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Reducing the pH of sodium lactate to get lactic acid
If we add 5% active sodium lactate to water and reduce the pH with citric acid to 3.5. will it function as 5% lactic acid at pH 3.5?
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22 Replies
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If you took a strong acid such as hydrochloric or sulfuric acid: Yes, absolutely.Citric acid on the other hand is only slightly more acidic. You will be able to achieve a pH of 3.5 but that’s within the buffering ranges of lactic acid and two out of three carboxylic acid groups of citric acid. Such a blend will not perfom the same as a buffer of lactic acid plus sodium lactate. I don’t know if it’s stronger (a lot more total acids) or weaker (better buffering). -
Thanks
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Why don’t you just add lactic acid instead?See, if you use an acid to turn a salt into one, you end with a salt… Either combine lactic acid with sodium lactate or use ~5% lactic acid and set the pH to 3.5 using sodium hydroxide.
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@Pharma i am using lactic acid. I just wanted to know if i reduce the pH of salt, does it function as acid or not.
Now if it is so, how does preservatives like sodium benzoate and potassium sorbate at low pH function as there acid?
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Preservatives are used in their salt form because of solubility. Were the acids water soluble, then using them as salts would be stupid. So many people take the salts, mix them in, and lower the pH with whatever to turn the preservatives into active acids. The amount used is also way smaller than 5%
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@Pharma yes but my point is about percentage in any quantity.
For example
If we take two formulas that are the same, add 0.3% sodium benzoate in one formula and 0.3% benzoic acid in another formula, if we adjust the pH to 6, only 1.6% of preservative would be in acid form in both, and if we adjust the pH to 4, 61.3% of preservative would be in acid form.
Am i correct in this?If yes, it means the availability of benzoic acid or sodium benzoate in acid form depends on final pH, not the form you have added it.
So why availability of lactic acid or salicylic acid in acid form is depended on the form you have added it and not the final pH?
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Theoretically, you’re correct (I didn’t do the maths but I sounds about right).The ‘problem’ with larger quantities is:Add ‘active acid’ -> increase pH with strong base = part ‘active acid’ & part ‘active salt’Add ‘active salt’ -> lower pH with strong acid = part ‘active acid’ & part ‘active salt’ & part saltAdd ‘active salt’ -> lower pH with weak acid = part ‘active acid’ & part ‘active salt’ & part acid & part saltThis may not be an issue when the ‘active’ is a preservative at 0.2% but in case of 5% sodium lactate and citric acid the electrolyte load gets huge (sodium lactate plus sodium dihydrogen citrate) and you’ll also have ‘active’ citric acid, not just ‘active’ lactic acid.
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Pharma said:Theoretically, you’re correct (I didn’t do the maths but I sounds about right).The ‘problem’ with larger quantities is:Add ‘active acid’ -> increase pH with strong base = part ‘active acid’ & part ‘active salt’Add ‘active salt’ -> lower pH with strong acid = part ‘active acid’ & part ‘active salt’ & part saltAdd ‘active salt’ -> lower pH with weak acid = part ‘active acid’ & part ‘active salt’ & part acid & part saltis this part acid, citric acid in example of reducing pH of sodium lactate with citric acid?
Thanks ????
What about salicylic acid?
If we add 0.29% sodium hydroxide to 1% salicylic acid in water,it solubilizes it but the pH is about 7. If we then reduce the pH with citric acid or lactic acid to 2.9 or 3, would there be about 50% of salicylic acid in acid form? Forgot about inactive acid or salt. -
It will fall out of solution cause salicylic acid isn’t really soluble in water
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@Pharma i have done it and it is stable. Increase the pH with sodium hydroxide did solubilize salicylic acid in water. The ph was high about 7 so i reduced the pH with citric acid back to 3. Now i am not sure if it is in acid form or salt form in pH 3. Any idea?
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At pH 3 and in conjunction with citric acid, most is in salt form and most citric acid is in acid form. Nothing gained here.
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@Pharma what about lactic acid?
Whith which acid instead of citric acid most of salicylic acid would be in acid form?
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No. lactic acid is weaker than citric… Best go with a strong mineral acid such as HCl
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@Pharma thanks ????
Which one is stronger acid? Salicylic acid or citric acid?
In a comparison at same percentage citric acid reduced the pH of a Shampoo more than salicylic acid. -
Salicylic is stronger by pKa but poorly soluble and has a lower ‘charge density’ (1 M salicylic acid gives less acid that 1 M citric acid).
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@Pharma is it because of charge density that 1 M salicylic acid gives less acid that 1 M citric acid?
If yes then what does it do that is is considered strong acid than citric acid?
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Salicylic acid carries one carboxylic acid group, citric acid has three. Under physiological conditions, citric acid is ‘twice as acidic’ than salicylic acid or, in other words, 1 M citric acid is 2 N whilst 1 M salicylic acid is 1 N.
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@Pharma does having less carboxylic acid group mean Stronger acid?
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No, the carboxylic group is the acid part of the molecule
. Meaning that one molecule citric acid carries three a acids = more acid per mol and more acid per gram. It doesn’t make it a stronger acid… quite the opposite: the second acid is fairly weak and the third very weak (due to increasing charge). -
@Pharma got it ????????.
Just didn’t get this part that what makes an acid stronger or weaker.
Does less chare make an acid stronger or what makes it? -
Naw, the structure determines how strong an acid is (the value used is the pKa). However, if a molecule carries more than one acid functionality, each additional one has a lower strenght. Citric and phosphoric acid with three acid groups each has three different pKa values for ‘pronon’. This is due to an increased charge once the first functional group is deprotonated, the created negative charge reduces the acidity of the other remaining ones and so on.
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Pharma said:Naw, the structure determines how strong an acid is (the value used is the pKa). However, if a molecule carries more than one acid functionality, each additional one has a lower strenght. Citric and phosphoric acid with three acid groups each has three different pKa values for ‘pronon’. This is due to an increased charge once the first functional group is deprotonated, the created negative charge reduces the acidity of the other remaining ones and so on.
Thanks a lot
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