Nappy Knowledge!

Curriculum links:

• Chemistry – Physical chemistry – Investigate how materials may be changed by wetting and drying (hydroscopic)

Learning objectives:

1. All children will learn that baby nappies contain a chemical that soaks up liquids like water or urine (wee!) and that this chemical changes from a powder to a jelly to a solid and can be changed back again.
2. The chemical is called Sodium Polyacrylate and it is also used in other things you can buy like gardening and animal products.
3. Chemistry is all about change and how tiny things called molecules interact with each other and can be used to help us in our daily lives.

Materials:

• Sodium Polyacrylate or nappies if not available
• Water
• Measuring jugs
• Cups
• Spoons
• Table salt
• Scissors (if using nappies)

Safety:

• Be careful using scissors

Instructions:

This lesson is all about introducing the children to how chemistry is a part of everyday life and how a material can change due to a chemical reaction. They will learn how chemical reactions can be seen happening in front of their eyes as a material changes from a powder to a jelly to a solid and then back again.

• Cut open a nappy and show the class the powder that comes out and explain that this powder is a chemical called sodium polyacrylate, which is a kind of salt, but not one you would put on your food, so they shouldn’t eat it! It really, really likes water. So much so, that when it touches water it interacts with the water, soaking it up to make a fluffy powder a bit like snow. In fact this is how fake snow is made!

• Divide the class into groups of 2 – 4 children.

• Give each group some Sodium Polyacrylate in a cup, a measuring jug/graduated cylinder, water, a spoon and a pot of salt.

• Instruct the children to measure out 100 mls of water using the jug and to check at eye-level to ensure they have the right amount. Remind them that chemists must be very precise!

• The children should pour the water slowly into the cup containing the sodium polyacrylate, stopping as they pour to see how the powder is changing. Ask the children to note when the powder becomes like a jelly and when it becomes more like a solid.

Ask the children about what they saw happen. “Did we have a chemical reaction?”, “What happened as you added the water?”, “What happened to the water?”. Point out to them that they had a powder and water, which changed to a jelly and then became a solid. The sodium polyacrylate “likes” the water and they grab a hold of each other and so expand and become a white fluffy solid.

Now tell the class that they are going to add in salt and ask them what they think will happen? Ask them how they might get the water to come back? Tell the children that they are going to separate the sodium polyacrylate from the water by reversing the reaction they saw using salt, the same salt they would find at home and put on their chips!

• Tell the children to slowly use the spoon to spoon salt into the new substance they have made. Ask the children to describe what they see happening as they add the salt.

Explain to the children that they have successfully brought the water back by adding in the salt. Tell them that sodium polyacrylate really likes water, but that it loves salt! When the salt was poured in, the sodium polyacrylate “let go” of the water and “grabbed a hold of the salt” and so the water was released and that’s why it came back.