Let's analyze the situation step by step and then explain what happens when Jane puts her glass and sugar pot back on the scales.
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Initial Setup:
The balance scale is initially balanced. On both sides (Abi and Jane), there are:
- A glass of water
- A small container of sugar
So,
the total mass on both sides is equal at the start.
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What Happens Next?
-
Jane takes her glass of water off the scales and pours
some sugar into her glass, then stirs it until the sugar granules disappear (i.e., the sugar dissolves in the water).
- She then puts her
glass (now with dissolved sugar) and her
sugar pot (which now has less sugar) back onto the scales.
-
Abi leaves her glass and sugar alone — so her side remains unchanged.
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Key Scientific Concept: Conservation of Mass
When sugar dissolves in water, it does
not disappear — it simply disperses into the water as individual molecules. The
total mass of the system remains the same.
Even though you can't see the sugar granules anymore, the
mass of the sugar is still present in the solution.
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What Happens to the Scale?
Let’s compare the two sides after Jane’s actions:
####
Abi’s Side:
- Glass of water (unchanged)
- Sugar pot (unchanged)
→ Total mass = original mass
####
Jane’s Side:
- Glass of water + dissolved sugar → this has
more mass than just water
- Sugar pot → has
less sugar than before (because some was added to the water)
But here’s the key point:
> The amount of sugar removed from the sugar pot is
exactly equal to the amount that was added to the water.
So:
-
Mass lost from sugar pot =
Mass gained by water
- Therefore,
total mass on Jane’s side remains unchanged
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✔ Conclusion:
The scale will remain balanced.
Even though the sugar is no longer visible, its mass is still part of the system. The total mass on both sides is the same.
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Sketch Description (since I can't draw):
Imagine the same balance scale as before, but:
- On Jane’s side:
- The glass now contains a sugar-water solution (clear, no granules)
- The sugar pot is slightly lighter (less sugar)
- But the
total weight on Jane’s side is
equal to Abi’s side.
So, the
scale stays level —
balanced.
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📌 Final Answer:
>
The scales will remain balanced.
> Although Jane dissolved the sugar in her water, the mass of the sugar is still present in the solution. The sugar pot has less sugar, but the glass now contains more mass due to the dissolved sugar. Since mass is conserved, the total mass on Jane’s side is unchanged. Therefore, the scale remains balanced.
Parent Tip: Review the logic above to help your child master the concept of law of conservation of matter worksheet.
