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, why does sand settle in the water, Luz?
- 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
- 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
The jar stayed sealed. What does the table show about mass when salt dissolves, Milo?
- The mass fell, since dissolved salt is spread so thin that it no longer adds to the weight
- 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
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 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
- The water turned into sugar, which is why 25 g of solid was left in the dish
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 water and the dissolved salt pass through, and the sand grains stay on the paper
- The sand, salt and water pass through, because the liquid that came through weighs 230 g
- The water passes through, and the dissolved salt is destroyed so it appears in neither place
- Just the water passes through, because the dissolved salt is a solid and stays on the paper with the sand
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?
- Neither, since the most sugar that dissolves is the same each time, so stirring changes nothing
- 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
- 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 has more surface touching the water, so water reaches more sugar at once
- 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
- Powder lets more sugar dissolve in total, because each tiny grain holds extra sugar
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?
- No: warmer water dissolves less table salt than colder water does, by a small amount
- Yes: 60 °C water dissolves far more salt than 0 °C water, as it does for most solids
- No: about 1 g more salt dissolves between 0 °C and 60 °C, a very small change
- Yes: warm water dissolves salt faster, so a greater amount of salt dissolves