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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: xhandol on December 27, 2014, 04:11:03 PM

Title: ionic strength question
Post by: xhandol on December 27, 2014, 04:11:03 PM

Hello, Nice to meet you everyone~!

I have a question about ionic strength.
I am not familiar with chemistry (I am a mechanical engineering student).

I am using gold colloid and the gold colloid is suspended in HAuCl4 solution.
And I will mix gold colloid (suspended in HAuCl4 solution) with DI-water to adjust number concentration, and I have to keep the solution pH10 and change the ionic strength of the diluted gold particle solution like 0.001, 0.01, 0.1, and 0.2 by adding NaCl.

How do I calculate current ionic strength before adjusting the ionic strength? for example, MW for HAuCl4 is 340 g/mol. and the product information says it is 0.01 % solution, so in 1 g (1 ml), the mol of HAuCl4 is 0.01/340, which is 2.94E-5. Therefore, if I dilute this 1 g of HAuCl4 solution with 99 ml of Di-water. Now, HAuCl4 has 2.94E-7 mol in 1 g of this diluted solution.

After this process, I am not sure about how to calculate the initial ionic strength for the solution.

Thanks sincerely!

Title: Re: ionic strength question
Post by: mjc123 on December 31, 2014, 12:20:27 PM

Ionic strength = 0.5*Σ_iC_iz_i²
where the sum is over all ionic species in solution, C is the molar concentration and z is the ionic charge.
E.g. for 1M NaCl, I = 2*0.5*1*1² = 1M.