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Chapter 5: Q4TY (page 109)

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

Expert verified

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

Step by step solution

01

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, Xf be the original concentration which was 25.00 times greater.

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

4.2辫辫产脳25=105辫辫产

Now we need to convert ppb to M (molarity)

105gHormone109gSolution脳1mol373gHormone脳1g1mLsolution脳1000mLsolution1Lsolution=0.28脳10-6M=0.28渭M

The original concentration will be 105 ppb or 0.28渭M

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Most popular questions from this chapter

Standard addition. An unknown sample of Ni2+gave a current of 2.36渭础in an electrochemical analysis. When 0.500mLof solution containing role="math" localid="1654761474124" 0.0187MNi2+was added to 25.0mLof unknown, the current increased to 3.79渭础.

(a) Denoting the initial, unknown concentration as [Ni2+], write an expression for the final concentration, [Ni2+]f, after role="math" 25.0mLof unknown were mixed with 0.500mLof standard. Use the dilution factor for this calculation.

(b) In a similar manner, write the final concentration of added standard Ni2+, designated as [S]f.

(c) Find[Ni2+]in the unknown.

Olympic athletes are tested to see if they are using illegal performance-enhancing drugs. Suppose that urine samples are taken and analyzed and the rate of false positive results is 1 %. Suppose also that it is too expensive to refine the method to reduce the rate of false positive results. We do not want to accuse innocent people of using illegal drugs. What can you do to reduce the rate of false accusations even though the test always has a false positive rate of 1 %?

Explain the meaning of the quotation at the beginning of this chapter: 鈥淕et the right data. Get the data right. Keep the data right.鈥�

Internal standard graph -- Data are shown below for chromatographic analysis of naphthalene (C10H8), using deuterated naphthalene (C10D8, in which D is the isotope 2H) as an internal standard. The two compounds emerge from the column at almost identical times and are measured by a mass spectrometer.

(a) Using a spreadsheet such asFigure 4-15, prepare a graph of Equation 5-12 showing peak area ratio(C10H8/C10D8)versus concentration ratio role="math" localid="1663559632352" ([C10H8]/C10D8) . Find the least-squares slope and intercept and their standard uncertainties. What is the theoretical value of the intercept? Is the observed value of the intercept within experimental uncertainty of the theoretical value?

(b) Find the quotientrole="math" localid="1663559638520" [C10H8]/[C10D8]for an unknown whose peak area ratio (C10H8/C10D8) is 0.652. Find the standard uncertainty for the peak area ratio.

(c) Here is why we try not to use 3-point calibration curves. For n = 3 data points, there is n - 2 = 1 degree of freedom, because 2 degrees of freedom are lost in computing the slope and intercept. Find the value of Student's for confidence and 1 degree of freedom. From the standard uncertainty in (b), compute the 95 % confidence interval for the quotient[C10H8]/[C10D8] . What is the percent relative uncertainty in the quotient[C10H8]/[C10D8]? Why do we avoid 3-point calibration curves?

5-28. Ititandard addition. Lead in dry river sediment was extracted with 25wt%HNO3at35掳Cfor1h.then1.00mLof filtered extract was mixed with other reagents to bring the total volume to V0=4.60mL.pb(ll)was measured electrochemically with a series of standard additions of 2.50pb(ll).


(a) Volume is not constant, so follow the procedure of Figures 5-5 and 5-6 to find ppmpb(ll)inthe1.00-mL

extract.

(b) Find the standard uncertainty and 95%confidence interval for the x-intercept of the graph. Assuming that uncertainty in intercept is larger than other uncertainties, estimate the uncertainty in ppm pb(ll)inthe1.00-mLextract.
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