Uncertainty

[god_is_atheist]

I hope this is within guidelines. The uncertainty is the smallest unit(resolution) of the instrument divided by two. How do I get the uncertainty of pycnometer?

 

[The Highlander]

I hope this is within guidelines. The uncertainty is the smallest unit(resolution) of the instrument divided by two. How do I get the uncertainty of pycnometer?

As you have just 'defined' it yourself.
If the instrument reads out in (whole) cubic centimetres, for example, then the uncertainty is half a cc.
If it gives readings to a set number of decimal places (of whatever volumetric unit it uses) then the uncertainty is ±5 in the decimal place following the final one in the readout.
For example, if your instrument displays readings in m³ to 4 decimal places and you get a reading of, say, 5.4728 m³ then that might be recorded as 5.4728 ± 0.00005 m³ or 5.4728 m³ ± 10 cm³.
If the readings are given directly as measurements of Density then, since that is essentially a ratio, the same principle applies: ±5 in the decimal place after the final one in the reading (in kg/m³ or g/cm³ or whatever units the instrument displays).

 

[The Highlander]

@god_is_atheist

NB: If you are using a basic glass jar type pycnometer where you are taking repeated measurements (by weighing it with different contents?) and then calculating your final result via some formula then a method for calculation of the 'final' uncertainty (error) can only be offered if the measurements involved and the formula used are known.

If you wish to find a value for some property, \(\displaystyle P \), and its associated error, \(\displaystyle ΔP \), when you first have to measure two quantities, say, \(\displaystyle Q_1\) and \(\displaystyle Q_2\) (and the errors for each are \(\displaystyle ΔQ_1\) & \(\displaystyle ΔQ_2\) respectively) then the final error \(\displaystyle (ΔP)\) will depend on the calculation(s) involved.

For example:-

if \(\displaystyle P = Q1 ± Q2\), then \(\displaystyle ΔP = \sqrt{(ΔQ_1)^2+(ΔQ_2)^2}\)​

whereas,

if \(\displaystyle P = Q_1\)×\(\displaystyle Q_2\textbf{ or }\frac{Q_1}{Q_2}\), then \(\displaystyle ΔP = P ×\)\(\displaystyle \pmb{\sqrt{\left(\frac{ΔQ_1}{Q_1}\right)^2+\left(\frac{ΔQ_2}{Q_2}\right)^2}}\) ​

So, in a situation like that, you would need to provide much more information about what you are doing (and how you are doing it) before anyone could offer you any help on how to calculate the uncertainty (error) you are looking for.

 

[god_is_atheist]

@The Highlander Okay, its not a graduated bottle. When the top is placed on the pycnometer the displacement of water leaves 50mL remained in the bottle. Your help is appreciated

 

[Dr.Peterson]

@The Highlander Okay, its not a graduated bottle. When the top is placed on the pycnometer the displacement of water leaves 50mL remained in the bottle. Your help is appreciated

Please give details, as requested! What do you see when you read this device? What resolution does it show? Which of several kinds is it?

A picture might help, as well as an example of what you have done - in detail.

 

[god_is_atheist]

Its just 50mL. There are no marks to get a resolution from. So I see that the uncertainty cant be determined.

 

[Dr.Peterson]

Its just 50mL. There are no marks to get a resolution from. So I see that the uncertainty cant be determined.

So you don't have to make any measurements at all in using this thing? Then there's nothing to be uncertain about!

Once again, if you want help, you need to give us some information. I doubt that I've ever seen a pycnometer, but I find several different kinds of pycnometers online, so I don't even know what kind you have or how you use it, except that somewhere you make some sort of measurement (maybe a weight or a pressure?), and that measurement has some sort of resolution. And there's probably some calculation you do. That's what we want to know! Tell us how you use it, and we can probably help.

My guess is that the 50 ml marking just means its maximum capacity, and you don't use that number in your calculations at all; you just have to measure something separately, maybe a volume, or maybe something else.