Alka-Seltzer + Soap reaction rate

[chemkid1234]

Hello,

I have seen that adding dish soap to water and then dissolving Alka-Seltzer in the solution causes the reaction rate to slow. Does anybody have any idea as to why this happens?

 

[chemisttree]

The surfactant must coat the tablet and this coating slows the reaction between the solid surface and the water. The tablet is a mix of bicarbonate and citric acid. These both must dissolve into the water before a reaction can occur. Perhaps the detergent has an affinity to one of reactants, likely citric acid, and forms a weak coating over it.