The Three States of Water
FoundationWater comes as solid ice, liquid water and gaseous vapour; cold freezes and condenses it, heat melts and evaporates it.
- Water's three states: ice, water and vapour.
- Below zero degrees, water freezes into ice.
- Heated to one hundred degrees, water boils and evaporates.
文體小知識：說明文用三個小實驗演示冰、水和水蒸氣怎樣互相轉換，還教你解釋杯外的水珠。
§Text Passage
1Water is one of the most common things on Earth, and it takes three forms: solid ice, liquid water and gaseous water vapour. Its form changes with temperature — these are the three states of water.
2Put water in the freezer; when the temperature falls below zero degrees Celsius, it freezes into ice. Bring the ice back to room temperature, and it takes in heat and melts back to water. On a summer drink cup, the tiny drops on the outside are vapour from the air condensing on the icy cup.
3Heat water to one hundred degrees Celsius and it boils, turning rapidly into vapour that rises into the air — this is evaporation. The white puffs at a kettle's spout are not vapour but tiny droplets formed when vapour meets cooler air; true water vapour is invisible.
4The three states cycle through nature without stop: water evaporates from the sea into the sky, gathers into clouds, and falls as rain; the snow on high mountains in winter is water in its solid state. Ask an adult to handle the heating in experiments, and beware of hot water.
1Summary 重點摘要
Water comes as solid ice, liquid water and gaseous vapour; cold freezes and condenses it, heat melts and evaporates it.
2Vocabulary cards Vocabulary
The three forms of matter: solid, liquid and gas.
The form with a fixed shape, such as ice.
The flowing form without a fixed shape, such as water.
The form spread through the air, such as water vapour.
Vapour turning into tiny drops when cooled.
Water turning into vapour and spreading into the air when heated.
The bubbling of water at about one hundred degrees Celsius as it turns to vapour.
A solid taking in heat and becoming liquid, such as ice to water.
Water in its gaseous state — invisible and spread through the air.
3Step by step Steps
- Step 1: Know the three statesWater has three forms in nature. Ice is solid: it keeps a fixed shape and does not spread even on a plate. Water in a cup is liquid: it flows and takes the shape of its container. The vapour from boiling water is gas: invisible and untouchable, it mixes into the air. Some people think the white puffs are water vapour, but they are tiny droplets; true vapour cannot be seen. The same water, it turns out, can wear three different appearances.
- Step 2: Experiment one — freezingThe first experiment watches water turn to ice. Half fill a plastic cup, mark a line, and leave it in the freezer for two hours. Take it out: the water has become solid ice and has even swollen a little above the line. Some people think volume stays the same when water freezes, but ice expands — a sealed drink in the freezer may burst. Below zero degrees Celsius water changes from liquid to solid, a change called freezing.
- Step 3: Experiment two — meltingThe second experiment watches ice turn back to water. Take the ice from the freezer and leave it on a plate at room temperature for thirty minutes: the block slowly shrinks, liquid water gathers on the plate, and the weight is just the same as before. Some people think melting adds or loses water, but only the form changes — the weight stays. This change is called melting: ice takes in heat and turns from solid back to liquid, just as a snowman melts on a warm day.
- Step 4: Experiment three — evaporation and condensationThe third experiment is the most fun, and an adult must help. Boil some water; puffs of white rise from the spout as water keeps turning into vapour and spreading into the air — this is evaporation. Hold a cold plate near the white puffs and its underside is soon covered with tiny drops, for the vapour meets the cold plate and turns back to liquid — this is condensation. Some people think these are abstract ideas, yet boiling a kettle and rain clouds are the same thing.
- Step 5: Explain the drops on the cupOn a summer day a cold drink's cup is soon covered with drops on the outside. Some people think the drink leaks through, but it does not: the air always holds invisible water vapour, which meets the icy cup, cools, and condenses into tiny drops clinging outside. Wipe them with a dry towel and a new layer appears — that is why. Some people think the drops come from inside the cup; everyday observation is the finest test of what the books say.
- Step 6: Follow the safety rulesWater experiments involve hot water, so safety comes first. Always let an adult do the heating and the pouring while you watch from the side; never reach for the hot kettle or the flame. Use small tongs to take ice from the freezer instead of holding it bare-handed for long, so you are not frostbitten; wipe the table dry and tidy the materials away. Some people think a moment of carelessness is nothing, yet burns come exactly in careless moments. Keep the safety rules, and the experiment stays happy and safe.
4Diagrams Diagrams
5Worked example Example
Example: Wai left an ice cube on a plate. After ten minutes there was extra water on the plate; later the water kept shrinking. Explain the two changes.
- Ice is water in its solid state, taking in heat at room temperature.
- The ice melted into liquid water, so extra water gathered on the plate.
- The water then evaporated into invisible vapour that spread into the air, so the water shrank.
- The whole journey is solid to liquid, then liquid to gas — all changes driven by temperature.
- Answer: The ice took in heat and melted into water, solid to liquid, so the plate gained water; the water then evaporated into vapour, liquid to gas, so it gradually lessened.
6Common mistakes Mistakes
7Quick check Quick check
Q1What are water's three states?
Q2At what temperature does water freeze?
Q3At what temperature does water boil?
Q4Where do the drops on the outside of the cup come from?
Q5Can we see water vapour?
8Recap Recap
- Water's three states: ice, water and vapour.
- Below zero degrees, water freezes into ice.
- Heated to one hundred degrees, water boils and evaporates.
- White puffs are droplets; true vapour is invisible.
- The three states cycle endlessly through nature.