When chromite ore `FeCr_(2)O_(4)` is fuse with NaOH in presence of air, a yellow coloured compound (A) is obtained which on acidification with dilute sulphuric acid gives a compound (B). Compound (B) on reaction with KCl formed an orange colured crystalline compound (C). (i) Write the formula of the compounds (A),(B) and (C). (ii) Write one use of compounds (C).

When chromite ore `FeCr_(2)O_(4)` is fuse with NaOH in presence of air

1.	When chromite ore `FeCr_(2)O_(4)` is fuse with NaOH in presence of air, a yellow coloured compound (A) is obtained which on acidification with dilute sulphuric acid gives a compound (B). Compound (B) on reaction with KCl formed an orange colured crystalline compound (C). (i) Write the formula of the compounds (A),(B) and (C). (ii) Write one use of compounds (C).
Answer» `A = Na_(2) CrO_(4)` (Sodium Chromate) Yellow coloured `B = Na_(2) Cr_(2) O_(7)` (Sodium dichromate) `C = K_(2) Cr_(2) O_(7)` (Potassium dichromate) (orange crystal) Use of potassium dichromate : It is used as a primary standard for the estimation of `Fe^(2+)` and `I^(-)` ions in redox titration.

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(i) Arrange the following compounds in an increasing order of basic strength : `C_(6)H_(5)NH_(2), C_(6)H_(5)N(CN_(3))_(2), (C_(2)H_(5))_(2)NH and CH_(3)NH_(2)` (ii) Arrange the following compounds in a decreasing order of `pK_(b)` values: `C_(2)H_(5)NH_(2), C_(6)H_(5)NHCH_(3), (C_(2)H_(5))_(2) NH and C_(6)H_(5)NH_(2)`
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