HYDROLYSIS OF THE CARBONATE ION
(A then
Submitted by: Noojin Walker and James Mintz, Pensacola Junior College, Pensacola, Fla. 32504 Tested by:
Willard D. Houston, Wadsworth High School, Wadsworth, Ohio 44281
PREPARATION
Provide 20 ml 0.1 F Cu(NOa)z, 10 ml 0.1 F NaCOa, 10 ml 0.1 F NaOH, 1.0 g powdered CuCOa, three large test tubes marked 1, 2, and 3, respectively. DEMONSTRATION
In test tube (1) pour 10 ml C U ( N O ~ )add ~ ; 10 ml of Na&08. Elicit statements about the nature of the precipitate. To 20 ml of water in tube (2) add 1.0 g of CuCOa. Mix thoroughly. Compare with tube (1). Pour 10 ml of Cu(NO& into tube (3) and add 10 ml of NaOH. Display all three tubes and discuss. REMARKS
Initially most students will assume the blue precipitate in (1) to be CuCO3. Demonstration (2),
however, shows this assumption to be questionable. Furthermore, demonstration (3) produces evidence that the original blue precipitate in (1) is more like Cu(OH),. This could have been formed only as a result of the hydrolysis of the carbonate ion COP
+ HOH = HCOI- + OH-
The questionable possibility of forming copper car-, bonate and the more likely formation of basic copper carbonate has been described by Sneed et al.' Students can be encouraged to predict other similar reactions.
' SNEED,M. C., MAYNARD, J. L.,A N D BRASTED, R. C., "Cornprehensive Inorganic Chemistry," Vol. 11, D. van Nostrand Co., 1954, p. 86.
Volume 47, Number 2, February 1970
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A 119
