Question

Complete the following reactions:
${\mathrm{Cr}}_2\left({\mathrm{SO}}_4{)}_3\right(\mathrm{aq})+6\mathrm{NaOH}(\mathrm{aq})\to 3{\mathrm{Na}}_2{\mathrm{SO}}_4(\mathrm{aq})+$
${\mathrm{Cr}}_2\left({\mathrm{SO}}_4{)}_3\right(\mathrm{aq})+6{\mathrm{NH}}_4\mathrm{OH}(\mathrm{aq})\to$$+2\mathrm{Cr}\left(\mathrm{OH}{)}_3\right(\mathrm{ppt}.)$

• A. 3$(N{H}_4{)}_{2}S{O}_4$(aq)
• B. 3$(N{H}_4{)}_{2}S{O}_4$(s)
• C. 2$Cr(OH{)}_3$(ppt.)
• D. 2$C{r}_2{O}_3$(ppt.)

Answer 1

Answer: (A), (C)

The correct options are
A 3$(N{H}_4{)}_{2}S{O}_4$(aq)
C 2$Cr(OH{)}_3$(ppt.)

In most of the ionic salts, the cationic identification is commonly done by using two water soluble bases (alkalis), i.e. $NaOH$ and $N{H}_{4}OH$.
The given reactions represent identification of $C{r}^{+3}$ ion.
$C{r}_2\left(S{O}_4{)}_3\right(aq)+6NaOH(aq)\to 3N{a}_{2}S{O}_4(aq)+2Cr(OH{)}_3(greenppt.)$
$C{r}_2\left(S{O}_4{)}_3\right(aq)+6N{H}_{4}OH(aq)\to 3(N{H}_4{)}_{2}S{O}_4\left(aq\right)+2Cr\left(OH{)}_3\right(greenppt.)$