Concept Test 1

Internet Concept Test Chemistry 22
Prof. J. C. Baird
Forms, CGI and Database by Marn-Yee Lee, Class of '96

Concept Test on Solutions: I

Topic: Substances Dissolved in other Substances,
Or Why One Thing Dissolves in Another

Credits

Click here to find out how credit works.

Up to 4 people can work together on this test.

There are 4 questions -- you don't have to complete all of them. However, any blank entries will overwrite previous submissions.

To get credit for this problem:

Leave your names in the form at the bottom after answering the questions. Then submit the results.

Question 1

In the text under "Carbon Dioxide, Seashells, and Killer Lakes" there is a graph of CO2 concentration in parts per million vs year. In the text below the figure is the statement: "(The concentration of CO2 is given in parts per million, that is, in units of milligrams per kilogram of air.)"

Parts per million by volume in air and parts per million by weight in air

Reason for Answer:

Question 2

Henry Eyring, a famous chemist, once gave a talk in Houston, Texas decades ago giving a reason that ethyl alcohol (ethanol) caused problems in people. It went something like this: "Ethyl alcohol is composed of an oily group and a water group. When someone drinks an alcoholic beverage the oily group of ethanol dumps itself down the center of the helix of proteins. As everyone knows, the helix is held together by hydrogen bonds. Since water is repelled by oil, the ethyl part of the alcohol molecule repells the H-bonds and the protein uncoils laying prostrate on the cell wall."

Certainly there is much wrong with this story, and of course it was told by Eyring for a reason. But what were the chemical ideas that formed Eyring's tale?

Possible Reasons Henry Eyring might have had:

Reason for Answer:

Question 3

The enthalpy change for potassium fluoride, KF(s), going into solution is negative,

The meaning of this fact is:

Reason for Answer:

Question 4

The enthalpy change for potassium fluoride, KF(s), going into solution is negative,

and it is said of this "that the compound should be water-soluble."

On the other hand, the enthalpy of solution of salt, NaCl, is calculated from the thermochemical enthalpy tables as being positive,

Does this mean that salt should not be water-soluble?

heat energy

Reason for Answer:

Question 5 - A Modern Example

Scientists at Woods Hole Oceanographic Institution discovered hot vents at the bottom of the ocean at a depth of about 9,130 ft. The temperatures at these vents were about 543 F and the pressure about 270 atmospheres. In the region of these vents there is life. At these temperatures and pressures water is in the neighborhood of its critical temperature and pressure. Above Tc, Pc water is said to be in the supercritical region.

To view a movie of a hydrothermal vent click here.

In the supercritical region the properties of water are different from its properties at ordinary temperatures. For example, the dielectric constant, a measure of H-bonding and other liquid stuctures, is more than 10 times less than at room temperature.

In hyperthermal vents, where water is supercritical, molecules like methane, nitrogen, oxygen and hydrogen sulfide would be:

Reason for Answer:

Question 6

As the critical region of water is approached the shielding between two solute molecules due to water solvent shells is

Reason for Answer:

Don't forget to register before you submit the form! Please enter only the 5-digit of your Brown ID, e.g. for SISD12345, enter 12345.

   Student #1
   Brown ID (nnnnn)   : 
   Last Name          : 
   First Name         :
   Email              :

   Student #2
   Brown ID (nnnnn)   : 
   Last Name          : 
   First Name         :
   Email              :

   Student #3
   Brown ID (nnnnn)   : 
   Last Name          : 
   First Name         :
   Email              :

   Student #4
   Brown ID (nnnnn)   : 
   Last Name          : 
   First Name         :
   Email              :

Return Home