Weight by Difference

In this video, you're going to learn how to use the weight by difference technique.

Before watching this video, make sure you've watched the open pan balance video

and the analytical balance video.

When transfering a solid sample from a weighting vile to a receiving vessel

some of the sample will be left behind around the edge of the container.

This is no fault of experimenter and can not be avoid, however, it has to be accounted for.

If you assume all the mass was transfer you will get significant error in your results.

To do this a technique of weight by difference is used.

This uses the intial and final mass of the weighting vile

with and without the sample in it to account for only the mass that was transfered.

You can do this using either type of balance.

but for visability I will be using open pan balance.

Weigh your sample just as shown to you

in the open balance and analytical balance videos.

Making sure you have the combined mass of the vessel and the sample

You can see that my sample weights 22.85 grams

record this mass as the intial mass

Now carefully transfer your sample into your receiving vessel.

Make sure not to spill any of your sample when you are doing this because it will alter your results.

A good way to do this is to keep

your sample capped.

Now re-weigh your weighing vile.

As you can see, there is still some of the sample remaining in the weighing vile.

Place the vile back on the same balance and

and record the value.

The mostly empty vile weights

22.25 grams. Record this as your final mass.

The last step is to take the difference between the two values, which I will show you on the board.

You subtract the final mass from the initial mass

you'll get the mass of the sample you transfered.

As you see I have transfered 0.60 grams of my sample.

The weight by difference technique is common practice to most chemists.

If you practice the method I outlined for you it will become second nature to you too.