What we know about dissolving

Arrival decision: Pick the step cards or the written frame. Both are full answers. You can change your mind later.

On your table are four step cards. One shows salt going into water. One shows a clear solution. One shows a dish being warmed. One shows what is left at the end.

Put them in the order you think they happen. That is all you need to do to begin.

Nobody has to come to the bench. You can see the whole test from your seat.

Set the seat route out loud at the start, not as a fallback later. Goggles for everyone at the bench, and an adult heats the dish.

Where does the salt go?

Only one of these can be right. They cannot both be true. So we can test them.

That is the need for this lesson. If Answer B is right, the salt should come back when the water leaves. If Answer A is right, nothing will be left.

We can weigh the salt before it goes in. Then we can weigh what comes back out. Two numbers settle the argument.

A test that could go either way is a real test. Today the answer is not written down anywhere in advance.

Do not confirm either answer. The prediction has to be made while both are still open.

The four steps

Look at the picture. There are four steps and they go left to right.

In step two the salt is still there. You just cannot see it. That is what a solution is.

In step three the water turns into a gas. It goes into the air. The salt cannot do that, so it stays.

Step four is the test. If salt is in the dish, Answer B was right.

Three numbers. Empty dish. Dish with solution. Dish at the end. The last one minus the first one is the salt.

We write the numbers down as we go. Numbers written later are memories, not measurements.

Say each number out loud as it is written. A learner who has not seen the balance read cannot use the numbers later.

Predict what will be in the dish

Predict first: write your choice and hold it. Nobody says it out loud. Everyone commits at the same time, and then we hold up the boards together before you check.

After the test, one person from each table says what they predicted and what they saw. If those two are different, that is a good thing to say out loud.

Changing your mind after you see the dish is not losing. It is what the test is for.

Take the prediction from every table before heating starts. A prediction written afterwards is not a prediction.

What the two masses tell you

The picture shows the two numbers. The first one is bigger. The second one is smaller.

What went missing between them is the water. The water left as a gas.

The salt is in both numbers. It was in the dish before, and it is in the dish now.

So the salt never left. It was spread out in the water the whole time.

That sentence is the answer to the question we started with.

Keep the reasoning on the numbers. A learner who says the salt came back has the right result and the wrong mechanism; the numbers correct it.

Work out what is left

Three grams. That is the salt. It was there before it dissolved and it is there now.

Then we ask the second question. The dish with the solution was 78 grams. What has gone? Where is it now?

Take the subtraction from a learner who has not spoken today. Scribe exactly what is said.

Your record: predict, test, explain

Finished early? Work out what would happen if we used twice as much salt. Then say what would stay the same.

If you are stuck on the last sentence, read the two numbers out loud. The difference between them is the water.

Nobody has to go to the bench, and nobody will ask why.

Your record is done when the prediction, the two masses and one sentence about the salt are all on it.

Record the route used and any scribing on the evidence line, keeping adult support visible and separate from the learner own words.

Audience receives; influence changes something

Did the listener say it was there the whole time? Write that down too. A sentence that already works is worth noting.

Next week we look at what happens when a solid will not dissolve at all. Keep your record.

Nothing goes outside this room unless you say so.

Close by naming one learner who changed a word after their partner heard the wrong thing. That is the influence record, and it belongs to the learner.