You need to create 5 serial Dilutions of CI^- standards with a total volume of 3

Question

You need to create 5 serial Dilutions of CI^- standards with a total volume of 30 mL each. You are provided with a 0.13 M stock CI^- solution. The first concentration required 114 mmol/L is provided in the table below. Create a series of dilutions by cutting the concentration to 1/3 each time. Complete the following table based on the use of the information above to make the following mmol/L concentrations of CI^-. (30 mL of total volume is used) (Give answers to 3 sigfigs): If you titrate 50.0 mL of patient sample using 0.297 M HCI and find the first end point to be at 0.000956 L and the second at 0.0140 L, what is the concentration(M) of your HCO_3^-? HCO_3^- = M

Explanation / Answer

In part 1, the [Cl-] = 114 mmol/L

Each dilution is made by cutting the concentration to 1/3.

In dilution 1, [Cl-] = 114 mmol/L

In dilution 2, [Cl-] = 114/3 = 38 mmol/L

Similarly each dilution is calculated by dividing previous concentration by 3.

In 2nd column, volume of Cl- needed is calculated by using formula M1V1 = M2V2

For Cl-, stock solution concentration is 0.13 M

for 1st dilution [Cl-] = 114 mmol/L = 114 mM = 0.114 M

Volume to be prepared = 30 ml

M1 = 0.114 M, V1 = 30 ml

M2 = 0.13 M, V2 = ?

From the formula above, we get V2 = 26.3 ml

So, volume of Cl- needed = 26.3 ml

Buffer needed = 30-26.3 ml = 3.7 ml

As these are serial dilutions, so 2nd dilution is formed from 1st dilution.

Here M1 = 0.038 M, V1 = 30 ml

M2 = 0.114 M, V2 = ?

V2 = 10 ml

So, like this other volumes are calculated.

Part -2,

in titration, formula used is M1V1 = M2V2

cabonate ion reacts with HCl to form first HCO3- and then H2CO3.

First end point means HCO3- is formed and second end point means HCO3- is neutralized.

To calculate concentration of HCO3-, we need to take 2nd end point.

For HCl, M1 = 0.297 M, V1 = 0.0140 L = 24.0 ml

For HCO3-, M2 = ?, V2 = 50.0 ml

M1V1 = M2V2

0.297*14.0 = M2 *50.0

M2 = 0.083 M

HCO3- concentration is 0.083 M

Dilution [Cl-] (mmol/L) Volume (ml) Cl- needed (serial dilution) volume ISA buffer (ml) needed 1 114 26.3 3.7 2 38 10 20 3 12.7 10 20 4 4.22 10 20 5 1.41 10 20

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