[Ishneya]

Hello everybody!

I am having a doubt. Could someone please help me?
When you dissolve KOH(s) into H2O(l), does the volume of the latter remain constant?
Say you have a volume of H2O(l) of 25cm3 and you dissolve 1.2g of KOH(s) into it. What would be the volume of the resulting KOH(aq)?

Thanks a lot!! 

[Borek]

Volume changes, but there is no simple method of exactly predicting what it will be.

For diluted solutions you can assume density didn't change much, so the new volume can be calculated from the known mass of the mixture. That yields only an approximate answer - whether the error is acceptable or not depends on the needed accuracy.

The best - and most reliable method - is to use density tables for predictions.

[Ishneya]

Volume changes, but there is no simple method of exactly predicting what it will be.

For diluted solutions you can assume density didn't change much, so the new volume can be calculated from the known mass of the mixture. That yields only an approximate answer - whether the error is acceptable or not depends on the needed accuracy.

The best - and most reliable method - is to use density tables for predictions.

How would you use the density tables? I'm afraid we haven't yet covered this topic.
I only have the information written above: 1.2g of KOH(s) dissolved into 25cm3 of H2O(l).

[Borek]

Density table just lists concentrations and densities.

25 mL of water means 25 g of water (actually it depends on the temperature, at room temp. it will be slightly less, 25mL×0.9991g/mL).

Plus 1.2g of KOH - what is the mass of the solution?

Can you calculate its % concentration?

Then, you have to read the density from the table, that looks like that:

C%	g/mL
0	0.999
1	1.008
2	1.018
3	1.027
4	1.036
5	1.045
6	1.054

(and so on, such tables were prepared many years ago and they can be find in databases or handbooks).

If there is no exact concentration, either use the closest one, or try to interpolate (if you have no idea what it means - don't worry, use the closest one).

Then, from the known mass of the solution, and its density, you can calculate the volume.