One way the u. s. environmental protection agency (epa) tests for chloride contaminants in water is by titrating a sample of silver nitrate solution. any chloride anions in solution will combine with the silver cations to produce bright white silver chloride precipitate. suppose an epa chemist tests a sample of groundwater known to be contaminated with iron(iii) chloride, which would react with silver nitrate solution like this: (aq) (aq) (s) (aq) the chemist adds m silver nitrate solution to the sample until silver chloride stops forming. she then washes, dries, and weighs the precipitate. she finds she has collected of silver chloride. calculate the concentration of iron(iii) chloride contaminant in the original groundwater sample. be sure your answer has the correct number of significant digits.

3.8x10⁻⁵ M

Explanation:

By the reaction given, the stoichiometry between FeCl3 and AgNO3 and AgCl is 1:3:3. The molar mass of AgCl is 143.32 g/mol, so the number of moles that was formed is:

n = mass/molar mass

n = 0.0036g/143.32g/mol

n = 2.51x10⁻⁵ mol

Thus, the number of moles of FeCl3 that had precipitated was:

1 mol of FeCl3 3 moles of AgCl

x 2.51x10⁻⁵ mol

By a simple direct three rule:

x = 8.37x10⁻⁶ mol

The precipitation is a reversible reaction, and, for the AgCl, is has an equilibrium constant Kps = 1.8x10⁻¹⁰, then, the solubility, S, (the maximum concentration of the ions that will not precipitate) can be calculated:

S² = Kps

S = √1.8x10⁻¹⁰

S = 1.34x10⁻⁵ mol/L

The volume of the sample was 250 mL = 0.250 L, so the number of moles of Cl⁻ that was not precipitated is:

n = 1.34x10⁻⁵ mol/L*0.250 L

n = 3.35x10⁻⁶ mol

Because of the stoichiometry:

1 mol of FeCl3 3 moles of Cl-

y 3.35x10⁻⁶ mol

By a simple direct three rule:

y = 1.12x10⁻⁶ mol of FeCl3

The total number of moles of FeCl3 is then:

n = x + y

n = 9.5x10⁻⁵ mol

The concentration is the number of moles dived by the volume:

9.5x10⁻⁵ /0.250 = 3.8x10⁻⁵ M

when—without warning—something provokes your anger, you may struggle not to succumb to it. since what typically makes you mad is feeling powerless in the face of what seems unfair, your anger is mostly an attempt at a “quick fix” to right the balance. it’s as though you’re raising a fist in protest, proclaiming that you’re not going to capitulate to such injustice.

there are, however, a multitude of problems related to this immediate, push-back reaction of anger. and probably the key one is that almost never does it resolve the issue that gave rise to it. such reactive anger is probably best understood as self-defeating. as david burns, the author of the seminal self- book feeling good, observes: if realistically, acting on your anger is to make any sense, it needs to meet two criteria—which, in almost every case, is frankly impossible. that is, your anger must:

be directed toward a person who has intentionally (and needlessly) behaved in a hurtful way toward you; and

be beneficial or advantageous to you (i.e., assist you in achieving a desired goal).

i think you’ll agree that only rarely can you claim that your anger is both warranted and , whether to yourself or the relationship.

so let me offer you a two-step alternative to abandoning your better judgment and giving in to the temptation of anger—one that should neutralize your anger in seconds. or, when you’re really angry, in minutes.

but keep in mind that you must really want to execute these steps, be sufficiently motivated to perform them. which means overcoming more unconscious resistance than you might ever have imagined. because there are many immediate “advantages” of anger that can interfere with your resolve, i’ll suggest a few of them that might interfere with your employing this powerful method to rid yourself of counter-productive anger.

explanation: