37. A 0.1500 g sample containing dichromate is analyzed iodometrically. The reac

Question

37. A 0.1500 g sample containing dichromate is analyzed iodometrically. The reactions are: Ch072-+ 61-(excess) + 14H+-2Cr3+ +312+7H20 12 + 2S2032-= 21-+ S4062 Calculate the percent of dichromate in the sample if a volume of 35.00 mL of 0.100 M Na2S2O3 is required for titration of the liberated I2. 0. 100mol-S203-x 0.03500 LX × zg cr207 -- mol x 100 (A) 0. 1500 g 0. 100mol-S203-x 0.03500 L*T × 6 216 g Cr2o5 mol (B) %= x 100 0. 1500 g 0.100 mol S203 x0. 03500 LX1x 1216 g Cr202 mol (C) x 100 0. 1500 g 0. 100mo1S203_ × 0.03500 L*T × 216 g Cr 2 07 2 1 (D) % x 100 0. 1500 g is 38. Direct potentiometric measurements with an ion selective electrode (A) produce measurements of the activity of a chemical species (B) work because junction potentials are constants. (C) require the use of the calomel reference electrode. (D) always are specific only for the ion of interest.

Explanation / Answer

Ans 37 : A)

The option A is correct

The number of moles of S2O32- = 0.035 x 0.100 moles

Number of moles of I2 = (0.035 x 0.100) / 2

Number of moles of Cr2O72-= ( 0.035 x 0.100) / 6

Mass of Cr2O72- = [(0.035 x 0.100) / 6 ] x 216 g

% amount = [(0.035 x 0.100) / 6 ] x 216 g } / 0.1500 ] x 100

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