UWORLD (gen/ochem)

How is the boiling point of the protein solutions affected by the purification described in the passage? A. Increased, because the solution exhibits a lower vapor pressure after the removal of the solutes. B. Increased, because the solution exhibits a higher vapor pressure after the removal of the solutes. C. Decreased, because the solution exhibits a lower vapor pressure after the removal of the solutes. D. Decreased, because the solution exhibits a higher vapor pressure after the removal of the solutes.

D. Decreased, because the solution exhibits a higher vapor pressure after the removal of the solutes. According to the passage, purifying the protein solution removes unwanted nonvolatile solutes. Therefore, purifying the solution results in a decreased boiling point due to the purified sample exhibiting a higher vapor pressure.

What is the product formed by the reaction of hexanoic acid and ethanol described in the passage? A. Acetic hexanoic anhydride B. Hexanoic ethanoic anhydride C. Hexyl ethanoate D. Ethyl hexanoate

D. Ethyl hexanoate

A particular igneous rock sample is dated to an age of 2.5 billion years. A researcher claims that this particular rock contained 40K but no 40Ca when it originally formed. What is the most likely 40K : 40Ca : 40Ar ratio observed by the researcher? A. 25 : 67.5 : 7.5 B. 50 : 45 : 5 C. 75 : 22.5 : 2.5 D. 92.5 : 0 : 7.5

A. 25 : 67.5 : 7.5 The passage states that the half-life of 40K is 1.25 billion years. Accordingly, a rock that is dated at 2.5 billion years old has undergone two half-lives, and 25% of the original amount of 40K remains (ie, 75% has decayed). The passage further states that of the daughter nuclides formed, 90% are 40Ca and 10% are 40Ar. Consequently, of the 75% of 40K nuclides that have decayed, 10% have become 40Ar for a total of 7.5% of the nuclides (10% × 75% = 7.5%). The remaining 67.5% have been converted to 40Ca.

If a channel of a particular cell preferentially transmits smaller ionic species across the membrane, given the following biologically relevant, isoelectronic ions, the channel is LEAST likely to transmit: A. S2−. B. Cl−. C. K+. D. Ca2+.

A. S2−. Sulfur has the lowest atomic number (fewest number of protons) in this isoelectronic series, Zeff is smallest in S2−, making it the largest ion. Given that the cell channel preferentially transmits smaller ions, S2− is least likely to be transmitted.

In Reaction 1, what hybridization state changes do the methylated carbon atom in the ringed structure of vitamin K hydroquinone and the oxygen atom involved in epoxide formation undergo? A. sp2 to sp3 for the methylated carbon and sp2 to sp3 for the oxygen atom B. sp2 to sp3 for the methylated carbon and sp to sp2 for the oxygen atom C. sp2 to sp3 for the methylated carbon and sp2 to sp2 for the oxygen atom D. sp to sp2 for the methylated carbon and sp2 to sp3 for the oxygen atom

A. sp2 to sp3 for the methylated carbon and sp2 to sp3 for the oxygen atom (60%) The methylated carbon atom on vitamin K hydroquinone has three sigma bonds (sp2) and becomes sp3 with four sigma bonds when the epoxide is formed. The oxygen atom (from O2) has one sigma bond and two lone pairs of electrons (sp2). The epoxide oxygen atom on vitamin K 2,3-epoxide has two sigma bonds and two lone pairs of electrons (sp3).

Which of the following characterize or are included in gas-liquid chromatography? I Gas mobile phase II Liquid stationary phase III Separation based only on polarity IV Room-temperature column conditions A. I only B. I and II only C. I and III only D. I, II, and IV only

B. I and II only (53%) Gas-liquid chromatography is used to seperate molecules based on their boiling points! The mobile phase is an inert gas (helium or nitrogen) while the stationary phase is a liquid. The column must be placed in a heated environment to allow volatile molecules to remain in the gas phase, columns kept at room temperature would not separate the molecules

Electrolytes are solutes that enable the conduction of electricity within a solvent. Based on its composition, the dextrose saline solution from Table 1 is: A. conductive, because dextrose is an electrolyte. B. conductive, because sodium chloride is an electrolyte. C. conductive, because both dextrose and sodium chloride are electrolytes. D. nonconductive, because neither dextrose nor sodium chloride are electrolytes.

B. conductive, because sodium chloride is an electrolyte. Dextrose is NOT an electrolyte and does not conduct electricity in solution because it is a molecular compound made of covalently bonded non metal atoms. NaCl is an electrolyte bc it is an ionic compound

Carboxylic acids BP

Carboxylic acids have higher boiling points than molecules of a similar molecular weight that cannot hydrogen bond to themselves and have weaker intermolecular forces. Thus, in a distillation, a carboxylic acid would distill last due to the higher boiling point

Solving for atomic weight of an element

multiply the mass of each isotope by its natural abundance (as a decimal) then add up the results for all isotopes.

bond dissociation energy

the more bonds (triple) the higher the bond dissociation energy

If a compound has longer retention time then:

theres a greater affinity for the stationary period and a lower affinity for the mobile phase compared to compounds with shorter retention times

Which carboxylic acid would be needed to form Compound A (shown below) based on the reaction described in the passage? A. 2-sec-butylbutanoic acid B. 2-ethyl-3-methylpentanoic acid C. 2,3-diethylbutanoic acid D. 4-ethyl-3-methylpentanoic acid

B. 2-ethyl-3-methylpentanoic acid (start numbering at the carbonyl carbon to give it the lowest number)

An ionic hydroxide compound formed from an unknown metal M exhibits the equilibrium M(OH)2(s) ⇄ M2+(aq) + 2 OH−(aq) which results in a saturated aqueous solution wherein the molar concentration of M2+(aq) is half the molar concentration of OH−(aq). If the solution pH is 10, the solubility product constant Ksp of the compound is: A. 5.0 × 10−31. B. 5.0 × 10−13. C. 1.0 × 10−12. D. 1.0 × 10−8.

B. 5.0 × 10−13. Ksp = [M2+][OH-]2 pH + pOH = 14, so pOH = 14-10 = 4 (pH=10) (see continued on image)

Assuming all atoms return to the ground state immediately after nuclear decay, which of the following best describes the change in effective nuclear charge when a 40K+ ion undergoes nuclear decay? The effective nuclear charge: A. decreases in 90% of cases and increases in 10% of cases. B. increases in 90% of cases and decreases in 10% of cases. C. increases regardless of the mode of decay. D. decreases regardless of the mode of decay.

B. increases in 90% of cases and decreases in 10% of cases. Zeff for a specific atom or ion is calculated as: Zeff=Z-S where Z is the total charge of the nucleus (ie, the total number of protons) and S is the shielding constant. S can be approximated as the number of core electrons in the atom or ion. Potassium contains 19 protons and K+ contains 18 electrons. Because K+ has an empty 4th shell, its 3rd shell is its valence shell, which means K+ has 8 valence electrons and 10 core electrons. Based on this count, the effective nuclear charge of any isotope of K+ is approximately: Zeff≈19-10=+9 According to the passage, 90% of decay events are β− decay, and Figure 1 shows that this results in a Ca2+ ion. Ca2+ has 20 protons and 18 electrons, 10 of which are core electrons. Consequently, for Ca2+, Zeff is approximately: Zeff≈20-10=+10 Therefore, in the 90% of decay events that produce Ca2+, Zeff increases from +9 to +10. The remaining 10% of decay events occur through electron capture, which produces neutral argon (Ar) according to Figure 1. Ar contains 18 protons and 18 electrons, 10 of which are core electrons. Consequently, for Ar, Zeff is approximately: Zeff≈18-10=+8 Therefore, in 10% of decay events, Zeff decreases from +9 to +8.

What is the maximum Cp,ex of sample 1? A. 0.018 J/(g∙°C) B. 0.040 J/(g∙°C) C. 2.4 J/(g∙°C) D. 40 J/(g∙°C)

C. 2.4 J/(g∙°C)

If 90.5 g of isotopically labeled dextrose is fully metabolized into carbon dioxide and water, how many moles of unlabeled carbon dioxide are produced? (Note: The molar mass of the 13C-labeled dextrose is 181 g/mol.) A. 0.42 mol B. 0.50 mol C. 2.50 mol D. 3.00 mol

C. 2.50 mol 90.5 g/181 g = 0.500 mol CC5H12O6 0.500 mol * 5/1 - 2.50 mol CO2

A reaction between chloride and permanganate ions occurs in an acidic solution, as shown below: 5 Cl−(aq) + 2 MnO4−(aq) + 11 H+(aq) → 2 Mn2+(aq) + 5 HClO(aq) + 3 H2O(l) Which element undergoes a change in oxidation state corresponding to a loss of two electrons? A. Mn B. O C. Cl D. H

C. Cl For the reaction equation given in this question, the assessed oxidation numbers show that the oxidation state of chlorine increases from −1 to +1, demonstrating that chlorine loses two negatively charged electrons and is oxidized.

In the second step, Glu35 creates a good nucleophile that breaks the glycosidic bond formed by Asp52 in the first step. Given that the local environment of the enzyme significantly increases the pKa of the Glu35 side chain, which of the following molecules does Glu35 most likely deprotonate to produce the nucleophile? A. NH3 B. H3O+ C. H2O D. OH−

C. H2O A glycosidic bond is the α- or β-linkage between a sugar and an -OH of another molecule. Hydrolysis of a glycosidic bond is cleavage of the linkage by addition of H2O, breaking the molecule into two smaller units.

Which labeled intermolecular interaction in Figure 1 represents an attractive ion-dipole interaction? A. I B. II C. III D. IV

C. III

Which statements correctly describe electrolysis? During electrolysis: I an electrochemical decomposition reaction occurs. II electric current is supplied as the energy to perform an endergonic reaction. III the electrochemical cell operates with a negative ΔG. IV electric current flows in a nonspontaneous direction within an electrochemical cell. A. I and IV only B. I, II, and III only C. II and IV only D. I, II, and IV only

D. I, II, and IV only The operation of an electrolytic cell causes electrolysis, which is the nonspontaneous, electrochemical decomposition of a compound (Number I). Because electrolysis uses an electrolytic cell, the supplied electrical current flows in a nonspontaneous direction within the electrochemical cell (Number IV), which supplies the energy needed to perform a nonspontaneous (endergonic) decomposition reaction (Number II). Electrolysis uses an electrolytic cell that as a POSITIVE, not a negative deltaG

Which position in Compound 2 corresponds to the hydrogen(s) that appear as a doublet at approximately 4.0 ppm in the 1H NMR spectrum? A. I B. II C. III D. IV

D. IV The splitting pattern can be determined by the n + 1 rule (n = number of nonequivalent hydrogen atoms on adjacent carbons). I: 3 adjacent carbons II: 0 adjacent carbons III: 2 adjacent carbons IV: 1 adjacent carbon

Which of the following reactions will produce the same organic product whether performed on hexanoic acid or on the carboxylic acid derivative described in the passage? A. Base-catalyzed aldol condensation B. Decarboxylation C. Oxidation with NaBH4 D. Reduction with LiAlH4

D. Reduction with LiAlH4 Hydride reagents, such as LiAlH4 and NaBH4, contain a metal atom surrounded by hydride ions. LiAlH4 is a strong reducing agent and will reduce carbonyl compounds, including esters and carboxylic acids, to alcohols.

A Galileo thermometer consists of a cylinder filled with a variable solution mixture and several sealed glass bulbs partially filled with water. The density of the solution in the cylinder varies significantly with temperature, but the change in the density of the water inside each bulb is negligible. If one of the bulbs has the same density as the cylinder solution at 25 °C, how will the bulb's position and the density of the cylinder solution change as the temperature decreases from 25 °C to 20 °C? A. The cylinder solution density will decrease, and the glass bulb will sink. B. The cylinder solution density will decrease, and the glass bulb will float C. The cylinder solution density will increase, and the glass bulb will sink. D. The cylinder solution density will increase, and the glass bulb will float

D. The cylinder solution density will increase, and the glass bulb will float Liquids tend to become more dense as it cools since the molecules move closer together. Molecules expand when heated and contract when cooled. Solid objects float in liquids with a higher comparative density and sink in liquids with a lower density. (due to bouyancy)

Which of the following pairs of Lewis structures best represents a dipole-dipole interaction between permanent dipoles in two lactate molecules in a Plasma-Lyte A solution?

Dipole-dipole interactions occur when the opposite partial charges of the permanent dipoles of the polar bonds in neighboring molecules form a mutual attraction

Fischer esterification

Esters are carboxylic acid derivatives that can be formed from a carboxylic acid and an alcohol through a Fischer esterification. The ester oxygen bonded to both the carbonyl carbon and the alkyl group originates from the alcohol, a fact that can be confirmed by isotopically labeling the hydroxyl oxygen of the alcohol starting reagent. *O18 must be an alcohol*

Glutamate vs Glutamine

Glutamate: negatively charged, polar amino acid containing one carboxyl group Glutamine: uncharged, polar amino acid containing an amine group (not carboxyl)

Which of the following expressions describes the equilibrium concentrations of folded and unfolded protein at Tm for sample 1?

[unfolded]/[folded] = 1 The passage states that folded and unfolded proteins exist in equilibrium showing that if divided they should equal 1.