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The resulting neutralised (which wasn't actually neutralised due to not realising CaCO3's insolubility) solution between Hydrochloric Acid and Calcium Carbonate, as per balanced equation CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O

turned red litmus paper blue, and universal indicator solution orange (repeated twice).

I performed another reaction between Citric Acid and Calcium Carbonate and I received consistently acidic results. There is a chance I might've mixed up these results though, and the Citric Acid reaction WAS the conflicting one.

I'm wondering if anyone could shed some light on why this might've happened? I'm guessing it can't be due to the insoluble calcium carbonate, as my other reaction didn't have issues.

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  • $\begingroup$ It seems there is several subjective effects involved, affecting results. I suggest to repeat experiments in defined manners, allow establishing of equilibrium, that do measurements before and after filtration of excess carbonate. $\endgroup$ – Poutnik Jun 25 at 4:25
  • $\begingroup$ Make sure you mix the contents well before pH measurements. I would also assume that calcium citrate will be a basic solution (salt of a weak acid with very strong base). $\endgroup$ – M. Farooq Jun 25 at 4:57

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