Gen 1 - Stochiometry

Question 1

What is a molecule ?

Answer 1

The smallest unit of a compound that presents the properties of that compound.

Question 2

What is the empirical formula of a compound ?

Answer 2

The simplest whole number ratio between the numbers of atoms of different elements that make up the compound.

Question 3

What is the molecular formula of a compound ?

Answer 3

The number of the different atoms that make up a molecule

Question 4

What is Avogadro’s number ?

Answer 4

The number of atoms in 12g of the most abundant carbon isotope.

Question 5

Why do we need Avogadro’s Number ?

Answer 5

Large numbers of molecules need to be observed in reactions to bring microscopic chemical reactions to our macroscopic scale.

Question 6

How do you calculate moles of an element or compound ?

Answer 6

Question 7

What is the difference between the atomic weight of an element, and the mass of a single atom ?

Answer 7

Atomic weights are dimensionless numbers based on Carbon-12 as the reference standard Isotope. The mass of a single atom can be measured experimentally (!)

Question 8

What is an Isotope of an element ?

Answer 8

An atom of an element with the same number of protons but a different number of neutrons.

Question 9

Define atomic weight

Answer 9

The weight in grams of a mole of atoms

Question 10

Define molecular weight

Answer 10

The weight in grams of a mole of molecules

Question 11

How would you calculate % yield ?

Answer 11

Question 12

How would you calculate theoretical yield ?

Answer 12

Theoretical yield is the calculated amound of product that can be predicted from a balanced chemical equation.

Question 13

Give two examples of double replacement reactions

Answer 13

1. Precipiation
2. Acid-Base neutralisation

Question 14

Define Oxidation

Answer 14

• An increase in Oxidation number
  OR
• Loss of one or more electrons

(Oxidation Is Loss)

Question 15

Define Reduction

Answer 15

• Decrease in Oxidation number
  OR
• Gain of one or more electrons

(Reduction Is Gain)

Question 16

Is Oxidation state equal to Ionic charge ?

Answer 16

No.

Monatomic ions are the only species where charges and oxidation numbers coincide.

Question 17

What is the oxidation state of an uncombined element ?

Answer 17

In elementary substances, the oxidation number of an uncombined element regardless of whether it is monatomic, diatomic or polyatomic is always ZERO.

Question 18

What is the oxidation number of an Ion ?

Answer 18

In monatomic ions, the oxidation number of the element that makes up the ions is equal to the charge of the ion.

Question 19

What is the sum of the Oxidation numbers in a neutral molecule ?

Answer 19

Zero.

Question 20

What is the sum of the Oxidation numbers of a Polyatomic Ion ?

Answer 20

Equal to the charge of the Ion.

Question 21

What is the Oxidation number of Hydrogen ?

Answer 21

+1

Question 22

What is the Oxidation number of Oxygen ?

Answer 22

-2.

Question 23

What is the Oxidation number of the Alkali Earth Metals ?
E.g. Be, Mg, Ca, Sr

Answer 23

2+

Question 24

What is the Oxidation number of the Alkali metals ? E.g. H, Li, Na, K

Answer 24

+1

Question 25

Name 3 common reducing agents

Answer 25

1. Lithium Aluminium Hydride LiAlH₄
2. Sodium Borohydride (NaBH₄)
3. Ferrous Ion (Fe²⁺)

Question 26

Name 5 common Oxidising agents

Answer 26

1. Iodine (I₂) and other Halogens
2. Permanganate salts (MnO₄)
3. Peroxide compounds (H₂O₂)
4. Ozone (O₃), Osmium Tetroxide (OsO₄)
5. Nitric Acid (HNO₃), Nitrous Oxide (N₂O)