Stoichiometry.

Question 1

Valency or combining power tells you how many bonds an atom can make with another atom. What is the valency for the following groups:

• I.
• II.
• III.
• IV.
• V.
• VI.
• VII.
• VIII.

Answer 1

• I = 1 valency.
• II = 2 valencies.
• III = 3 valencies.
• IV = 4 valencies.
• V = 3 valencies.
• VI = 2 valencies.
• VII = 1 valency.
• VIII = 0 valencies.

Question 2

For example, SO2 is called sulfur dioxide. Why?

Answer 2

It is called sulfur dioxide because there are two oxygen atoms.

Question 3

For example, N2O4 is called dinitrogen tetroxide. Why?

Answer 3

It is called dinitrogen because there are two nitrogen atoms. Tetroxide is called this because it have four oxygen atoms.

Question 4

What is the symbol for relative atomic mass?

Answer 4

The symbol for relative atomic mass is Ar.

Question 5

What is the relative atomic mass (Ar)?

Answer 5

The average mass of naturally occurring atoms of an element on a scale where the carbon-12 atom has a mass of exactly 12 units.

NOTE - The relative atomic mass for each element can be found in the periodic table along with the atomic number (The larger number is the relative atomic mass of an element).

Question 6

What is the symbol for relative molecular mass?

Answer 6

The symbol for relative molecular mass is Mr.

Question 7

How do you calculate the relative molecular mass of a substance?

Answer 7

To calculate the Mr of a substance, you have to add up the relative atomic masses of all the atoms present in the formula.

Question 8

What are the state symbols for the following states:

• Gas.
• Liquid.
• Aqueous.
• Concentrated.
• Dilute.
• Solid.

Answer 8

• Gas = g.
• Liquid = l.
• Aqueous = aq.
• Concentrated = conc.
• Dilute = dil.
• Solid = s.