Problem 71 - Chemistry: The Central Science

Question

The water supply for a midwestern city contains the following impurities: coarse sand, finely divided particulates, nitrate ion, trihalomethanes, dissolved phosphorus in the form of phosphates, potentially harmful bacterial strains, dissolved organic substances. Which of the following processes or agents, if any, is effective in removing each of these impurities: coarse sand filtration, activated carbon filtration, aeration, ozonization, precipitation with aluminum hydroxide?

Step-by-Step Solution

Answer

To remove the impurities from the water supply, the following processes or agents are effective: Coarse sand filtration for coarse sand removal, precipitation with aluminum hydroxide for finely divided particulates and dissolved phosphorus in the form of phosphates, ozonization for nitrate ion and potentially harmful bacterial strains removal, and activated carbon filtration for trihalomethanes and dissolved organic substances removal.

Step 1: Removing Coarse Sand

To remove coarse sand from the water supply, we can use coarse sand filtration. This process uses a filter made of coarse sand which is effective in removing larger particles from the water.

Step 2: Removing Finely Divided Particulates

Finely divided particulates can be removed using precipitation with aluminum hydroxide. When aluminum hydroxide is added to the water, it reacts with the particulates, causing them to coagulate and settle out of the water.

Step 3: Removing Nitrate Ion

Nitrate Ion is difficult to remove from water using the given processes or agents. However, ozonization can help in reducing the nitrate ion concentration as ozone oxidizes nitrites to nitrates and nitrates to nitrogen gases.

Step 4: Removing Trihalomethanes

Trihalomethanes, which are a group of organic compounds, can be effectively removed using activated carbon filtration. This process uses activated carbon to adsorb the trihalomethanes from the water.

Step 5: Removing Dissolved Phosphorus in the Form of Phosphates

Dissolved phosphorus in the form of phosphates can be removed by precipitation with aluminum hydroxide. The aluminum hydroxide reacts with the phosphates and forms a gel-like precipitate which can be separated from the water.

Step 6: Removing Potentially Harmful Bacterial Strains

Potentially harmful bacterial strains can be effectively removed using ozonization. Ozone is a powerful oxidant that destroys bacteria, viruses, and other microorganisms by reacting with the organic matter present in them.

Step 7: Removing Dissolved Organic Substances

Dissolved organic substances can be removed using activated carbon filtration. The activated carbon adsorbs the dissolved organic substances, thereby separating them from the water.