Chapter 8.6, Problem 66PPS

a.

To determine

To find whether the engineer should worry about the high arsenic content.

Answer to Problem 66PPS

Yes, he will worry.

Explanation of Solution

Given:

The safe standard for arsenic level is less than $0.025$ parts per million (ppm) and the pH for the arsenic level should be less than $9.5$ .

Calculation:

Consider the formula for the hydrogen ion concentration:

  $pH=-\log H$

Consider the hydrogen ion concentration of the well is $1.25\times {10}^{-11}$ . Therefore,

  $\begin{array}{l}pH=-\log H\\ pH=-\log (1.25\times {10}^{-11})\\ =10.9\end{array}$

As the pH level is greater than $9.5$ therefore, the environmental engineer must be worried about the high arsenic content.

b.

To determine

To find whether the well is safe.

Answer to Problem 66PPS

No, the well is not safe.

Explanation of Solution

Given:

The safe standard for arsenic level is less than $0.025$ parts per million (ppm) and the pH for the arsenic level should be less than $9.5$ .

Calculation:

Consider the environmental engineer finds $1$ milligram of arsenic in a $3$ liter sample in some well site. Consider for water:

  $1\text{ kg}=\text{1 liter}$

And,

  $1\text{ ppm}=\text{1 mg/kg}$

Therefore, the arsenic content is the well side is:

  $\begin{array}{l}\text{=}\frac{1}{3}\text{ ppm}\\ \text{=0}\text{.3333 ppm}\end{array}$

As the ppm level is greater than $0.025$ therefore, the environmental engineer must be worried about the high arsenic content.

c.

To determine

To find the hydrogen ion concentrationlevel that meets the troublesome pH level.

Answer to Problem 66PPS

  ${10}^{-9.5}$

Explanation of Solution

Given:

The safe standard for arsenic level is less than $0.025$ parts per million (ppm) and the pH for the arsenic level should be less than $9.5$ .

Calculation:

Consider if the hydrogen ion concentration level $H$ then the corresponding pH level will be $9.5$ therefore:

  $\begin{array}{l}-\log H=9.5\\ \log H=-9.5\\ H={10}^{-9.5}\end{array}$

Therefore the required hydrogen ion concertation level that meets the troublesome pH level is ${10}^{-9.5}$