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Physical Change
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Physical change is a change in which the substance changes form but keeps its same chemical composition - therefore the action is reversible.
Changes of state are defined as physical changes – for example liquid water and ice (frozen water) are both the same substance, water, even in a liquid or solid from the chemical composition remains the same.
Folding a piece of paper is also defined as a physical change, because the form of the paper has been altered but not the papers chemical composition.
(KentChemistry, n.d.)
Changes of state are defined as physical changes – for example liquid water and ice (frozen water) are both the same substance, water, even in a liquid or solid from the chemical composition remains the same.
Folding a piece of paper is also defined as a physical change, because the form of the paper has been altered but not the papers chemical composition.
(KentChemistry, n.d.)
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Chemical Change
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Chemical change is a change in which something new is formed therefore making the process irreversible. The original chemicals change into an entirely different substance which has a different chemical composition.
For example the reaction of iron with air (rusting) or the reaction of a metal and acid is completely irreversible.
Certain observations will indicate that a chemical change has occurred. These are:
- The reaction produces a change in temperature – either becoming hotter or colder.
- Formation of gas bubbles.
- Formation of a solid.
- A change in colour.
- Formation of a different odour.
(KentChemistry, n.d.)
For example the reaction of iron with air (rusting) or the reaction of a metal and acid is completely irreversible.
Certain observations will indicate that a chemical change has occurred. These are:
- The reaction produces a change in temperature – either becoming hotter or colder.
- Formation of gas bubbles.
- Formation of a solid.
- A change in colour.
- Formation of a different odour.
(KentChemistry, n.d.)
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Learning experience activities
Chemical Changes
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Tie- Dyed Milk
Watch as the surface tension of the milk is disrupted by the soaps fat dissolving properties
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Equipment:
- A shallow dish
- Full cream milk – room temperature
- Food colouring – various colours
- Liquid dish soap
- A dropper
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Method:
1. Pour a layer of milk (1 cm deep) into the dish.
2. Carefully place one small drop of each of the food colours on the surface of the milk – evenly spaced.
3. Using the dropper, place one drop of dish soap onto the surface of the milk in the centre of the dish - Prepare to observe
the changes!
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Observations:
- What happens to the food colouring when it is first added to the milk?
- What happens when the soap has been added?
- In which directions does the food colouring move when the soap is first added?
- What direction does the food colour move after the experiment has been running for a while?
- Does the movement go on forever? What happens?
- What would happen if you add another drop of soap after the colours have stopped moving?
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Explanation:
When the food colouring was placed on the surface of the milk, nothing really happened. That is because food colouring is less dense than milk, so it floats on the surface, and the colours do not mix unless you manually stir the mixture.
The chemical reaction began with the drop of soap! The soap disrupts the surface tension of the milk by dissolving the fat molecules found in the milk – causing the food colouring to move with the surface which streams away from the soap. As the soap becomes evenly mixed with the milk, the action slows down and eventually stops.
As the soap becomes evenly mixed with the milk, the action slows down and eventually stops. Addition of another drop of soap may start the process again.
- A shallow dish
- Full cream milk – room temperature
- Food colouring – various colours
- Liquid dish soap
- A dropper
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Method:
1. Pour a layer of milk (1 cm deep) into the dish.
2. Carefully place one small drop of each of the food colours on the surface of the milk – evenly spaced.
3. Using the dropper, place one drop of dish soap onto the surface of the milk in the centre of the dish - Prepare to observe
the changes!
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Observations:
- What happens to the food colouring when it is first added to the milk?
- What happens when the soap has been added?
- In which directions does the food colouring move when the soap is first added?
- What direction does the food colour move after the experiment has been running for a while?
- Does the movement go on forever? What happens?
- What would happen if you add another drop of soap after the colours have stopped moving?
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Explanation:
When the food colouring was placed on the surface of the milk, nothing really happened. That is because food colouring is less dense than milk, so it floats on the surface, and the colours do not mix unless you manually stir the mixture.
The chemical reaction began with the drop of soap! The soap disrupts the surface tension of the milk by dissolving the fat molecules found in the milk – causing the food colouring to move with the surface which streams away from the soap. As the soap becomes evenly mixed with the milk, the action slows down and eventually stops.
As the soap becomes evenly mixed with the milk, the action slows down and eventually stops. Addition of another drop of soap may start the process again.
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Vinegar and baking soda bomb
experience how extreme chemical reactions can be
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Equipment:
- Vinegar
- Baking soda
- 750ml plastic bottle and cap
- Paper towel
- Table spoon
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Method:
1. Half fill the plastic bottle with vinegar.
2. Spread two table spoons of baking soda over a piece of paper towel.
3. Roll up paper towelling so the baking soda will not fall out.
4. Gently push the paper towel into the bottle and quickly replace the bottle cap.
5. Quickly shake bottle then throw away from people as far as possible – observe the explosion!
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Explanation:
By mixing vinegar (acid) and baking soda (base) an ACID-BASE reaction occurs and the two chemicals work together to create a gas (carbon dioxide). Gasses need a lot of room and the carbon dioxide starts to fill the bottle, and keeps filling the bottle until the bottle can no longer take the pressure – that’s when the explosion occurs.
- Vinegar
- Baking soda
- 750ml plastic bottle and cap
- Paper towel
- Table spoon
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Method:
1. Half fill the plastic bottle with vinegar.
2. Spread two table spoons of baking soda over a piece of paper towel.
3. Roll up paper towelling so the baking soda will not fall out.
4. Gently push the paper towel into the bottle and quickly replace the bottle cap.
5. Quickly shake bottle then throw away from people as far as possible – observe the explosion!
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Explanation:
By mixing vinegar (acid) and baking soda (base) an ACID-BASE reaction occurs and the two chemicals work together to create a gas (carbon dioxide). Gasses need a lot of room and the carbon dioxide starts to fill the bottle, and keeps filling the bottle until the bottle can no longer take the pressure – that’s when the explosion occurs.
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Physical Changes
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Shape-shifting water
observe as water changes from solid to a liquid from and back again
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Equipment:
- Ice cubes
- Plastic cup - transparent
- Freezer access
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Method:
1. Place a few ice cubes into the plastic cup.
2. Place cup in direct sunlight and observe the melting process.
3. When the water has become a liquid again place the cup into the freezer and allow to freeze - periodically observe the freezing
process.
4. Repeat process.
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Explanation:
The change of water from a liquid to a solid due to the change in temperature is classed as a physical change. the water is able to change its form but the chemical composition remains the same and the action is reversible.
- Ice cubes
- Plastic cup - transparent
- Freezer access
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Method:
1. Place a few ice cubes into the plastic cup.
2. Place cup in direct sunlight and observe the melting process.
3. When the water has become a liquid again place the cup into the freezer and allow to freeze - periodically observe the freezing
process.
4. Repeat process.
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Explanation:
The change of water from a liquid to a solid due to the change in temperature is classed as a physical change. the water is able to change its form but the chemical composition remains the same and the action is reversible.
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origami
physical form may change but the chemical composition remains the same
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Origami is the Japanese art of folding paper into shapes representing objects - physically changing the form and appearance of the paper but the chemical composition remains the same - and the change is reversible.