Here are the answers to the questions provided:
3. To represent the particles of a solid, Polly should:
Pack the bowl with marbles and then tap it gently.
This demonstrates how particles in a solid are closely packed and can only vibrate in fixed positions.
4. A chemical change is represented by:
Fireworks exploding.
This is a classic example of a chemical reaction where new substances are formed, unlike the other options which are physical changes.
5. If a physical change has taken place, the most likely true statement is:
The changed substance retains its unique properties.
Physical changes involve changes in state or appearance but do not alter the composition of the substance.
6. The reason why using carbon dioxide and water to form food and oxygen is a chemical change is:
The properties of carbon dioxide and oxygen are different.
During photosynthesis, the compounds change into different substances with new properties.
7. The mass of water is likely to increase by:
30 g.
When sugar dissolves in water, the mass of the solution is the sum of the masses of the solute (sugar) and the solvent (water).
8. The mass of hydrogen gas expected to be formed is:
6 g.
According to the law of conservation of mass, the total mass before and after a reaction must be equal. Therefore, 10 g HCl + 20 g Zn = 24 g ZnCl2 + x g H2, leading to x = 6 g of H2.
9. Is mass conserved when 200 g of water undergoes a physical change?
Yes, mass is conserved when 200 g of water undergoes a physical change. In a physical change, such as freezing or boiling, the substance changes state but retains its mass. This can be demonstrated by measuring the mass of water before and after it undergoes a change. For example, if you start with 200 g of liquid water and it freezes, it will still have a mass of 200 g as ice. Thus, no mass is lost in the transition.
10. When the temperature of a chemical reaction is increased, the most likely occurrence is:
Molecules speed up.
Increasing the temperature gives the molecules more energy, increasing their movement and collision rates, which facilitates a faster reaction.
11. Comparing the chances for particles to bounce off each other during a chemical reaction at 39 °F and 51 °F:
Lower at 39 °F.
Higher temperatures increase molecular motion, which increases the chances for particles to collide with each other.
12. The best explanation for the time taken for the tablet to dissolve in tap water is:
Less than 68 seconds as the rate of reaction is higher for tap water.
Typically, warmer temperatures (tap water is warmer than cold water) will increase the rate at which the tablet dissolves.
13. The best description of the two substances based on the graph is:
Particles are farther apart in gases so substance X is water vapor.
The graph shows that water vapor occupies a much larger volume than liquid water, indicating that the particles in a gas are more spread out.
14. To determine if the law of conservation of mass holds true in this case:
The initial mass of copper carbonate was 123.6 g, and the mass of the black residue (the product) was 79.6 g. To find the mass lost, we subtract:
123.6 g - 79.6 g = 44.0 g.
This indicates that there was a loss of mass, which violates the law of conservation of mass, as the total mass before the reaction should equal the total mass after the reaction. Thus, the law does not hold true in this investigation.