You are provided with stock solutions of sodium chloride (~ 1.0 M), hydrochloric

Question

You are provided with stock solutions of sodium chloride (~ 1.0 M), hydrochloric acid (1.00 M), and sodium hydroxide (0.313 M). Using these stock solutions, prepare Solutions A – F. Use deionized water as the diluent.

Solution Total volume (mL) [NaCl], M [HCl], M [NaOH], M Potential (mV)

A 50.0 0.10 3.0 × 10–3 none added 235.5

B 50.0II 0.10II 1.0 × 10–3II none addedII 214.9

C 50.0II 0.10 II 4.0 × 10–4 II none added II 197.0

D 50.0 II 0.10 II none added II none added II 28.0

E 50.0 II 0.10 II none added II 4.0 × 10–4 II -209.5

F 50.0 II 0.10 II none added II 1.0 × 10–3 II -149.0

a. Construct a graph of potential (in mV) versus pH for the constant ionic medium solutions.   
      Calculate pH based on the known composition of each solution. Activity coefficients
      do not need to be considered for the constant ionic medium scale (because all solutions have
      nearly identical ionic strengths). Assess the linearity of the graph. Use a linear regression
      to determine the line of best fit (do you think it is appropriate to include all six data points?).

b. What are the slope and y-intercept? Report each value with their associated 95% confidence
      intervals.

c. Determine the values of w and . Report w in mV.

Please clearly show work for the calculations.

Explanation / Answer

The best fit can be obtained through determining the trendline in some spreadsheet package like excel using the values derived in the following image. In a linear fit of ax+b, a will give the slope, and b the intercept.

Determination of pH.

Note that in solution 1-4 we have only acid and in solution 5-6 we have only base. For an acidic solution pH is given by -log[H+]. But for a basic solution the way is to calculate pOH= - log [ OH-] and using pH = 14- pOH.

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