Why water dissolves so many things
Grade 8 Science Worksheet - Building Confidence
Circle the best answer, or write your answer on the line.
A teacher handles potassium nitrate. A teacher dissolves potassium nitrate in 250 g of water at 60 °C until no more dissolves. How many grams dissolve, Bo?
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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 water is warm enough to melt the salt, so the salt turns into a liquid that mixes in
- Water's slightly charged ends attract the salt ions and pull them apart into the water
- Water dissolves any solid it touches, so salt is just one more solid in the long list
- The salt particles disappear when the water touches them, so nothing is left to see in the cup
Using the table, why does olive oil float in a layer instead of dissolving, Kira?
- 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
- Oil is lighter than water, and lighter liquids cannot dissolve in a heavier liquid like water
Using the table, why does sand settle in the water, Luz?
- Sand is heavier than water, and heavy solids cannot dissolve in a lighter liquid
- Sand's atoms are joined in a strong network that water cannot pull apart
- Sand grains are too big to fit among water particles, even though water attracts them strongly
- Sand needs warmer water to melt, and the water in the cup was too cool to melt it
The jar stayed sealed. What does the table show about mass when salt dissolves, Milo?
- Nothing can be said, since the salt cannot be seen once it has dissolved in the water
- The mass stayed 280 g, so the dissolved salt is still in the jar with its mass
- 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
A teacher heated the dish. Where did the other 100 g go when the water evaporated, Noah?
- The water and some sugar were destroyed, and the 25 g in the dish is what was left over
- The water turned into sugar, which is why 25 g of solid was left in the dish
- The water left as vapor into the air, while the 25 g of sugar stayed in the dish
- The water is still in the dish, hidden inside the sugar, which is why it weighs 25 g
Filtering a mixture (example data)
what is measured grams Sand on the filter paper 15 Salt dissolved in the water 30 Water in the mixture 200 Liquid that passed through 230 Pia filters a mixture of sand, salt and water. What passes through the filter paper?
- The sand, salt and water pass through, because the liquid that came through weighs 230 g
- The water and the dissolved salt pass through, and the sand grains stay on the paper
- Just the water passes through, because the dissolved salt is a solid and stays on the paper with the sand
- The water passes through, and the dissolved salt is destroyed so it appears in neither place
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 is left over, since harder stirring makes the sugar disappear faster
- How fast the sugar dissolves, but not how much sugar the water can hold
- Neither, since the most sugar that dissolves is the same each time, so stirring changes nothing
- How much sugar the water can hold, since harder stirring made 10 g dissolve sooner
All three were at 20 °C. Why does the powder dissolve fastest, Tala?
- Powder lets more sugar dissolve in total, because each tiny grain holds extra sugar
- Powder is a different substance from the cube, with a higher solubility in water
- Powder is warmer than the cube, so its particles move faster and it dissolves sooner
- Powder has more surface touching the water, so water reaches more sugar at once