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Solved problems for the chapter:

Molecular Model

View the theory »

Atomic and Molecular Masses

1. Mass of atoms

2. Mass of molecules

3. Mass of substance, kilomole, and Avogadro's number

4. Forum

↓ Show theory [1] ↓

Detailed solution steps are available at:

https://en.openprof.com/wb/chapter:molecular_model/3524/

Example 1.

Calculate the mass of a lead atom. The relative atomic mass of lead is 106 and the atomic mass unit is .

Example 2.

Oxygen in the gaseous state appears in the form of a molecule with two oxygen atoms . The molar mass of an oxygen molecule in kilogram is 32 kg. Calculate the number of oxygen atoms in 10 kg of oxygen and take Avogadro constant as .

Sulphuric acid has the chemical formula . How many atoms of hydrogen, sulphur and oxygen are in 2 kg of sulphuric acid? The relative atomic mass of hydrogen is 1, sulphur 32, and oxygen 16.

Avogadro constant is .

0.5 kg of hydrogen combines with oxygen to form water vapour. How many water vapour molecules do we have? The relative atomic mass of hydrogen is 1 and that of oxygen is 16.

Avogadro constant is .

Calculate the mass of carbon C in 10 kg of carbon dioxide . The relative atomic mass of carbon is 12 and that of oxygen is 16.

Avogadro constant is and atomic mass unit is .

How many kg of sodium is in 10 kg of table salt ? The relative atomic mass of sodium is 23 and that of chlorine is 35.

Avogadro constant is and atomic mass unit is .

1 g of table salt is dissolved in 10 litres of water. How many molecules of salt are in each cubic millimetre of water? The molar mass of table salt in kilogram is 58 kg.

Avogadro constant is .

Imagine 1g of gold is evenly distributed over the entire Earth's surface. How many gold atoms would there be per square centimetre on the surface? The radius of the Earth is 6400 km and the molar mass of gold in kilogram is 197 kg.

Avogadro constant is

One liter of oil spilled on water. The oil spreads over the water so that the thickness of the oil layer is equal to the size of the oil molecule. What will be the surface area of the oil layer? The density of oil is , the molar mass of oil in kilogram is 282 kg and the diameter of the molecule is 0.8 nm.

Avogadro costant is .

10.

Imagine a water droplet in the shape of a ball with a diameter of 6 mm spreads over the entire surface of the Earth. How many water molecules would you get per square centimetre of the Earth's surface area? The density of water is , the relative molecular mass of water is 18, the radius of the Earth is 6400 km and the atomic mass unit is .

11.

Why can a gas be compressed easily into a smaller volume?

The particles are far apart.
The particles do not attract each other.
The particles move randomly.
The volume of each particle can be reduced.

12.

In the diagrams, the black circle represents a smoke particle in air. Which diagram shows a likely path that the particle takes because of Brownian motion?

13.

Brownian motion is the random motion of particles. In which states of matter is Brownian motion observed?

gases, liquids and solids
gases and liquids only
gases and solids only
liquids and solids only

14.

Which row correctly describes the arrangement and the motion of particles in a solid?

	arrangement of particles	motion of particles
A	far apart	moving randomly from place to place
B	far apart	vibrating about one position
C	tightly packed	moving randomly from place to place
D	tightly packed	vibrating about one position

15.

A sealed bottle of constant volume contains air. The air in the bottle is heated by the Sun. What is the effect on the average speed of the air particles in the bottle and the average distance between them?

	average speed of air particles	average distance between air particles
A	decreases	decreases
B	decreases	stays the same
C	increases	increases
D	increases	stays the same

16.

Gases, liquids and solids are made up of small particles. Which row gives the relative separation of the particles?

	gas	liquid	solid
A	far apart	far apart	far apart
B	far apart	far apart	close together
C	far apart	close together	close together
D	close together	close together	far apart

17.

Four students are asked to state and explain the relative magnitudes of the thermal expansion of solids and gases. Which student is correct?

Gases expand more than solids because the molecules in a gas are in random motion.
Gases expand more than solids because the attractive forces between molecules are much weaker in gases.
Solids expand more than gases because the molecules are closer together in solids.
Solids expand more than gases because the molecules in a solid are in a regular pattern.

18.

A sample of gas is trapped in a rigid container. As the temperature of the gas is increased, the pressure increases. Which statement is not correct?

The gas molecules have greater kinetic energy.
The gas molecules hit the walls of the container harder.
The gas molecules hit the walls of the container more frequently.
The gas molecules move further apart.

19.

A fixed mass of gas is trapped in a container. The temperature of the gas is increased but the volume of the gas is kept constant.

How does this change affect the average kinetic energy of the molecules and the pressure on the walls of the container?

	average kinetic energy	pressure
A	increases	increases
B	stays the same	increases
C	increases	decreases
D	decreases	increases

20.

A particular state of matter consists of molecules that move freely in random directions at high speed. The average speed of the molecules is decreasing. Which state of matter is being described?

a gas cooling
a gas being heated
a solid cooling
a liquid being heated

21.

A sealed rigid container has a fixed volume. The container is filled with air. The container is placed in a freezer cabinet and the temperature of the air in the container decreases. Which row correctly describes what happens to the air in the container?

	average distance between air particles	average speed of air particles
A	decreases	increases
B	decreases	decreases
C	no change	increases
D	no change	decreases

22.

The diagram shows gas particles hitting the wall of a container. The system is at room temperature.

Why do the gas particles exert a pressure on the wall?

When the particles hit the wall, their momentum changes, which causes a force.
When the particles hit the wall, their average kinetic energy increases.
The particles expand when they hit the wall.
The particles collide with each other.

23.

Smoke particles, illuminated by a bright lamp, are seen through a microscope. They move about randomly. What causes this motion?

attraction between the smoke particles and the molecules of the air
collisions between the smoke particles and the molecules of the air
evaporation of the faster-moving smoke particles
warming of the smoke particles by the lamp

24.

Very small pollen grains are suspended in water. A bright light shines from the side. When looked at through a microscope, small specks of light are seen to be moving in a random, jerky manner.

What are the moving specks of light?

pollen grains being hit by other pollen grains
pollen grains being hit by water molecules
water molecules being hit by other water molecules
water molecules being hit by pollen grains