I need help on finding the original unknown concentration in question 5-17 of th

Question

I need help on finding the original unknown concentration in question 5-17

of the spike and the concentration detection limit. 5-16. Standard addition. Vitamin C was measured by an hat electrochemical method in a 50.0-mL sample of lemon juice. se A detector signal of 2.02 A was observed. A standard addi- a tion of 1.00 mL of 29.4 mM vitamin C increased the signal to al 3.79 A. Find the concentration of vitamin C in the juice. 1- 5-17. Standard addition. Analyte in an unknown gave a signal s of 10.0 mV. When 1.00 mL of 0.050 0 M standard was added to 100.0 mL of unknown, the signal increased to 14.0 mV. Find the concentration of the original unknown. 5-18. Standard addition graph. Tooth enamel consists mainly of the mineral calcium hydroxyapatite, Ca1o(Po)OH) Trace elements in teeth of archeological specimens provide

Explanation / Answer

Ans. 5.17. Given, 1.0 mL of 0.050 M standard analyte is added to 100.0 mL unknown solution.

Final volume of resultant solution = 1.0 mL (Std. analyte) + 100.0 mL (unknown)

= 101.0 mL

Now, final [Analyte] in the working solution (101.0 mL) can be calculated using-

C1V1 (Standard analyte)= C2V2 (spiked unknown)

            Or, C2 = (C1 V1) / V2 = (0.050 M X 1.0 mL) / 101.0 mL = 4.9505 x 10-4 M

Hence, [analyte] in spiked unknown solution = 4.9505 x 10-4 M

# Given, signal of spiked unknown solution = 14.0 mV

            Signal of un-spiked unknown solution = 10.0 mV

            Increase in signal due to spiking = 14.0 mV – 10.0 mV = 4.0 mV

Since, the increase in signal by 4.0 mV is solely due to addition of analyte-standard, a signal of 4.0 mV units is equivalent to 4.9505 x 10-4 M analyte - the increase in [analyte] due to spiking.

So,

            4.0 mV of signal is equivalent to 4.9505 x 10-4 M analyte

     Or, 10.0 mV          -           -           - (4.9505 x 10-4 M / 4.0 mV) x 10.0 mV

                                                                             = 1.238 x 10-3 M

That is, the signal 4.0 mV unit for un-spiked unknown solution 1.238 x 10-3 M.

Thus, [analyte] in original unknown solution = 1.238 x 10-3 M

Related Questions

Navigate

• Browse (All)
• Browse I
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.