Why water dissolves so many things
Grade 8 Science Worksheet - Building Confidence
Circle the best answer, or write your answer on the line.
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Potassium nitrate in 100 g of water (approximate reference data)
water temperature (°C) grams that dissolve 0 13 20 32 40 64 60 110 A teacher handles potassium nitrate.
Ari's teacher dissolves potassium nitrate in 400 g of water at 20 °C until no more dissolves. How many grams dissolve?
A teacher dissolves potassium nitrate in 250 g of water at 60 °C until no more dissolves. How many grams dissolve, Bo?
Table salt in 100 g of water (approximate reference data)
water temperature (°C) grams that dissolve 0 36 20 36 40 36 60 37 Esme stirs table salt into 300 g of water at 20 °C until no more dissolves. How many grams dissolve?
Four stir tests (example data)
substance what its particles are like after 1 minute of stirring in water Table salt charged ions dissolves, clear liquid Sugar polar molecules with slightly charged ends dissolves, clear liquid Olive oil molecules with no charged ends floats in a layer Sand atoms joined in a strong network settles to the bottom Using the table, which explanation fits the particle model for salt dissolving, Jun?
- The salt particles disappear when the water touches them, so nothing is left to see in the cup
- The water is warm enough to melt the salt, so the salt turns into a liquid that mixes in
- Water dissolves any solid it touches, so salt is just one more solid in the long list
- Water's slightly charged ends attract the salt ions and pull them apart into the water
Using the table, why does olive oil float in a layer instead of dissolving, Kira?
- Oil is lighter than water, and lighter liquids cannot dissolve in a heavier liquid like water
- Oil particles are larger than sugar particles, so they cannot fit between the water particles
- Oil's particles have no charged ends, so water has little to attract and pull away
- Oil does dissolve, but water needs far longer than one minute to pull its particles apart
Using the table, why does sand settle in the water, Luz?
- Sand grains are too big to fit among water particles, even though water attracts them strongly
- Sand's atoms are joined in a strong network that water cannot pull apart
- Sand needs warmer water to melt, and the water in the cup was too cool to melt it
- Sand is heavier than water, and heavy solids cannot dissolve in a lighter liquid
The jar stayed sealed. What does the table show about mass when salt dissolves, Milo?
- The mass stayed 280 g, so the dissolved salt is still in the jar with its mass
- Nothing can be said, since the salt cannot be seen once it has dissolved in the water
- The mass rose, since the dissolved salt spreads out and takes up more room in the jar
- The mass fell, since dissolved salt is spread so thin that it no longer adds to the weight
Sugar in 100 g of water at 20 °C (example data)
stirring seconds for 10 g to dissolve most sugar that dissolves (g) none 120 204 gentle 60 204 hard 30 204 What does stirring change in this table, Ren?
- How much sugar the water can hold, since harder stirring made 10 g dissolve sooner
- How fast the sugar dissolves, but not how much sugar the water can hold
- How much sugar is left over, since harder stirring makes the sugar disappear faster
- Neither, since the most sugar that dissolves is the same each time, so stirring changes nothing
All three were at 20 °C. Why does the powder dissolve fastest, Tala?
- Powder has more surface touching the water, so water reaches more sugar at once
- Powder lets more sugar dissolve in total, because each tiny grain holds extra sugar
- Powder is warmer than the cube, so its particles move faster and it dissolves sooner
- Powder is a different substance from the cube, with a higher solubility in water
Table salt in 100 g of water (approximate reference data)
water temperature (°C) grams that dissolve 0 36 20 36 40 36 60 37 Does warming the water help a lot to dissolve more table salt, Zee?
- Yes: warm water dissolves salt faster, so a greater amount of salt dissolves
- Yes: 60 °C water dissolves far more salt than 0 °C water, as it does for most solids
- No: warmer water dissolves less table salt than colder water does, by a small amount
- No: about 1 g more salt dissolves between 0 °C and 60 °C, a very small change