Answer:
Depends, but in most cases, 2.
It's best to use as many digits as possible to keep it accurate.
Explanation:
This varies between teachers, as most schools go with 2 decimal places.
This is something that depends in your situation.
You technically want as many decimals as possible to keep it as accurate, but most people stick with 2.
I personally do 3, and commonly do 5 sometimes.
I am assuming that the apparatus you're referring to would be a container wherein there is water placed inside. To answer your question, I expect the water level to rise when it's placed in warm water and I expect it to fall when placed in cool water. This is because the water molecules get excited when placed in water molecule, thus, moving with more kinetic energy. The opposite goes with cool water.
The trick for this problem is to understand atomic mass: the fact that different atoms have different masses. What we need to do is add up all the atomic masses of the compound and work out the ratio of mass of water to the mass of sodium carbonate. Atomic masses are often given for each atom in the periodic table, but you can look them up on google too.
You can do this by adding up individual atoms for each molecule, or you can shortcut and lookup the molar mass of the compound (i.e.the task already done for you).
The molar mass of water is 18.01g/mole so for 10 moles of water we have a mass of 180.1g.
The molar mass of sodium carbonate is 106g/mole (google).
So the total mass of the sodium carbonate decahydrate compound is 180.1+106 = 286.1g, of which water would make up 180.1g, so the percentage of water is is 180.1/286.1 = 0.629, so we can round this to 63%
:)
