Why is calcium better than table salt at stopping soap lathering

Why is calcium better than table salt at stopping soap lathering  

People whose houses are built on chalky ground find that their kettles and boilers become lined with a hard scale . We say that the water in the area is hard , meaning that minute amounts of chalk are dissolved in it. The hard layer of scale is chalk that precipitated onto the inside surface of the kettle or boiler during heating. 

Having discussed ionic screening and its effects on the value of y , we now consider the ionic charge z. When assessing the influence of z, we first define the extent to which a solute promotes association, and thus screening. The preferred parameter is the ionic strength I, as defined by 

Worked Example 7.12 Calculate the ionic strength of a simple 1 1 electrolyte, such as NaCl, that has a concentration of c = 0.01 mol dm  

In dynamic electrochemistry (when currents flow) we need to be careful not to mistake ionic strength and current, since both have the symbol I. 

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