Chloride Levels - Chemistry Experiments - page 114

6. Which water sample contained the most chloride ions? What do you
think caused it to have more than the other two?
7. Did your results match your hypothesis in Analysis question 1?
If not, explain why it may have been different from what you first
thought.
What's Going On?
In a titration, a precise amount of one substance is added to another to
react with it. A titration is carried out to its equivalence point , the point at
which all of the solution in the flask has reacted with the solution from the
burette. In this experiment, potassium chromate was used as an indicator
to show when the silver nitrate had reacted with all of the chloride ions.
Chloride ions react with the silver ions from silver nitrate to form a white
precipitate . Once all of the chloride ions had reacted with silver, the silver
began reacting with the chromate ions from potassium chromate, forming
silver chromate, a red precipitate. The lingering red color indicated that all
of the chloride ions in the water had been removed.
Because the molarity and the volume of the silver nitrate is known,
the moles of silver nitrate involved in the chemical reaction could be
determined. Using the balanced chemical reaction for the production of
silver chloride from silver ions and chloride ions (Ag + + Cl −  AgCl), you
can determine that one mole of silver is needed to react with each mole
of chloride ions. Therefore, the number of moles of chloride in each water
sample could be calculated.
Connections
Although it has not been officially documented that trace amounts of
chemicals within drinking water can have adverse health effects, many
individuals choose to remove these chemicals. There are many filtration
techniques that can remove ions from drinking water. Water can be heated
to evaporate it then condensed in a purified form in a process called
distillation . Distillation is effective at disinfecting and removing some
chemicals, but it is a slow process and generally filters are more efficient
for use in homes.
Two of the most effective and commonly used types of filters in homes
are reverse osmosis and activated carbon filters. Reverse osmosis filters
pressurize water and force it through a semipermeable membrane so
that only water molecules move through (see Figure 3). These filters