Measurement of Volume

[Maryam]

Whenever volume of water is measured, its lower layer is noted. While in the case of any colored liquid, upper layer is noted. Is it so? Why?

[John Cuthber]

Is this a homework question?

[studiot]

5 hours ago, Maryam said:

Whenever volume of water is measured, its lower layer is noted. While in the case of any colored liquid, upper layer is noted. Is it so? Why?

 

Or are you actually referring to the meniscus line?

[Maryam]

8 hours ago, John Cuthber said:

Is this a homework question?

No, it is not. Actually, I have started my research degree a few months ago and many basic questions strike my mind regularly. That's why I signed up here to ask and let my concept become clearer.

4 hours ago, studiot said:

 

Or are you actually referring to the meniscus line?

Yes, kindly make it more clear according to the question about volume of colored liquids. What is the role of their color to note their volume?

 

[ALine]

 

48 minutes ago, Maryam said:

No, it is not. Actually, I have started my research degree a few months ago and many basic questions strike my mind regularly. That's why I signed up here to ask and let my concept become clearer.

I think it has something to do with the make up of the fluid itself. Being either polar or non-polar. Water, being a polar molecule, would be more attractive to the glass surface. This would produce a concave shape. And because you are looking for the waters volume I believe, do not quote me on this, that due to this affect you would need to measure taking this into account. As for the color liquids I am not sure. An idea would be that most color liquids used in chemistry are usually non-polar. Again I am not sure. 

[studiot]

2 hours ago, Maryam said:

Yes, kindly make it more clear according to the question about volume of colored liquids. What is the role of their color to note their volume?

Do we have a language problem?

Can you supply more detail about what you are trying to do?

Everyone here is just guessing - not a good way to help.

[taeto]

      My first reaction, and I have not been in a chem lab for ages, is that the shape of the liquid is generally going to be as in figure A. It certainly is for water.

The lower layer provides the most accurate measurement, since it is usually much wider than the upper narrow portion. 

Since water is transparent, you can observe the height of the lower layer from the side, which gives the optimal value.

If a liquid is not transparent, you cannot see the lower layer, and you have to measure the height of the upper layer.

I ready myself for being made fun of for a simpleton explanation of something that is probably infinitely more subtle.

[Maryam]

On 2/11/2019 at 10:51 PM, studiot said:

Do we have a language problem?

Can you supply more detail about what you are trying to do?

Everyone here is just guessing - not a good way to help.

No, I think we don't have. 

I was just wondering about the point that does only color has any role in the volume or at least in noting a volume?

[Strange]

6 minutes ago, Maryam said:

I was just wondering about the point that does only color has any role in the volume or at least in noting a volume?

No.

[Maryam]

6 minutes ago, Strange said:

No.

Do chemical interactions i.e. the forces of adhesion to the wall make differences in the curves in both cases then?

[Strange]

3 minutes ago, Maryam said:

Do chemical interactions i.e. the forces of adhesion to the wall make differences in the curves in both cases then?

I imagine multiple factors will change the shape of the meniscus (if that is what you are talking about) but I can't see how it would change the volume in any significant way (just make it more difficult to calculate, perhaps). 

But colour is irrelevant.

[studiot]

31 minutes ago, Maryam said:

No, I think we don't have. 

I was just wondering about the point that does only color has any role in the volume or at least in noting a volume?

 

Colour has only a minor peripheral role in noting volumes.

There are many different graduated volume measuring vessels.
Such as measuring jugs, measuring cylinders, burettes, pipettes, syringes....

They all serve different purposes and introduce their own special pros and cons.
And each has its own way of using it.

There is no meniscus in a syringe for instance.

So I say again, explain what you want to do, or do you want to discuss measurement of volume in general, in relation to these or something else again.

On 2/11/2019 at 5:07 AM, Maryam said:

Whenever volume of water is measured, its lower layer is noted. While in the case of any colored liquid, upper layer is noted. Is it so? Why?

 

When you are talking about "the upper layer" do you mean the meniscus or do you mean there are (coloured) layers or what.

Help us to help you.

[Maryam]

23 hours ago, studiot said:

 

Colour has only a minor peripheral role in noting volumes.

There are many different graduated volume measuring vessels.
Such as measuring jugs, measuring cylinders, burettes, pipettes, syringes....

They all serve different purposes and introduce their own special pros and cons.
And each has its own way of using it.

There is no meniscus in a syringe for instance.

So I say again, explain what you want to do, or do you want to discuss measurement of volume in general, in relation to these or something else again.

 

When you are talking about "the upper layer" do you mean the meniscus or do you mean there are (coloured) layers or what.

Help us to help you.

Thanks for your detailed response. Yes, I was talking about meniscus. Furthermore, I can not understand that how does the liquid above the line of 20 (in this figure) not affect the accuracy of noting its volume as 20?

[studiot]

This looks like you are asking about burettes and titrations.

A general rule of thumb in Science (and engineering) is that accurate measurements are made when you 'measure by difference'

For a burette this means you never empty the burette.

So when you draw off a desired volume of liquid the amount drawn is the difference in readings on the burette.

You should always measure from the same part of your meniscus and the most suitable part is the centre of the curve, away from the sides of the burette.

You want the centre because it is difficult to visually estimate where the top of the liquid actually lies at the edges.
This is partly because the triangle becomes thinner and thinner and you can't tell exactly where the top lies against the glass sides.
And partly to avoid a phemenon known as parallax.
Parallax is where you get the reading on the scale slight wrong because you are viewing at a slight angle (to the horizontal in this case).

So if you open the burette tap until the bottom of the meniscus at the centre reads 21 in your picture, you will have drawn off exactly 1mL as there is still just the same amount of meniscus liquid above that line as before.

Finally I commented that colour has a minor impact.

Some liquids are hard to distinguish from the background because of their colour.
Good practice would suggest holding up a card (usually white but a contrast colour) to improve the image.

 

So can you think of a situation where we might want to do things differently and so minimise any other characteristic of the meniscus?

28 minutes ago, Maryam said:

Thanks for your detailed response. Yes, I was talking about meniscus. Furthermore, I can not understand that how does the liquid above the line of 20 (in this figure) not affect the accuracy of noting its volume as 20?

 

[studiot]

Thank you for the upvote.

How about trying my question at the end?

It was not a trick but meant to lead to more help.