Question

Assign oxidation numbers to each atom in each substance. a) \(\mathrm{C}_{6} \mathrm{H}_{6}\) b) \(\mathrm{B}(\mathrm{OH}) 3\) c) \(\mathrm{Li}_{2} \mathrm{~S}\) d) \(\mathrm{Au}\)

Short answer

a) C: -1, H: +1. b) B: +3, O: -2, H: +1. c) Li: +1, S: -2. d) Au: 0.

Step-by-step solution

Determine Oxidation Numbers for C and H in \( \mathrm{C}_{6} \mathrm{H}_{6} \)

For this compound, the rule is that hydrogen (H) typically has an oxidation number of +1. Since there are 6 hydrogens, their total oxidation number is +6. The compound \( \mathrm{C}_6\mathrm{H}_6 \) (benzene) is neutral, so the sum of all oxidation numbers must be zero. Let the oxidation number of carbon (C) be \( x \). We have 6 total carbons, so:\[6x + 6(+1) = 0\]Solving for \( x \) gives us the oxidation number of carbon:\[6x + 6 = 0\]\[6x = -6\]\[x = -1\]Thus, C is -1 and H is +1.

Determine Oxidation Numbers for B and O in \( \mathrm{B}( ext{OH})_3 \)

For the hydroxide ion (OH), oxygen typically has an oxidation number of -2, and hydrogen has +1. Therefore, the net oxidation number of OH is -1. Since there are three OH groups, their total oxidation number is -3. The oxidation number of Boron (B) will balance this to zero:Let the oxidation number of B be \( x \).\[x + 3(-1) = 0\]\[x - 3 = 0\]\[x = +3\]Therefore, B is +3, O is -2, and H is +1.

Determine Oxidation Numbers for Li and S in \( \mathrm{Li}_2\mathrm{~S} \)

Lithium (Li) typically has an oxidation number of +1. Since there are two lithium atoms, their total is +2. The compound is neutral, so sulfur's oxidation number must balance this:Let the oxidation number of S be \( y \).\[2(+1) + y = 0\]\[2 + y = 0\]\[y = -2\]Therefore, Li is +1 and S is -2.

Determine Oxidation Number of Au in \( \mathrm{Au} \)

This is a pure element. Pure elements have an oxidation number of 0. Therefore, the oxidation number of Au is 0.

Key concepts

Chemical Compounds

Chemical compounds are substances formed when two or more elements combine in fixed proportions through chemical bonds. They have distinct properties that differ from the individual elements that compose them.
An essential aspect of understanding chemical compounds involves recognizing the typical oxidation numbers associated with the elements within them.

• Hydrogen typically has an oxidation number of +1 when combined with non-metals.
• Oxygen usually has an oxidation number of -2.
• In compounds like \( \mathrm{C}_{6} \mathrm{H}_{6} \), each element maintains known oxidation states to make the compound neutral.

Recognizing patterns in oxidation numbers helps in predicting properties of compounds and can guide chemical reactions. For example, \( \mathrm{Li}_{2} \mathrm{S} \) is composed of lithium and sulfur, where lithium generally shows +1 oxidation and sulfur adjusts to balance it.
In general, understanding these aspects helps to decipher the molecular structure and reactivity of chemical compounds.

Redox Reactions

Redox reactions, short for reduction-oxidation reactions, play a vital role in chemistry. They involve a transfer of electrons between two substances. A key feature of redox reactions is the change in oxidation states of the elements involved. This process can lead to significant changes in the properties and composition of the substances.

• Reduction involves a decrease in oxidation number, signifying a gain of electrons.
• Oxidation involves an increase in oxidation number, signifying a loss of electrons.

Tracking how oxidation numbers change can reveal the substances being oxidized or reduced. For example, in a reaction involving \( \mathrm{B}(\mathrm{OH})_3 \), boron has an oxidation number of +3 while the hydroxide acts differently with oxygen at -2 and hydrogen at +1.
Understanding redox reactions is crucial for grasping processes like energy production in cells and various industrial applications.

Elemental Oxidation State

The elemental oxidation state refers to the oxidation number assigned to an element in a chemical compound. This number helps in understanding how an element is likely to behave in a chemical reaction.
For elements in their pure form, such as gold (\(\mathrm{Au}\)), the oxidation state is 0, as there is no transfer of electrons between different atoms. This defines a baseline for comparison in compounds.

• In simple ions, the oxidation state corresponds directly to the charge of the ion.
• In complex molecules, elements may have unique oxidation states that contribute to the overall balance of the compound's charge.

Calculating oxidation states involves using known rules about particular elements and balancing charges across the entire compound. Knowing the oxidation state provides insight into the probable chemical reactions and stability of a compound. This principle helps chemists predict reactivity and guide synthesis processes efficiently.