Answers to Problems of the A Groups
457
(d) Saturate a KOH solution with CO 2 gas, then evaporate off water
K
+ + OH + CO 2 -» K
+ + HCO,
(e) Heat a mixture of solid NH 4 C1 and CaO [or Ca(OH) 2 ] in generator of Figure
27-2b, or add NaOH solution to NH 4 C1 in generator of Figure 27-2a, and warm
Dry NH 3 with solid CaO, NaOH, or CaCl 2
2NH 4
+ + 2C1- + CaO -> 2NH 3 t + Ca
2+ + 2C1~ + H 2 O
(f) Add NaOH to a CuSO 4 solution, and filter off the precipitate NH 3 cannot be
used.
Cu
2+ + 20H- -» Cu(OH) 2 |
(g) Divide a given volume of H 2 SO 4 in half Neutralize one-half with NaOH,
then add the remaining half of H 2 SO 4 to the neutralized solution Evaporate off the water
2Na
+ + 2OH- + 2H
+ + SO 4
2
- -> 2Na
+ + SO 4
2 - + 2H 2 O
2Na
+ + SO
2 ~ + 2H
+ + SO
2 ~ -» 2Na
+ + 2HSOr
(h) Heat Al metal with excess of S, and distill off excess S A1 2 S 3 will not precipitate
from solution with H 2 S
2A1 + 3S 4, A1 2 S 3
(i) Add excess NH 3 to a FeCl 3 solution Filter off the precipitate of Fe(OH) 3 , then
heat it vigorously
Fe
3+ + 3NH 3 + 3H 2 0 -+ Fe(OH) 3 | + 3NH 4
+
2Fe(OH) 3 4, Fe 2 0 3 + 3H 2 O|
0) Add HC1 or NaCl solution to solution of Hg 2 (NO 3 ) 2 , then filter off precipitate
Hg 2
2+ + 2C1
(k) Add H 2 SO 4 to CaCO 3 using generator of Figure 27-2a Dry the CO 2 with P 4 O 10 ,
SiO 2 , concentrated H 2 SO 4 , or dry ice
2H
+ + SO 4
2 + CaCO, -» CaSO 4 | + H,O + CO 2 |
(1) Add HBr to MnO 2 or KMnO 4 Warm Condense Br, in very cold container
Perform under a hood
MnO 2 + 4H
+ + 2Br- -* Mn
2+ + Br 2 t + 2H 2 O
(m) Add excess metallic Zn to AgNO 3 solution to reduce Ag
+ , then add excess dilute
HNO 3 to dissolve the excess Zn (Ag will not dissolve) Filter off the Ag
Zn + 2Ag
+ -^ Zn
2+ + 2Ag
8H
+ + 2NO 3 - + 3Zn -H> 3Zn
2+ + 2NOt + 4H 2 O
(n) Vigorously heat KH 2 As0 3
KH 2 AsO 3 4, KAsO 2 + H,Ot