Understanding Avogadro's Number and Moles

The Mole, Avogadro Constant and Ideal Gases

by Miza Lodfi

​Let's try this quiz first..

Multiple Choice

Which of the following units should be used for the molar mass of a substance?

• g mol

• g mol^-1

• kg mol^-1

• mol g^-1

Multiple Choice

How many atoms are there in 0.5g of sodium?

• 0.0217

• 1.3 x 10²²

• 6.02 x 10²³

• 3.01 x 10²³

Multiple Choice

How many moles of phosphoric acid (H₃PO₄) are there in 15cm³ of 0.15mol dm⁻³ phosphoric acid solution?

• 1.1 x 10^-3 mol

• 1.25 x 10^-3 mol

• 2.25 x 10^-3 mol

• 6.75 x 10^-3 mol

Multiple Choice

Solution A has a concentration of 3.75mol dm⁻³, while solution B has a concentration of 2×10⁻⁵mol dm⁻³. Which of the following statements about solutions A and B is correct?

• Solution A is dilute, solution B is concentrated.

• Solution A is concentrated, solution B is dilute

• Both solutions are dilute

• Both solutions are concentrated

​The Mole and Avogadro Constant

​Let's watch the video

Multiple Choice

Which of the following statements is the correct definition of the mole?

• A mole is the amount of a substance that contains the same number of particles as 1g of carbon-12

• A mole is the amount of a substance that contains the same number of particles as 12g of carbon-12

• A mole is the amount of a substance that contains the same number of particles as 14g of nitrogen-14

• A mole is the mass of a substance that contains the same number of particles as 12g of carbon-12

Multiple Choice

Which of the following units should be used for the molar mass of a substance?

• g mol

• g mol^-1

• kg mol^-1

• mol g^-1

Multiple Choice

How many moles are there in 0.064g of sulphur?

• 0.064 mol

• 2 x 10^-1 mol

• 2 x 10^-2 mol

• 2 x 10^-3 mol

Multiple Choice

How many atoms are there in 1g of gold?

• 1.2 x 10²⁶

• 3.0 x 10²⁵

• 6.02 x 10²³

• 3.0 x 10²¹

​Concentration and Volume Calculations

Multiple Choice

How many moles of oxalic acid (H₂C₂O₄) are there in 1dm³ of 0.375mol dm⁻³ oxalic acid solution?

• 3.75 x 10^-2 mol

• 7.5 x 10^-2 mol

• 0.375 mol

• 0.75 mol

Multiple Choice

Hydrochloric acid, or HCl, can take part in the reaction shown below:

KOH(aq) + HCl(aq) → KCl(aq) + H₂O(l)

Calculate the volume of 0.05mol dm⁻³ KOH that reacts exactly with 50cm³ of 0.1mol dm⁻³ HCl.

• 0.1 cm³

• 10 cm³

• 100 cm³

• 200 cm³

Multiple Choice

Solution A has a concentration of 3.75mol dm⁻³, while solution B has a concentration of 2×10⁻⁵mol dm⁻³. Which of the following statements about solutions A and B is correct?

• Solution A is dilute, solution B is concentrated

• Solution A is concentrated, solution B is dilute

• Both solutions are dilute

• Both solutions are concentrated

Multiple Choice

Which of the following statements about concentrated and dilute solutions is correct?

• Concentrated solutions contain more solute in a given volume than dilute solutions

• Dilute solutions contain more solute in a given volume than concentrated solutions

• Concentrated solutions contain more solute than dilute solutions

• Dilute solutions contain more solute than concentrated solutions

​THE IDEAL GAS EQUATION DIAGNOSTIC QUIZ

Multiple Choice

What is the molar gas volume of any gas measured at room temperature and pressure?

• 24dm³ mol^-1

• 22.4dm³ mol^-1

• 24000dm³ mol^-1

• 24000cm³

Multiple Choice

Which of the following equations is the ideal gas equation?

• $$n=\frac{V}{Vm}$$  

• pV = nRT

• $$\frac{pV}{T}=$$  constant

• $$n=\frac{m}{M}$$  

Multiple Choice

How many moles of fluorine are present in a volume of 25cm³ at a temperature of 45.0^∘C and a pressure of 100kPa? (R=8.31JK⁻¹mol⁻¹)

• 9.46 x 10^-7 mol

• 4.73 x 10^-4 mol

• 9.46 x 10² mol

• 9.46 x 10^-4 mol

​IDEAL GASES QUIZ

Multiple Choice

How many moles of ammonia are there in 0.6dm³ of gas at room temperature and pressure?

• 40 mol

• 24 mol

• 2.5 x 10^-1 mol

• 2.5 x 10^-2 mol

Multiple Choice

Which of the following statements are true for ideal gases?

• There are intermolecular forces acting between the particles that make up the gas

• The particles that make up the gas are in constant motion and act as though they are soft spheres

• Relative to the volume of their container, the volume occupied by the particles themselves is negligible

• All of these options

Multiple Choice

In the presence of a catalyst, potassium chlorate decomposes to form potassium chloride and oxygen, according to the equation below:

2KClO₃(s) → 2KCl(s)+3O₂(g)

A 0.1225g sample of KClO₃ was heated and completely decomposed. Calculate the volume, in cm³, of oxygen produced at 100^∘C and 100kPa. (R=8.314JK⁻¹mol⁻¹)

• 46.5 cm³

• 4.65 x 10⁴ cm³

• 12.5 cm³

• 24000 cm³

Multiple Choice

A gas occupies a volume of 20cm³ at a temperature of 50^∘C and a pressure of 105kPa. What values can be substituted in to the ideal gas equation in this case?

• V= 2 x 10^-5,

  T= 323,

  P= 1.05 x 10⁵

• V= 0.02,

  T= 323,

  P= 105

• V= 20,

  T= 323,

  P= 0.105

• V= 2 x 10⁷,

  T= 323,

  P= 105

​Proceed to Task 2.1 in GC