Sulfuric Acid; Please Check My Math.

[Sean Clark]

I would like someone to double/triple check my math.

I posted this earlier in the Reef Hobbyist Experiments and Research Forum but it has not received the attention that I think that it will here; so I am going to try, try, try again.

I would like to make a 0.02N / 0.01M solution of sulfuric acid.

This is where I am at so far:
Starting with a 98% ACS sulfuric acid concentration with a normality of 36.8, I was going to first make a 1000ml solution at 1N by adding 27.2ml to 972.8ml of RODI water.
I was then going to take that 1N solution and dilute it with 49 parts RODI and 1 part 1N sulfuric acid solution to get a 0.02N solution.
So 20ml of 1N solution to 980ml RODI for 1000ml to make a 0.02N solution.

Am I thinking about this correctly or am I missing something super obvious?

Thanks for any input.

 

[Randy Holmes-Farley]

The only issue is that 27.2 mL conc. sulfuric plus 972.8 mL water may not make 1 L, but less than 1 L.

What level of accuracy is needed here?

 

[Sean Clark]

The only issue is that 27.2 mL conc. sulfuric plus 972.8 mL water may not make 1 L, but less than 1 L.

What level of accuracy is needed here?

I wanted relatively high accuracy. +- 1٪ at most. I am confused why the first dilution would make less than one liter.

 

[Randy Holmes-Farley]

I wanted relatively high accuracy. +- 1٪ at most. I am confused why the first dilution would make less than one liter.

There is a volume contraction on mixing sulfuric acid and water. The sulfuric acid interacts so strongly with water that it pulls the water in tighter than water is generally by itself.

To ways around this are to either use a volumetric flask for the mixing so you add water to a fixed final volume instead of adding a fixed volume, or to determine how much of each of sulfuring acid and water are actually in a 0.1 N solution, and add those together (accounting for the bit of water in your initial sulfuric acid).