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| |  Posted 7/10/2007 12:36:25 AM | |
| Junior Member
 
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| | Hi, I would like for someone to explain the difference between percent by weight and percent by volume. The bleach we use is 12.5 percent by weight and 15 percent by volume. I have asked the difference, but I can't get anyone to explain . Thanks Nick |
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| | | Posted 7/10/2007 2:53:18 AM | |
| Supreme Being
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| | Nick, I am going to have a go at explaining it. It all comes down to relative density(mass/volume). In one litre of the solution there is 150ml of Hypo. If the one litre was all water it would weigh 1kg. However that 150ml of hypo has a different weight to water. Therefore we have 850ml of water weighing 850grams and 150ml of hypo which because the hypo has a lower mass/volume relationship than the water its 150ml does not weigh 150 grams. In this case the 850grams of water weighs 88% of the total , therefore the hypo weighs 115 grams or 12 % of the total. Hope this helps. Regards Terry F |
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| | | Posted 7/10/2007 2:58:48 AM | |
| Supreme Being
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| | Sorry, i used 12% instead of 12.5 but the principle is the same. |
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| | | Posted 7/10/2007 6:40:33 PM | |
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Supreme Being
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| | Weight % and volume are the same only if in nearly pure water where 1 liter = 1 KG. The density of hypo is 1.159 - 1.170 Lets assume 1.165. A liter of hypo weighs 1,165 grams. Using % volume you assume it weighs 1,000 grams which it does not. If you take a 10 ml sample and dilute it in chlorine demand free water and test for chlorine you get the % by volume result. If you weigh 10 grams and dilute you will end up with the lower % by weight value. This is our old procedure to get % by volume. To do it Std. Methods you would need to make chlorine free, chlorine demand free water: Procedure: 1. Take sample of concentrated hypochlorite that represents contents of tank. 2. Pipet 10 mls of hypochlorite into 1,000 ml volumetric flask A. Bring to volume with DI water and mix. 3. Take 1 ml of diluted solution A and add to 1,000 ml volumetric flask B. Bring up to volume with DI and mix. 4. Titrate 200 mls of solution B on W&T titrator. 5. Percent Cl2 = 10 times mg/l titration. 1.1 mg/l titration = 11% hypochlorite solution. |
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| | | Posted 7/14/2007 12:05:24 AM | |
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| | Thanks for the replies I see what the difference is now. Nick |
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