Home School - Investigate Dissolving

Summer holidays are over and we are now back in the swing of Home Education.

With this in mind I thought that there is no better way than kicking off with a science experiment.

I wanted to spend a couple of lessons looking at the concept of dissolving and specifically which substances dissolve and the ones that don't.

That some substances can dissolve in water.

 

To select and explore activities and resources independently

To use basic vocabulary as well as extend to learning new sounds, words and meanings

To explore, record and summarise the different changes

To ask questions about why things happen and how things work

Materials

1.       Cold Water

2.       White Sugar

4.       Salt

5.       Soil

6.     Flour

7.     Coffee

8.     Small bowls/See through glasses

9.       Spoons

We started off by discussing the difference between the substances provided. Both of the boys felt to see if they could distinguish the difference and looked at each substance carefully.



For the sugar, salt, sand and coffee they thought that they were like little balls and William used the word "grainy". They also discussed how the flour was really soft and that the soil was really hard.

We started off investigating with cold water so we could then compare later the difference between hot and cold.

The boys each had a glass each filled half way with cold water and discussed what we thought might happen if we put a spoonful of soil into the glass.  

(I wanted to start with soil because I wanted them to consider that it wouldn’t dissolve within the experiment and to subsequently see if they use prior understanding of sugar and salt)

Both of the boys said that they didn't think that the soil would dissolve but that it would make the water dirty like it would dissolve because it would make mud.

I then asked if they thought it would make a difference if we stirred the water and soil with a spoon.

Again, they specified that it would become mud but they agreed that it would happen quicker. James did say that he thought some might dissolve because the spoon would break some of the soil up and make it smaller but it would still be mud.

Now it was time to test!

Putting the soil in the water just made the soil sink to the bottom. The colour of the water changed to a dirty brown colour but didn't go to the colour that the boys expected. When James stirred the water with the soil in we discovered that the soil was more likely to either clump together in bigger pieces or to be broken down more and change the water colour darker.

I asked the boys if this meant that the water dissolved the soil. William was very quick to say that he thought it was more likely that the spoon broke the soil rather than it dissolving.

We then repeated this with each substance.

William was quick to identify coffee and what he thought would happen to it. He said that he was certain that the granules would dissolve because he's seen it happen before when I make my coffee. James was in agreement but said that he thought it would only work if I stirred it as he had seen that I do that with my coffee too. I did try to suggest that it might not be correct as I have my coffee with hot water but they both stood by their decision.

The coffee as a whole started dissolving nearly instantly within the cold water. The boys were a little surprised that more didn't happen until they realised that they hadn't stirred it. Once William had used the spoon the remaining granules soon disappeared. The water became darker and it appeared that everything had fully dissolved.

I wanted to test the boys logic and problem solving by asking how they could be sure that the coffee had dissolved rather than hiding in the dirty water like the soil.

William did suggest that we could use a sieve to drain the glasses and see what we were remained with. I liked that he thought of this but wanted to see if there was another way.

Eventually they considered to use the spoon through the water and compared this technique with both the soil and coffee. The glass with the soil showed that there were still some in the bottom when the spoon scrapped the bottom; the coffee glasses showed nothing but water, even after several attempts.

Subsequently, the boys declared that the coffee dissolved in the cold water and worked quicker once the spoon stirred it. 

(Sugar)

(Salt)

We repeated the test with both sugar and salt. The boys instantly relied on the evidence that they had with the coffee and predicted that the both substances would be affected in the same way. Their basis for this was that both sugar and salt are added to liquids and stirred and if that worked for the coffee that it would work for these.

The boys were both impressed at how much quicker the salt and sugar had dissolved! I asked them what they thought caused this.

The positive and negative areas of water molecules are attracted to the oppositely charged ions in salt and to the positive and negative areas on sugar molecules the same way that two magnets would attract. Due to this the water would overwhelm the molecules quicker to dissolve.

We finally used the flour.

I wanted to leave the flour to last; I knew that the boys would rely on the fact that they had prior knowledge that flour "dissolves" in liquid where we have used it in cooking. I also knew that they would guess that stirring it would make it dissolve. However, I knew that it would clump together and even stirring it in cold water wouldn't dissolve the flour as it doesn't dissolve.

 The boys did exactly what I expected. They predicted that the flour would dissolve quickly, just like the coffee, sugar and salt, and for the same reason that we use it in cooking.

As I thought the flour clumped together and was partially disappearing (as seen below). The boys were confused and thought that it needed stirring and mixing more; William suggested it just dissolves slowly.

I explained that flour never really dissolves and that it just gets smaller and sits next to the water. I also explained that this is why when using it in cooking and baking that it adds to the process and if it dissolved then it wouldn't be able to do that. (Like using self raising flour to create a rise in baking. The combination of salt, flour and baking powder remains within the mix)

I discussed with them that when a solid is mixed with a liquid that it becomes a solution or a suspension. A solution (Sugar and Salt) will go clear and never settle where a suspension (Flour and Soil) is cloudy and will settle eventually even if it takes longer with different substances. I said that coffee was the only thing that broke this rule; explaining that coffee is a solution as it is a solid that dissolves but doesn't produce a clear liquid.

I loved doing this as it tested what the boys already knew and what they didn’t and within that focus on what exactly was happening. They clearly both had different ideas at what would and wouldn’t work but each engaged fully to find out. They both were able to identify features from prior knowledge and eventually use correct terminology.

It is a great little activity and one that is perfect for varied ages. Following this we will be expanding our understanding to see if hot water makes a difference.

So what do you think? Will you give this a try?