Question

144. In a conductometric experiment for estima- tion of acid dissociation constant of acetic acid, the following values were obtained in four sets of measurements: 1.71 x 10-5. 1.77 x 10-5, 1.79 x 10-5 and 1.73 x 10-5. The standard deviation of the data would be in the range of - (A) 0·010 x 10-5 -0.019 x 10-5 (B) 0.020 x 10-5 -0.029 x 10-5 (C) 0·030 x 10-5 - 0039 10-5 (D) 0·040 x 10-5-0-049 x 10-5 145. Silver clystallizes ir face-centered cubic structure. The 2nd order diffraction angle of a beam of X-ray ( = 1A) of (111) plane of the crystal is 30°. Therefore, the unit cell length of the crystal would be- (A) a = 3-151 Å (B) a = 3-273 Å (C) a = 3·034 Å (D) a = 3-464 Å

solve both I will rate 144,145

Answer 1

Q144

Mean of values = Sum of all values/ number of values

$Mean = \frac{(1.71+1.75+1.73+1.79)*10^{-5} }{4}$

Standard deviation = sqrt(sum of(value-mean)^2)/number of values )

$Standard deviation = \sqrt{\frac{ (1.71*10^{-5}-1.75*10^{-5})^2 +(1.75*10^{-5}-1.75*10^{-5})^2 + (1.73*10^{-5}-1.75*10^{-5})^2 +(1.79*10^{-5}-1.75*10^{-5})^2 }{4}}$
(-0.04 * 10-5)2 + (0)2 + (-0.02 * 10-5)2 + (0.04 * 10-5)2 Standar ddeviation = 1

Thus option c is correct

Q145.

Bragg's law states that

$n.\lambda = 2.d.sin(\theta)$

Where n is number of order of diffraction =2

Lambda is wavelength = 1 Angstrom

d is interplanar distance

Theta is angle of diffraction = 30 deg

Thus equation gives d = 2 Angstroms

While $d = \frac{a}{\sqrt{h^2+k^2+l^2}}$

Where a is lattice constant

And h,k,l are plane miller indices which are (1,1,1)

Therefore a = 2*√3 = 3.46 Angstroms

Thus option D is correct