Secondary Science - Solids Liquids Gasses
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Chapter 9 Solids, Liquids and Gases
The Solid State
Younger children – state of matter depends on appearance and behavior. A solid is any “rigid” material, a powder is a liquid because it pours and any non-rigid material such as cloth or a sponge is an intermediate between solid and liquid because it is soft or can be torn. Age 11 – powder is an intermediate state of matter. Teachers should explain that powders are composed of small pieces of a solid.
The Liquid State
Children use phrases such as “runny” or that it “can be poured” to identify a liquid. Children compare liquids to water. Therefore, they have trouble classifying viscous liquids such as paste or honey. Also, children may describe a liquid as having less weight than a solid.
The Gaseous State
Young children – air and smoke don’t possess material characteristics; only abstracts. Children understand that air and smoke exists but don't understand that existence has matter or mass. Also, many believe air is good because it is needed for life but gas is bad because it is poisonous or dangerous. Age 9 - 11 – children are aware that gases have material characteristics but still may not know a gas has mass or weight. They believe gases have “negative weight” so the more you have the lighter you become. They must connect the idea that gases have mass to understand conservation of mass in a chemical reaction that produces gas. When items turn to gas, children believe they lose mass.
Melting
At ages 5 – 6 – 5% of children think a solid loses weight or mass when it melts. Age 7 – 50%; age 10 - 75%. Many children cannot distinguish between melting and dissolving. Students age 8 – 17 often regard melting as unrelated to temperature.
Freezing
Students often do not see a specific temperature causing a change of state.
Evaporation
Young children do not understand the concept of conservation but can see the material disappears as it evaporates yet they do not try to explain this. At 8 – 10 yrs. of age as their sense of conservation improves they state that the evaporated substance must go into a “receptacle.” Once students develop an understanding of conservation, atomism and air at 12 – 14 yrs. of age they also develop a conception of evaporation. Young children view evaporation as a loss of mass or weight as the substance seems to disappear. They explain the gaseous form of a substance as having no weight. At age 9 only 5% of children explain conservation of mass during evaporation but by age 14 that increases to 80%. Older pupils suggest liquid states as heavier than gaseous states of the same substance. Students understand boiling before evaporation. 70% of 6 – 8 yr. olds explained when water boils it produces a vapor made of water but failed to recognize a wet saucer drying as evaporation.
Boiling
Time and energy supply can affect boiling point. 40% of 12 yr. olds believe that pure water
Kimberly A. Tafoya
Solids, Liquids and Gases
The three states of matter cab be a challenge in terms of classification for different age groups. In addition, the process involved in a change of state can be misunderstood more often than not by children that many not be ready developmentally to comprehend this level of reasoning.
This section describes the outcome to various answers of different aged pupils as they were questioned on the states of matter and the processes that occur between the states. Researchers suggest that before pupils learn particular theory, they should be capable of classifying materials.
The Solid State:
• Israeli Children (Ages 5-13) o Regard solids as rigid (associated solids as harness and strength) o Regarded powders as liquids because they can be poured. o By age 11 pupils described powders as intermediates, the in between.
The Liquid State:
• Children identify liquids as ‘runny’ or ‘can be poured’. • Liquids are ‘watery’ or made of water. • The more viscous the material the more difficult it was for children to classify.
The Gaseous State:
• Unaware that gases have material character. • Contain misconceptions about gases. o Air is good-used for breathing and life. o Gases are bad-poisonous or dangerous. o Pupil’s awareness of gases as materials comes later when they are able to understand that some gases have observable colors and odors whereas most are colorless and odorless. Children 9-13 o Consider gases as having negative weight, the container becomes lighter the more gas put in. o Pupils are unlikely to conserve masses of gases in a chemical reaction.
Melting:
o Pupils may believe that there is a loss in mass o When asked if mass is conserved the following ages stated yes: o Age 5: 5% o Age 7: 50% o Age 16: 75% Students in a sample of ages between 8-17 also could not discriminate dissolving as different from melting.
Freezing:
o Pupils generally do not regard a change of state as being related to a specific temperature. Evaporation: o Ages 5-6 impressed by materials disappearing but could not give any explanation. o Ages 8-10 suggested that disappearing liquid must go somewhere. o Ages 12-14 link the notion of conservation, atomism and air. o Because liquid changes to gas, many kids believe that the material is not conserved because it disappears.
Children’s understanding of boiling is greater than evaporation. Students have a difficult time understanding that the water disappears from surfaces of objects.
Boiling:
Andersson, proposed 2 questions of the students.
1. What happens if water continues to heat for 5 more minutes? o The following percentages of pupils stated the temperature would rise above 100°C. o Age 12 40% o Age 15 16% o Those that suggested that water would remain at 100°C. o 12-13 years 25% o 14 years 35% o 15 years 32% 2. What would happen if the stove setting increases? o The following percentages of pupils stated the temperature would rise above 100°C. o Age 12: 80% o Age 13 63% o Age 14 60% o Age 15 54% Even by age 15 only 31% gave the correct answer. Student’s logic led them to believe that the energy supply could increase the boiling point. They related heat and temperature to be the same.
Condensation:
o Less than 20%, ages 10-14 believed that water condensed from water vapor in the air. o Researchers found that pupils understood that vapor can change to water. o Applying the knowledge was difficult. o Many ages 12-17 thought coldness in air caused the H2 and O2 in air to form water. o 60% ages 12-15 o 30% age 17
o The proportion who expressed condensation form water in air increased 10-55% over ages 12-17. o When given the scenario of a hand held over a pot of water using the same age range the percentages ranged from 20-55%.
Sublimation:
o Pupils associated a loss in mass as the solid changes to a gas. o An demo using I2 in sealed glass tube which was heated gave the following results. o Age 9 30% conserved mass o Age 11-13 50% conserved mass o Age 15 80% conserved mass
Dissolving:
o Up to age 8, pupils focus on solute only and say it just disappears, it melts away. o The melting away is an association to ice in water. o Research in the conservation of the solute uncovered that: o 67 % of 8 year olds thought the solute is preserved. • Only 50% of those that said it was preserved say it contains mass. • The other 50% thought of weight of the solute suspending in the water. o It wasn’t until age 12 that students suggest weight of the solute in the solution. o Also the concept of a homogeneous mixture isn’t clear, children still suggest that the sugar can be filtered out of the water.
