"Published in Newark, California, USA"
"Hard" water contains small amounts of the salt calcium bicarbonate [Ca(HCO3)2] and calcium sulfate [CaSO4, molecular weight = 136 grams/mole]. These react with soap before it has a chance to lather, which is responsible for its cleansing ability. Ca(HCO3)2 is removed by boiling to form insoluble CaCO3. CaSO4 is removed by reaction with washing soda [Na2CO3, molecular weight = 106 grams/mole] according to the following equation:
If the rivers surrounding New York City have a CaSO4 concentration of 1.8 x 10-3 grams/liter, how much Na2CO3 is required to "soften" [remove CaSO4] the water consumed by the city in one day [about 6.8 x 109 liters]?
Solution:
The first thing that we have to do is to get the amount of CaSO4 in the rivers surrounding New York City as follows
Moles of CaSO4:
From the given reaction above
Moles of Na2CO3:
Therefore, the amount of Na2CO3 required to "soften" or remove CaSO4 in the rivers surrounding New York City is
In metric tons, the weight of Na2CO3 is
