KVPY 2020-21 SB SX Exam Previous Papers

Question : 109 of 120

Marks: +1, -0

When a mixture of NaCl,

K_2Cr_2O_7

and conc.

H_2SO_4

is heated in a dry test tube, a red vapor (X) is evolved. This vapor (X) turns an aqueous solution of NaOH yellow due to the formation of Y. X and Y, respectively, are:

$CrCl_3 \and Na_2Cr_2O_7$
$CrCl_3 \and Na_2Cr O_7$
$CrO_2Cl_2 \and Na_2CrO_4$
$Cr_2 (SO_4 )_ 3 \and Na_2Cr_2O_7$

Validate

Solution:

4NaCl + K_2Cr_2O_7 + 6H_2SO_4 → 4NaHSO_4

+ 2KHSO_4 + 2CrO_2Cl_2(X) + 6H_2O

CrO_2Cl_2 + 4NaOH → Na_2CrO_4(Y)

+ 2NaCl + 2H_2O

X = CrO_2Cl_2

Y = Na_2CrO_4

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