Leaving Cert Chemistry - Bonding

Free elements are assigned an oxidation number of 0. Which one of the following statements is incorrect?
1. The oxidation number of calcium in the calcium ion (Ca²⁺) is 0.
2. The oxidation number of hydrogen in the hydrogen molecule (H₂) is 0.
3. The oxidation number of sodium (Na) in the metal sodium is 0.
4. Ions cannot have an oxidation number of 0.
The oxidation number of a monatomic ion equals the charge on the ion. Which one of the following statements is correct?
1. The oxidation number of aluminium in the Al³⁺ ion is +3.
2. The oxidation of the fluoride ion is 0.
3. The oxidation number of the hydroxide ion (OH^-) is -1.
4. Every atom may have only one oxidation number.
The Alkali metals of group I are always assigned an oxidation number of +1. Which one of the following statements is incorrect?
1. Hydrogen has an oxidation number of -1 in lithium hydride (LiH).
2. When sodium is bonded to chlorine in NaCl, it has an oxidation number of +1.
3. When there is an increase in the oxidation number of an atom in a chemical reaction, oxidation is said to occur.
4. Free potassium has an oxidation number of +1.
If the halogens have an oxidation number of -1, what is the oxidation number of calcium in calcium chloride (CaCl₂)?
1. +2
2. +1
3. 0
4. -2
Oxygen in a compound has an oxidation number of -2. One of the exceptions to this rule is when oxygen
1. is bonded to the more electronegative fluorine.
2. is bonded to chlorine.
3. is bonded to a metal forming a metallic oxide.
4. is bonded to hydrogen in water.
Hydrogen has an oxidation number of +1 except in
1. metal hydrides.
2. hydroxides.
3. acids.
4. hydrogencarbonates.
The sum of the oxidation numbers of all of the atoms in a neutral compound is 0. What is the oxidation number of sulfur in H₂SO₄?
1. +6
2. -6
3. +1
4. -2
If the sum of the oxidation numbers in a complex ion is equal to the charge on that ion, what is the oxidation number of manganese in MnO₄^-?
1. +7
2. +2
3. +8
4. -7
The alkaline earth metals (Be, Mg, Ca, Sr, Ba, and Ra) are always assigned an oxidation state of +2. What is the oxidation number of sulfur in magnesium sulfide (MgS)?
1. -2
2. -1
3. -4
4. +2
Which one of the following elements can only have one oxidation number?
1. Fluorine
2. Hydrogen
3. Oxygen
4. Chromium
True or false? All monatomic ions have an oxidation number of +1.
1. FALSE
2. TRUE
Which one of the following elements does NOT have a fixed oxidation number?
1. Sulfur
2. Magnesium
3. Fluorine
4. Sodium
What is the oxidation number of carbon in the carbonate ion (CO₃^2-)?
1. +4
2. +2
3. -4
4. +6
What is the oxidation number of nitrogen in N₂O₄
1. +4
2. +3
3. +5
4. -3
What is the oxidation number of iron in Fe₂O₃?
1. +3
2. +2
3. +4
4. -2
What is the oxidation number of chlorine in KClO₃?
1. +5
2. +1
3. -1
4. +3
What are the oxidation numbers of copper on the left and right hand sides of the following equation?
Cu + 2AgNO₃ ---> 2Ag + Cu(NO₃)₂
1. 0 and +2
2. 0 and +1
3. +2 and +1
4. +1 and +2
Which one of the following species has an oxidation number of 0 in sucrose whose chemical formula is C₁₂H₂₂O₁₁
1. Carbon
2. Hydrogen
3. Oxygen
4. None of them
In which of the following species does nitrogen have an oxidation number of +1?
1. N₂O
2. NO₃^-
3. NO₂
4. N₂O₄
When mercuric oxide is heated it breaks down to mercury and oxygen as follows:
HgO ---> Hg + O₂
What is the oxidation number of mercury in mercuric oxide?
1. +2
2. +1
3. -2
4. -1

Leaving Cert Chemistry - Bonding - Oxidation Numbers

Multiple Choice Quiz