Question

How to calculate rate of dissolution?

The problem states, 'A student wants to determine how long it takes to dissolve 51.3 g of common table salt (sodium chloride) in 1L of water by monitoring the solution. It takes 26.7 seconds for the salt to completely dissolve. Determine the rate of dissolution.'

I'm afraid I just don't know where to start with this. Do I just divide the mass by the time to get a rate in grams per second?

Thanks!

Answer 1

You can calculate an average rate of dissolution... I'm guessing it is supposed to be in `"M/s"`.

`"51.3 g NaCl" xx "1 mol"/"58.442 g NaCl" = "0.8778 mols NaCl"`

And since we have `"1 L"` of water, we assume the water volume doesn't rise so that

`color(blue)("rate"("avg")) = ("0.8778 mols NaCl"/"1 L soln")/("26.7 s") = color(blue)("0.0329 M/s")`

So, ON AVERAGE, `"0.0329 mols"` of `"NaCl"` dissolve in `"1 L"` of aqueous solution at this temperature per second.

(This would be the instantaneous rate of dissolution after around `10-12` seconds of waiting, but it depends on the dissolution curve.)