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Assignment for primary school children: Growing crystals

Primary school children are particularly curious and there are many exciting things to discover, especially in the house. For example in the bathroom: Why are there sometimes white spots on the mirror? Hasn't it just been cleaned? 
We have prepared an assignment from our teaching material "Lilus House - Language Skills through Experiments" in which children get to the bottom of this phenomenon. With just a few household objects they grow crystals and at the same time learn that there is more in the water than they can see. 

The assignment

Lilu, Alina and the spider are at home, but they are not bored. Now they can go on a discovery tour of scientific phenomena! And they quickly find something interesting in the bathroom. The spider notices it first: "Look at the mirror! We just cleaned it, but now there are all these little white spots. But why? Where do all these stains come from?"

Alina replies: "It is lime. It comes from the water we used to clean the mirror." "But the water was clean. I didn't see any lime in it", the spider says confusedly. "There are many minerals in the water, even if you can't see them. Come on, I'll show you with an experiment," exclaims Lilu.


  • cup of hot water
  • clean jar
  • salt
  • spoon
  • coffee filter
  • funnel
  • cord
  • pencil
  • paper clip
  • food colouring (optional)


  • Take a cup of hot water.
  • Add one teaspoon of salt and stir.
  • Keep adding salt and stirring until the salt stops dissolving.
  • Place the coffee filter in the funnel.
  • Pour the saltwater through the coffee filter into the clean jar.
  • Add food colouring if you want your crystals coloured and stir.
  • Tie a paper clip to the cord.
  • Tie the cord to the pencil, so the paper clip hangs in the water while the pencil balances on the top of the jar.
  • Wait to see what happens.
  • Make a drawing of the final result!

Safety! Be careful with the hot water!

Lilu takes a glass of water: "Look, I put a spoonful of salt in the water. After I stir it, you can’t see the salt anymore. That's because the salt has dissolved in the water. But when the water evaporates, the salt crystallises." The spider asks, "What happens now?" "Now we must wait." Lilu attaches a paper clip to a piece of string and ties the string to a stick. Every morning, the spider goes down from its web to find out if you can finally see crystals in the glass with the string.

One morning Lilu and Alina wake up because the spider crawls around on their faces: "You scared me! What are you doing?" shouts Lilu.  "Now you can finally see something: It looks as if there are lots of little white stones on the string and on the paper clip. It seems as if the salt wants to climb out of the glass. Come and see!" Together, the friends look at the crystals they have grown. Now even the spider understands the white spots on the mirror. The lime cannot be seen with the naked eye, but it is there. If you clean the mirror with water, the water will evaporate and the lime will stay behind!

This assignment is taken from our brochure "Lilu's House: Language Skills through Experiments". You can download the brochure here


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