Common Ion Effect -- (ref. Shakhashiri v3 p155 -- modified LCM)

[ --------------- Variation (LCM)

  + Use 3 tall-form 1.8L cylinders as reaction vessels.
  + Instead of CaCO3 use 20g NaHCO3 dissolved in about 100 mL H2O.
  + Add squirt of dish soap to each 1.8L cylinder to make foam.
  + Provide large lasagna dish to catch foam overflow.

  + Three Reactions of 20g NaHCO3 with 200 mL each of
    - HCl 2M
    - HAc 2M
    - HAc 2M (and) NaAc 2M (25g) ---------------------- ]

Compare reaction of CaCO3 (25g) with 100 ml each of:

1.  HCl 2M 			[H+] = ~2M

2.  Acetic acid (HAc) 2M 	[H+] = ~0.006M

3.  HAc 2M + NaAc 2M 		[H+] = ~0.00002M

	(BZS - 27g NaAc + 80 ml 2M HAc, dilute to 100 ml)
	(LCM - 33 ml 6M HAc (or equivalent) + 27g NaAc, 
	 dilute to 100 ml)

* Rate of reaction increases as [H+] increases. 
* Additional acetate (common) ion in case 3 shifts equilibrium to 
	undissociated HAc. Therefore [H+] decreases for case 3. 
* Use of insoluble carbonate increases contrast of reaction rates.
* Try universal indicator (BZS) or dish soap solution (LCM) for effect. 
* Increase scale for larger classes (LCM).
* See BZS for additional information. 
===================================================================
BZS .. author "Chemical Demonstrations" Bassam Z. Shakhashiri, 
		Univ. Wisconsin Press
NaAc . sodium acetate trihydrate
HAc .. acetic acid
LCM .. Lonnie C. Martin, UCBerkeley, College of Chemistry Demo Lab