I’m trying to precipitate out FePO4.

Following the reaction: H3PO4 + FeCl3 = FePO4(s) + 3HCl
I reacted phosphoric acid to ferric chloride, and according to the reaction, there should be a precipitate. But I haven’t observed a precipitate for the last 3 hours. Is there a need for a buffer to stop the pH changing due to the formation of HCl?

P.S. This not a homework, it's a project.

I do not think there are many chemistry tutors on this website. I have noticed that most chemistry questions do not get answered. I hope that you do well on your project though! :)

I can not do

What do you mean there are many chem tutors on this site? Ridculous. Most chem questions are answwered within a few hours.

I would not be as concerned with the HCl formed from the reaction as I would from the initial H3PO4. FePO4 is soluble in acid. With strong H3PO4 complexes can form AND the H3PO4, although a weak acid, is relatively strong for the first ionization. I would prepare FePO4, if that is the project, with Na3PO4 and FeCl3.

To determine if a buffer is necessary in your reaction to precipitate out FePO4, it's helpful to understand the role of a buffer in maintaining a stable pH.

In your reaction, when H3PO4 reacts with FeCl3, FePO4 (iron(III) phosphate) and HCl are formed. The formation of HCl can contribute to a change in pH, potentially affecting the precipitation of FePO4.

A buffer is a solution that resists changes in pH when acid or base is added. It typically consists of a weak acid and its conjugate base (or a weak base and its conjugate acid). Buffers work by neutralizing any added acid or base, minimizing the change in pH. Adding a buffer to your reaction mixture can help maintain a relatively constant pH, which may promote the formation and precipitation of FePO4.

So, to answer your question, the need for a buffer depends on the initial pH of your reaction mixture and the desired pH range for the precipitation of FePO4. If you suspect that the pH change due to the formation of HCl might be interfering with the precipitation, using a buffer could be beneficial.

To prepare a buffer, you would typically choose a weak acid with a pKa value close to the desired pH range. Phosphoric acid (H3PO4) itself can act as a weak acid and form a buffer system when mixed with its conjugate base, such as monosodium phosphate (NaH2PO4). By adjusting the ratios of H3PO4 and NaH2PO4, you can create a buffer solution with a specific pH.

Here are the general steps you can follow to prepare a buffer:

1. Determine the desired pH range for the precipitation of FePO4.
2. Choose a weak acid with a pKa value close to the desired pH range. In this case, phosphoric acid (H3PO4) can be used.
3. Select a conjugate base for the weak acid. For phosphoric acid, monosodium phosphate (NaH2PO4) can be used.
4. Calculate the appropriate ratios of weak acid and conjugate base to achieve the desired pH using the Henderson-Hasselbalch equation (pH = pKa + log([A-]/[HA])).
5. Prepare the buffer solution by mixing the calculated amounts of weak acid and conjugate base with the appropriate amount of water.

If you decide to use a buffer, it's important to note that the exact pH range for FePO4 precipitation may vary depending on the specific conditions and concentrations of reactants in your experiment. Therefore, you may need to do some experimentation and optimization to find the most suitable buffer system for your desired outcomes.

Remember to exercise caution when working with chemicals and follow appropriate safety procedures. If you have any doubts or concerns, it's best to consult with a knowledgeable mentor, instructor, or professional.