12: Reacting Masses

Question 1

What is the definition of one mole?

Answer 1

The mole is defined as the amount of substance that contains as many particles as there are atoms in exactly 12.0g of carbon-12 of the substance.

Question 2

How many particles does one mole of particles contain?

Answer 2

6.02 x 10²³

Question 3

What is the Avogadro constant?

Answer 3

6.02 x 10²³ mol ^-1

Question 4

How is the number of particles in a substance calculated?

Answer 4

number of particles = number of moles of the substance x Avogadro’s constant

Question 5

How can the number of moles of substance be calculated from the Avogadro’s constant?

Answer 5

number of moles of substance (mol) = number of particles in substance / Avogadro’s constant (mol^-1)

Question 6

What is the definition of molar mass and what is its unit?

Answer 6

The mass of one mole of a substance is molar mass. Its unit is g mol^-1.

Question 7

What do the values of molar mass equal to for atoms, covalent compounds, and ionic compounds respectively?

Answer 7

Atoms: value of molar mass = relative atomic mass
Covalent compounds: value of molar mass = relative molecular mass
Ionic compounds: value of molar mass = formula mass

Question 8

How can the number of moles of substance be calculated from the mass of the substance?

Answer 8

number of moles of substance (mol) = mass of substance (g) / molar mass of substance (g mol^-1</sup)

Question 9

How is the percentage by mass of an element in a compound measured?

Answer 9

Percentage by mass of an element in a compound = (number of atoms of the element in formula x relative atomic mass of the element) / formula mass or relative molecular mass of the compound x 100%

Question 10

What is the difference between anhydrous compounds and hydrated compounds?

Answer 10

Compounds that contain water of crystallisation are described as hydrated, while those that have lost the water of crystallisation are described as anhydrous.

Question 11

What is the empirical formula of a compound?

Answer 11

The empirical formula of a compound gives the simplest integral ratio of atoms or ions in the compound.

Question 12

What is molecular formula?

Answer 12

Molecular formulae are used for compounds that exist as molecules. It tells us the number of each type of atom that make up a molecule of the compound.