EXAM 3
Write a balanced chemical equation based on the following description: solid chromium reacts with solid iodine to form solid chromium(III) iodide.
2 Cr(s) + 3 I₂(s) → 2 CrI₃(s)
Plants store excess glucose as starch which is composed of amylose and amylopectin. Identify the characteristics of amylose. A) A straight chain polysaccharide containing only straight chain α-1-4 linkages of glucose residues B) A polysaccharide containing α-1-4 linkages of glucose units and branching due to α-1-6 linkages of glucose residues C) A straight chain polysaccharide with α-1-4 linkages of glucose and galactose residues D) A branching polysaccharide containing α-1-4 linkages of glucose and galactose residues E) A branching polysaccharide containing α-1-4 linkages and α-1-6 linkages of glucose and galactose residues Time's
A) A straight chain polysaccharide containing only straight chain α-1-4 linkages of glucose residues Solution: Amylose and amylopectin are both polysaccharides composed of only glucose residues.\n\nAmylose is a straight chain polysaccharide with only α-1-4 linkages while amylopectin also contains branching due to α-1-6 linkages.
In the following chemical reaction, which element is the reducing agent? 2 Ag(s) + 2Cl⁻(aq) + 2 H₂O(l) → 2 AgCl(s) + H₂(g) + 2 OH⁻(aq) A) Ag B) Cl C) H D) O
A) Ag solution: Reducing agents lose electrons and are oxidized. In this reaction, Ag loses one electron to become Ag⁺.
Is the reaction that is described by this energy diagram exergonic or endergonic? A) Exergonic B) Endergonic C) Not enough information given
A) Exergonic
Which of the following statements are always true for a reaction at equilibrium? * I. The rate of the forward and reverse reactions are equal. * II. The concentrations of the reactants and the products remain constant. * III. The amount of reactants is equal to the amount of products. A) I and II B) I and III C) II and III D) I, II, and III
A) I and II Solution: When a system is at dynamic equilibrium, the rates of the forward and reverse reactions are equal. This also means that the concentrations of reactants and products will appear to remain constant.
What is the major product of the reaction shown below? A) butane B) 1-butene C) 1-butyne D) 2-butyne E) No reaction occurs.
A) butane Solution: The reaction of alkene with hydrogen in the presence of a metal catalyst such as platinum or palladium leads to the formation of an alkane. Thus hydrogenation of 2-butene leads to the formation of butane as the product.
What type of reaction is represented by the following equation: 2Na(s) + Cl₂(g) → 2NaCl(s) A) combination B) decomposition C) double displacement D) single displacement
A) combination Solution: This is a combination reaction, involves two compounds reacting to form one new compound. This type of reaction is also known as a synthesis reaction.
What type of reaction converts 4-decene into decane? A) hydrogenation B) hydration C) halogenation D) hydrohalogenation E) halohydrogenation
A) hydrogenation Solution: The conversion involves addition of hydrogen atoms to the double bonded carbons, so the process is called hydrogenation.
Classify the carbohydrate shown here. A) ketohexose B) ketopentose C) aldohexose D) aldopentose E) aldotetrose
A) ketohexose solution: This structure contains six carbons, and the carbonyl group is on the second carbon forming a ketone, so it is classified as an ketohexose.
Choose the best classification based on the chain length for the monosaccharide shown. A) triose B) tetrose C) pentose D) hexose E) heptose
A) triose Solution: Monosaccharides are categorized by the number of carbons in the backbone. The prefix indicates the number of carbons. Prefixes: Tri = 3; Tetr = 4; Pent = 5; Hex = 6; Hept = 7
An exothermic reaction causes the surroundings to A) warm up B) become acidic C) condense D) decrease in temperature E) release CO₂
A) warm up solution: An exothermic reaction transfers energy from the system to the surroundings. That tells us the surroundings will get warmer.
Consider the reaction profile shown below. Choose the best description of the thermodynamics of the reaction. A. Exothermic B. Endothermic C. Thermoneutral
A. Exothermic Solution The reaction is exothermic. In exothermic reactions, energy is released, so the enthalpy of the products must be lower than the enthalpy of the reactants.
How many chiral centers are in the compound shown here? A) 0 B) 1 C) 2 D) 3 E) 4
B) 1 solution: A chiral center is formed at a carbon with four different groups attached to it. Only the third carbon from the top fits that criterion, so there is only one chiral center.
Which of the following species would be the major product in this condensation reaction? A) 1 B) 2 C) 3
B) 2
Which one of the following processes is endothermic? A) Boiling a liquid. B) Freezing a solid. C) Condensation of a gas into a liquid. D) Condensation of a gas into a solid.
B) Boiling a Liquid Solution: An endothermic process requires heat. Freezing a solid, condensation of a gas into a liquid, and condensation of a gas into a solid all release heat. Gases have more energy than liquids. For a liquid to become a gas, energy would be need to be added to the system.
The representation of a monosaccharide shown here is known as a(n) _____ A) Fischer projection. B) Haworth projection. C) anomeric projection. D) aldose projection. E) ketose projection.
B) Haworth projection. solution: This horizontal ring structure portraying monosaccharides is called a Haworth projection, named after the English chemist Sir Norman Haworth.
D- and L- designations are used to distinguish between the two possible enantiomers of the monosaccharide, fructose. From the Fischer projection, determine the designation of this monosaccharide. A) D B) L C) D, L D) L, D E) This monosaccharide contains no chiral centers
B) L solution: L. The L designation means that the hydroxy on the chiral carbon furthest from the top of the Fischer projection is pointing to the left.
Identify the polysaccharide that is produced by plants and is an important source of carbohydrates in the human diet. A) Glycogen B) Starch C) Cellulose D) Dextrins Time's
B) Starch solution: Starches are large polysaccharides that are produced by plants and these carbohydrates are found in the diet of most mammals. Keep in mind that dextrins are smaller carbohydrates that are formed by the partial digestion of these large polysaccharides (sometimes found in bread or beer).
Determine which anomer is represented in the structure shown here. A) alpha B) beta C) gamma D) cis E) trans
B) beta solution: There are only two types of anomers, alpha and beta. In the beta anomer, the hydroxy (-OH) group at C1 is on the same side of the Haworth projection ring as the terminal carbon (in this case, both are up), so this is the beta anomer. (This is a D sugar, and another way to remember the designation is that the beta anomer is up and the alpha anomer is down in a D sugar. It is the opposite for an L sugar.)
Which monosaccharide is used in the formation of nucleosides in DNA? A) ribose B) deoxyribose C) fructose D) mannose E) glucose
B) deoxyribose solution: Deoxyribose. This is an aldopentose monosaccharide that is a component of the nucleosides of DNA.
Lactose, the sugar found in dairy products, is what type of saccharide? A) monosaccharide B) disaccharide C) polysaccharide D) starch E) none of these Time's
B) disaccharide Solution: Lactose is formed from two sugars, glucose and galactose, so it is called a disaccharide.
Lactose is classified as what type of carbohydrate? A) monosaccharide B) disaccharide C) oligosaccharide D) polysaccharide
B) disaccharide solution: Lactose, or milk sugar, is a disaccharide composed of one glucose and one galactose.
What is the relationship between these two sugars? A) identical structures B) enantiomers C) diastereomers D) constitutional isomers E) non-isomeric
B) enantiomers solution: Enantiomers. Enantiomers have the same molecular formula, the same functional groups, the same atomic connectivity, but they are mirror images of each other.
What type of linkage bonds monosaccharides together to form disaccharides and polysaccharides? A) anomeric B) glycosidic C) ester D) ether E) hydrogen bond
B) glycosidic solution: A full ketal or acetal linkage between the anomeric carbon (C1) of one monosaccharide and a hydroxy (-OH) group of another monosaccharide is called a glycosidic linkage.
A carbohydrate containing a chain of four carbon atoms is known as a(n) _____ A) triose B) tetrose C) pentose D) hexose E) quadrose
B) tetrose solution: Carbohydrate names end in -ose. One containing four carbon atoms is classified as a tetrose, from the Greek prefix "tetra-" meaning four.
Disaccharides are described by the position of the anomeric carbon and the numbering of the atoms involved in the glycosidic bond. Identify the type of linkage present in this maltose disaccharide. A) α-1,2 B) α-1,4 C) α-1,6 D) β-1,2 E) β-1,4
B) α-1,4 solution: α-1,4. Glycosidic linkages are defined by the anomeric configuration and the numbers of the carbons involved in the glycosidic linkage (alpha or beta). Then, numbering of each monosaccharide carbon chain is done to give the anomeric carbon the lowest number.
Carbohydrates can be classified based on the number of sugar units that compose the molecules. An oligosaccharide has _______ units. A) a single sugar unit B) only 2 or 3 sugar units C) 2-10 sugar units D) > 10 sugar units
C) 2-10 sugar units solution: Carbohydrates are categorized by the number of sugar units within the structure. Monosaccharides contain only one sugar. Oligosaccharides are short chains with 2-10 sugar units and polysaccharides contain long chains with > 10 sugar units.
Which carbon is the anomeric carbon in the structure shown here? A) A B) B C) C D) D E) E
C) C solution: The anomeric carbon is the carbon which is in a hemiacetal or hemiketal linkage. In this structure that is carbon C. It is easily recognized as the carbon which has two oxygen atoms attached to it.
Which of the following does the change in the free energy of a reaction predict? A) the work done B) the speed C) the spontaneity D) the final temperature E) the heat released
C) The spontaneity solution: The change in the free energy of a reaction predicts the spontaneity of a reaction. A positive change in free energy indicates a nonspontaneous reaction. A negative change in free energy indicates a spontaneous reaction.
The reaction of 1-butene and hydrogen in the presence of a Pd catalyst produces A) 2-butene B) 1-butyne C) butane D) methane and propane E) two ethane molecules
C) butane solution: Hydrogen in the presence of a Pd catalyst will add to the carbons of a double bond producing a saturated product. This reaction converts an alkene to an alkane, so the product with butene would be butane.
The Haworth projection of D-allose is shown. What type of cyclic sugar is formed? A) glucose B) furanose C) pyranose D) hexanose
C) pyranose Solution: This is a pyranose. Cyclic monosaccharides usually form five- or six-membered rings. Five-membered rings are called furanoses and six-membered rings are called pyranoses.
Benedict's test is used to identify the presence of what type of sugar? A) pentose B) hexose C) reducing D) oxidizing E) starch
C) reducing solution: In the Benedict's test, the blue Cu²⁺ ion is reduced to red Cu₂O. So the test indicates the presence of a reducing sugar.
Which of the following is true about a spontaneous process? A. It release energy B. It will occur quickly C. It will continue on its own once begun D. It is never endothermic
C. It will continue on its own once begun Solution: A spontaneous process will continue on its own once begun.
What will be the major organic product from the acid-catalysed hydration of 1-methyl-1-cyclohexene?
D) 1-methyl-1-cyclohexanol Solution: - Hydration of alkenes in the presence of an acid will add H-OH to the C=C double bond producing an alcohol product. The reaction proceeds through Markovnikov addition: * the hydrogen atom (H-) from water forms a bond with the carbon atom that is less substituted, or having more hydrogen atoms * the -OH group from water forms a bond with the carbon atom that is more substituted, or having fewer hydrogen atoms - The acid-catalyzed hydration of 1-methyl-1-cyclohexene results in the formation of 1-methyl-1-cyclohexanol.
What is the number of carbon atoms in the carbohydrate fructose? A) 3 B) 4 C) 5 D) 6 E) 7
D) 6 solution: Fructose is an ketohexose that is a common monosaccharide with six carbon atoms and the molecular formula C₆H₁₂O₆.
Carbohydrates can be classified based on the number of sugar units that compose the molecules. A polysaccharide has _______ units. A) a single sugar unit B) only 2 or 3 sugar units C) 2-10 sugar units D) > 10 sugar units
D) > 10 sugar units solution: Carbohydrates are categorized by the number of sugar units within the structure. Monosaccharides contain only one sugar. Oligosaccharides are short chains with 2-10 sugar units and polysaccharides contain long chains with > 10 sugar units.
What monosaccharide is the product of the hydrolysis of glycogen? A) Fructose B) Galactose C) Sucrose D) Glucose E) Maltose Time's
D) Glucose Solution: Glucose is the subunit monomer of glycogen. Glycogen is a large polysaccharide composed of glucose units linked with an alpha 1-4 linkages and alpha 1-6 linkages
Benedict's reagent converts an aldehyde into what functional group? A) alcohol B) alkene C) ketone D) carboxylic acid E) ester
D) carboxylic acid solution: In the Benedict's test, the blue Cu²⁺ ion is reduced to red Cu₂O, while an aldehyde is being oxidized to a carboxylic acid.
The base hydrolysis of ethyl propanoate followed by addition of acid produces what two organic products? A) propane and ethanol B) propanoic acid and ethane C) propanal and ethanol D) propanoic acid and ethanol E) propanoic acid and ethanal
D) propanoic acid and ethanol Solution: Propanoate becomes propanoic acid, and the ethyl group becomes ethanol.
Which of the following will decrease the rate of a reaction? A) Removing a catalyst from the reaction. B) Decreasing the temperature. C) Decreasing the surface area of a solid reactant. D) Decreasing the concentration of the reactants. E) All of these will decrease the rate of a reaction.
E) All of these will decrease the rate of a reaction. Solution: The rate of reaction is affected by the concentration of the reactants, the presence of a catalyst, the surface area of the reactants, and the temperature of the reaction. Removing or decreasing each of these would result in a decreased reaction rate.
Consider the following reaction: Mg²⁺(aq) + Cu(s) → Cu²⁺(aq) + Mg(s). In this reaction, Mg²⁺(aq) is: A) Oxidized B) Reduced C) A reducing agent D) An oxidizing agent E) Both (B) and (D)
E) Both (B) and (D) solution: Oxidizing agents gain electrons and are reduced. Reducing agents lose electrons and are oxidized. In this reaction, Mg²⁺ gains two electrons when it becomes Mg.
In a ___________ reaction, the components of water (H-OH) are added across a carbon-carbon double bond (C=C). A) hydration B) hydrogenation C) bromination D) combustion E) elimination
E) elimination solution: An elimination reaction involves losing two substituents from a molecule. Consider another word that signifies adding water to a system.
Animals store excess glucose as glycogen. Glycogen is a _________. A) monosaccharide B) oligosaccharide C) monopolysaccharide D) heteropolysaccharide E) homopolysaccharide Time's
E) homopolysaccharide solution: Homopolysaccharide. Animals store excess glucose as glycogen. This polymer is composed of glucose sugars only.