used $2000 electric balance, mass= 75.357g. used less expensive.bal. it is 75.4g. any benifit of using $2000?

Question

significant figures chapter... using a $2000 balance we found mass to be 75.375 g. using less expensive balance we found it to be 75.4 g. was there any befefit of using a $2000 balance to measure the mass of our sample? what precision would be adequate in a balance for this experiment assuming no other apparatus was changed? i am at a loss on just this one question. please help me!!! i have been out of high school for 10 years and am going back for nursing after a 5 year stroll along an arts degree!

Answer 1

It depends on the accuracy that you require. This will largely be determined by the analysis/experiment that you are doing.

If the analysis has to be very accurate then you would need the expensive balance. If the analysis is less accurate then you would need the cheaper balance, although the more accurate one would be okay; it is just overkill.

An example:
If you are preparing an IV saline solution in which the amount of salt needs to be correct but not precise then you will probably get away with the cheaper balance. Especially if you are making large volumes.

If you are analysing the pH of a solution and need to know this extremely accurately then you will use the more expensive balance.

In summary:
Cheap balance
- making large amounts of a material
- general use
- when accuracy is not important

Expensive balance
- analytical work
- precision needs to be high
- masses measure are small

Answer 2

The expensive balance gives you more sig figs(5 compared to 3), but the experiment will likely use other equipment i.e. a graduated cylinder or a burette that will only yield 3 sig figs.

The measurement that you use that has the lowest number of significant figures will limit the number of significant figures that the your final calculation can give you.

So if it is the case that another piece of equipment in the experiment will give you less than 5 sigfigs there is no reason to use the more expensive balance in the context of a significant figures discussion.

Answer 3

with the 2000 balance you get a three digit reading, that's a great benefit for analytical purposes, but it would be a waste of money for other uses. It will depend on the application.