I think Coke will be safe for the short period you will be touching it. You could also wear rubber gloves. Stomach acid is hydrochloric acid at a pH of 1 and you would not want prolonged contact with that level of acidity. You can get pH papers that measure all the way from 1 to 14, or you can get other kinds that measure very fine differences in particular regions of the scale--like from 1 - 6. You might try local high school or university labs. Maybe an older brother or sister could check for you. I don't think you need a pH meter. Good pH paper should be fine. I did a google search and found this Canadian laboratory supply house that sells pH paper.
Ibuprofen is not very soluble in water, but very soluble in acetone, methanol, and ether.
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