Help me dilute a solution to a desired level

October 31, 2015 6:40 AM

I have a solution of (14%) sandalwood essential oil in jojoba oil. I also have pure jojoba oil. I would would like to end up with a 15 ml solution of 2% sandalwood in jojoba oil. How do I get there?
posted by entropicamericana to Grab Bag (8 answers total)

Fill your 15ml vial 1/7th of the way (2.14ml) with your 14% solution. Then fill the rest of the way with pure jojoba oil.

It might be easier to make a larger batch, depending on how precise you want the percentages to be.
posted by 256 at 6:47 AM on October 31, 2015 [1 favorite]

Response by poster: Crap, I shouldn't have posted this early... I meant 25 ml!
posted by entropicamericana at 6:52 AM on October 31, 2015

Exactly the same for any size. Fill up your vial 1/7th of the way with the 14% solution and then the rest of the way with the pure jojoba. 1/7th of 25ml is 3.57ml.
posted by 256 at 6:56 AM on October 31, 2015 [1 favorite]

You can use the formula C(1) x V(1) = C(2) x V(2) to determine how much sandalwood to include in the final solution and then make up the rest of the volume with jojoba oil.

In this case, initial sandalwood oil concentration (C1) is 14%, final concentration (C2) is 2%, and final volume is 25mL (V2). 14% x V(1) = 2% x 25mL

Solving for V(1) = (2% x 25mL) / 14%

So you'll need 3.57mL of the 14% solution and 21.43mL of jojoba oil.
posted by zenzicube at 6:57 AM on October 31, 2015 [2 favorites]

Response by poster: Thanks, chemistry and math are definitely not my subjects. Maybe I would have paid attention more if I knew how expensive pre-made beard oil is!
posted by entropicamericana at 7:00 AM on October 31, 2015 [1 favorite]

Best answer: Unless you have a micropipetter, it will be easier for you to make a larger stock of 2% sandalwood oil and then just pour some of it into the 25 ml container.

Living in America, you may not even have any metric measuring stuff. Use any unit you like, and just dilute 1:7. If you use tablespoons, 1 tbsp of 14% solution plus 6 tbsp of jojoba oil will give you about ½ cup of 2% solution. Decant some of this master stock into your 25 ml container, and then store the remainder somewhere cool and dark in a sealed jar.

Trying to measure accurately enough to do your dilution straight into the 25 ml container would probably not work unless you have access to (basic) laboratory equipment. However, the above method is equally accurate and can be done with stuff you probably already have.
posted by Anticipation Of A New Lover's Arrival, The at 7:40 AM on October 31, 2015 [3 favorites]

This would be much easier to do by weight and measuring out six teaspoons. I like this scale.
posted by supercres at 8:28 AM on October 31, 2015

Depending on where you live, you might have access to purchasing disposable syringes (1ml, 5ml, 10ml, 20ml), which should be good enough to measure these volumes.

Here is the formula rephrased :

(% I have) x (Volume in ml I need to find out) = (% I want) x (Volume in ml I want)

(all 'wants' on one side of the equation...)

then fill in the numbers...

(14) x Vol I need to find out = 2 x 25

Vol I need = 50/14 = 3.57 ml

To make the final solution ready for use: take 3.57 ml of the 14% solution and add 21.43 ml (i.e. 25 - 3.57) of pure jojoba oil.
posted by xm at 11:51 PM on October 31, 2015