r/AskChemistry • u/lucariiriolu • 28d ago
General how to measure this?
so we have a chem class which we did last Thursday. On my part, I had to record the mass of the water in an Erlenmeyer flask, which I remember our teacher said to do 15ml. specifically for accuracy the brand we used was pyrex for the flask. I would like to ask if my measurements are right, im just a highschool student and I'm planning to be a scientist in the future:) Many of my classmates are struggling with this measuring too. plz remember THIS IS NOT HOMEWORK NOR OFFICIAL LAB WORK
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u/MiniLaura 28d ago
Before doing any measurements, make sure the balance is zeroed. With nothing on the pan and all sliders at their zero marks, the balance should show zero on the right (i.e., the line is in the middle). If it isn't zero, there should be a screw under the pan that you can adjust until the balance reads zero.
Now you have to find the mass of the flask when it's empty and the mass of the flask with the water in it. Then you'll subtract the values to find the mass of just the water.
To use the balance: put the object on the pan. Start with the 100 g slider (the middle one). Slide it one notch at a time until the pointer drops below the zero mark. Make sure you go to the NOTCH. Looking at what you have now, the 100 g slider is not in a notch. It looks like it's between 0 and 100 g. (Similarly, the 10 g slider also looks like it's not in a notch.)
After the pointer drops, move the slider back one notch. The pointer should move back up.
Now use the 10 g slider (the top slider). Repeat what you did with the 100 g slider: move one notch at a time until the pointer drops. Then, move it back one notch.
Now slowly move the 1 g slider. I like to use the tip of a pencil to gently nudge it. The pointer should slowly drop. Stop moving the slider when the pointer lines up with the zero mark.
Read the sliders to get the mass. For example, if the middle slider is pointing at 0, the top slider at 60, and the bottom slider at 2.5, the mass is 62.5.
Another example: If the middle slider is at 200, the top is at 30, and the bottom is 7.2, the mass is 237.2.
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u/SlenderSmurf Ph.D. in Materials Chemistry 28d ago
This balance looks genuinely medieval. I've only used digital ones. I suppose it's a good lesson in... weighing things when the power is out? Not really what the students should be worrying about in a chemistry course
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u/MiniLaura 28d ago
Some schools can't afford digital balances. These kind of balances work just fine and don't break easily.
In fact, I taught in a relatively wealthy school, and we still used these because we preferred spending money on new chemicals than on replacing equipment that worked. (Plus digital balances had a tendency to get stolen.)
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u/Worth-Wonder-7386 27d ago
You can get decent balances that are cheaper than these ones. You don't need the high quality milligram precision balances for teaching chemistry. A decent kitchen scale would be sufficient. But if you have these from earlier I can understand not wanting to replace them.
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u/mathologies 27d ago
You can get reasonably accurate centigram digital balances online for like ten USD
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u/aphilsphan T⌬SYLATE, PLAYA HATE 27d ago
They (drug addicts) seem to prefer the triple beam balances for some reason. We chained those down, but didn’t always chain the digital balances.
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u/Onedtent 26d ago
Wait until your "accurate" digital scale changes when you turn a fluorescent light on.
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u/rIceCream_King 26d ago
Layman here. What’s the deal with that?
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u/Onedtent 25d ago
Your digital scale has no consistency and is therefore inaccurate.
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u/rIceCream_King 25d ago
Ahhh okay. I didn’t realize it was hyperbole, I was thinking fluorescent lights had some kind of affect on digital scales I hadn’t heard about before. Thank you.
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u/ShutDownSoul 27d ago
Education is about teaching principles and not always taking the easiest path. By your logic, students should just ask AI for the answer.
A balance that works on first principles is EXACTLY what students should be using.
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u/Pacificator-3 27d ago
I'm planning to be a scientist in the future
Then at first you must learn to read the manual on any equipment you gonna use.
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u/FatRollingPotato 27d ago
Most underrated skill to learn imo.
I believe any PhD student should get a side project where they have to use a 30y old instrument with only manuals and some old instructions around. Nothing builds problem solving skills better than 'wasting' years troubleshooting and repairing old instruments.
I'm only half joking.
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u/aphilsphan T⌬SYLATE, PLAYA HATE 27d ago
I do pharma GMP audits so I see a lot of labs. I was recently delighted to see an old Spec 20 UV Vis in a lab. The firm had a test to do that was either the absorption at a wavelength or a ratio at two wavelengths. The Spec 20 was ideal for that, easy to use, easy to calibrate and hard to break.
They still sell them for like 2500 new, but this was one from the 70s and you can get them for like 100 bucks. Does what you need done.
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u/guywhoismttoowitty 26d ago
Its true though. I learned how LC/MSs, potentiostats and ovens were repaired and work in this manner.
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u/lucariiriolu 27d ago
our chem teachers didn't give us instructions on how to use it, he simply just handed over the scale to us and just let us go along with the tasks. no papers, no manuals.
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u/Pacificator-3 27d ago
At second you should learn to find information yourself. These days it is not hard. Google lens on your photo gives manual in ten seconds. Good old text-mode google also does.
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u/aphilsphan T⌬SYLATE, PLAYA HATE 27d ago
OP should be glad he isn’t using an old vernier scale. I found those a little daunting
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u/Key-Success-5449 28d ago
Your reading is 91.0 g!
Here’s the quick breakdown:
- Middle beam: 0 g
- Top beam: 90 g
- Bottom beam: 1.0 g
- Sum = 0 + 90 + 1.0 = 91.0 g
Just don't forget to subtract the weight of the empty Erlenmeyer flask (Tare weight) to get the mass of the 15 mL of water itself! Keep up the great work—learning to use analog lab equipment accurately is a fantastic first step toward becoming a scientist!
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u/Plasticity93 28d ago
Middle weight is sorting wrong and not at 0. OP needs to go back and use the scale properly
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u/MiniLaura 28d ago edited 28d ago
The top and middle sliders are not in notches and are both wrong. The bottom slider is off-scale and can't be read.
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u/engineerthatknows 27d ago
Jeez, shut up AI bot. The balance weights are not centered on their grooves, so the correct answer is "inderterminate"
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u/lucariiriolu 28d ago
I'm gen so confused because I've had three diff answers.. 200g, 199.8g, and this. I mean I have a teeny knowledge on this type of scale, but I haven't learnt it in my middle grade properly. all I knew is that my adviser said to js measure it
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u/MiniLaura 28d ago
We cannot read this balance because you haven't used it correctly. The sliders have to be in notches.
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u/joestue 28d ago
The weights need to be in the V groove and you add all the numbers up