To setup the titration:
The process outlined in this post will aid anyone in determining the concentration of pretty much any acid, using any base. You simply need to know the molar masses and the molar relationship/ratio between the acid and base involved, then switch out the values in the formulas included below.
As always: accurately record the masses of the acid, bicarb, and water as you weigh them. This way if something goes wrong, you may not need to start over and you can double check your work.
1. Weigh a quantity of the acid into an appropriate container, I'll use 20g. [Since we will be working w/ molar masses, the weight in grams doesn't really matter. But it can still be easier to work w/ whole numbers.]
2. Get your base ready. Weigh out a quantity of bicarb, double the mass of acid you plan on using should be plenty. You can work with the bicarb dry but I prefer to work with it in solution. It's more accurate to add drop-wise and, in the event that you have a very strong acid, you will have a less violent/dangerous reaction. A 2:1 by mass water:bicarb should be fine.
(I'm using sodium bicarbonate because we're already working w/ a strong acid, and I see no reason to add more danger by using lye. Plus bicarbonate is cheaper and safer to put on skin if needed)
3. Slowly add the base to the acid (it should foam and sizzle a bit), continue to slowly add the bicarb. Give the solution a gentle swirl/stir on occasion to ensure that everything is reacting as intended.
4. Test the PH of the solution as you go, especially as the bubbles and sizzling decrease.
5. Once you reach a PH of 7 (or as close to it as possible), weigh your bicarb solution and the neutralized acid, record their masses.
6. If the bicarb solution was 20g + 40g of DI water and you have 50g of solution left over, then it took 2g of bicarb to neutralize the 30g of H2SO4 solution.
So now we have the data from our titration, and are into the math side of things:
First we need to determine the relationship between the acid and base we are using. To do this I balance (or look up) the equation for the two compounds. Ex:
The two negatively charged hydrogens from the sulfuric acid requires two positive sodium ions from the bicarb in order to balance out/neutralize.
2 NaHCO3 + H2SO4 → Na2SO4 + 2 H2O + 2 CO2
So our molar ratio is 2:1 between the bicarb and the sulfuric.
The basic formula works out like this:
Now let's do this with our numbers:
[mass of bicarb used] ÷ [molar mass of bicarb] = [mol of bicarb used]
[mol of bicarb used] × [molar ratio of acid:base] = [mol of acid neutralized]
[mol of acid] × [molar mass of acid] = [mass of acid in starting solution]
[mass of acid in starting solution] ÷ [starting mass of acid] = [acid concentration]
Good luck to all, and be safe when following these procedures. Skin and eye/face protection is important.
NaHCO3 = 84.007g/mol
H2SO4 = 98.079g/mol
2g NaHCO3 ÷ 84.007 = 0.0238075398 mol
0.0238075398 × 2 = 0.0476150796 mol of H2SO4
0.0476150796 × 98.079 = 4.6700393921g of H2SO4
4.6700393921 ÷ 20 = 0.2335019696
0.2335019696 × 100 = 23.35% concentration of sulfuric acid
Edited by HrVanker, 24 July 2022 - 04:54 PM.