Secondary Science - Water
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Contents |
'Chapter 12 – Water
By Alejandra Caino
Water as a Liquid
• Children often think of water as the exemplary liquid, and all liquids are “watery” or have water.
• Students think that particles are not closely packed and rolling over one another, but rather as moving freely away from each other.
• They saw no reason why liquids should have a fixed volume therefore making it compressible.
Freezing Water and Melting Ice
• Students don’t think that freezing takes place at a specific temperature. • In a particle model of the process of freezing, water particles become packed together. • Ice doesn’t take as much space as when the particles are at room temperature. • They think that there is a loss when the particles freeze.
Boiling Water
• In a study, 40% of 12 year-olds believed that if water boiled for an extra 5 minutes the temperature would be higher than 100 °C.
• 25% of 12 – 13 year-olds believed that the number on the knob of the stove determined the temperature of the water.
• Children appear to think that heat and temperature are the same thing. If you add heat then the temperature goes up.
• When water boils students see vapor but when they see a wet surface dry they think that water disappears or penetrates the object.
Evaporation
• Children of ages 5 & 6 are fascinated by the process of evaporation and cannot explain what happens.
• By ages 8 – 10 children can then suggest that the water is going someplace.
• By ages 12 – 14 children have a correct conclusion of evaporation which links conservation of matter.
Condensation
• Children responded that coldness changed into water and cold caused hydrogen and oxygen to change into water.
• Researchers agreed that students know that vapor can be changed into water it is still hard to grasp.
• Researchers also asked to explain how hands become wet when held above boiling water and there were even responses to
o #1) vapor changes into water and
o #2) the hand becomes wet from the vapor.
Dissolving Substances in Water
• From an early age to adulthood individual have different conceptions of dissolving:
• Up to age 8 they believe that the solute (sugar) just disappears, melts away, dissolves away.
• 2/3 of the 8 year-olds thought that the dissolved sugar was preserved in some way.
• Only ½ would admit the sugar weights something, they seem to think that it is up in the water and not weighting down on the container.
• Although students are taught that solutions are homogenous mixtures of two or more substances they seem to hold a various ideas about solutions.
• Some students thought there were two phases:
o A sugar particle could be filtered out from water.
o A solution was one single pure substance.
• Molecules were rarely mentioned in the earlier years but at age 15 & 17 children depicted molecular particles of sugar and not molecules of water.
Water Cycle
• Researchers concluded that students need to understand the concepts of evaporation and condensation as well as that water vapor and drops of water have weight and undergo free fall before they understand the water cycle.
• Students between 5 – 15 years old were interview about the water cycle.
o Ages 5 – 7 say that rain falls when (God) opens a water reservoir, clouds are made of smoke or cotton or wool: clouds and rain were not related in their thinking.
o Ages 6 -8 say clouds go into the sea and collect water then give rain.
o Ages 6 – 9 say clouds were made of vapor created when the sea is heated by the sun (begin to get the idea).
o Ages 7 – 10 say that it’s like a sponge having drops of water.
o Ages 9 – 10 clouds are made of water evaporated from puddles.
o Ages 11 – 15 clouds are made when vapor becomes cold.
o Above age 15 weight was attributed to vapor and small drops of water.
Water and Living Things
• Children think that plants take in water as food. They think that the main function of leaves is to take in water and used for photosynthesis.
• Pre- school children thought that water would cause body weight gain.
Floating and Sinking
• Children 7 – 14 years old were surveyed on understanding of floating:
o Objects that floated with a significant proportion above the surface were consired “floating”
o When a small portion was above the surface students thought they were somewhat floating and somewhat sinking.
o Some thought they were beginning to sink and eventually go down.
o Some thought they were not really floating but they were being held up by the water’s skin.
o Some believed that objects such as fish and submarines were not floating.
o They believe that objects float because they are light.
• Children have 4 ways of looking at buoyancy:
o Role played by the type of material
o Role played by shape, holes, cavities
o Role of air
o Role of water
