Author Topic: Dilution ratio  (Read 1050 times)

Offline mainebrewer

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Dilution ratio
« on: July 25, 2013, 11:39:44 AM »
Need some math assistance here.
If I have 32 oz of phosphoric acid 85% concentration, how do I calculate the amount of water to dilute the 85% to some other percentage?
I'm having a brain cramp here!
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Online morticaixavier

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Re: Dilution ratio
« Reply #1 on: July 25, 2013, 11:48:27 AM »
assuming we are talking about volumetric %

85% of 32 is 27.2. (Total Volume X %pa) = volume pa)
if you want 75% you need to have

Total Volume X .75 = 27.2

so total volume = 27.2/.75

so 36.266

so add 4.266 oz water and you have 75% concentration.
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Offline erockrph

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Re: Dilution ratio
« Reply #2 on: July 25, 2013, 12:28:58 PM »
volume A x concentration A = volume B x concentration B

Say you want to make 10 mL of a 8.5% concentration:

10 * 8.5 = x * 85 - solve for x

(10 * 8.5)*85 = x

You would need 1 mL of your concentrated solution to make 10mL of your dilute solution.
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Offline ynotbrusum

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Re: Dilution ratio
« Reply #3 on: July 25, 2013, 12:50:35 PM »
You math guys!  My problem is once I have solved for X, I don't have a container with the gradients needed!
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Online morticaixavier

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Re: Dilution ratio
« Reply #4 on: July 25, 2013, 12:51:52 PM »
You math guys!  My problem is once I have solved for X, I don't have a container with the gradients needed!

what's the trouble? are you trying to measure out tenths of a ml? you can probably find an appropriately graduated syringe at the drug store.
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Offline ynotbrusum

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Re: Dilution ratio
« Reply #5 on: July 25, 2013, 12:57:42 PM »
Just kidding - but 4.266 ounces is just going to have to be a heavy 4.25 ounces!
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Re: Dilution ratio
« Reply #6 on: July 25, 2013, 01:02:12 PM »
Just kidding - but 4.266 ounces is just going to have to be a heavy 4.25 ounces!

ahh yes. well we do the best we can. easier if you use metric.

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Offline kramerog

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Re: Dilution ratio
« Reply #7 on: July 25, 2013, 01:05:02 PM »
Generally chemicals when indicated as being a certain % concentration are in weight %.  ABV is somewhat of an aberration.

Thus
mass A x conc A = mass B x conc B.

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Offline mtnrockhopper

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Re: Dilution ratio
« Reply #8 on: July 25, 2013, 01:37:29 PM »
You can measure water by weight too. 4.26 oz (weight) = 4.26 oz (volume)
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Re: Dilution ratio
« Reply #9 on: July 25, 2013, 01:57:48 PM »
You can measure water by weight too. 4.26 oz (weight) = 4.26 oz (volume)
only at 39*f
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Re: Dilution ratio
« Reply #10 on: July 25, 2013, 02:00:42 PM »
You can measure water by weight too. 4.26 oz (weight) = 4.26 oz (volume)

Only at 4°C, and only if we're talking about avoirdupois fluid ounces. At 20°C one US customary fluid ounce of water has a mass of 1.041 avoirdupois ounces.

Anyway, the problem with solutions is that mass/volume don't usually scale linearly with concentration. If it's important to get a precise result, you'll need to look up a table for that particular solute/solvent.
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Offline ynotbrusum

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Re: Dilution ratio
« Reply #11 on: July 25, 2013, 02:18:56 PM »
You can measure water by weight too. 4.26 oz (weight) = 4.26 oz (volume)

Only at 4°C, and only if we're talking about avoirdupois fluid ounces. At 20°C one US customary fluid ounce of water has a mass of 1.041 avoirdupois ounces.

Anyway, the problem with solutions is that mass/volume don't usually scale linearly with concentration. If it's important to get a precise result, you'll need to look up a table for that particular solute/solvent.

Yeah, what he said.
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Offline kramerog

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Re: Dilution ratio
« Reply #12 on: July 25, 2013, 02:28:25 PM »
I checked the CRC handbook.  I have gravity and other properties up to 80% lactic acid.  D'Oh!  Anyway the gravity at 85% should be 1.19 g/l based on interpolation of 80% lactic acid and pure lactic acid.
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Offline mtnrockhopper

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Re: Dilution ratio
« Reply #13 on: July 25, 2013, 02:42:10 PM »
You can measure water by weight too. 4.26 oz (weight) = 4.26 oz (volume)

Only at 4°C, and only if we're talking about avoirdupois fluid ounces. At 20°C one US customary fluid ounce of water has a mass of 1.041 avoirdupois ounces.

Anyway, the problem with solutions is that mass/volume don't usually scale linearly with concentration. If it's important to get a precise result, you'll need to look up a table for that particular solute/solvent.
Eh, it's an art.
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Re: Dilution ratio
« Reply #14 on: July 25, 2013, 05:31:14 PM »
That's what you always say! ;)
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