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I am a student in my last year of high school and currently making a research on how to find sulfites in dried fruits. I've collected data and different methods online and combined few of them into one. In my method I use hydrogen peroxide and barium chloride to create a white precipitate (result should be barium sulfite).

But the problem is that I never get any precipitate. During my research it mentioned that I was to leave the dried fruit in distilled water over night (I used dried apricots). I had 26g, 30g, 40g of dried apricot in 100mL of distilled water. Once done, I filter out all of the liquids into a different beaker. Then filter it using filter paper. Once done I separate them into different beakers to test. And this is where I find the problem, I've done 6 trials so far, and all 6 have failed. Because I don't know what amount of H2O2 or what amount of the concentration I need to put into the apricot liquid for it to properly react, or for how long I should leave it in for it to react (I've waited 3 and 5 minutes). I'm then supposed to drop a single drop of barium chloride into the solution to produce the white precipitate. But so far I haven't gotten any sign of any precipitate. I've tried different amounts of H2O2 (1mL, 5mL, 10mL, 15mL, 20mL & 25mL with a 35% concentration in the first trials but rest of the trials were with a 3% concentration). Each with a drop of barium chloride. Seeing that they did not react to a drop, I tried to use 5 drops each on the first few trials. Yet I still got no reaction.

Could I get some help or advice please?

Thank you

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The colorimetric method using rosaniline and formaldehyde is more sensitive and it is well documented.

A somewhat safer version of the test (avoiding use of highly dangerous $\ce{HgCl2}$) is documented at MDPI - Open Access Publishing:

"A concentrated pararosaniline stock solution (3.088 × 10 −3 mol/L) was made by dissolving pararosaniline hydrochloride in a 10% aqueous ethanol solution. The concentrated stock solution was used to make... [a] working solution contain[ing] pararosaniline hydrochloride, hydrochloric acid (HCl) and formaldehyde in the molar ratio of 1:1255:125 respectively. For example, a working solution with PRA concentration of 4.68 × 10 −4 mol/L in 25 mL contained 3,790 μL of concentrated PRA stock (3.088 × 10 −3 mol/L), 1,439 μL of 32% HCl, 189 μL of 36% formaldehyde solution and 25 mL with water."

Pararosaniline is available from Sigma-Aldrich, though it seems a bit pricey at ~$US82/25 g; perhaps your school would obtain some for use by yourself and by other students, as you would need perhaps a gram for your experiments.

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