Lesson 2.1 Atoms

Answers to Review Questions

  1. The atoms of a particular element have the same number of protons in their nuclei. Different elements have different numbers of protons in their nuclei. Atoms of the same element can differ in the number of neutrons in their nuclei.
  2. Atoms of the same element with different numbers of neutrons are called isotopes.
  3. An element is a material consisting of one particular type of atom. Compounds consist of more than one type of atom. The atoms in a compound are chemically combined with different atoms.
  4. From the periodic table, we can see that boron has an atomic number of 5. This means that there are 5 protons in a boron atom’s nucleus.
  5. Yes. Aluminum atoms have an atomic mass (weight) of 26.98 whereas boron atoms have an atomic mass of 10.81. The densities will depend on how closely the atoms are packed together but with aluminum having about 2.5 times more mass than boron atoms, it is probable that boron will be less dense than aluminum.
  6. The mass of one carbon atom = 12.011 g divided by 6.02 x1023 = 2 x10-23 grams.
  7. Electron orbitals are 3-dimensional whereas the orbits of planets are flat.
  8. The diameter would be of the order of 1 kilometer.
  9. Rutherford fired tiny alpha particles at solid objects such as gold foil. He found that most of the alpha particles passed right through the gold foil, a small number of alpha particles passed through at an angle (as if they had bumped up against something) and some bounced straight back like a tennis ball hitting a wall. Rutherford's experiments suggested that gold foil, and matter in general, was composed largely of empty space.
  10. 32
  11. No. If all carbon atoms had the same number of neutrons, the relative atomic mass would be a whole number.
  12. No. The relative atomic mass of carbon is 12.011. Silicon has a relative atomic mass of 28.09.

 

Physics Lab 2.1 Hydrogen

Questions

  1. Is hydrogen lighter than air? How can we illustrate this?
  2. Why are foil-lined balloons more suitable than conventional balloons for containing light gases like helium and hydrogen?
  3. Is hydrogen gas flammable or explosive?

Answers

  1. Yes. Hydrogen will collect inside an inverted open container.
  2. Conventional balloons are slightly porous. Gas molecules diffuse through the pores an with time, these balloons deflate. Because hydrogen molecules are so much smaller than nitrogen or oxygen molecules, conventional balloons inflated with hydrogen tend to deflate more rapidly than when filled with air. Metals are much less porous than rubber or plastics. Foil lined materials are therefore better suited to containing hydrogen.
  3. Probably both. Hydrogen is definitely flammable. Explosions occur when gasses expand rapidly. Explosions are often caused by flames that move quickly and cause gases to expand rapidly. The difference between an explosion and a rapidly moving flame is difficult to define. Hydrogen flames do tend to move rapidly and are therefore often regarded as explosions.

 

 

Lesson 2.2 States of Matter

Activity Question

Why did the temperature remain constant while the ice was melting and also while the water was boiling?

Answer

In both cases, the ice or water continued to absorb energy from the heating device even though there was no increase in temperature. The absorbed energy was used to cause a change in phase (from solid to liquid or from liquid to vapor).

The temperature at which ice melts is fixed and so all of the added energy is used to complete the melting process before any increase in temperature can take place. The temperature at which water boils is also fixed (at a particular pressure) and so the boiling process also needs to be completed before there is any increase in temperature.

Answers to Questions

  1. Yes.
  2. When particles gain energy, they move faster and further. A vibrating or oscillating particle will increase its average distance from the midpoint of its movement.
  3. Yes. The forces of attraction are present at all times but the rapid movement of the particles cause a net reduction in the forces of attraction between particles as they gain more and more energy.
  4. Particles in the liquid phase have more energy than they would have in the solid phase. This results in a net reduction in the forces of attraction between particles.
  5. Yes. The temperature should remain constant until all of the solid has melted. The time taken to transfer heat from a hot part of the mixture to a colder part could result in uneven heating and an apparent increase in temperature nearer to the heating device.
  6. During the melting process, energy is needed to supply the latent heat of fusion. If heating continues after all of the solid has melted, the temperature of the liquid will increase.
  7. Provide the missing words:
  8. The quantity of energy needed to convert 1 kg of a solid to liquid at the same temperature is known as the LATENT HEAT OF FUSION
  9. The quantity of energy needed to convert 1 kg of a liquid to vapor at the same temperature is known as LATENT HEAT OF VAPORIZATION
  10. GASES are compressible.
  11. LIQUIDS AND SOLIDS have much higher densities than gasses.
  12. SOLIDS usually have higher densities than the corresponding liquid.
  13. WATER has a higher density in the liquid phase at 0ºC than its solid at 0ºC.
  14. GASES (AND SOME LIQUIDS) mix easily with one another.
  15. GASES expand to occupy the available volume and take the shape of the container.
  16. The shape of a LIQUID can easily change but its volume does not.
  17. The shape and volume of a SOLID does not easily change.

 

Physics Lab 2.2 States of Matter

Questions

  1. Why did the temperature remain constant during the time that most of the naphthalene around the thermometer bulb was solidifying?
  2. What is the melting point of naphthalene?

Answers

  1. The temperature remained constant even though the naphthalene continued to lose energy. The loss in energy allowed the naphthalene to change phase from liquid to solid.
  2. During the cooling process, the temperature should have "leveled off" while the naphthalene solidified. This temperature is the melting point of naphthalene.

 

Lesson 2.3 Solids

Answers to Questions

  1. Crystalline materials are made up of particles that are boded together in a regular pattern. The particles that make up an amorphous solid are not bonded together in any regular pattern.
  2. The osmium atoms are more closely packed together.
  3. The volume of 1 gram of gold = 1 / 19.3 = 0.0518 cm3.
    The volume of 100 kilograms of gold = 100 x 1000 x 0.0518 = 5180 cm3.
  4. Yes. The density of osmium is greater than that of gold and it could be diluted with other materials until a mixture had the same density as that of gold.
  5. An elastic material returns to its original shape after a stress that has been applied to it has been removed. Inelastic materials change shape slightly every time they are distorted.
  6. If the shape of an elastic material is distorted by an applied force, it will return to its original shape after the force is removed provided that its elastic limit has not been exceeded. The elastic limit is the stress (force) above which the object will not return to its original shape after the stress has been removed.
  7. Stretched.
  8. Forces of attraction and repulsion between the particles that make up the rod cause the rod to return to its original shape.
  9. Under tension: The particles move further apart.
    Under compression: The particles move closer together.
  10. 100 grams of the mixture will contain 50 grams of gold and 50 grams of silver.
    The volume of gold = 50 / 19.3 = 2.591 cm3. The volume of silver is 50 / 10.5 = 4.762 cm3.
    The total volume is 2.591 cm3 + 4.762 cm3 = 7.353 cm3.
    The volume % of gold = (2.591 / 7.353) x 100 = 35.24%.
    The volume % of silver = 100 – 35.25 = 64.76%.
  11. 100 grams has a volume of 7.353 cm3. The density = 100 / 7.353 = 13.6 grams per cm3.
  12. The extension appears to be 10 cm per kg. For 3 kg the extension should be 30 cm.

 

Physics Lab 2.3 Elasticity

Questions

  1. Does the shape of the plot of distance versus added weight indicate that Hooke’s law is valid for the spring?
  2. Was the extension of the spring proportional to the added weight after the elastic limit was exceeded?

Answers

  1. The shape of the plot prior to exceeding the elastic limit should conform with Hooke’s Law.
  2. The answer to this question should be "No".

 

Lesson 2.4 Fluids

Answers to Review Questions

  1. A fluid with no upper surface is called a GAS
  2. The ratio of mass to volume is called DENSITY
  3. A rock will sink in water because its DENSITY is more than that of water.
  4. Pressure is the ratio of force applied to the AREA over which it is applied.
  5. A blunt knife does not cut as easily as a sharp knife does because force is applied over a LARGER area.
  6. P = r g h = 1000 x 9.81 x 5 = 49050 N / m2 (or Pa.)
  7. P = r g h = 1100 x 9.81 x 5 = 53955 N / m2 (or Pa.) Above atmospheric pressure.
  8. If an object sinks, it displaces its own volume of liquid.
    1 m3 = 100cm x 100cm x 100cm = 1,000,000 cm3. 5 cm3 = 5 / 1000000 = 5 x10-6 m3.
    This has a mass = 5 x10-6 m3 x 1000 kg/m3 = 5 x10-3 kg = 5 g.
    (We also know that a density of 1000 kg / m3 is equivalent to a density of 1 g / cm3. 5 cm3 therefore has a mass of 5 g.)
  9. Archimedes Principle states that the buoyant force on a submerged object is equal to the weight of the fluid that is displaced by the object.
  10. 300 grams.
  11. Yes. According to Archimedes’ Principle, the buoyant force on the object will equal to the weight of the fluid displaced by the object.
  12. It will sink because its density is greater than that of water. (Provided that the object is not shaped to contain air when it is placed in water.)
  13. The buoyant force will be equal to the weight of the fluid it displaces.
    4 cm3 of a fluid with a density of 1100 kg/m3 has a mass of (4 / 1000000) x 1100 = 4.4 grams.
    The weight of 4.4 g = (4.4 / 1000)kg x 9.81 N / kg = 0.0432 N.
  14. An object with a density of 1200 kg/m3 has a volume of 10 cm3. What is its weight in Newtons? What weight of water with a density of 1000 kg/m3 would it displace? If it is completely submerged in the water and suspended at the end of a thin thread attached to a balance, what weight would the balance indicate?
    10 cm3 ob ject with density of 1200 kg / m3 has mass = (10 / 1000000) x 1200 = 0.012 kg
    Weight = 0.012 kg x 9.81 N / kg = 0.1177 N

    This would displace 10 cm3 of water with a density of 1000 kg / m3 = 0.01 kg = 0.0981 N.

    Submerged in water a balance would indicate 0.002 kg or (0.1177 – 0.0981) = 0.0196 N.
  15. Pascal's law states that when there is an increase in pressure at any point in a confined fluid, there is an equal increase at every other point in the container.
  16. 300 kPa. The pressure is that same for all points at the same depth.
  17. Pressure on small piston = pressure on large piston.
    (Force on small piston / area of small piston) = (Force on large piston / area of large piston)
    Force on large piston = Force on small piston x (area of large piston / area of small piston)
    = 300 N x { [    p (4/2)2 ] / [p (1/2)2 ]} = 300 x 16 = 4800 N.

 

Physics Lab 2.4 Eureka

Questions

  1. How would you use a Eureka can to determine the volume an object that has a density less than that of water? (i.e. the object floats in water)
  2. Could you use a Eureka can to estimate the density of an object that floats without weighing the object? How?

Answers

  1. Attach a weight to the object that will cause it to sink in the liquid. (First use the Eureka can to determine the volume of the weight and subtract this volume from the combined volume of the object plus weight.)
  2. The mass of water displaced by a floating object is equal to the mass of the object. If we then determine the volume of the object as described in 1) above, we can calculate the density.