through titration.
The concentration of the solution has been precisely determined through titration.
Phenolphthalein, a pH indicator, is added to the titration before the procedure begins. Why? Because the phenolphthalein is a standardized solution To provide a basic solution for the titration reaction To create a color change when the titration endpoint is reached To keep the solution from evaporating while the titration takes place
To create a color change when the titration endpoint is reached
In the "Spectrophotometric Determination of Iron" lab, why is o-phenanthroline used in the experiment? To form a colorful complex with iron To dilute the solution To reduce the iron(III) ion to iron (II) ion To zero the spectrophotometer
To form a colorful complex with iron
For the reaction of Al(NO3)3 and OH- , two different products can form depending on the amount of OH- added. When excess hydroxide ions are added, Al(OH)4- forms. Is this substance in the aqueous state or a solid? solid aqueous
aqueous
A solution is made with 20 mL of 0.40 M ammonia, NH3, and 20 mL of 0.40 M ammonium chloride, NH4Cl. Which of the following best describes the resulting solution. weak acid weak base buffered solution neutral solution
buffered solution
In the Beer's law equation, what does "c" stand for? concentration of absorbing species molar absorptivity absorbance wavelength of light
concentration of absorbing species
If a reaction is first order, which type of graph for that reaction will produce a linear function? temperature vs time ln [R] vs time 1/[R] vs time [R] vs time
ln [R] vs time
The following are the reactions for this lab: 3I−(aq) + S2O82− (aq) yields 2SO42− (aq) + I3−(aq) I3-(aq) + 2S2O32-(aq) yields S4O62-(aq) + 3I-(aq) I3-(aq) + starch yields blue color After a period of time, the reaction solution turned blue. This blue color appeared when which substance ran out (concentration went to zero)? sulfate ion, SO42- iodide ion, I- starch thiosulfate ion, S2O32-
thiosulfate ion, S2O32-
Every time you change the spectrophotometer to a new wavelength, you should re-zero the instrument using the pure solvent in a cuvette. True or False.
true.
