Question

Which is not true about borax ?
A. It is a useful primary standard for titrating against acids
B. One mole of borax reacts with four moles of `HCI`
C. Aqueous solution of borax can be used as a buffer
D. It is made up of two triangular `BO_(3)` units and two tetrahederal `BO_(4)` units

Answer 1

Correct Answer - B
In Borax `(Na_(2)B_(4)O_(7).10H_(2)O)` Among 10 water molecules 2molecules are part of structure i.e. exists as `Na_(2)[B_(4)O_(5)(OH)_(4)]cdot8H_(2)O`

`Na_(2)[B_(4)O_(5)(OH)_(4)]cdot8H_(2)O+2HClto2NaCl+4H_(3)BO_(3)+5H_(2)O`
Methyl orange (`ph=3.7`) is used to detect end point. Aq. solution of borax acts as a buffer, as borax is salt of strong base NaOH & weak acid `H_(3)BO_(3)`.