I'm going to update my reply to your original thread here as you have been starting a new topic nearly everyday on the same line of questions and it's getting hard to follow, so I'm directing my reply back to your original thread here:
Original Reply to Rh Questions
Now some footnotes:
1) As Lou said, be sure you dilute the red-brown sulfuric acid solution with the Rh in it.
2) Add Sodium Hydroxide (NaOH) until the pH reaches 2-3.
3) Heat and add dry baking soda (sodium bicarbonate, NaCO3H) until pH is 6-7.
4) Slight boil or 30 minutes at pH 7 (check a few time to be sure it does not change).
5) Cool and collect Rh(OH)3.
Here are some photos of the various stages of the footnotes above:
1) Red-Brown sulfuric acid:
Please keep track of the amount of sulfuric acid you use. 1 mL of 18.4 Molar 98% H2SO4 (concentrated sulfuric acid) contains 0.0184 moles (18.4 / 1000) of H2SO4.
The equation for lye (NaOH) plus sulfuric acid (H2SO4) is:
2NaOH + H2SO4 --> Na2SO4 + 2H2O
Notice the OH from the lye combines with the two H from the sulfuric acid, this is what changes the pH. Since the above equation is balanced, the pH is neutral or pH 7.
Now some math:
2NaOH =~ 80g
therefore we need 80 grams of lye per mole of sulfuric acid to make the pH 7.
Since we know the molarity of concentrated 98% H2SO4 is 0.0184
moles per mL we can theoretically determine how much lye to add to make the pH 7 by multiplying 80 times the number of milliliters of H2SO4 we used to dissolve the Rh.
For 20 mL of H2SO4
80 g/mole x 20 mL x 0.0184 moles/ mL = 29.44 g of NaOH to neutralize 20 mL of H2SO4 to pH7.
The solubility of lye is about 1.1 grams per milliliter, so we need to add an amount of water in mL equal to the weight of the lye required or about 30 mL to keep everything dissolved. Add the acid to the water, not the water to the acid.
The directions given state to bring the pH to around 2-3 with lye so we won't need the entire 29.44 grams of lye, this number was calculated to give you an idea of how much lye you would need at an absolute maximum when performing the reaction.
Here's a photo of the pH tests at various stages of the reaction:
The pink strip on the left is the original test of the acidic diluted red-brown solution.
The orange strip on the right is the correct color of the strip after approximately 20 grams of lye was added to the diluted red-brown solution. I started with 20mL of concentrated red-brown solution. You can see the diluted solution after the lye additions in the background of the photo above.
Here's the solution boiling while I'm adding the sodium bicarbonate (NaCO3H):
and the photo below shows the pH test at the finish point of the neutralization reaction adding the NaCO3H:
The test strip (yellow-green) on the extreme right of the photo is the one after the bicarbonate additions are completed.
Only a few pinches of bicarbonate were required to complete the neutralization.
If you find you have added too much lye or bicarb, simply add a drop of 1 molar sulfuric acid solution to bring the pH back down.
Once the pH stays at 6-7 for 10 minutes of boiling, stop adding NaCO3H and gently boil another 30 minutes before cooling.
More later.
Steve