Question

In: Chemistry

Say you are given a buffer at 25 C in pH 6.881. The glass combination electrode...

Say you are given a buffer at 25 C in pH 6.881. The glass combination electrode gave a reading of -18.3 mV. When it was placed in a pH 4.002 buffer at 25 C, this same electrode gave a reading of +146.3 mV. What is the electromotive efficiency of the glass electrode? (3 sig figs)

Solutions

Expert Solution

Below is a typical combination pH electrode that incorporates a glass electrode and reference electrodes into a single cell.

Reference Electrode Glass membrane Reference Electrode

Ag(s)|AgCl(s)|Cl-(aq)||H+ (aq, outside) : H+ (aq, inside),Cl-(aq)|AgCl(s)|Ag(s)

The overall measured cell potential is

E = Eouter reference + Einner reference + Ejunction + Eglass

Since the reference electrode potentials and junction potential are constant, at 25 °C

E = Constant - [(2.303 R T / n F) log (ainner ion / aouter ion)]

E = Constant - β (0.05916) pH

where β is the electromotive efficiency

Using the above equation, we have

-18.3 mV = Constant - β (0.05916) (6.881) =====> 0.0183 = (0.40707) β - Constant ------ (I)

146.3 mV =  Constant - β (0.05916) (4.002) =====> 0.1463 = Constant - (0.23675) β ----- (II)

(I) + (II) =====> 0.1646 = 0.17032 β

β = 0.1646 / 0.17032 = 0.966

Electromotive efficiency of the glass electrode = 0.966


Related Solutions

Consider a glass electrode or [pH electrode (combination electrode). a. Identify the reference part. b. Identify...
Consider a glass electrode or [pH electrode (combination electrode). a. Identify the reference part. b. Identify the indicator part. c. Explain how the potential of the electrode is determined. d. Describe a two-point calibration of the electrode. e. State any five of the eight possible errors that might occur in pH measurements with the electrode.
A student was given buffer solutions to calibrate the pH electrode that were labeled incorrectly. The...
A student was given buffer solutions to calibrate the pH electrode that were labeled incorrectly. The pH's of both buffer solutions were actually lower than the pH's shown on the labels. Explain how such an error would affect the experimental result for the Ka of acetic acid.
Calculate the pH at 25°C of 176.0 mL of a buffer solution that is 0.210 M...
Calculate the pH at 25°C of 176.0 mL of a buffer solution that is 0.210 M NH4Cl and 0.210 M NH3 before and after the addition of 1.50 mL of 6.0 M HNO3. (The pKa for NH4+ = 9.75)
Calculate the equilibrium constant for each of the reactions at 25∘C. Standard Electrode Potentials at 25...
Calculate the equilibrium constant for each of the reactions at 25∘C. Standard Electrode Potentials at 25 ∘C Reduction Half-Reaction E∘(V) Fe3+(aq)+3e− →Fe(s) -0.036 Sn2+(aq)+2e− →Sn(s) -0.14 Ni2+(aq)+2e− →Ni(s) -0.23 O2(g)+2H2O(l)+4e− →4OH−(aq) 0.40 Br2(l)+2e− →2Br− 1.09 I2(s)+2e− →2I− 0.54 Part A 2Fe3+(aq)+3Sn(s)→2Fe(s)+3Sn2+(aq) Express your answer using two significant figures. Part B O2(g)+2H2O(l)+2Ni(s)→4OH−(aq)+2Ni2+(aq) Express your answer using two significant figures. Part C Br2(l)+2I−(aq)→2Br−(aq)+I2(s) Express your answer using two significant figures.
Calculate [H3O+] and [OH−] for each of the following solutions at 25 ∘C given the pH....
Calculate [H3O+] and [OH−] for each of the following solutions at 25 ∘C given the pH. Part A.) pH= 8.65 Part B.)  pH= 11.40 Part C.)  pH= 2.94
What is the reduction potential at 25∘C for the hydrogen electrode in each of the following...
What is the reduction potential at 25∘C for the hydrogen electrode in each of the following solutions? The half-reaction is as follows: 2H+(aq)+2e−→H2(g,1atm) Part A 1.0 M HCl. Part B A solution having pH = 4.16. Part C Pure water. Part D 1.1 M NaOH.
you want to make 100ml of 0.20M acetic acid buffer with pH=50. you are given a...
you want to make 100ml of 0.20M acetic acid buffer with pH=50. you are given a stock of 1.0M acrtic acid and a bottle of solid sodium acetate sale (MW=82g/mol). what is the ratio of [A-]/[HA] when your buffer pH is 5.0? determine the concentration of weak acid and conjugate base in the buffer. how many mL of 1.0 acetic acid will you need? how many grams of sodium acetate will you need? if you now have add 1mL of...
if you want to prepare a buffer at pH = 5.2 which buffer would you choose?...
if you want to prepare a buffer at pH = 5.2 which buffer would you choose? a) MES --> Ka = 7.9 x 10^-7 b) CHES --> Ka = 5.0 x 10^-7 c) Tris --> Ka = 6.3 x 10^-9 d) acetic aid --> Ka = 1.8 x 10^-5
Calculate the pH of the following aqueous solutions at 25°C. Kw at 25°C is 1.01e-14. (a)    2.9 ...
Calculate the pH of the following aqueous solutions at 25°C. Kw at 25°C is 1.01e-14. (a)    2.9 ✕ 10−11M KOH (HINT: Does it make sense to get an acidic pH for this? A neutral solution may have a higher concentration of OH- than this solution.) 1 (b)    9.1 ✕ 10−7M HNO3 2
Consider a glass of 274 mL of water at 25°C. Calculate the mass of ice at...
Consider a glass of 274 mL of water at 25°C. Calculate the mass of ice at -15°C that must be added to cool the water to 10°C after thermal equilibrium is achieved. To find the mass of water use the density of water = 1.0 g/mL.
ADVERTISEMENT
ADVERTISEMENT
ADVERTISEMENT