This practical seeks to address aspects of the Working Scientifically and Physical World sections of the syllabus. In this experiment, students will cover the following dot points:
make and test predictions about the effect of temperature on the state of some substances, eg adding and removing heat from water
observe and describe some readily observable reversible changes that materials can undergo, eg by melting and then solidifying chocolate, and dissolving and retrieving salt or sugar from water
Equipment List
Practical
Water
Small (250 mL) bottle
Food colouring
Salt
Thermometer
Blu-tack
Clear straws
Parafilm
Permanent marker
Worksheets
Teacher information sheet
Student activity questions and instructions
Method
Complete Student Inquiry sheet.
Part A (Assembling the thermometer):
Fill the bottle to the brim with water mixed with a few drops of food dye.
Cover carefully with a piece of parafilm (parafin wax) and insert the straw through the parafilm into the water.
Make sure the seal around the straw and the neck of the bottle is airtight using more parafilm and/or blu-tack.
Blow gently into the straw to test the seal. The water should come up the straw a little when you stop blowing.
Set the thermometer on a stable surface and use a permanent marker to mark the level of the water in the straw and room temperature.
Attach the pre-made thermometer to your bottle using sticky tape and record the temperature.
Part B (Measuring changes in temperature):
Use a hairdryer to warm the bottle. Mark the new height of the water and the reading from the thermometer.
Measure the height difference between the original marking and the new marking. Also calculate the difference in temperature from the starting temperature to the new thermometer reading.
Allow the thermometer and the bottle to return to room temperature and repeat steps 1 and 2.
Part C (Repeat with salt water):
Dissolve 35 g of salt into 1 L of water to simulate ocean salinity.
Repeat Part A and Part B using the salt water instead of plain water.
Complete Student Reflection sheet.
Background Information
When substances are subjected to changes in temperature, they undergo observable physical changes aside from the obvious changes in state. When water is heated (but before it reaches its boiling point and converts to a gas), the molecules vibrate faster due to the input of energy in the form of heat. These vibrations cause the water to expand as heat is applied, so each molecule requires more space. This reduces the density of the water so the water goes up the straw. Density is the mass of a substance (e.g. in grams or kilograms) per unit volume (e.g. liters or milliliters). It is often recorded in the units grams per unit cubed (g/cm^3).
When salt is added to the water, the density of the water increases and so the amount water that goes up the straw when the salt is added is slightly less.
If the water were subjected to cooling (this is another test you could perform), it would contract, thus increasing in density. However when water is frozen it expands again! This means that ice is less dense than water. Another way to know that ice is less dense than water is to drop an ice cube into water. If it floats on the water, it is less dense. One natural phenomena where this is demonstrated is icebergs that float in the ocean.
So now you know that when water is heated it expands, when it is cooled it contracts and when it is frozen it expands again. And all these changes are changes in density. So, what impact does this have in real life?
Rising sea levels:
Global warming is the gradual increase in global temperatures which is often attributed to the human over production of greenhouse gases. This is linked to the melting of the polar ice-caps and rising sea levels which threaten some island and coastal communities as well as the habitats of many animals.
However, other factors also contribute to the rise of sea levels.
These include the expansion of water (decrease in density) due to these warmer temperatures. It looks like a tiny change on the small scale of the home-made thermometer, but on the massive scale of the ocean, this change has a large impact on sea levels.
Teachers Information Sheet
This practical seeks to address aspects of the Working Scientifically and Physical World sections of the syllabus. In this experiment, students will cover the following dot points:
Equipment List
Practical
Worksheets
Method
Complete Student Inquiry sheet.
Part A (Assembling the thermometer):
Part B (Measuring changes in temperature):
Part C (Repeat with salt water):
Complete Student Reflection sheet.
Background Information
When substances are subjected to changes in temperature, they undergo observable physical changes aside from the obvious changes in state. When water is heated (but before it reaches its boiling point and converts to a gas), the molecules vibrate faster due to the input of energy in the form of heat. These vibrations cause the water to expand as heat is applied, so each molecule requires more space. This reduces the density of the water so the water goes up the straw. Density is the mass of a substance (e.g. in grams or kilograms) per unit volume (e.g. liters or milliliters). It is often recorded in the units grams per unit cubed (g/cm^3).
When salt is added to the water, the density of the water increases and so the amount water that goes up the straw when the salt is added is slightly less.
If the water were subjected to cooling (this is another test you could perform), it would contract, thus increasing in density. However when water is frozen it expands again! This means that ice is less dense than water. Another way to know that ice is less dense than water is to drop an ice cube into water. If it floats on the water, it is less dense. One natural phenomena where this is demonstrated is icebergs that float in the ocean.
So now you know that when water is heated it expands, when it is cooled it contracts and when it is frozen it expands again. And all these changes are changes in density. So, what impact does this have in real life?
Rising sea levels:
Global warming is the gradual increase in global temperatures which is often attributed to the human over production of greenhouse gases. This is linked to the melting of the polar ice-caps and rising sea levels which threaten some island and coastal communities as well as the habitats of many animals.
However, other factors also contribute to the rise of sea levels.
These include the expansion of water (decrease in density) due to these warmer temperatures. It looks like a tiny change on the small scale of the home-made thermometer, but on the massive scale of the ocean, this change has a large impact on sea levels.