Name:
Names of Group Members:


Date:

The following questions require more thought than calculations. Think carefully and when writing your answers use complete sentences or risk losing credit!

1) Your instructor adds 0.1 mol NaCl to 500 mL of water. Describe the following:

1. What is the concentration (in mol/L) of the solution?
2. What are the ratios of each type of particle present? (e.g., the ratio of water molecules to Na⁺ cations)
3. Are any of the atoms from the NaCl still in solid form? Why or why not?
4. Does this solution conduct electricity? Why?
5. What word best describes the situation that occurs when it is not possible to increase concentration of salt by adding more?
6. Draw a picture or pictures showing what happens at the atomic level in a solution like that just described.

2) Compare and contrast a weak electrolyte such as acetic acid (CH₃COOH) and a strong electrolyte such as sodium hydroxide (NaOH).

1. In an acetic acid solution, which is the major substance (not counting the water): CH₃COOH or CH₃COO^– + H⁺?
2. Write down the major substances present in NaOH solution (hint: what type of ion does Na form in solution?)
3. Which of these two substances conducts electricity better?
4. What effect on the conductivity does raising the concentration of each have?
5. If the acetic acid were literally 10 million times more concentrated would it match the conductivity of the NaOH solution? Why or why not?

 

The same directions apply to these questions as applied to the previous questions.
Necessary conditions for equilibrium:

1. Opposing rates of change must be equal. These are the only things that have to be equal. Take note especially of the fact that the amount of each substance in an equilibrium are not always equal.
2. The equilibrium is dynamic at the particulate level. Particles are continually changing from what is represented on the left side of the equation to what is represented on the right side, and vice versa. The process will appear static at the macroscopic level.
3. The change must be reversible. An equilibrium cannot be established with a system for which there is no forward and reverse reaction or change.
4. The system must be closed. This is why filling a funnel is a poor example of an equilibrium. There is no equilibrium if particles are being added to and subtracted from the system.

3) A mountain river flows into a lake. The level of the lake varies depending on the amount of water flowing in. Water from the lake also evaporates. On a certain day, the rate of flow into the lake from the river was exactly equal to the rate of evaporation. The level of water in the lake remained constant. Did an equilibrium system exist on this day? Explain




















5) Chemical equilibria are referred to as dynamic equilibria. What is meant by the term dynamic? Explain your answer on both the particulate and the macroscopic levels.

4) When an established equilibrium is stressed the equilibrium strives to reestablish itself. Knowing this, predict what will happen given the following situations:

1. A saturated solution of sodium acetate at 25°C, with some of the solid salt at the bottom of the container, is heated until the temperature is 100°C
2. A slow exothermic reaction is cooled by putting the reaction vessel in an ice bath
3. Consider a reversible reaction that nevertheless goes nearly to completion. What would happen if more of the reactants were added?
4. The reaction of nitrogen and hydrogen gases to form ammonia has a poor yield even under conditions of high pressure and temperature. What effect would adding a catalyst have on this reaction?

6) Using the concept of stressed equilibria explain the following:

1. When you exercise, you breather harder
2. When you sweat, you need to ingest salt and water
3. Humans cannot drink ocean water without becoming sick