Choice Answers with Solutions

Note Many chemistry essays on certification exams consist of quantitative problem solving with the requirement to show your work. The first of the two sample essays is of this type. For additional practice, I recommend solving quantitative problems from the multiple choice sample test with an essay mindset and comparing your essays to the solutions shown in the Answers with Solutions section. Some chemistry essays require little or no quantitative problem solving, but they ask for an experimental design or analysis of a design. The second of the two sample essays is of this type. These essays usually have no single correct solution. 

Calculations — These questions require you to quickly calculate mathematical solutions. Since you will not be allowed to use a calculator for the multiple-choice questions, the questions requiring calculations have been limited to simple arithmetic so that they can be done quickly, either mentally or with paper and pencil. Also, in some questions, the answer choices differ by several orders of magnitude so that the questions can be answered by estimation. 

Directions No Calculators may be used with Part B. Write the formulas to show the reactants and the products for any FIVE of the laboratory situations described below. Answers to more than five choices will not be graded. In all cases a reaction occurs. Assume that solutions are aqueous unless otherwise indicated. Represent substances in solution as ions if the substances are extensively ionized. Omit formulas for any ions or molecules that are unchanged by the reaction. You need not balance the equations. The Section II score weighting for this question is 15%. 

Some substances will dissolve in a particular solvent and others will not. There is a general rule in chemistry that states that like dissolves like. This general statement may serve as an answer in the multiple-choice questions, but does not serve as an explanation in the free-response questions. This simply means that polar substances (salts, alcohols, etc.) will dissolve in polar solvents such as water, and nonpolar solutes, such as iodine, will dissolve in nonpolar solvents such as carbon tetrachloride. The solubility of a particular solute is normally expressed in terms of grams solute per 100 ml. of solvent (g/mL) at a specified temperature. The temperature must be specified because the solubility of a particular substance will vary with the temperature Normally, the solubility of solids dissolving in liquids increases with increasing temperature, while the reverse is true for gases dissolving in liquids. 

The new Test Bank contains 25% new multiple-choice and short-answer problems and solutions with approximately 50 problems and solutions per chapter. Each problem is keyed to the corresponding chapter of the text and rated by level of difficulty. 

The results of the SCRF models depend strongly on the radius Rx used for the definition of the spherical interface between the solute and the solvent. Unfortunately, the dielectric theory does not provide an answer for the question of which value is appropriate for this radius. Owing to the implicit assumption of the dielectric continuum models that the electron density of the solute should be essentially inside the cavity, any value of Rx below a typical van der Waals (vdW) radius would not be meaningful. On the other hand, at least at the distance of the first solvent shell, i.e., typically at two vdW radii, we should be in the dielectric continuum region. However, there is no clear rationale for the right value between these two limits other than empirical comparison of the results with experimental data. Among others, the choice of spherical cavities which correspond to the liquid molar-solute volume has proved to be successful. 

For questions that ask you to find the solution to an equation, you can simply substitute each answer choice into the equation and determine which value makes the equation correct. Begin with choice c. If choice c is not correct, pick an answer choice that is either larger or smaller. 

The correct answer is (E). The molality, because it is only dependent on the mass of the solute and solvent, does not change as temperature changes. Volume does vary with temperature, which is why choices (C) and (D) are not appropriate. Mole fractions are unaffected by volume changes, but they do remain constant during heating (unless vaporization accompanies the heating). 

A is correct For all practical purposes, choices A and B are the same. However, since the question asks you to compare them, a one molar solution is 1 mole of NaCl in slightly less than a liter of water. This is because the NaCl requires some volume. A one molal solution is one mole in one full liter of water. (This question assumes that a liter of water has a mass of 1 kg. This is true at 1 atm. and approximately 3°C. Water at 1 atm. is at its most dense state at a temperature of slightly over 3°C.) There are 55.5 moles of water in a liter (grams/molec-ular weight = moles). 1/100 = 0.01 and 1/50 = 0.02. Thus a solution with a mole fraction of 0.01 is closer to a 0.5 molar solution than a 1 molar solution. The last answer choice is less than one mole of NaCl in one liter of water. 

The correct answer is (D). It s very important that you remember the definition of molarity molarity is the number of moles of solute per liter of solution. That means that the contents of the solute and solvent must equal 1.00 liter. In this problem, the solution is to be 0. lOO-molar, which means that there are 0.100 moles of solute per 1.00 liter. 0.100 mol x 40.0 g mol = 4.00 g. The correct answer is (D). The solute that produces the most particles in solution will produce the solution with the highest boiling point. (E) is a tempting choice because the concentration is twice that of any other. Glucose, however, is not an electrolyte. (A), (B), and (C) will all have van t Hoff factors of 2, while MgC l, has a van t Hoff factor of 3, which will produce the greatest boiling point elevation. 

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