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Question about physical changes vs chemical reactions?
Hi guy, I need help with this assignment I have, please help me out, I wanna understand this, so f you can gimme the answer but with the reason and stuff, that would be much appreciated, thanks.
Here is assignment question:
As our weekly overview explains, solutions are mixtures. Dissolving one substance in another substance is a physical change.
How do you know? Consider a solution of salt or sugar in water:
1) There are no fixed proportions.
2) All of the substances keep their own properties.
3) The mixture can be separated into its parts through one or more physical changes.
To complete this journal, explain what is meant in practical terms by each of the numbered statements above. In other words, if you had water, sugar, and a container to mix them in, how could you demonstrate each of the numbered statements?
3 Answers
- 7 years agoFavorite Answer
1. If you dissolve sugar in water, you cannot separate the two entities because they are a homogenous mixture.
2. H2O remains a liquid and shares liquid properties along with keeping its color. The sugar/salt are still solids, but they are dissolved during the hydration phase. They do not change into a new substance, but simply break apart.
3. This means if you have salt and water mixed, you can separate them back if you were to heat up the water and evaporate it. The sugar/salt will be back to how it was and the water would be gone.
- 7 years ago
Chemical reactions involve a loss or gaining of ATOMS or an irreversible change in the atomic BONDS. In the example you've given of dissolving sugar in water all the MOLECULES still remain the same. The sugar is made of crystals of glucose molecules. The crystals are broken up into smaller pieces but the glucose molecules still stay the same. That makes it a physical change, breaking up crystals, not a chemical change, turning either the water or sugar into something different. You just have glucose molecules floating in water.
However, the changes can be reversed through further physical changes. If you boil the water, a physical change to the water because molecularly it is still H20 just in its gas state, the solutes, salt or sugar, will come out of solution into crystals along the side of the container. if you then grind those crystals, a physical change, you can return the solids to the granular form they were in when you added them to the water.
Oh and your first question about fixed proportions: Water is H20. No matter how large or small a sample, there will always be 2 hydrogen atoms for every 1 oxygen atom. If there isn't then it isn't water. However SOLUTIONS don't have fixed ratios. You can have as water molecules per sugar molecule as you want and still have sugar water (there is such a thing as too much sugar in water though that's irrelevant to this example. If you are curious though, look up supersaturated solutions)
