Question

1.00 mL of blood serum was diluted to 25.00 mL in each flask of a standard addition experiment like Figure 5-7 to measure a hormone with a molecular mass of 373 g/mol. The x-intercept of the graph was 4.2 ppb (parts per billion). Find the concentration of hormone in the serum and express your answer in ppb and molarity. Assume that the density of serum and all solutions is close to 1.00 g/mL

Short answer

The final concentration of hormone in the serum will be 105 ppb or 28µM.

Step-by-step solution

Determine the concentration

Blood serum was diluted by a factor of 25.00 mL/1.00 mL = 25.00 in each flask. The x-intercept is the final concentration of hormone in blood serum. It is given as 4.2ppb from the graph.

Let, X_f be the original concentration which was 25.00 times greater.

Therefore, the original concentration of hormone in the blood serum will be

4.2ppb×25=105ppb

Now we need to convert ppb to M (molarity)

$$\begin{gathered} \frac{105gHormone}{{10}^{9}gSolution}\times \frac{1mol}{373gHormone}\times \frac{1g}{1mLsolution}\times \frac{1000mLsolution}{1Lsolution} \\ =0.28\times {10}^{-6}M \\ =0.28\mu M \end{gathered}$$

The original concentration will be 105 ppb or 0.28$\mu M$