Adding sugar to water; water level doesn't go back to the original volume

[musicgold]

Homework Statement

This is not a homework problem. I am doing a Chemistry experiment with my kid. As per the booklet, we have added 5ml sugar to a glass with 50ml of hot water. The booklet says that the water level should go back to 50ml after the sugar is dissolved.

Relevant Equations

It has been 2 hours since we dissolved the sugar, but the water level is still close to 54ml. When the sugar was added the water level increased from 50 to 55ml.

What are we missing in this experiment?

Thanks

 

[Borek]

Booklet is wrong, final volume should be larger than 50 mL, but smaller than 55 mL (I would expect something above 53 mL, 54 sounds in a right ballpark).

Volumes of solutions are not additive (the final volume is typically not equal to sum of volumes, unless you mix same with same). Same holds when dissolving solids in any solvent.

 

[musicgold]

Booklet is wrong, final volume should be larger than 50 mL, but smaller than 55 mL (I would expect something above 53 mL, 54 sounds in a right ballpark).

Volumes of solutions are not additive (the final volume is typically not equal to sum of volumes, unless you mix same with same). Same holds when dissolving solids in any solvent.

Just a follow up, after 24 hours, the water level settled at 51 mL. Could we have lost some water because of evaporation?

 

[Borek]

Just a follow up, after 24 hours, the water level settled at 51 mL. Could we have lost some water because of evaporation?

Most likely.

Bulk density of sugar is around 0.8-0.9 g/mL. Let's make it 1g/mL for brevity. You took 5 mL, so around 5 grams.

You started with 50 mL of water of 1 g/mL density. That means 50 g of water. After adding sugar you had 55 g of the solution. 5 g of the sucrose in 55 g of the solution means 9.1 % w/w. Sucrose solution density tables say such a solution has a density of 1.0344 g/mL. 55 g of the solution of 1.0344 g/mL density has a volume of 53.2 mL.

Give or take half a mL here and there, as your numbers are approximate.

 

[chemisttree]

Did you measure 50 mL of HOT WATER or did you start with 50 mL of RT water, heat it and then dissolve the sugar?

If the former, consider thermal expansion/contraction as well.