Geology 141 - Marine Geology                        Name: ANSWER KEY
Problem Set II
Due In Class October 9, 2002

1)     Assuming the Principle of Constant Proportions holds true, how much (in grams) of the following elements would be present in one kilogram (1000 grams) of seawater of salinity 34 parts per thousand? (Show your work).

Sodium (Na⁺)

1000g x 34‰  = 34g salts
34g salts x 30.6% Na = 10g Na

Chlorine (Cl^-)

1000g x 34‰  = 34g salts
34g salts x 55.04% Cl = 18.7g Cl

Sulfate (SO₄^2-)

1000g x 34‰  = 34g salts
34g salts x 7.68%  = 2.6g SO₄

Bicarbonate (HCO₃^-)

1000g x 34‰  = 34g salts
34g salts x 0.41% HCO₃^-  = 0.14g HCO₃^-

2)     The Messinian Salinity Crisis was an event long ago in which the entire Mediterranean Sea evaporated several times.  This produced huge salt deposits.  It is estimated that the global ocean's salinity went from about 36 parts per thousand to 34 parts per thousand during this time because of salt loss.  If the world's oceans contain about 1.4 x 10²⁴ kilograms of seawater, how many kilograms of salt were deposited in the Mediterranean? (Show your work)

Volume of ocean = 1.4x10²⁴ kg water

Salinity loss = 36‰ - 34‰ = 2‰ lost

1.4x10²⁴ kg water x 2‰ salt lost = 2.8*10²¹ kg salt lost  

3)     How many calories of heat would you have to remove from one can (355 g) of President's Choice Cola to bring it from a liquid at room temperature (25 degrees C) to a frozen solid at 0 degrees C?  For the purposes of this question (and for most other purposes), you may assume that President's Choice Cola is water. (Show your work)

Cooling from 25 to zero degrees (a 25 degree change)
355g x 25°C x 1 cal/g°C = 8,875 calories  

Freezing to a solid at zero degrees
355g x 80cal/g = 28,400 calories