Volumetric Analysis questions

[macca69831]

Q1. Explain why burettes must be rinsed with the solution they are to contain, but volumetric flasks are only rinsed with water during a volumetric analysis.

Q2. A student weighed out the required mass of a primary standard and placed it in a flask. 1.0L of water was then added to the flask. Explain why this prodecure would not produce a standard soltuion of accurately known concentration?

[Edmund]

1. Burettes must be rinsed with the solution it is filled with, so its pH will not be affected (E.g. water will dilute the solution placed in burette and therefore yield inaccurate titre). Volumetric flasks are used for preparing a standard. During the preparation, the volumeric flask will eventually be filled (diluted) to the mark, so rinsing in with water will have no effect.

2. I'm not sure about this but here's what I think. A volumetric flask needs to be used in order for a standard solution to be accurately produced. Measurements have to be precise.

[macca69831]

Thank-you

[Studyinghard]

1. Burettes must be rinsed with the solution it is filled with, so its pH will not be affected (E.g. water will dilute the solution placed in burette and therefore yield inaccurate titre). Volumetric flasks are used for preparing a standard. During the preparation, the volumeric flask will eventually be filled (diluted) to the mark, so rinsing in with water will have no effect.

2. I'm not sure about this but here's what I think. A volumetric flask needs to be used in order for a standard solution to be accurately produced. Measurements have to be precise.

for b) I would say that when you measured it and then transferred into a volumetric flask not ALL of the measured substance would go in hence you wouldnt get the most precise answer.

[chem-nerd]

2. Adding 1.0L to a mass of primary standard will result in a volume greater than 1.0L and hence not an accurately known concentration.

This is why you place an accurately determined mass of the standard into the volumetric flask and then fill it to the calibration mark with water.

[physics]

it wouldn't matter that ur volumetric flask was rinsed with water b/c u fill it wiht the standard solution and then end up adding water to it to make it 250ml anyway. :0 i hope i'm right

and basically what u fill ur burette/pipeet with is what u rinse it with cause if u do it the other way round,some of the acid/base would neutralise with each other and cause an extra few ml which isn't an acid or base but water...(i'm quite sure )

[simonhu81292]

you're right... annihinh ...!!
you asked this question before..
haven't you? 

[physics]

you're right... annihinh ...!!
you asked this question before..
haven't you? 

^^ thanks to you i understand so might as well tell other ppl and share the knowlege around :3

[simonhu81292]

you're right... annihinh ...!!
you asked this question before..
haven't you? 

^^ thanks to you i understand so might as well tell other ppl and share the knowlege around :3

that's good ... spread it around
so this year our average VN enter would be higher