Introduction to Chemistry

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Questions and Answers

Consider a scenario where a chemist is attempting to synthesize a new compound by reacting two known substances. The reaction vessel is placed in an ice bath to control the reaction rate. During the reaction, it is observed that the vessel becomes colder. Which of the following conclusions can be definitively drawn?

The reaction is exothermic and thermodynamically favorable at all temperatures.
The reaction is endothermic and spontaneous only at sufficiently high temperatures.
The reaction is exothermic, and the change in temperature implies that Gibbs free energy is positive.
The reaction is endothermic, and the decrease in temperature indicates Le Chatelier's principle is shifting the equilibrium towards the reactants. (correct)

A researcher measures the pH of a solution after adding a strong acid to a buffer solution and observes a slight decrease in pH. Which of the following best explains the buffering action in terms of chemical equilibria?

The buffer system shifts to favor the formation of the strong acid's conjugate base, which neutralizes the excess hydronium ions.
The buffer system shifts to favor the formation of the acid component, thereby neutralizing the effect of the added acid. (correct)
The buffer system shifts to increase the concentration of the conjugate base, consuming hydroxide ions.
The buffer system maintains a constant concentration of both acid and base, preventing significant pH changes.

In a complex chemical reaction, the rate-determining step involves the formation of an intermediate with a relatively high activation energy. Which of the following strategies would be most effective in accelerating the overall reaction rate without altering the reaction mechanism?

Raise the temperature of the reaction, which equally affects all steps in the reaction mechanism.
Add an inert gas to increase the total pressure, thereby favoring the forward reaction.
Increase the concentration of the reactants that participate in the final step of the reaction.
Introduce a catalyst that lowers the activation energy of the rate-determining step. (correct)

Consider a scenario where a radioactive isotope undergoes a series of decay processes, including both alpha and beta decay, to eventually form a stable isotope. How would you determine the number of alpha and beta particles emitted during the entire decay series if you know the initial and final isotopes?

By calculating the total change in mass number and atomic number, where the number of alpha particles is half the change in mass number, and the number of beta particles equals the change in atomic number minus twice the number of alpha particles. (C) Signup and view all the answers

A chemist analyzes a gaseous sample containing nitrogen and oxygen, finding that it deviates significantly from ideal gas behavior at high pressures. Which of the following factors contributes most to this deviation?

Significant intermolecular attractive forces between gas molecules reduce the effective volume. (A) Signup and view all the answers

In a chromatographic separation of several organic compounds with similar structures, a chemist observes that one compound elutes much later than expected. Which of the following is the most probable cause for this behavior?

The compound is irreversibly adsorbed onto the stationary phase. (B) Signup and view all the answers

A scientist is studying a reaction in a closed system that has reached equilibrium. According to Le Chatelier's Principle, which of the following changes would NOT shift the equilibrium position?

Adding an inert gas to the system while maintaining constant volume. (B) Signup and view all the answers

A chemist is attempting to identify an unknown organic compound using mass spectrometry. The mass spectrum shows a molecular ion peak at `m/z = 128` and a prominent fragment ion peak at `m/z = 113`. What is the most likely neutral fragment lost during the fragmentation?

CH₃ (B) Signup and view all the answers

An analytical chemist is tasked with determining the concentration of a metal ion in a complex aqueous sample. The ion forms a colored complex with a specific ligand, but the complex's absorbance spectrum overlaps significantly with other components in the sample. Which method would best address the spectral interference and accurately quantify the metal ion?

Derivative spectrophotometry to resolve overlapping peaks. (B) Signup and view all the answers

A laboratory technician prepares a solution by dissolving 10.0 grams of NaCl in enough water to make 1.00 liter of solution. Given that the density of the solution is 1.07 g/mL, what is the molality of the solution?

0.171 m (A) Signup and view all the answers

A researcher is studying the kinetics of a reaction $A + B ightarrow C$ and finds that the reaction is first order with respect to A and second order with respect to B. If the initial concentrations of both A and B are doubled, by what factor will the initial reaction rate increase?

8 (B) Signup and view all the answers

Consider two voltaic cells. Cell I consists of $Zn(s) | Zn^{2+}(1M) || Cu^{2+}(1M) | Cu(s)$. Cell II consists of $Zn(s) | Zn^{2+}(0.1M) || Cu^{2+}(0.1M) | Cu(s)$. Which of the following is true about the cell potentials?

Both cells have the same cell potential. (A) Signup and view all the answers

A researcher performs a gas chromatography-mass spectrometry (GC-MS) analysis on an unknown sample, obtaining a complex chromatogram with several peaks. To identify a specific compound eluting at a particular retention time, which aspect of the MS data provides the most definitive information?

The fragmentation pattern and mass-to-charge ratios of the fragment ions. (B) Signup and view all the answers

In the context of thermodynamics, under what conditions will a reaction be spontaneous at all temperatures?

When enthalpy (H) is negative and entropy (S) is positive. (A) Signup and view all the answers

A chemist is designing a buffer solution with a target pH of 4.75. Which of the following acid-base pairs would be most suitable for preparing this buffer?

Acetic acid (pKa = 4.75) (D) Signup and view all the answers

A sample of an ideal gas is placed in a closed container at a constant temperature. If the volume of the container is halved, what happens to the average kinetic energy of the gas molecules?

It remains the same. (C) Signup and view all the answers

Which of the following is the most accurate description of metallic bonding?

Delocalized electrons moving freely throughout a lattice of metal cations. (A) Signup and view all the answers

In a voltaic cell, zinc is oxidized and copper is reduced. Which of the following statements is correct regarding the flow of electrons and ions?

Electrons flow from the zinc electrode to the copper electrode, and anions move towards the zinc half-cell. (A) Signup and view all the answers

You have a mixture of three organic compounds: benzoic acid, phenol, and naphthalene. Design a separation scheme using liquid-liquid extraction to isolate each compound. Which order of steps and solvents would achieve the most effective separation?

<ol> <li>Extract with aqueous NaHCO₃, 2) Extract remaining organic layer with aqueous NaOH, 3) Evaporate remaining solvent to obtain naphthalene. (B)</li> </ol> Signup and view all the answers

Flashcards

What is Chemistry?

The study of matter, its properties, and how it changes.

What is Matter?

Anything that has mass and occupies space; composed of atoms and molecules.