Question

(20 points) Students performed an experiment in which each flask contained 2.50 ml of with varying additions of 2.640 M NaCl standard, and a total volume of 50.00 mL. Prepare standard addition graph and find (Na+) in the serum. FLASK VSTD, ML Na Signal, my 1.000 2.000 3.000 3.13 5.40 7.89 10.30 12.48 4.000

Answer 1

Solution contains Serum + Standard.

In the flask 1, only serum is present and the signal is due to serum only.

In all other flasks, the signal is due to combination of serum and NaCl.

The value of the emission signal for the flask one is subtracted from the value of emission signals for flasks 2 to 5.

The resulting values gives the emission signal due to standard present in flasks 2 to 5.

This value is plotted against the volume of standard.

The graph is as shown:

emission signal (mV) signal (mV) less signal of serum Volume of emission standard (mL) 0 3.13 0 1 5.4 2.27 2 7.89 4.76 10.3 7.17 12.48 9.35

10 y 2.36x-0.01 6 emission signal (mV) less signal 4 of serum 2 0 0 2 -2 Volume of standard (mL) Ln 9

The equation of the graph is,

y = 2.36 x -0.01

Substitute, y = 3.13 in the above equation

3.13 = 2.36 x - 0.01

x = 1.33

This is the volume of standard (mL) which will correspond to sodium ion concentration in the serum.

The sodium ion concentration in the serum will be = 2.640 mole/L x 1.33 mL/2.5 mL = 1.40 M