CHEM 3303 Exam 1 Review Questions And Answers Guaranteed Pass

What properties make water the best solvent for life? - Correct Answers Due to its polarity and ability to form hydrogen bonds, water makes an excellent solvent What is the geometric and molecular structure for water? - Correct Answers Geometric - distorted tetrahedral Molecular - H2O What is hydrogen bonding? What are the requirements? - Correct AnswersA strong dipole-dipole or charge-dipole interaction that arises between an acid (proton-donor) & a base (proton-acceptor). A Hydrogen donor and acceptor must be present. The donor is usually electronegative like N, F, O that is covalently bonded to a Hydrogen. Why is carbon not able to do hydrogen bonding? - Correct AnswersDue to its electronegativity not being strong enough compared to oxygen and nitrogen. What makes hydrogen bonds weak or strong (generally)? - Correct AnswersHydrogen bonds are strongest when the bonded molecules are oriented to maximize the electrostatic interaction. Ideally the three atoms are in a line. Non-covalent interactions - Correct Answersdo not involve sharing a pair of electrons. Between metal and nonmetal. Ionic (coulombic) interactions - Correct AnswersElectrostatic interactions between permanently charged species or between the ion and a permanent dipole. Dipole Interactions - Correct AnswersElectrostatic interactions between uncharged, but polar molecules Van Der Waals Interactions - Correct AnswersWeak interactions between all atoms, regardless of polarity. Attractive (dispersion) and repulsive (steric) components. Hydrophobic effect - Correct AnswersComplex phenomenon associated with the ordering of water molecules around non-polar substances. Review over colligative properties; the ones mentioned in class are boiling point, melting point, and osmotic pressure. - Correct AnswersColligative properties do not depend strongly on the nature of dissolved solute.(boiling, melting, and osmolarity) Non-colligative properties - Correct AnswersNon-colligative substances depend strongly on the chemical nature of the solute. (viscosity, surface tension, taste, color, etc) Hypertonic - Correct AnswersHypertonic solution will have higher osmotic pressure; water moves out from the cell and it will look shriveled. Isotonic - Correct AnswersIsotonic solution will have same osmotic pressure; cell will look the same. Hypotonic - Correct AnswersHypotonic solution will have a lower osmotic pressure; water moves into the cell causing it to burst Between butane and butanol, butanol has a much higher boiling point. Explain why this occurs. - Correct AnswersButane is nonpolar and contains only weak van der waal interactions. In comparison, Butanol is a polar molecule due to the presence of a polar hydroxyl group and has intramolecular hydrogen bonding. The greater the intermolecular forces, the more energy it will take to break apart the bonds, hence the higher boiling point. Know how many hydrogen bonds are possible for one water molecule in ice and liquid. - Correct AnswersWater molecule in an ice state has 4 hydrogen bonds. In liquid state, it will have less than 4 hydrogen bonds (# of hydrogen bonds present will decrease as entropy increases). Room temperature water usually has 3 hydrogen bonds. The higher the temperature of water, the higher the entropy and hydrogen bonds decrease. The two most common functional groups involved in ionic interactions are carboxylic group and amino group. True or False: increase in entropy of water equals to increased energy of interaction. - Correct Answerstrue Why is the solid form of NaCl readily soluble in water? (hint: entropy as a solid vs. entropy in aqueous solution) - Correct AnswersIn an aqueous solution, the charged Na+ and Cl- will be attracted to the slightly negative and positive dipoles in a water molecule (ion dipole interactions). High dielectric constant reduces the attraction between oppositely charged ions in salt crystals (NaCl). Low entropy is thermodynamically unfavorable, entropy will increase as the solid NaCl (crystal lattice) is dissolved. Define Entropy - Correct AnswersEntropy is the measure of the disorder of a system or energy unavailable to do work. True or False: hydrophobic interactions are not attraction between nonpolar molecules (only dispersion forces); folding/association of nonpolar molecules in aqueous solution. - Correct AnswersTrue For enzymes and receptors, understand how the entropy concept is relevant. Do the same for fatty acids with hydrophobic interactions. Enzymes & receptors: - Correct AnswersBinding sites in enzymes and receptors are often hydrophobic. Water molecules around these hydrophobic binding sites will disperse in order to bind the substrate and receptors. The disordered water due to this hydrophobic bind increases and so does entropy. For enzymes and receptors, understand how the entropy concept is relevant. Do the same for fatty acids with hydrophobic interactions. Fatty acids with hydrophobic interactions: - Correct AnswersFatty acids have a nonpolar tail and a polar head. The nonpolar tail (hydrophobic) will have highly ordered H2O molecules around it and only the polar head (hydrophilic) can interact with water. This is energetically unfavorable and has low entropy. Fatty acids will associate and form clusters and micelles that will keep the nonpolar parts of the amino acid away from water. This decreases the amount of ordered H2O and increases entropy. Non-polar molecules come together in order to decrease the disruption of favorable hydrogen bonds. How can this be related to the entropy concept? Understand the same concept for micelles - Correct AnswersThe water molecules that were caged around the nonpolar molecules decreased when they aggregated. Less caged water molecules increases the entropy. In micelles, all nonpolar parts are inside the core away from the water molecules. When micelles are formed, more water molecules are freed to be more random instead of caged. This causes higher entropy. What is a buffer solution? What does it consist of? Be able to use the Henderson-Hasselbalch equation. - Correct AnswersA buffer is an aqueous solution of either a weak acid and its conjugate base or a weak base and its conjugate acid. Buffers resist change in pH. What does the pKa reveal of a weak acid in a titration curve? Know and understand the relevance of pKa. When does pH = pKa? - Correct AnswerspKa of a weak acid in a titration curve reveals its pH. pH = pKa when the weak acid and salt concentrations in a buffer are equal. 50:50 mixture of acid and anion forms of the compound. How many hydrogen bonds a CH3 - O - CH3 molecule can make with itself? What about with water? - Correct Answers1 AND 1 Why is pH maintenance important in biological systems? - Correct AnswersEnzyme catalyzed reactions, solubility of polar molecules and the equilibrium of CO2 and HCO3- depends on pH. Which of the following will be most/least soluble in water? a) Methanol/heptanol b) butanol/pentane c) heptanol/methanol d) pentanol/butanol - Correct Answersb) butanol/pentane How many hydrogen bonds can one ammonia molecule form with water molecules? - Correct Answers1 H bond What are the functions of proteins? - Correct AnswersProteins are the "main agents of biological function" Catalysis Transport Structure Motion