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What should be the pH of 5% lactic in water?
I purchased some samples of lactic acid from different suppliers locally. Mixed 5% solution of each one in water and each one had different pH.
pH 1.2
pH 2.5
pH ~0.5As the local sellers here don’t have much information about what they are selling, just name or some small other details and if they mix think no one will know, i want to know what should be the pH of 5-10% lactic acid in water?
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4 Replies
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How did you measure pH? pH paper won’t work properly and cheap electrodes may not be linear below pH 1-2. Also, concentrated acid solutions will often not match the calculated/predicted value.Feel free to calculate it yourself, HERE‘s how. Simply calculate Ka for lactic acid and the used concentration in molar and use these values instead. -
I have lotioncrafter 90% lactic acid. I mixed 5% and 10% solutions by mass of lactate to water.Mixing 5% lactate to water: 2.50g lactate and 47.5g water. With a 90% lactate solution to start with, I mixed 2.778g lactate(90) and 47.222g additional distilled water. I calibrated both my pH meters and measured the distilled water measured at pH 5.5 and 5.30. After adding the 2.778g lactate(90), got pH 1.9 and pH 1.84.For 10% lactate to water: 5.306g lactate and 47.812g water. Added 3.118g lactate(90) to existing solution (not including calculations here, got messy). Got pH 1.7 and pH 1.68.I am suspicious of the 1.2 and 0.5 because I don’t think lactic acid can get that low at 5% based on my measurements. If it’s that low, I wonder if it could be adulterated with HCl or some other strong acid. How are you measuring pH? -
Pharma said:How did you measure pH? pH paper won’t work properly and cheap electrodes may not be linear below pH 1-2. Also, concentrated acid solutions will often not match the calculated/predicted value.Feel free to calculate it yourself, HERE‘s how. Simply calculate Ka for lactic acid and the used concentration in molar and use these values instead.
Thanks
I was using pocket pH meter. -
Mayday said:I have lotioncrafter 90% lactic acid. I mixed 5% and 10% solutions by mass of lactate to water.Mixing 5% lactate to water: 2.50g lactate and 47.5g water. With a 90% lactate solution to start with, I mixed 2.778g lactate(90) and 47.222g additional distilled water. I calibrated both my pH meters and measured the distilled water measured at pH 5.5 and 5.30. After adding the 2.778g lactate(90), got pH 1.9 and pH 1.84.For 10% lactate to water: 5.306g lactate and 47.812g water. Added 3.118g lactate(90) to existing solution (not including calculations here, got messy). Got pH 1.7 and pH 1.68.I am suspicious of the 1.2 and 0.5 because I don’t think lactic acid can get that low at 5% based on my measurements. If it’s that low, I wonder if it could be adulterated with HCl or some other strong acid. How are you measuring pH?
Thanks
I use pocket pH meter.I was wondering too if they are adulterated.