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When does a gas behave most like an ideal gas?
At low temperatures, low volume, low intermolecular interactions
At high temperatures, high volume, low intermolecular interactions
At low volumes, high temperatures, and high intermolecular interactions
At high temperature, high volumes, and high intermolecular interactions
At low temperatures, high volume, and low intermolecular interactions
Explanation
The ideal gas law assumes the gas particles are non-interacting and small relative to the size of their container. At high temperatures the gas molecules are moving fast enough to shorten the time scale for any interactions. At high volumes, the molecular size becomes small relative to the size of the container, and the low interactions mean the molecules act more independently.
Which of the following will increase the pH of an buffer solution?
I. Removing carbonic acid
II. Adding sodium bicarbonate
Both I and II
I only
II only
Neither of these options
Explanation
To answer this question we need to look at the reaction below:
An increase in the pH will result in a decrease in the concentration of hydrogen ions (). Using Le Chatelier’s principle we can find out which answer choices will decrease
.
Removing carbonic acid will decrease the concentration of . To maintain equilibrium, the reaction will shift to the left and make more reactants from products; therefore, there will be a decrease in the
and an increase in pH.
Recall that salts like sodium bicarbonate, or , will dissociate in water and form ions. Sodium bicarbonate will form sodium (
) and bicarbonate (
) ions. This side reaction will result in an increase in the bicarbonate ion concentration. Le Chatelier’s principle will shift the equilibrium of the given reaction to the left and, therefore, decrease the
. Adding sodium bicarbonate will increase the pH.
Calculate the standard cell potential of the following reaction:
Cd(s) + MnO2 (s) + 4 H+ (aq) + -> Cd2+ (aq) + Mn2+ (aq) + 2 H2O (l)
Given:
MnO2 (s) + 4 H+ (aq) + 2e- -> Mn2+ (aq) + 2 H2O (l) Eo = 1.23 V
Cd2+ (aq) + 2 e- -> Cd (s) Eo = -0.40 V
1.63 V
0.83 V
-1.63 V
-0.83 V
0.0 V
Explanation
Eocell = Eo cathode - Eoanode
Eocell = 1.23 – (-0.40) = 1.63 V
When does a gas behave most like an ideal gas?
At low temperatures, low volume, low intermolecular interactions
At high temperatures, high volume, low intermolecular interactions
At low volumes, high temperatures, and high intermolecular interactions
At high temperature, high volumes, and high intermolecular interactions
At low temperatures, high volume, and low intermolecular interactions
Explanation
The ideal gas law assumes the gas particles are non-interacting and small relative to the size of their container. At high temperatures the gas molecules are moving fast enough to shorten the time scale for any interactions. At high volumes, the molecular size becomes small relative to the size of the container, and the low interactions mean the molecules act more independently.
What is the percent of carbon by mass in acetone CH3C(O)CH3?
62%
50%
75%
10%
25%
Explanation
To calculate the percent mass of a particular element within a substance I like to use a formulaic approach.
First multiply the number of moles of the atom of interest (C) by its molar mass.
3moles* 12 g/mol= 36g
Then divide by the overall molar mass of the molecule, obtain this by adding the atomic weights of each atom present in the molecule:
36g/58g= 62%
The following ReDox reaction takes place in acidic solution:
Fe2+ + Cr2O72– → Fe3+ + Cr3+
What is the sum of coefficients in this redox reaction?
36
35
34
33
37
Explanation
When you balance the redox reaction in acidic conditons, there are 6Fe2+, 1 Cr2O72–, 14 H+, 6 Fe3+, 2 Cr3+, and 7 H2O. Don't forget to add the 1 in front of the Cr2O72–
Which of the following factors will increase the reaction rate of the following reaction, if it is an endothermic, zero order reaction?
An increase in the temperature at which the reaction occurs
An increase in \[A\]
An increase in \[B\]
A decrease in the temperature at which the reaction occurs
Explanation
An increase in temperature leads to an increase in reaction rate for endothermic reactions, while a decrease in temperature will slow down their rate.
For zero order reactions, reaction rate is independent of reactant concentrations; therefore, changing \[A\] and \[B\] will have no effect on reaction rate.
The rate law for this reaction would simply be , where k is the rate constant at a given temperature.
How many grams of Cr can be obtained by the electrolysis of a Cr(NO3)3 if 10 amps are passed through the cell for 6 hours?
38.8 g
19.4 g
103 g
12.5 g
56.3 g
Explanation
(slow)
(fast)
The mechanism for decomposition of ozone is shown. What is the intermediate of the process?
Explanation
Intermediate is created and destroyed, and therefore does not appear on the net equation, which is . Thus, the intermediate is
. Note that when asked for an intermediate, the coefficient in front of it is not used, rather we are looking for the species that is a product of one reaction and a reactant in a subsequent step.
The rate law of the reaction, , is
. Which of the following does not increase the rate of the reaction?
Increasing the concentration of
Adding the catalyst to the reaction
Increasing the temperature of the reaction
Increasing the concentration of
Explanation
The reactant is not included in the rate law expression, and therefore altering its concentration does not affect the rate of the reaction. Catalysts always increase the rate of reactions by lowering its activation energy. Increasing temperature (average kinetic energy of the molecules) increases the frequency of collisions, and increases the proportion of collisions that have enough energy to overcome the activation energy and undergo a chemical reaction. Increasing the concentration of
will increase the rate of the reaction as indicated by the rate law.