Chemical Composition and Atomic Mass

This video tutorial covers the concept of relative formula mass and how to calculate it for compounds. It explains the difference between mass number and relative atomic mass, using examples like magnesium chloride and sulfuric acid. The video also demonstrates how to calculate the percentage mass of an element within a compound, with examples including sulfur in sulfuric acid and oxygen in calcium hydroxide.

What does the mass number of an element represent?

• The number of protons in the element

• The average mass of all isotopes of the element

• The number of protons and neutrons in the nucleus

• The number of electrons in the element

How is the relative atomic mass (Ar) of an element determined?

• By averaging the mass of all isotopes

• By counting the number of electrons

• By adding the number of protons and neutrons

• By measuring the atomic radius

What is the relative formula mass (Mr) of magnesium chloride (MgCl2)?

• 71

• 120

• 95

• 59

How do you calculate the relative formula mass of a compound?

• By multiplying the atomic masses of all elements

• By dividing the total mass by the number of atoms

• By adding the relative atomic masses of all atoms in the molecular formula

• By adding the atomic numbers of all elements

What is the relative formula mass (Mr) of sulfuric acid (H2SO4)?

• 112

• 98

• 64

• 80

How do you calculate the percentage mass of an element in a compound?

• By subtracting the atomic mass from the total mass

• By dividing the atomic number by the total mass

• By multiplying the atomic mass by the number of atoms and dividing by the Mr

• By adding the atomic masses of all elements

What is the percentage mass of sulfur in sulfuric acid (H2SO4)?

• 32.7%

• 25.0%

• 16.3%

• 50.0%

What is the relative atomic mass of oxygen used in calculations?

• 16

• 32

• 12

• 8

What is the percentage mass of oxygen in calcium hydroxide (Ca(OH)2)?

• 60.0%

• 50.0%

• 30.0%

• 43.2%

Which of the following is the correct formula for calcium hydroxide?

• Ca(OH)2

• Ca2O

• CaO

• CaH2