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Solutions

A Case of Double Identity?     

Baking powder is used in making many baked goods, pastries, pancakes, and pizza dough because it is a good leavening agent (that is, it lightens a dough or batter by producing a gas). Most baking powders contain 26-30% sodium bicarbonate (baking soda, NaHCO3) as the active ingredient, an acid, and inert ingredients. One of the acids that is commonly used in baking powder is the monoprotic acid potassium acid tartrate (KHC4H4O6; "Cream of Tartar")

When baking power is dissolved in a liquid, such as water or milk, a reaction occurs and a gas is produced. The gas produced from the leavening action is non-flammable, does not support combustion, and has no net dipole moment. Does NaHCO3 function as an acid or a base in this reaction? Write an equation for this reaction and identify the gas that is produced.


Is a solution that contains 20 g of sugar and 5 g of NaCl a strong electrolyte, a weak electrolyte, or a nonelectrolyte? Explain your answer.


The drawings below represent beakers of aqueous solutions. Each o represents a dissolved solute particle.

Drawing of six solutions

1. Which solution is most concentrated?

2. Which solution is least concentrated?

3. Which two solutions have the same concentration?

4. When Solutions E and F are combined, the resulting solution has the same concentration as Solution _____.

5. When Solutions B and E are combined, the resulting solution has the same concentration as Solution _____.

6. If you evaporate off half of the water in Solution B, the resulting solution has the same concentration as Solution _____.

7. If you place half of Solution A in another beaker and then add 250 mL of water, the resulting solution has the same concentration as Solution _____.


Sketch a qualitative graph of the equilibrium pressure of water vapor above a sample of pure water and a qualitative graph of the equilibrium pressure of water vapor above a sugar solution as the liquids evaporate to half their original volume.


Compare the processes that occur when methanol (CH3OH), hydrogen chloride (HCl), and sodium hydroxide (NaOH) dissolve in water. Write equations and prepare sketches showing the form in which each of these compounds is present in its respective solution.

(This could be conceptual or could be memorization, depending on the text and your class work.)


A 1 m solution of HCl in benzene has a freezing point of 0.4oC. Is HCl an electrolyte in benzene? Explain.


A 0.100 m solution of H2SeO4 in water freezes at -0.37oC. Which of the following statements is consistent with this observation? 

For water:  

F.P.(oC)  Kf B.P.(oC)  Kb
0 1.85 100 0.515

(a) Two H2SeO4 molecules form an (H2SeO4)2 dimer by forming hydrogen bonds.
(b) The H2SeO4 molecule does not dissociate in water.
(c) Each H2SeO4 molecule forms an H3O+ ion and an HSeO4- ion in water.
(d) Each H2SeO4 molecule forms two H3O+ ions and an SeO42- ion in water.
(e) Each H2SeO4 molecule forms two H3O+ ions, an Se2- ion, and four O2- ions in water.

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