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molecular weight and dilution
Hello,
How does this math work?I have 100g (powder) of an ingredient that has a molecular weight of 180.00 g/mol
I want to dissolve this ingredient in water to make a 50% solution. How many milliliters of water do I need?Thank you. -
11 Replies
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Hi!
To obtain a 50% solution, just add the same amount of water (in grams). See, if you’ve decided to use all 100g of powder, add 100g of water and that’s enough. There is not much reason to use another measurement scale in this case.
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Thank you for the reply. I misread the molecular wight of this product. It’s 1310.0 g/mol. What do you suggest?
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% concentration is usually referring to weight-% (unless it’s ethanol, then it might as well be volume-%). Hence, it doesn’t matter which molecular weight your product has. If you were to make an X molar solution, then it would… but you’re not, are you?Anyway, a 50% solution usually means (most likely also in your case) that the final solution contains 50 weight-% of a solid: 200 g solution contains 100 g solvent and 100 g solute. Mind, the resulting volume may not be what you’d expect it to be (namely 200 ml)! Depending on what you dissolve, there can be more or less no increase in volume (often with inorganic salts where some even cause a minute shrinkage of the volume) or an increase more or less corresponding to the density of the solute (mostly nonionic solutes). Here, many mixtures don’t have a linear concentration-density (or volume) correlation (ethanol as a prominent example). -
Same!Let me try to explain…100g of powder + 100g of water = 200g (solution)(we have 50% powder and 50% water; 100g of each)Molecular weight doesn’t matter in this situation, we’re talking about weight itself, not volume, density or any other scale. You can just ignore the “milliliters” because we’re using grams.So, you just need to weigh the amount of powder you want and the same weight of water (in grams!). Example:- In a laboratory, you can use the balance to weigh 10g of powder.- Then, you weigh 10g of water.
- Mix both.- You now have a final product (20g) that consists of a 50% solution (half is powder and half is water)Sorry if your question is different from what I understand, but if you use the same unit of measurement (grams), there is no need to deal with molecular weight…
Let me know if there’s anything else in your question that I should consider (:
P.S. As Pharma honorably pointed out, final weight may vary. To make it simpler to understand, don’t get hung up on it if your question is just about how to make the solution and not about its final weight/volume
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Thank you so much, everyone!
This is great help. I’ve never dealt with any cosmetic products. I bought a bunch of ingredients. I’m trying to conserve usage while formulating my beginner trials.
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TeslaPilot said:I’m trying to conserve usage while formulating my beginner trials.
Hello,
Are you trying to conserve your ingredients by making solutions so you can use smaller amounts when you make batches? If so this might create an issue (depending on what the ingredient dissolved is) with microbes growing in solutions if you try to store these for extended periods of time.
If you’re trying to store the solutions you might want to add a preservative to them to stop this.
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Why not freeze the excess until you need it?
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Pharma said:Why not freeze the excess until you need it?
I didn’t think of that but this is smarter. Having to thaw out the ingredients would be a bit annoying but I guess that’s better than having a preservative in there that might not be compatible with all formulas.
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Disposable ice cube plastic bags? :smiley:Or use more eco-friendly silicone moulds, also available for mini-cubes… all you have to do there is refilling them into a jar once frozen.
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@Pharma
I like that idea, if I ever need to do this I’ll keep that in mind. -
BTW is you freeze powders and other solids: Thaw them thoroughly (an hour or two) prior to opening the container or moisture gets in. It may pay off to put a smaller amount into a separate jar or two (faster thawing and less freeze-thaw cycles).
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