"Published in Newark, California, USA"
In a salt manufacturing firm in California, there's a spill of 10 gallons of concentrated hydrochloric acid (37.5% HCl solution) from the gate valve of 1,000 gallon tank that contains concentrated hydrochloric acid. Before the disposal of the spill, the state law requires to neutralize the hazardous waste first by adding sodium bicarbonate and then wipe-off the neutralized spill. How many bags of sodium bicarbonate will be needed for neutralization process? One bag of sodium bicarbonate weighs 50 pounds. Is it safe to dispose the blankets used to wipe-off the neutralized spill? What is the pH of the neutralized spill? The pH range required for the disposal of industrial waste in California is 2.0 to 12.5. Outside of the range is considered as a corrosive. (density of concentrated hydrochloric acid = 1.19 g/mL; density of sodium bicarbonate = 2.20 g/mL; molecular weight of hydrochloric acid = 36 g/mole; and molecular weight of sodium bicarbonate = 84 g/mole)
Solution:
Since the spill is a strong acid, then the state law of California requires to neutralize it with a weak base. We cannot use any strong base because they are hazardous and corrosive, too. Same thing with a strong base. We need to neutralize it with a weak acid. That's the law for the safety of everyone and the environment as well.
The weight of concentrated hydrochloric acid which is also 37.5% HCl solution is
The weight of pure hydrochloric acid in 37.5% HCl solution is
The number of moles of hydrochloric acid in 37.5% HCl solution is
If sodium bicarbonate is added to the spill that contains concentrated hydrochloric acid, then the chemical reaction is
The weight of sodium bicarbonate used to neutralize hydrochloric acid is
Therefore, the number of bags of sodium bicarbonate used is
If the spill is happened in daytime especially in warmer climate, then the neutralization of concentrated hydrochloric acid with sodium bicarbonate is
Carbon dioxide is not soluble in water. When you add sodium bicarbonate to the spill which contains concentrated hydrochloric acid, then bubbles will form. Those bubbles are carbon dioxide that are escaping from the spill.
Since sodium chloride is a neutral salt (product of strong acid and strong base), then sodium ion and chloride ion have no reaction with water. Because of this, the pH of a neutralized spill is
Since the pH of a neutralized spill is less than 12.5, then it is safe to dispose the blankets used to wipe-off the neutralized spill.
If the spill is happened in nighttime especially in colder climate, then the neutralization of concentrated hydrochloric acid with sodium bicarbonate is
Since carbonic acid is a weak acid, then it is partially ionized as follows
The number of moles of carbonic acid is
The total volume of a neutralized spill is
The concentration of carbonic acid in molarity is
From Table of Ionization Constant of Acids and Bases, carbonic acid is ionized in two steps as follows
In this neutralization process, we will use the ionization constant at the first equation.
The ionization constant of carbonic acid is
where x is the amount of carbonic acid that is converted into hydrogen carbonate ion and hydrogen ion.
Since the value of Ka is less than 1 x 10-3, then we can neglect x at the denominator as follows
Hence, the concentration of hydrogen ion is
Therefore, the pH of a neutralized spill is
Since the pH of a neutralized spill is greater than 2.0, then it is safe to dispose the blankets used to wipe-off the neutralized spill.