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Sharing hypotheses
- Write your hypothesis on the conservation of mass and volume in dissolutions. Is mass conserved during dissolution? What about volume?
Once the objectives are known and the experiments have been designed, the students start to draw up their hypotheses
about whether mass and volume remain the same in dissolution. On this occasion, they have designed the experiment before making the hypothesis.
In other cases this order is reversed. The design can help to develop the hypothesis, and vice versa.
- What do you think, Andrea, if it true or not? - Yes.
- And is this true? - Yes... No.
- Yes or No? Okay. Not this. Why? Did you say why? - No.
- You didn’t say why. Okay, let’s see, Eva, what did you say? - We said no.
- No, neither mass nor volume? - No. Yes to mass and no to volume.
- Yes to mass and no to volume. Okay. What about Silvia’s group? - Yes to mass and no to volume.
- Yes to mass and no to volume. Is they any discrepancy or did you all say the same thing? Yes? You all said the same thing?
So, your hypothesis is that the mass stays the same but the volume doesn’t. Who can explain why? Let’s see... Eva.
- Supposedly, the particles... the water molecules are bigger than those in alcohol and, so the alcohol ones will fill up the spaces between the water molecules.
- And what does that mean? - Less volume.
- That volume is not conserved. What about mass? Let’s see... Paloma? - That even though they don’t take up the same space, they still weigh the same.
- moving the particles amongst each other, they still weigh the same. - There is the same number of particles.
In order to explain the phenomena of nature, scientific theories are needed – in this case a kinetic-corpuscular theory.
The students already knew this theory and their hypotheses are correct. Sometimes it is better to do the experiment before learning the theory.
- But you have all started talking about particles. I haven’t mentioned particles at all.
It is important to differentiate between phenomenological and theoretical things. What we are doing here, at the moment, is phenomenological:
what happens, what is going to occur. But when I want to explain why, I have to turn to the theory. Do you see?
Now we are going to see if our hypotheses are true, and then we will see- you’ve jumped ahead, because you’ve already got the explanation
from the tubular-molecular theory, which were the last two questions we were going to answer, and then one of you will come out and do it.