Answer:
1.) Physical
2.) Physical (probably)
3.) Chemical
Explanation:
Physical changes are changes to substances in which the intramolecular structure does not change. The intermolecular bonds (bonds between molecules) may change, but the actual chemicals involved are not altered.
Chemical changes occur when intermolecular bonds are broken/formed, changing the old substance into something new. Chemical reactions are taking place and the ratio of the elements in molecules are changing.
1.) Melting is an example of a physical change. When melting occurs, the intermolecular bonds between molecules are breaking in response to the introduction of more heat. However, the substance is still the same substance (ex. ice melting is still water as H₂O has not been changed). In this example, scientists are most likely calculating velocity.
2.) Because the original substance is able to be completely removed from the water in the flask, this is probably just a physical change. I say probably because no changes are really occurring here. It is unclear but not probably that any reactions are taking place between the water and the sample as they are easily separated. This may be an example of (can't decide) depending on how must they want you to assume. The property being measured is probably density.
3.) While dissolving the sample was an example of a physical change because just the state of matter changed, when it reacts with sodium hydroxide, a chemical change occurs. Most likely, new bonds are being formed between the elements in the original sample and the elements in sodium hydroxide. This is what allows scientists to measure the pH of a solution.
