CHM II Lab Final
Suppose that the absorbance of an aspirin tablet solution is 0.427. Also, the molar absorptivity of acetylsalicylic is 120. M-1 cm-1, and the path length of the light through the cuvette is 1.00 cm. Calculate the concentration of acetylsalicylic acid in the aspirin tablet solution using Beer's law: A = εbc.
0.0036
A buret was used to add 1.020 M HAn into a volumetric flask. The initial reading of the buret was 0.3 mL, and the final reading was 40.55 mL. How many moles of HAn were added to the flask?
0.0411
Initially, a beaker contains 50.0 mL of a buffer. Then, 5.0 mL of 0.10 M HCl solution was added to the buffer, and the pH of the solution was measured. Then, 10.0 mL more of the HCl solution was added. The total volume of HCl solution added was The final volume of solution in the beaker was
15.0 mL 50 mL
Enter the number of valence electrons in KrF2.
22.00
A buffer contains 0.500 M of formic acid (HCHO2) and 0.500 M of sodium formate (NaCHO2). Formic acid is a weak acid that dissociates in water as following: HCHO2(aq) + H2O(l) ⇌ H3O+(aq) + CHO2-(aq) The equilibrium constant expression for this equilibrium is K subscript straight a equals fraction numerator open square brackets straight H subscript 3 straight O to the power of plus close square brackets open square brackets CHO subscript 2 to the power of minus close square brackets over denominator open square brackets HCHO subscript 2 close square brackets end fraction equals 1.8 cross times 10 to the power of negative 4 end exponent Calculate the pH of the buffer solution. Recall that pH = -log[H3O+].
3.74
The gases NO2 and N2O4 are in equilibrium according to this equation: 2NO2(g) rightwards harpoon over leftwards harpoon N2O4(g) First, write down the equilibrium constant expression, Kc, for this reaction. Then, calculate the value of Kc if experiment shows the equilibrium concentrations to be 0.014 for NO2 and 0.017 for N2O4.
86.7
Know how to determine polarity:
A molecule can be polar when the four groups on the central atom aren't identical.
Which of the following are true? Select all that apply.
A volumetric flask without a stopper is useless. A volumetric flask should be inverted and swirled before use.
The inside of the flask must be absolutely dry before it is fitted with the stopper assembly and weighed. The main reason is that
Any remaining water inside the flask would be hard to get to evaporate.
In this experiment, the hand-held device used to produce electricity is called a/an
DC generator
The electronic geometry gives the "actual" shape of a molecule.
False
The volume occupied by air inside the Erlenmeyer flask is equal to the volume engraved on the flask.
False
Know how to calculate formal charges:
Formal charge is the difference between the valence electrons and the actual amount of electrons the element has.
Know how to determine viable resonance structures:
Just look for certain things that need to stay the same.
The reaction, 2H2(g) + O2(g) rightwards harpoon over leftwards harpoon 2H2O(g), actually goes to completion, forming water, but if this is treated as an equilibrium, the equilibrium constant expression, Kc, is
Kc=[H2O]2/[H2]2[O2]
The pinch clamp on the flask assembly should be opened before heating the flask assembly in boiling water. If the clamp was left closed during heating, which of the following is the most likely problem that might result?
Pressure would buid-up in the flask, possibly blowing the stopper assembly into the ceiling.
Electrical work is produced when the crank of the hand-held device is turned.
Sometimes
When the dissociation constant of a weak acid, Ka, is calculates for this lab, which one of the following is used in the final step of the calculation?
The concentration of the weak acid at equilibrium.
Which of the following count as one electron domain? (Select all that apply.)
The four electrons in a double bond. The pair of electrons in a single bond. Lone pairs of electrons
How can you tell when vaporization of the unknown liquid is complete?
The ring of liquid around the boiling stone is nearly gone.
Be able to read a cooling curve:
The substance will go below its freezing point while being supercooled before actually freezing. You need to extrapolate the cooling curve to reach the point at which the substance will have actually frozen.
Which of the following is the least accurate method of determining the volume of liquid in a completely full Erlenmeyer flask?
Use the volume etched into the surface of the flask (e.g., 125 mL).
A cuvette is
a sample holer for measuring absorbance.
A buffer solution resists changes in pH when
a strong acid is added. a solution is diluted. a weak acid is added. a strong base is added. a weak base is added.
In today's lab bumping is prevented by
adding boiling stones to the flask.
A beaker contains the following equilibrium system: 2CrO42-(aq, yellow) + 2H+(aq) ⇌ Cr2O72-(aq, orange) + H2O(l) The H+ concentration is increased by adding concentrated HCl(aq) to the equilibrium mixture. The color of the mixture will
become more orange.
Suppose a chemical reaction is initially at equilibrium, but then a change is made in the equilibrium system. To return to equilibrium, the equilibrium position will shift so as to
counteract the change.
A blank is a solution that contains
everything that the sample contains except for the species to be determined.
As the "load" connected to the hand-held device increases, the effort required to operate the device increases. The effort needed to operate the device is best assessed by
how hard it is to turn the crank
According to Beer's law, a plot of absorbance vs. concentration is
linear
Suppose 1 mole of acetic acid (a weak acid) is placed in 1 L of water. In this solution dissociation of the acetic acid
occurs to only a small extent.
According to Le Chatelier's principle, adding heat to a system is equivalent to
raising the temperature.
A beaker contains the following equilibrium system (as before): 2CrO42-(aq, yellow) + 2H+(aq) ⇌ Cr2O72-(aq, orange) + H2O(l) If solid Na2CrO4 is added to the solution, the equilibrium will
shift to the right
The instrument used to measure the amount of voltage from the reaction between a metal and an ionic compound is a/an
voltmeter