Question

A cyanide ion-selective electrode obeys the equation given below.E = constant − 0.05916 log [CN⁻ ]

The potential was −0.237 V when the electrode was immersed in 1.21 mM NaCN. (Assume that the Nernst potential is 0.05916 V.)

(a) Evaluate the constant in the above equation.
c = _____?_____V

(b) Using the result from part (a), find [CN⁻ ] if E = −0.318 V.

−0.318	=	c − 0.05916 log(x)
x	=	___?___ mM

(c) Without using the constant from part (a), find [CN⁻ ] if E = −0.318 V.

−0.237	=	c − 0.05916 log(1.21 mM)
−0.318	=	c − 0.05916 log(y)
			−
y	=	____?__ mM

Answer 1

. The eyanide ion-selective electrode obeys the equation . Es const. - 0.05916 log [en] .....(j (a) E= -0.237V when the electrode was immersed in 1.21 mM NOCN- 3. [en-] = 1.21 mM 21:21X153 (mj. : (1mm 10² m) . : putting the value of E; [en] in eq w, we get, -0.237 = const. -0.05916 log (1.21x103): on Const. = -0.237 + 0.05916*(-2.917) constr = -0.237 - 0.1726. o const. 3.-0.4096 os. Const. =:-0.4096. V (b) E= -0.318 V, [en] =?. from eq.ci), Ez Const. - 0,05916 log [en] or, 0.05916 log [en] = Const. - E or log [eN] = consti - E. 0.05916. or, wg [en], -0.4096 - (-0.318) 10.05916. or,

0.05916 - or, log [en] = -0.4096 + 0.318 -0.0916 0.05916 or log [eN] = - 1:548 or, [ew] = 181.548) 3. Ten] 2 0.0'283.(M). = 28.3 m. Mi [eN] = 28.3 mm when E= -0.318 v.. (e) To find out [en] when E=-0.318 v. Without considering the const value. The two equations are as follows. -0.237 = const. -0.05916 log (1.21*173) -0. -0.318 = conat. -0.05916 log[en] .--Cit) (t (-) (+) 2009 be is 916 long bo 21 310 ) +0.0591t bojleri or, 0,081 = 0.05916 fugler] - log(12181537 ov, . = log [ex] - (-2.917) 08

- or, log [ew] +.2.917 = 1.369 or log [ew] = 1.369-2.917= -1,548 'or, ly [cm] = -1.548 . or; [en] = 101.548 : [en] = 0.0283(m) is [co] - 28.3 mm. [en] = 28.3 mm as it was in part (b). if E = -0.318 v.