Question

1. the following table shows the mercury concentrations in the body tissue of various animals.

animal	mercury concentration (ppm)
fish	0.23
polar bear	1.23

a. what is the mass of mercury in a 250 - g fish?

b. what is the mass of mercury in a 900 - kg polar bear?

c. briefly explain what may be causing the observed trend in mercury concentration in the table.

1. determine the amount concentration of 2.6 x 10^(-2) g of magnesium chloride dissolved in 45 ml of solution.

Explanation:

Step1: Recall ppm conversion formula

Parts - per - million (ppm) is defined as $\text{ppm}=\frac{\text{mass of solute}}{\text{mass of solution}}\times10^{6}$. Rearranging for the mass of solute gives $\text{mass of solute}=\frac{\text{ppm}\times\text{mass of solution}}{10^{6}}$.

Step2: Solve part a

The mass of the fish is $m_{fish}=250\ g$ and the mercury concentration in fish is $0.23\ ppm$. Using the formula $\text{mass of mercury}=\frac{0.23\times250}{10^{6}}$.
\[

$$\begin{align*} \text{mass of mercury}&=\frac{0.23\times250}{10^{6}}\\ &=\frac{57.5}{10^{6}}\\ & = 5.75\times10^{-5}\ g \end{align*}$$

\]

Step3: Solve part b

First, convert the mass of the polar - bear to grams. Since $1\ kg = 1000\ g$, the mass of the polar - bear $m_{bear}=900\ kg=900\times1000 = 9\times10^{5}\ g$. The mercury concentration in polar bears is $1.23\ ppm$. Using the formula $\text{mass of mercury}=\frac{1.23\times9\times10^{5}}{10^{6}}$.
\[

$$\begin{align*} \text{mass of mercury}&=\frac{1.23\times9\times10^{5}}{10^{6}}\\ &=\frac{11.07\times10^{5}}{10^{6}}\\ &=1.107\ g \end{align*}$$

\]

Step4: Answer part c

The observed trend in mercury concentration (plankton < fish < polar bear) is due to biomagnification. Biomagnification occurs as mercury accumulates in the bodies of organisms at lower trophic levels and is then passed on to organisms at higher trophic levels in a food chain. As organisms at higher trophic levels consume many organisms from lower trophic levels, the concentration of mercury in their bodies increases.

Answer:

a. $5.75\times10^{-5}\ g$
b. $1.107\ g$
c. The trend is due to biomagnification. Mercury accumulates in organisms at lower trophic levels and is passed on to higher - trophic - level organisms, causing an increase in mercury concentration in the bodies of organisms at higher trophic levels.