Which is the most important question for deciding If a chemical Reaction has occurred?
2 answers:
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Answer:
1. A. Group 1
2. B. A chemical change occurred which is evidenced by the change in color of the solution.
3. D. Physical change because the chemical properties of the salt and water remained the same.
4. D. Sphere B will float because it is less dense than water.
5. C. Shredding them into smaller pieces.
6. A. Her model uses eleven white pom-poms.
B. Her model uses twelve black pom-poms.
E. Her model uses eleven yellow pom-poms.
7. B. The liquids have different densities.
8. D. Physical Properties: color, texture Chemical Properties: ability to rust
9. A. Container A will have 1 liter of helium, and container B will have 1 liter of water.
Explanation:
1.
In the periodic table, <u>rows</u> represent the<em> period</em> that they are in, while columns represent the groups that elements are in. Elements in the same group (column) share similar properties. Since Sodium (Na) is found in group 1, elements that are similar in properties would be found in the same group.
2.
A chemical change is marked with a change in color, production of gas, heat, and sometimes smell and light. A chemical change results in new products formed, in which the properties and identities of the reactants change as well because their atoms were rearranged. In this case, the <u>change in color </u>of solution shows that a chemical change had occurred.
3.
Earlier we said that chemical change results in new products, for physical change it does not. The substance will keep its identity. Like in the scenario, the salt and water did mix together, but when they were separated through evaporation, the salt <u>retained its identity</u> and so did the water. The substances involved merely changed phases. So this was a physical change.
4.
If the density of the object is more than the density of the liquid, the object will sink. On the other hand, if the density of the object is <u>less than the density of the liquid, it will float. </u>
If water has a density of 1g/cm³, the object that has the lesser density will float. First you solve for the densities of each object and it can be computed using the formula:
D = m/v
where D = density; m = mass; and v = volume
Sphere A:
Sphere B:
So as you can see, only Sphere B has a density less or is less dense than water, so only Sphere B will float.
5.
The groundskeeper shredding leaves is an application of physical change. As you can see, the identity of the leaves would be the same if you just shred them. Even if they change in shape and size, the leaves are still leaves, only smaller.
6.
A stable atom has the same number of electrons and protons. The number of protons is represented by the atomic number of an element.
Sodium has an atomic number of 11. This means that there are 11 protons (yellow pom poms) in a sodium atom. Since it is stable, you can also say that there are 11 electrons (White pom poms) as well.
The number of neutrons can be determined by taking a look at the mass number of an atom. The mass number of sodium is 23. The mass number is the number of protons and neutrons combined.
23 = p + n
23 = 11 + n
23 - 11 = n
12 = n
The number of neutrons would be 12 (black pom poms).
7.
When two liquids do not mix, this means they are immiscible. The layers are formed because of the difference in density. Remember earlier about density and an object or substance's ability to float? Well it applies here too. The liquid on top is less dense than the one below it, so it floats up and the denser liquid sinks.
8.
Physical properties are things that you can observe using your senses. Chemical properties are properties that you can only observe when chemical structure is changed.
Seat cover has a <u>smooth texture. </u>
Physical because it was determined by touch.
The front basket of the <u>bike is purple. </u>
Physical because it was determined by sight.
The <u>bike is rusted.</u>
Chemical because the metal changed its chemical structure as a result of a reaction.
9.
The sealed containers represent a closed system, or a vacuum where nothing goes in or out. In a closed system, just remember that matter is not created, nor destroyed. Simply put, this means that whatever it started with is what will it end up with.
In container A you have 1 L of helium gas, so since the container is sealed, none escaped. This means that you will end up with the same amount of helium gas as you did before. The same goes for the 1L of water in container B.