|Description, Learning Objective:
||Understand some solids dissolve and some do not.
Know that some changes are reversible and some are irreversible
That dissolving, melting, condensing, freezing and evaporating are changes that can be reversed.
That irreversible changes result in a new material being produced, which may be useful.
That heating or cooling materials can cause them to change.
Ask children to explain what they know about dissolving. Use this as a basis to guide discussion of solutions and how to separate them. Tell them they are going to investigate some solids to see which dissolve in water and which do not. Bring up the online activity on an interactive whiteboard. Ask children to predict which of the solids in the menu (salt, flour, coffee, sand) will dissolve in the water to form a solution, and which will not dissolve. Write the predictions on the board.
Within the online activity, show children how to add a substance to the water by clicking and dragging a solid from the menu into the beaker. Click on the Reversing button. Show children how they can drag substances from the menu onto the screen and try to reverse changes that have taken place.
Divide the children into groups with a computer for each group. Let the groups work through the Dissolving and Reversing screens, following the tasks written (and read aloud) at the top of the screen.
Which solids dissolved and which did not? Compare their observations to their predictions made earlier. How can the change brought about by mixing a soluble or insoluble substance with water be reversed (by filtering or by evaporating)? In the reversing part of the activity, which changes were reversible and which were irreversible? Make a list. Tell them that irreversible changes result in the formation of new materials, which may be desirable (e.g. a baked cake) or undesirable (e.g. a rusty bike).
Hand out copies of the worksheet. Explain to children that they must write which of the changes shown are reversible and which are irreversible. Allow children to complete the worksheet independently.
Ask children to make a list of reversible and irreversible changes they observe in their home or garden.