Quote:
Originally Posted by ColeMan
I've got a scale that will weigh grams to the tenth - not hundredth. Do you think I need to invest in a different scale? I'm sure it's pretty important to get the .70g right on the money - .75 would screw things up pretty good, huh?
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Your starting solution can always be a larger volume and this would narrow down the possible error.
Instead of adding 0.70 grams of KNO3 to 429 mL of distilled water; you can double it and add 1.40 grams of KNO3 to 858 mL of distilled water.
0.70 grams of KNO3 in 429 mL of distilled water is 1000.72 ppm of NO3 and so is 1.40 grams of KNO3 in 858 ml of distilled water.
Let's check the possible error factor.
Let's say that your 1 decimal place scales actually gave you 0.75 grams instead of 0.70 grams. You have 1072.2 ppm then. That's an error of 7.1%
Now let's use the doubled amount and your scales gave you 1.45 grams instead of 1.40 grams. You then have 1036.46 ppm. That's an error of only 3.6%
Then you have to ask yourself, "is this good enough for your use?" Maybe or maybe not.
You can play around with numbers by hand or on the fertilator, Chuck's Windows based fert calculator or any other calculator to make your own 1000 ppm solution that will be close enough for your use.
Let's try one more example. You use 1 liter of distilled water for your solution. You weigh out 1.6 grams of KNO3 and that gives you 981.28 ppm. If you weight out 1.7 grams of KNO3 and that gives you 1042.61 ppm. Now let's say you figure out a way to weigh very close to 1.63 grams. That will give you 999.68 ppm or an error of 0.03%. That's very good!
It goes without saying that you can do the same kind of number crunching to get a very close to a 1000 ppm solution of PO4 too.
Does all of this babbling make any sense. I'm trying to help you use the scales that you have. One of the reasons that I chose 0.70 grams for making these solutions is for the people that have scales like yours that weigh to one decimal place to give you and them a very good chance of making good reference solutions. If you used scales that are accurate to 2 or 3 or more decimal places. That would be even better.
Also, you can use another starting solution other than a 1000 ppm one. It just boils down to the math and how accuract that you can measure these dilution solutions.