The ionic strength () of an solution (important in colloid science) is a measure

Question

The ionic strength () of an solution (important in colloid science) is a measure of the concentration of ions present in solution 2 where c, is the molar concentration of the ion i (mol/L), z, is the charge number of that ion, and the sum is taken over all ions in the solution. Create a spreadsheet to calculate ionic strength for a user that inputs concentration and the salts present in their solution. Demonstrate your spreadsheet works by calculating the ionic strength of a 4 mM MgSO solution. Calculate the ionic strength of a PBS buffer that is contains 1.44 g/L of potassium phosphate monobasic (anhydrous), 90.0 g/L sodium chloride, and 7.950 g/L sodium phosphate, dibasic anhydrous). Note: the less the user has to input the better.

Explanation / Answer

I will calculate the ionic strenght for a solution 4 mM MgSO4

the first thing to do is to write the dissociation equation of it

MgSO4 ===== Mg+2 + SO4-2

it is a 1 to 1 reaction so we dont need to perform stoichiometrical calculations, the concentration of MgSO4 is the concentration of each ion.

as you can see each ion have a charge of +/- 2 this is the letter "i"

now apply the equation

I = 1/2 * ([Mg] * 22 + [SO4]*-22)

concentration must be M so 4mM divided by 1000 will be 0.004 M

I = 1/2 *( 0.004 * 4 + 0.004* 4 ) = 0.016

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