Chpt 4 Solutions - CHAPTER 4 TYPES OF CHEMICAL REACTIONS...

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92 CHAPTER 4 TYPES OF CHEMICAL REACTIONS AND SOLUTION STOICHIOMETRY Questions 13. a. Polarity is a term applied to covalent compounds. Polar covalent compounds have an unequal sharing of electrons in bonds that results in unequal charge distribution in the overall molecule. Polar molecules have a partial negative end and a partial positive end. These are not full charges as in ionic compounds but are charges much smaller in magnitude. Water is a polar molecule and dissolves other polar solutes readily. The oxygen end of water (the partial negative end of the polar water molecule) aligns with the partial positive end of the polar solute, whereas the hydrogens of water (the partial positive end of the polar water molecule) align with the partial negative end of the solute. These opposite charge attractions stabilize polar solutes in water. This process is called hydration. Nonpolar solutes do not have permanent partial negative and partial positive ends; nonpolar solutes are not stabilized in water and do not dissolve. b. KF is a soluble ionic compound, so it is a strong electrolyte. KF(aq) actually exists as separate hydrated K + ions and hydrated F ions in solution: C 6 H 12 O 6 is a polar covalent molecule that is a nonelectrolyte. C 6 H 12 O 6 is hydrated as described in part a. c. RbCl is a soluble ionic compound, so it exists as separate hydrated Rb + ions and hydrated Cl ions in solution. AgCl is an insoluble ionic compound, so the ions stay together in solution and fall to the bottom of the container as a precipitate. d. HNO 3 is a strong acid and exists as separate hydrated H + ions and hydrated NO 3 ions in solution. CO is a polar covalent molecule and is hydrated as explained in part a. 14. 2.0 L × L HCl mol 0 . 3 = 6.0 mol HCl; the 2.0 L of solution contains 6.0 mol of the solute. HCl is a strong acid; it exists in aqueous solution as separate hydrated H + ions and hydrated Cl ions. For the acetic acid solution, HC 2 H 3 O 2 is a weak acid instead of a strong acid. Only some of the HC 2 H 3 O 2 molecules will dissociate into H + (aq) and C 2 H 3 O 2 (aq). The 2.0 L of 3.0 M HC 2 H 3 O 2 solution will contain mostly hydrated HC 2 H 3 O 2 molecules but will also contain some hydrated H + ions and hydrated C 2 H 3 O 2 ions. 15 . Only statement b is true. A concentrated solution can also contain a nonelectrolyte dissolved in water, e.g., concentrated sugar water. Acids are either strong or weak electrolytes. Some ionic compounds are not soluble in water, so they are not labeled as a specific type of electrolyte.
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CHAPTER 4 SOLUTION STOICHIOMETRY 93 16. One mole of NaOH dissolved in 1.00 L of solution will produce 1.00 M NaOH. First, weigh out 40.00 g of NaOH (1.000 mol). Next, add some water to a 1-L volumetric flask (an instrument that is precise to 1.000 L). Dissolve the NaOH in the flask, add some more water, mix, add more water, mix, etc. until water has been added to 1.000-L mark of the volumetric flask. The result is 1.000 L of a 1.000 M NaOH solution. Because we know the volume to
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