ENCE 433                                                                                          Dr. Alba Torrents

ENVIRONMENTAL ENGINEERING ANALYSIS                      Spring 2001

 

Homework Set # 1                             Out: February 1                     Due: February 8

 

 

1.                  An amount of 2.3 g of ethyl alcohol (C2H5OH) is added to 500 g of water.  The resulting solution is ................................... molal in  C2H5OH.

 

2.         Find the normality of the following solutions:

(a) 60 mg CO3-2/liter, given that carbonate participates in the precipitation reaction:

 

(b) 155 mg Ca3(PO4)2 /liter in the following dissolution reaction:

 

 

3.         Water that does not easily form lather with soap is termed "hard” whereas water that readily forms lather with soap is termed "soft".  The chief cause of hardness in water is the presence of small quantities of dissolved calcium salts such as calcium bicarbonate, Ca(HCO3)2, and calcium sulfate, CaSO4.  These calcium salts react with the soap before it has a chance to form lather with the water.  To soften water, the calcium compounds either must be precipitated from solution or converted to soluble sodium compounds.  Calcium bicarbonate can be removed from the water by boiling because insoluble calcium carbonate, CaCO3, is produced in the process.  This compound is removed by the addition of ordinary washing soda, Na2CO3, to the water.  The following reaction occurs:

 

     

 

            A typical concentration of CaSO4 in river water is 1.8 x 10-3 g/liter.  How many kilograms of Na2CO3 would be required to soften 6.8x109 liters of water.