Problem 1
A compound is made up of entirely silicon and oxygen atoms. If there are 14.0 g of silicon and 32.0 g of oxygen present, what is the empirical formula of the compound? (A) \(\mathrm{SiO}_{2}\) (B) \(\mathrm{SiO}_{4}\) (C) \(\mathrm{Si}_{2} \mathrm{O}\) (D) \(\mathrm{Si}_{2} \mathrm{O}_{3}\)
Problem 1
A stock solution of 0.100 \(\mathrm{M}\) cobalt (II) chloride is used to create several solutions, indicated in the data table below: \(\begin{array}{|c|c|c|}\hline \text { Sample } & {\text { Volume } \mathrm{CoCl}_{2}} & {\text { Volume }} \\ \hline & {(\mathrm{mL})} & {\mathrm{H}_{2} \mathrm{O}(\mathrm{mL})} \\ \hline 1 & {20.00} & {0} \\\ \hline 2 & {15.00} & {5.00} \\ \hline 3 & {10.00} & {10.00} \\ \hline 4 & {5.00} & {15.00} \\ \hline\end{array}\) (a) In order to achieve the degree of accuracy shown in the table above, select which of the following pieces of laboratory equipment could be used when measuring out the CoCl_{2} : \(150-\mathrm{mL}\) beaker \(\quad 400-\mathrm{mL}\) beaker \(\quad 250-\mathrm{mL}\) Erlenmeyer flask \(\begin{array}{ll}{\text { 50-mL buret }} & {\text { 50-mL graduated }} \\ {} & {\text { cylinder }}\end{array} \quad 100\) -mL graduated cylinder (b) Calculate the concentration of the CoCl, in each sample. The solutions are then placed in cuvettes before being inserted into a spectrophotometer calibrated to 560 \(\mathrm{nm}\) and their values are measured, yielding the data below: \(\begin{array}{|c|c|}\hline \text { Sample } & {\text { Absorbance }} \\\ \hline 1 & {0.485} \\ \hline 2 & {0.364} \\ \hline 3 & {0.243} \\ \hline 4 & {0.121} \\ \hline\end{array}\) (c) If gloves are not worn when handling the cuvettes, how might this affect the absorbance values gathered? (d) If the path length of the cuvette is \(1.00 \mathrm{cm},\) what is the molar absorptivity value for \(\mathrm{CoCl}_{2}\) at 560 \(\mathrm{nm}\) ? (e) On the axes on the next page, plot a graph of absorbance vs. concentrrion. The \(y\) -axes scale is set, and be sure to scale the \(x\) -axes appropriately (f) What would the absorbance values be for \(\mathrm{CoCl}_{2}\) , solutions at the following concentrations? (i) 0.067 (ii) 0.180 \(\mathrm{M}\)
Problem 2
A sample of liquid butane \(\left(\mathrm{C}_{\mathrm{L}} \mathrm{H}_{10}\right)\) in a pressurized lighter is set up directly beneath an aluminum can, as show in the diagram above. The can contains 100.0 \(\mathrm{mL}\) of water, and when the butane is ignited the temperature of the water inside the can increases from \(25.0^{\circ} \mathrm{C}\) to \(82.3^{\circ} \mathrm{C}\) . The total mass of butane ignited is found to be 0.51 \(\mathrm{g}\) , the specific heat of water is \(4.18 \mathrm{J} / \mathrm{g} \cdot^{\circ} \mathrm{C},\) and the density of water is \(1.00 \mathrm{g} / \mathrm{mL} .\) (a) Write the balanced chemical equation for the combustion of one mole of butane in air. (i) How much heat did the water gain? (ii) What is the experimentally determined heat of combustion for (ii) Whane based on this experiment? Your answer should be in \(\mathrm{kJ} / \mathrm{mol}\) . (c) Given butane's density of 0.573 \(\mathrm{g} / \mathrm{mL}\) at \(25^{\circ} \mathrm{C},\) calculate how much heat would be emitted if 5.00 \(\mathrm{mL}\) of it were combusted at that temperature. (d) The overall combustion of butane is an exothermic reaction. Explain why this is, in terms of bond energies. (e) One of the major sources of error in this experiment comes from the heat that is aboorbed by the air. Why, then, might it not be a good ide to perform this experiment inside a sealed container to prevent the heat from leaving the system?
Problem 3
\(2 \mathrm{N}_{2} \mathrm{O}_{5}(g) \rightarrow 4 \mathrm{NO}_{2}(g)+\mathrm{O}_{2}(g)\) The data below was gathered for the decomposition of \(\mathrm{N}_{2} \mathrm{O}_{5}\) at 310 \(\mathrm{K}\) via the equation above. \(\begin{array}{|c|c|}\hline \text { Time(s) } & {\left[\mathrm{N}_{2} \mathbf{O}_{5}\right](M)} \\ \hline 0 & {0.250} \\ \hline 500 . & {0.190} \\\ \hline 1000 . & {0.145} \\ \hline 2000 . & {0.085} \\ \hline\end{array}\) (a) How does the rate of appearance of NO_{2} \text { compare to the rate of } disappearance of \(\mathrm{N}_{2} \mathrm{O}_{5}\) ? Justify your answer. (b) The reaction is determined to be first order overall. On the axes below, create a graph of some function of concentration vs. time that will produce a straight line. Label and scale your axes appropriately. (c) (i) What is the rate constant for this reaction? Include units. (ii) What would the concentration of \(\mathrm{N}_{2} \mathrm{O}_{5}\) be at \(t=1500 \mathrm{s} ?\) (iii) What is the half-life of \(\mathrm{N}_{2} \mathrm{O}_{5}\) ? (d) Would the addition of a catalyst increase, decrease, or have no effect on the following variables? Justify your answers. (i) Rate of disappearance of \(\mathrm{N}_{2} \mathrm{O}_{5}\) (ii) Magnitude of the rate constant (iii) Half-life of \(\mathrm{N}_{2} \mathrm{O}_{5}\)
Problem 3
A solution of sulfurous acid, \(\mathrm{H}_{2} \mathrm{SO}_{3}\) , is present in an aqueous solution. Which of the following represents the concentrations of three different ions in solution? (A) \(\left[\mathrm{SO}_{3}^{2-}\right]>\left[\mathrm{HSO}_{3}^{-}\right]>\left[\mathrm{H}_{2} \mathrm{SO}_{3}\right]\) (B) \(\left[\mathrm{H}_{2} \mathrm{SO}_{3}\right]>\left[\mathrm{HSO}_{3}^{-}\right]>\left[\mathrm{SO}_{3}^{2-}\right]\) (C) \(\left[\mathrm{H}_{2} \mathrm{SO}_{3}\right]>\left[\mathrm{HSO}_{3}^{-}\right]=\left[\mathrm{SO}_{3}^{2-}\right]\) (D) \(\left[\mathrm{SO}_{3}^{2-}\right]=\left[\mathrm{HSO}_{3}^{-}\right]>\left[\mathrm{H}_{2} \mathrm{SO}_{3}\right]\)
Problem 5
\(\mathrm{SF}_{4}(g)+\mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{SO}_{2}(g)+4 \mathrm{HF}(g) \Delta H=-828 \mathrm{kJ} / \mathrm{mol}\) Which of the following statements accurately describes the above reaction? (A) The entropy of the reactants exceeds that of the products. (B) \(\mathrm{H}_{2} \mathrm{O}(l)\) will always be the limiting reagent. (C) This reaction is never thermodynamically favored. (D) The temperature of the surroundings will increase as this reaction Progresses.
Problem 6
20.0 \(\mathrm{mL}\) of 1.0 \(\mathrm{M} \mathrm{Na}_{2} \mathrm{CO}_{3}\) is placed in a beaker and titrated with a solution of \(1.0 \mathrm{M} \mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2},\) resulting in the creation of a precipitate. How much \(\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}\) must be added to reach the equivalence point? (A) 10.0 mL (B) 20.0 mL (C) 30.0 mL (D) 40.0 mL
Problem 6
Aniline, \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2},\) is a weak base with \(K_{\mathrm{b}}=3.8 \times 10^{-10}\) (a) Write out the reaction that occurs when aniline reacts with water. (b) (i) What is the concentration of each species at equilibrium in a solution of 0.25\(M \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2} ?\) (ii) What is the pH value for the solution in (i)?
Problem 7
A rigid, sealed 12.00 \(\mathrm{L}\) container is filled with 10.00 \(\mathrm{g}\) each of three different gases: \(\mathrm{CO}_{2}, \mathrm{NO},\) and \(\mathrm{NH}_{3}\) . The temperature of the gases is held constant \(35.0^{\circ} \mathrm{C} .\) Assume ideal behavior for all gases. (a) (i) What is the mole fraction of each gas? (ii) What is the partial pressure of each gas? (b) Out of the three gases, molecules of which gas will have the highest velocity? Why? (c) Name one circumstance in which the gases might deviate from ideal behavior, and clearly explain the reason for the deviation.
Problem 8
20.0 \(\mathrm{mL}\) of 1.0 \(\mathrm{M} \mathrm{Na}_{2} \mathrm{CO}_{3}\) is placed in a beaker and titrated with a solution of \(1.0 \mathrm{M} \mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2},\) resulting in the creation of a precipitate. What will happen to the conductivity of the solution after additional \(\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}\) is added past the equivalence point? (A) The conductivity will increase as additional ions are being added to the solution. (B) The conductivity will stay constant as the precipitation reaction has gone to completion. (C) The conductivity will decrease as the solution will be diluted with the addition of additional \(\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}\). (D) The conductivity will stay constant as equilibrium has been established.