Question

4. The Debye-Huckel limiting law is strictly valid only in the limit of infinite dilution. A more widely applicable equation is the Debye-Huckel equation: 0.510 z,z_|V7 1+(0.328aT log Y This equation applies at 25 °C in dilute aqueous solution. For a 0.00100 m aqueous solution of CaCl2 at 25 °C, the y is found experimentally to equal 0.888. Use this to determine the value of the constant a (which is related to the ion size and has units of A). a. b. Use the value of a from part a. to estimate y+ for a 0.0100 m aqueous CaCl2 solution at 25 °C.

Answer 1

log 8t = -0.510 17+7-17 7+(0.328 017) - - Where Is ionic strength, I = 1/2 Eziu a. For 0.0010 m aqueous solution of Cache Cal+= 0.0010 * = (2x 0.0010 ) = 0.0020 I= t{(2x0:00) + (-1* 0:002) 4x6x103 I = 3xjö}] Now, 8+ = 0.888 from equation, Ų we get, log(0-888) -- 0.510|42)(-11 738103 H+ (0.328 a 3x153) 70.0516 = + 0.510x 2X 0.05477 1+(0.328 ax 0.05477) 0.0516 - 0.05586 1+ 0.01796a 0.0516 +19.269x164) a = 0·05586 (9.269x174) a = 4.26x103 [a=4.596 4 Jug Ans.

b. From Part as a The value of a=4.596 Å .. . Now, 0.010om solution of cache, we Ca 2+ = 0.010m 200 = 0.020 m +1=$ 2x(0.0j0) + (-1°x(0.020)} = 4x006 I 20.03 From eq (1) we get, - log8+ - 0.510 16+2)x(-1) 10:03 it (0.328x 4596x 10.03 log 8+ --0-17666 It 0.2611 log 81 3-0.14 , 8+ = 0.72427 Any