Loptr
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Suggestions for a new lab scale (or you can make an offer)
I have been using a cheap pocket scale for a while now, but it is starting to lose its precision and have a hard time zeroing out. It's time to get a
real scale. I have an Ohaus triple beam scale, which I do for larger weights, but I need something I can use to reliably calculate denities and take
measures for reactions. Some reactions are more sensitive than others, and need pretty accurate measurements of materials.
So do you have a recommendation for the accuracy, resolution, and precision of a typical all-around lab scale, or do you have one for sale? Eventually
I will have a couple of them that will be used for separate things, such as an actual analytical scale, but for now I just need one that is a very
decent one that will accurately take measurements. Are general lab scales typically able to reliably measure <1g or <0.1g amounts, or is that
generally reserved for the more analytical scales? A lot of the scales I see, and I do like Ohaus, but they tend to be have a resolution around 0.1g,
and I just wanted to make sure this would be useful for my intended purposes.
[Edited on 11-4-2016 by Loptr]
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organicchemist25
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Quote: Originally posted by Loptr  | I have been using a cheap pocket scale for a while now, but it is starting to lose its precision and have a hard time zeroing out. It's time to get a
real scale. I have an Ohaus triple beam scale, which I do for larger weights, but I need something I can use to reliably calculate denities and take
measures for reactions. Some reactions are more sensitive than others, and need pretty accurate measurements of materials.
So do you have a recommendation for the accuracy, resolution, and precision of a typical all-around lab scale, or do you have one for sale? Eventually
I will have a couple of them that will be used for separate things, such as an actual analytical scale, but for now I just need one that is a very
decent one that will accurately take measurements. Are general lab scales typically able to reliably measure <1g or <0.1g amounts, or is that
generally reserved for the more analytical scales? A lot of the scales I see, and I do like Ohaus, but they tend to be have a resolution around 0.1g,
and I just wanted to make sure this would be useful for my intended purposes.
[Edited on 11-4-2016 by Loptr] |
I use this scale for very small measurements and it has always worked great. After I am done using it I take it out of the lab and back inside the
house. I dont like leaving anything digital or electronic in the lab except my pH bench meter which I put in a sealed container when finished. My
yields are usually good to real good to the theoretical. One day Ill buy and analytical balance, but Im happy with this one (and the price) 
For the price it isnt bad. It does milligrams. Hope it helps.
http://www.amazon.com/Smart-Weigh-GEM20-Precision-Milligram/...
[Edited on 11-4-2016 by organicchemist25]
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Sulaiman
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I have been using one of the cheap 300g x 0.01g scales for over a year,
Usually accurate to +/- 1 digit vs. Calibration weights, occasionally +/- 2 digit.
There is a 500g x 0.01g version slightly more expensive.
Super accuracy is not necessary, how accurate are your volumetric flasks etc. ?
My workmate has one of the 20 g x 0.001g scales as in the post above, also excellent.
Consider how may times more expensive a 'proper' scales cost, 10 x, 20x ?
cash better used elsewhere in my opinion
P.S. I have spent more on calibration weights than scales.
Incidentally our cheap kitchen scales, 2000 x 1g have no calibration function yet are accurate to 1g even though c7 years old.
Go shopping with Calibration weights in your pocket.
[Edited on 11-4-2016 by Sulaiman]
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Loptr
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I would expect my volumetric flasks to be accurate since they were new from the supplier, so they should be accurate as far as I know. I have never
subjected them to any conditions that would change that. The answer is that I haven't checked, to be honest.
I am looking for a general usage scale right now that I will use to tare the glassware, weigh out reagents, etc., and handle density calculations
until I have something more accurate.
[Edited on 11-4-2016 by Loptr]
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Texium
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I'm also looking to buy a good scale. I'm in the same predicament as you, Loptr, where the little pocket scale that I have had for a couple years is
starting to show its senility.
It's just hard to figure out what a good one to buy would be, to balance(no pun intended) the price with the quality... If I get another
relatively inexpensive scale that will only last for another two or three years it won't really be worth the money, in my opinion.
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crystal grower
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I want to buy a new scale too, this one seems to be best I found so far.
http://myweigh.com/product/triton-t3/
(I mean the 400g type)
It cost about 22€,
Measures with 0.01g accuracy,
It seems to be quite durable,
And it has 30years extended warranty.
Do anyone have experience with this one?
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Sulaiman
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What I meant was not that YOUR volumetric flask is in error, all volumetric flasks have errors,
Class-A tolerance is 0.08ml in 100ml, for example http://www.duran-group.com/en/products-solutions/laboratory-...
Weighing 100g to +/-0.02g is 4x more precise, and cheaper!
(and since it is often a mass ratio, calibration is not required, only an assumption of linearity)
P.S. If (allegedly) they are good enough for drug dealers ....
[Edited on 11-4-2016 by Sulaiman]
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Loptr
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| Quote: Originally posted by Sulaiman | What I meant was not that YOUR volumetric flask is in error, all volumetric flasks have errors,
Class-A tolerance is 0.08ml in 100ml, for example http://www.duran-group.com/en/products-solutions/laboratory-...
Weighing 100g to +/-0.02g is 4x more precise, and cheaper!
(and since it is often a mass ratio, calibration is not required, only an assumption of linearity)
P.S. If (allegedly) they are good enough for drug dealers ....
[Edited on 11-4-2016 by Sulaiman] |
What I meant to say is they are the best I have, and whether they are accurate, close, or completely off, I will be trying my best to not introduce
additional error into the calculations. I was depending on the linearity to use equivalent measures regardless of the measure with the hopes the
precision allows for them to be within reason.
Not that I have known many drug dealers over my lifetime, but what drug dealers do you know that use volumetric flasks? I knew a guy back in school
that apparently ended up following a bad path after we graduated. It turns out up until recently he was a shake and bake cook. I can assure you that
this guy had no use for a calibrated measure of any sort, and especially not a volumetric flask. He's now in jail after a heroin ring was broken up by
a local DEA task force. I happened to be looking through the paper one day and came across a half-page entry of mugshots from a recent sting, and low
and behold, there he was.
[Edited on 12-4-2016 by Loptr]
[Edited on 13-4-2016 by Loptr]
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CharlieA
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| Quote: Originally posted by Sulaiman | What I meant was not that YOUR volumetric flask is in error, all volumetric flasks have errors,
Class-A tolerance is 0.08ml in 100ml, for example http://www.duran-group.com/en/products-solutions/laboratory-...
Weighing 100g to +/-0.02g is 4x more precise, and cheaper!
(and since it is often a mass ratio, calibration is not required, only an assumption of linearity)
P.S. If (allegedly) they are good enough for drug dealers ....
[Edited on 11-4-2016 by Sulaiman] |
I don't understand. Weighing 100g +/- 0.02g produces 5 significant figures. Measuring 100 mL +/- 0.08 mL produces 5 significant figures. Where does
your "4x more precise" come in? I guess I am confused.
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kt5000
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I've been using a cheap 200 x 0.01g pocket scale as well. I got spoiled last semester with a lab scale that read +/- 0.0001g. I'm sure that one was
expensive, though something accurate to 0.001g would be nice to have at home.
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Sulaiman
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100ml +/- 0.08ml = 0.08% uncertainty
100g +/- 0.02g = 0.02% uncertainty, 4x more precise.
If you have accurate weighing scales and a thermometer you can calibrate your volumetric flask.
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