Calculate the number of millilitres of Ammonia, (aq) solution (d=0.986 g/mL) containing 2.5% by weight Ammonia , which will be required to precipitate iron as Fe`(OH)_(3)` in a 0.8 g sample that contains `50% Fe_(2)O_(3)`

Options

A. 0.344 mL
B. 3.44 mL
C. 17.24 mL
D. 10.34 mL

Answer

D

Explanation

The precipitation reaction is : `Fe ^(3+) + 3 NH _(3) + 3 H _(2) O to Fe ( OH ) _(3) + 2 NH _(4) ^(+)`
moles of `Fe _(2) O _(3)` in sample `= ( 0. 80 xx 0. 5)/( 160) = 2. 5 xx 10 ^(-3) ,` mole of `Fe ^(3+)= 2 xx 2. 5 xx 10 ^(-3) = 5 xx 10 ^(-3)`
Molaritiy of ammonia, `M _( NH _(3))= ( 0. 986 g // mL xx 1000 mL //"litre" xx 0. 0 25)/( 17) implies M _( NH _()) = 1. 45`
`3 xx` moles of `Fe ^(3+)=` moles of `NH _(3) implies 1. 45 xx V ` (in L): `V = ( 3 xx 5 xx 10 ^(-3))/( 1. 45 ) = 10. 34 xx 10 ^(-3) L or 10 . 34 mL`