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

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Discussion Overview

The discussion revolves around the observation that adding sugar to water does not result in the expected additive volume, with participants exploring the reasons behind this phenomenon. The scope includes theoretical considerations of solution volume, experimental observations, and potential factors affecting measurements.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Experimental/applied

Main Points Raised

  • Some participants suggest that the final volume after dissolving sugar should be larger than 50 mL but smaller than 55 mL, with expectations around 53-54 mL.
  • It is proposed that the volumes of solutions are not additive, as the final volume typically does not equal the sum of the initial volumes when mixing different substances.
  • A participant notes that after 24 hours, the water level settled at 51 mL and questions whether evaporation could have contributed to this change.
  • Another participant agrees that evaporation is a likely factor and provides calculations regarding the density of the sugar solution, suggesting that the final volume should be around 53.2 mL based on the density of the solution.
  • A question is raised about whether the initial measurement of 50 mL of water was taken at room temperature or after heating, with a suggestion to consider thermal expansion or contraction effects.

Areas of Agreement / Disagreement

Participants express differing views on the expected final volume and the factors influencing it, indicating that multiple competing explanations remain without consensus.

Contextual Notes

Participants note that the assumptions regarding the density of sugar and the conditions of the water (temperature) may affect the results, but these aspects remain unresolved.

Who May Find This Useful

This discussion may be of interest to those exploring solution chemistry, experimental design in physics or chemistry, and the effects of temperature on volume measurements.

musicgold
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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
 
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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.
 
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Borek said:
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?
 
musicgold said:
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.
 
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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.
 

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