When calibrating a glass electrode, 0.025 m potassium dihydrogen phosphate/0.025

Question

When calibrating a glass electrode, 0.025 m potassium dihydrogen phosphate/0.025 m disodium hydrogen phosphate buffer (see the NIST Buffers table) gave a reading of -19.3 mv at 30. Degree C and 0.05 m potassium hydrogen phthalate buffer gave a reading of +144.2 mv. What is the pH of an unknown giving a reading of +50.1 mv? (two significant figures) What is the slope of the calibration curve (mv/pH unit) and what is the theoretical slope at 30 degree C? calibration curve 57.6 mv/pH unit (three significant figures)| theoretical mv/pH unit (three significant figures)| Find the value of the electromotive efficiency, Beta. (three significant figures) A cyanide ion-selective electrode obeys the equation given below. E = constant - 0.05916 log[CN^-] The potential was -0.230 V when the electrode was immersed in 1.00 mM NaCN.

Explanation / Answer

1)RT/F can be substituted for 0.05916to determine an electrode responseat temperatures other than

25C.»E =(RT/F)pH =(0.06154)pHfor 37C»E =1 (0.06154) (4.00)= 0.246 Volts or 246 mV

2)6.6

3). The value of , theelectromotive efficiency, is close to 1.00 (typically >0.98)

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