The Dissolving Experiment
FoundationSalt and sugar dissolve in water; sand and stones do not. Stirring, warm water and fine grains all make sugar dissolve faster.
- Salt and sugar dissolve in water; sand and stones do not.
- Dissolved material is still in the water, only invisible.
- Stirring makes dissolving faster.
文體小知識：說明文配上小實驗，把溶解的知識一步一步講清楚：什麼會溶、什麼不會溶，還有怎樣溶得快。
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1When Mum adds a spoonful of salt to the soup and stirs, the grains disappear but the soup turns salty. That is because the salt dissolves in the water, breaking into tiny, tiny bits spread evenly through it. Our eyes cannot see them, but our tongue can taste them — that is the magic of dissolving.
2Run a little experiment: prepare four cups of clean water; add a spoonful of salt to one, sugar to the second, sand to the third and a small pebble to the last; stir each a few times and watch. The salt and sugar slowly vanish and the water tastes salty or sweet; the sand sinks to the bottom, the pebble lies at the bottom, and the water stays tasteless. Some materials dissolve in water; some do not.
3Is the dissolved salt still in the water? Yes. Pour the salty water onto a white plate and leave it in the sun for a few days; when the water evaporates, a layer of white salt remains on the plate. This proves the salt never disappeared — it only became invisible bits spread evenly through the water. Sugar is the same: dried sugar water leaves sugar behind.
4How can sugar dissolve faster? Three ways: first, stir with a spoon to help the grains spread; second, use warm water instead of cold — higher temperature means faster dissolving, but hot water scalds, so ask an adult for help; third, grind the sugar into fine powder first — fine grains touch more water and dissolve sooner.
5Dissolving is everywhere in life: making milk tea, mixing sugar water, adding salt to soup, dish detergent melting into water. In experiments, observe carefully and record honestly; wash the cups and spoons afterwards and tidy up. Remember: salt and sugar dissolve, sand and stones do not, and stirring and warm water speed things up — now you are a little scientist.
1Summary 重點摘要
Salt and sugar dissolve in water; sand and stones do not. Stirring, warm water and fine grains all make sugar dissolve faster.
2Vocabulary cards Vocabulary
To break into tiny bits spread evenly through water, like salt in water.
A white seasoning that dissolves in water and makes it salty.
A sweet seasoning that dissolves in water and makes it sweet.
Tiny grains of stone; they do not dissolve and sink in water.
A hard solid that does not dissolve in water.
To swirl a liquid with a spoon so things dissolve faster.
Water that is warm, not scalding; it dissolves things faster than cold water.
To go under the water, like sand and stones settling at the bottom.
To watch changes in an experiment carefully.
A hands-on way to find answers.
3Step by step Steps
- Step 1: Know what dissolving isPut a spoonful of salt into clean water and stir a few times: the grains grow smaller and smaller until they vanish, while the water turns salty. That is dissolving — the salt breaks into tiny, tiny bits spread evenly through the water, invisible to the eye but tasteable. Note two features: first, after dissolving the water is clear with nothing settled; second, the taste of the water changes. When both are true, we say the material dissolves in water. Sugar and salt both dissolve like this.
- Step 2: Run a sorting experimentPrepare four clear cups, half filled with clean water, labelled salt, sugar, sand and stone. Add one spoonful of material to each, stir each ten times with a clean spoon, leave them a while, then observe. The result: the salt and sugar disappear and the water turns salty or sweet; with sand the grains slowly settle to the bottom — the water clouds when stirred but clears as the sand sinks; the pebble lies at the bottom all along. Record your observations in a table and the sorting is clear: salt and sugar dissolve, sand and stone do not.
- Step 3: Prove the dissolved salt is still thereSomeone may ask: does dissolved salt disappear? Prove it with an experiment. Pour a little salty water onto a white plate and leave it on a sunny windowsill for two or three days. The water slowly evaporates and a layer of white powder appears on the plate; taste it (ask an adult first) — it is salty. That is the original salt. The experiment proves: dissolving is not disappearing; the salt only becomes invisible bits in the water. That is why salty water must not be used on plants — the salt is still there.
- Step 4: Speed up dissolving — stirTake the same spoonful of sugar into two equal cups of cold water: leave one untouched and stir the other with a spoon. The stirred one dissolves much faster. Why? Stirring sets the water moving, washing away the sweetened water around the grains and constantly bringing fresh water to touch them, so the sugar dissolves quickly. In daily life, Mum always swirls the spoon when making milk tea — same reason. Stirring is the simplest and safest way to speed up dissolving.
- Step 5: Speed up dissolving — warm water and fine grainsThe second way is warm water: dissolve sugar in cold water and in warm water side by side, and the warm cup is clearly faster, because higher temperature helps the grains spread. Stay safe: use water that is warm but not scalding, never pour hot water yourself, and always ask an adult. The third way is grinding the sugar first: fine powder touches much more water and dissolves at once. A sugar cube dissolves more slowly than granulated sugar for the same reason — one whole lump touches less water. Use all three ways together for the best effect.
- Step 6: Experiment rules and daily usesFollow the rules in experiments: observe carefully and record honestly — never guess the result; use clean cups and spoons, wash up afterwards and clear the table; never drink the experiment water. Dissolving knowledge is useful in life: stir your drinks, salt dissolves into soup, washing powder dissolves for laundry. On the other hand, the sand and stones in rivers never dissolve, which is why riverbeds are made of them. Telling dissolving from non-dissolving is an important property of materials.
5Worked example Example
Example: Long puts a spoonful of sugar into cold water, stirs a few times and drinks — but grains of sugar remain at the bottom. How can the sugar dissolve faster?
- Observe first: in cold water the sugar dissolves slowly and undissolved grains sit at the bottom.
- Way one: stir with a spoon; the moving water sweeps the sweet water away from the grains, so the sugar dissolves faster.
- Way two: use warm water (ask an adult to pour it); higher temperature clearly speeds up dissolving.
- Way three: grind the sugar into fine powder first; tiny grains touch much more water and dissolve at once.
- Answer: Stirring, warm water and fine grains all make sugar dissolve faster. Dissolved sugar does not disappear — it only becomes invisible bits in the water. Salt dissolves the same way, while sand and stones do not dissolve and simply sink to the bottom.
6Common mistakes Mistakes
7Quick check Quick check
Q1What happens when salt is stirred into clean water?
Q2Does sand dissolve in water?
Q3Name two materials that dissolve in water.
Q4Name two materials that do not dissolve in water.
Q5Name one way to make sugar dissolve faster.
8Recap Recap
- Salt and sugar dissolve in water; sand and stones do not.
- Dissolved material is still in the water, only invisible.
- Stirring makes dissolving faster.
- Warm water and fine grains speed up dissolving too.
- Observe carefully in experiments; beware of hot water.