why is preparing solutions in a larger batch less accurate?

Ok, so a technician is preparing various concentration solutions (1%, 2%, 3%, etc) of the enzyme trypsin.

The larger the volume of solution he prepares, the less accurate the concentration will be.

Why is this? I am looking for a few sentences to explain why the larger the volume produced, the less reliable the results obtained from a consequent experiment are because the concentrations would be less accurate.

I don't think I've explained this very articulately, but the answer is supposed to be relatively simple and I really need to know, so I would appreciate your help.

Thank you.

Reply 1

steppity-step

7

The larger the volume the better, as percentage errors are lower surely?

a mixing error??

It's easier to measure large volumes than small ones (as previously mentioned relative error increases with smaller volumes)?

Reply 4

eulerwaswrong

13

hmmmmmm - larger the volume lower the error? thats what ive always thought

Reply 5

46Bit

Hmm - the enzyme and anything else in the water might be more likely to not be mixed to equal concentrations throughout the solution maybe? It's too much of an open ended question really.

Reply 6

jumblebumble

OP

10

46Bit

Hmm - the enzyme and anything else in the water might be more likely to not be mixed to equal concentrations throughout the solution maybe? It's too much of an open ended question really.

Yes that's what I was thinking. The larger the batch, the less even the distribution, perhaps?

Reply 7

steppity-step

7

Yes, it was almost certainly the other way round. Do you understand the reasoning for it?

Reply 8

jumblebumble

OP

10

toasted-lion

Yes, it was almost certainly the other way round. Do you understand the reasoning for it?

I think so - the margin of error is smaller when more is prepared...?
I'm not quite sure how to phrase it, though.

Edit: however, from what it seemed, the answer is to do with the trypsin itself and the conditions it is stored in?

And is 'The larger the batch, the less even the distribution of trypsin' not a valid point? :smile:

Thank you for your help so far, everyone.

Reply 9

steppity-step

7

You can just state that at higher volumes the percentage error is lower. If you need to go into detail, talk about how when preparing a higher volume, the error you could make is exactly the same, but the total volume will be bigger, so the error as a proportion of the total volume is lower.

Reply 10

jumblebumble

OP

10

toasted-lion

You can just state that at higher volumes the percentage error is lower. If you need to go into detail, talk about how when preparing a higher volume, the error you could make is exactly the same, but the total volume will be the same, so the error as a proportion of the total volume is lower.

Ahh, I see! Thank you.

Reply 11

a.sheikh

ok i have a question then ... when preapring a standard solution of something of 250 cm3 using a volumetric flask... we first weigh out the solid using a weiging bottle and transfer it into a SMALL beaker where we add distilled water and stir the mixture to dissolve the solid and then ad the solutio to the volumetric flask and make it upto the markl... rigth so why do we need a small beaker why not any beaker? of any size ... they say if it's not small then they minus one mark '' for large beakers result in loss of mass and are less accurate'' please explain

Reply 12

46Bit

a.sheikh

ok i have a question then ... when preapring a standard solution of something of 250 cm3 using a volumetric flask... we first weigh out the solid using a weiging bottle and transfer it into a SMALL beaker where we add distilled water and stir the mixture to dissolve the solid and then ad the solutio to the volumetric flask and make it upto the markl... rigth so why do we need a small beaker why not any beaker? of any size ... they say if it's not small then they minus one mark '' for large beakers result in loss of mass and are less accurate'' please explain

I'm pretty sure that more liquid would be in contact with the sides of the beaker in a larger container, and so, bearing in mind that a very thin film of liquid is almost always left attached to a beaker after pouring, more of the liquid would be lost in this way with a larger beaker than with a small one.

The reason is that, in a large beaker compared to a smaller one, the contact between the liquid and the base of the beaker is increased due to the larger diameter. The height of the column of liquid within the beaker is reduced, so reducing the area of the contact between the beaker & liquid, but I reckon to a lesser extent than the contact area is increased by the larger diameter.

That's a guess really, but it makes sense to me.

Reply 13

chemistryhelper

in response to the last point - small vessels are better as less solution is left on the walls of the vessel (to do with the surface are to volume ratio of the sample and how that varies with the dimensions of the sample) - also the re is the practical difficuty trying to disperse solids through large volumes. ever tried making instant bournvita by adding the powder to a cupful of water - much easier to make a sludge first then dilute it.

re original post - assuming larger samples means more dilute - dilute protein solutions are more inaccurate because there is some capacity for protein to be adsorbed to the walls and in effect removed from solution -this could involve a larger proportion of the total protein when the solution is more dilute. also protein can be degraded by bugs etc, and dilute solutions will be affected proportionately more - imagine some bacteria manages to chew its way through 1 mM trypsin - if the concentration were only 1 mM in the first place there woud be effectivey none left - but if there were 10 mM there in the first place the concentration would only be down shifted by 10%

but assuming larger samples just means larger volume, and no more dilute - although the accuracy is generally worse for smaller volumes - the accuracyy/precision could be worse for larger vols if different glassware needed to be used with lower accuracy (buckets tend to be less accurate)

why is preparing solutions in a larger batch less accurate?

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