lab final
What was the boiling point of water?
100.0 C
A plot of log(rate) versus log[A] yields the following linear equation. What order is the reaction with respect to A? y=2.13x + 3.11
2
The following reaction is first order. If the rate at [A] = 0.1 M is 3, what will the rate be at [A] = 0.2 M? A⟶B+C
6
Between which pH values does phenolphthalein change from colorless to pink?
7.7 to 8.7
At what wavelength did the copper(II) sulfate solution absorb light most strongly? Choose the closest answer.
700 nm
Why does the pressure in the flask increase upon the addition of more HCl even after the reaction between NaHCO3 and HCl has stopped?
The HCl fills additional volume in the flask, decreasing the amount of volume to be taken up by the gas.
Given the results of your coarse titration, how does the concentration of the acetic acid compare to the concentration of sodium hydroxide?
The acetic acid solution has a lower molarity than the sodium hydroxide solution.
Suppose you did a similar experiment in which volume was held constant and pressure was allowed to vary with temperature. The measured value of absolute zero would be
identical
What happens to the volume of a gas as the temperature is reduced?
it decreases
Suppose 15.00 mL of a solution of a monoprotic strong acid of unknown concentration requires 12.80 mL of a solution of 0.250 M NaOH to reach the end point. What is the molarity of the strong acid?
0.213 M
What was the absorbance of cobalt(II) chloride at 500 nm? Choose the closest answer.
0.358 nm
What was the absorbance of copper(II) sulfate at 700 nm? Choose the closest answer.
0.517 nm
What was the purpose of measuring the freezing point of water?
to verify the accuracy of the apparatus and to determine the freezing point of the pure solvent
Given the data in the table below, what is the enthalpy of reaction for the following sulphur dioxide synthesis reaction? S(s)+O2(g)⟶SO2(g) 2SO2(g)+O2(g)⟶2SO3(g)ΔH=−196.8kj/molS(s)+32O2(g)⟶SO3(g)ΔH=−395.2kJ/mol
ΔH=−296.8kJ/mol
Which answer for the value of absolute zero is closest to the value determined from your data?
-273.2 C
What is absolute zero in degrees Fahrenheit?
-460 F
At what temperature did the water in the test tube begin to turn into ice?
0.0 C
What was the melting point of water?
0.0 C
Given that the temperature in kelvins is equal to the temperature in degrees Celsius plus 273.15, what is absolute zero in kelvins?
0.00
What was the absorbance of copper(II) sulfate at 400 nm? Choose the closest answer.
0.019 nm
What was the absorbance of cobalt(II) chloride at 440 nm? Choose the closest answer.
0.163 nm
What is the overall reaction order for a reaction with the following rate law? rate=k[A]2[B]
3
The value of the calorimeter constant is between
4 and 10 J/°C.
A reaction forms one mole of product in the balanced equation. If the reaction forms 2.3 × 10-3 M product in 46 seconds, what is the rate of the reaction?
5.0 x 10^-5 M/s
At what wavelength did the cobalt(II) chloride solution absorb light most strongly? Choose the closest answer.
520 nm
What was the purpose of calculating the calorimeter constant?
Because the calorimeter is not ideal, it absorbs some of the heat from its contents and this heat must be corrected for each time the calorimeter is used.
You observed that the products in the crucible weigh less than the reactants that you added. How is this possible?
CO2 and H2O were released as gases.
The purity of a substance will often affect the melting and boiling points. This is used by chemists to assess the purity of a product. How does the purity of the substance affect the melting and boiling points?
Impurities frequently cause melting point depression and boiling point elevation.
What happens to the volume of a gas as the temperature approaches infinity?
It approaches infinity
Which of the following characteristics are necessary for a primary standard?
It must be reasonably soluble.
What happened to the temperature of the water once it started to freeze?
It stayed constant for a period of time
What happened to the temperature of the water after it reached the boiling point?
It stayed constant while it boiled
In the enrichment of uranium for nuclear reactors, a gas called uranium hexafluoride (UF6) is generated and then placed in large gas centrifuges to separate different isotopes of uranium. Suppose you were to perform the same experiment with uranium hexafluoride. Given that uranium hexafluoride is much heavier than either of the gases used in this experiment, how would you expect the value of absolute zero measured from the experiment to compare to the one you measured?
It will be the same
Suppose you chose the other gas to measure. How would you expect the value of absolute zero measured from the experiment to compare to the one you measured?
It will be the same
A student conducting the iodine clock experiment accidentally makes an S2O82- stock solution that is too concentrated. How will this affect the rate measurement? Reaction 1: 3I−(aq)+S2O2−8(aq)⟶I−3(aq)+2SO2−4 slow Reaction 2: I−3(aq)+2S2O2−3(aq)⟶3I−(aq)+S4O2−6(aq) fast Reaction 3: I−3(aq)+starch⟶3I−−starch (bluish black) fast
It will take less time for the color to change, as rate increases with concentration of reactant.
The iodine clock experiment consists of the following three reactions, where Reaction 1 is slow relative to Reactions 2 and 3. Predict what would happen if Reaction 2 was slow relative to Reaction 1 (assume that Reaction 3 is still fast). Reaction 1: 3I−(aq)+S2O2−8(aq)⟶I−3(aq)+2SO2−4(aq) slow Reaction 2: I−3+2S2O2−3(aq)⟶3I−+S4O2−6(aq) fast Reaction 3: I−3(aq)+starch⟶3I−−starch (bluish black) fast
It will take longer for the color to change, which will increase Δt, resulting in a lower calculated rate.
What is the first experimental step to determine the molar mass using the freezing point depression method?
Measure the freezing point of the pure solvent and then measure the freezing point of the solution.
Based on the molar enthalpies calculated for Experiments 2 and 3, use Hess's Law to write a series of reactions that will sum up to the reaction of the decomposition of ammonium chloride. In addition to the molar enthalpies from Experiments 2 and 3, you will also need to include the following reactions, which account for the enthalpy change when HCl and NH3 change state. NH3(g)⟶NH3(aq) (ΔH = -34,640 J/mol) HCl(g)⟶HCl(aq) (ΔH = -75,140 J/mol) Choose the equation that shows the correct direction and sign for the enthalpy value for the reaction between NH3 and HCl in your series of reactions.
NH4Cl(aq)⟶HCl(aq)+NH3(aq) (+ΔH)
Why is standardization of NaOH necessary?
NaOH is hygroscopic and is hard to weigh accurately.
The iodine clock experiment, which consists of the following three reactions, is set up so [S2O32-] < [S2O82-]. What would happen if [S2O32-] > [S2O82-]? Reaction 1: 3I−(aq)+S2O2−8(aq)⟶I−3(aq)+2SO2−4(aq) slow Reaction 2: I−3(aq)+2S2O2−3(aq)⟶3I−(aq)+S4O2−6(aq) fast Reaction 3: I−3(aq)+starch⟶3I−−starch (bluish black) fast
No bluish black color would form because all the I3- formed in Reaction 1 would be converted back into I-.
How did you determine that the reaction between the sodium bicarbonate and hydrochloric acid had stopped despite the addition of more HCl?
No more bubbles formed in the solution
What happens if the reactants are not added in the correct ratio according to the chemical equation?
One of the reactants will be fully consumed whereas the other reactant will be in excess.
Why was a significant voltage change seen after all of the potassium dihydrogen arsenate was added?
Reduction of copper(II) could no longer occur once Cu2+ precipitated out as the insoluble salt copper(II) arsenate.
Given what you know about the melting point of a mixture, why do you think salt is sprinkled on icy sidewalks in the winter?
Salt will decrease the freezing point of water causing the ice to melt.
How could you use the liquid remaining in the flask to help you balance the equation?
The water could be boiled off to isolate the amount of NaCl formed in the reaction.
Suppose that the test tube you used for the experiment was not fully dry and there were some water droplets in the test tube. What effect would this have on the calculated molar mass of the unknown?
The calculated molar mass would be larger than the true molar mass.
The temperature at the boiling point remained constant despite the continued addition of heat by the Bunsen burner. What was the energy used for?
The energy was used to overcome the attractions between the water molecules.
What does Hess's Law state?
The enthalpy change of the overall process is the sum of the enthalpy changes of its individual steps and does not depend on the route taken.
Suppose you added 4.000 g of FP sample 1 instead of 2.000 g, what would happen to the freezing point temperature of the water?
The freezing point would be depressed twice as much.
Suppose that the NaOH sitting on the shelf had absorbed 1 g of water for every 1 g of NaOH. How would this have affected your results?
The molarity of the NaOH solution would have been half what you expected.
Suppose that the NaOH sitting on the shelf had absorbed 2 g of water for every 1 g of NaOH. How would this have affected your results?
The molarity of the NaOH solution would have been one third what you expected.
The mean velocity of molecules in a gas is equal to a constant times the square root of the temperature. What happens to the velocity of the molecules at absolute zero?
The molecules stop
In a real gas, the molecules will interact with each other. Supposing that the interactions between the molecules are attractive, why would this introduce errors?
The molecules would tend to be closer together at lower temperatures, leading to a lower-than-expected volume.
What change to the voltage is seen when the clips of the voltmeter are switched to the opposite electrodes?
The number is the same, but the sign (+ or -) is switched.
What will happen to the pH of the solution if you keep adding NaOH after the end point?
The pH will increase gradually.
What is a limiting reactant?
The substance that is fully consumed when a chemical reaction is complete and the reaction cannot proceed further without it.
What happened to the temperature of the solution in the calorimeter after the addition of NH4Cl?
The temperature decreased
In a real gas, as the temperature decreases, it is possible to cause a liquid to form. How would the formation of a liquid phase affect the measurement of absolute zero using the methodology employed in this experiment?
The volume of the liquid does not change much as the temperature is reduced, leading to errors in the measurement of the volume-temperature relationship.
What does the freezing point measured for water tell you about the water's purity?
The water is pure because the freezing point is exactly as expected.
Carbon dioxide is slightly soluble in water and its solubility increases with increasing pressure. How would the fact that some of the carbon dioxide produced by the reaction is dissolved in the aqueous solution affect your calculations?
This would cause the final pressure to be lower than theoretically expected.
What is the purpose of the salt bridge in an electrochemical cell?
What is the purpose of the salt bridge in an electrochemical cell?
What is meant by "freezing point depression"?
When a solute is added to a solvent, the freezing point of the solvent is lowered.
Based on the number of grams of CO2 and H2O produced during the reaction, does this account for the observed loss of mass?
Yes, this accounts for the mass lost in the reaction.
Suppose a student used one of the indicators you used to test the pH of an ammonia solution. Given the figure below, what indicator do you think he used? (11.64)
alazrin yellow
What color was the malachite after heating?
black
In Experiment 1, what color was the copper(II) sulfate solution?
blue
Suppose you wanted to monitor a pH change between 5.3 and 6.3. Which indicator would be most appropriate?
bromothymol blue
What kind of reaction took place upon heating?
decomposition
What happens to the volume of a gas as the temperature is reduced?
decreases
Which of the following conditions is not assumed from the variable Eo? a. gas pressure of 1 atm b. solution concentration of 1 M c. temperature of 25 oC d. electrode width of 1 cm
electrode width of 1 cm
What color was the malachite before heating?
green
What color did the solution become at the end point?
pale pink
Suppose you wanted to monitor a pH change between 8.7 and 7.7. Which indicator would be most appropriate?
phenolphthalein
What indicator was used to monitor the pH change?
phenolphthalein
What color was the cobalt(II) chloride solution?
pink
The following reaction is second order with respect to A and zero order with respect to B. Identify the correct rate law. 2A+B⟶C+2D
rate=k[A]2
Notice the wavelength that the copper(II) sulfate solution absorbed most strongly. What color light did the copper sulfate solution absorb most strongly?
red
For a zero order reaction, if the concentration of reactant is increased 4-fold, what happens to the reaction rate?
remains the same
What is the molality, m, of a solution?
the number of moles of solute in a kilogram of solvent