Problem 66 - Chemistry The Central Science

Question

Give the chemical formula for (a) carbonic acid, (b) sodium cyanide, (c) potassium hydrogen carbonate, (d) acetylene, (e) iron pentacarbonyl.

Step-by-Step Solution

Answer

The chemical formulas for the given compounds are: (a) Carbonic Acid: \(H_2CO_3\), (b) Sodium Cyanide: \(NaCN\), (c) Potassium Hydrogen Carbonate: \(KHCO_3\), (d) Acetylene: \(C_2H_2\), and (e) Iron Pentacarbonyl: \(Fe(CO)_5\).

Step 1: (a) Carbonic Acid

Carbonic acid is an oxyacid of carbon, with chemical formula H_2CO_3. It's derived from the carbonate ion (CO_3^(2-)). To obtain a neutral compound, we require two hydrogen ions (H^+) to balance the positive and negative charges.

Step 2: (b) Sodium Cyanide

Sodium cyanide is an ionic compound containing the sodium cation (Na^+) and the cyanide anion (CN^−). To achieve electrical neutrality, we need one sodium ion and one cyanide ion. So, the chemical formula for sodium cyanide is NaCN.

Step 3: (c) Potassium Hydrogen Carbonate

Potassium hydrogen carbonate, also known as potassium bicarbonate, is an ionic compound containing the potassium ion (K^+), and the hydrogen carbonate ion (HCO_3^−). To achieve electrical neutrality, we need one potassium ion and one hydrogen carbonate ion. The chemical formula for potassium hydrogen carbonate is KHCO_3.

Step 4: (d) Acetylene

Acetylene is an organic compound with the molecular formula C_2H_2. It's the simplest alkyne, containing a carbon-carbon triple bond. Remember that each carbon atom forms four bonds, so the structure of acetylene is H-C≡C-H.

Step 5: (e) Iron Pentacarbonyl

Iron pentacarbonyl is a coordination compound containing an iron atom (Fe) bonded to five carbonyl (CO) ligands. The chemical formula for iron pentacarbonyl is Fe(CO)_5.

Key Concepts

Ionic Compounds

Ionic compounds are formed from the transfer of electrons between metals and non-metals, resulting in the creation of positive and negative ions. These ions attract each other and form a stable ionic bond. For example, sodium cyanide is an ionic compound formed from sodium (Na^+) and cyanide (CN^-). To achieve neutrality, one Na^+ pairs with one CN^−, giving us the formula NaCN.

• Key properties of ionic compounds: Generally, they have high melting and boiling points due to strong ionic bonds.
• They conduct electricity when dissolved in water, as the ions are free to move.
• They are typically solid and have a crystalline structure at room temperature.

Organic Compounds

Organic compounds are primarily made of carbon atoms, often linked with hydrogen, oxygen, nitrogen, and other elements. One characteristic of these compounds is the presence of covalent bonds. For example, acetylene, with the formula C_2H_2, is an organic compound known as an alkyne, which contains a carbon-carbon triple bond.

• Characteristics of acetylene: It is the simplest alkyne and consists of strong covalent bonds.
• Organic compounds can range from simple molecules to complex polymers.
• They often participate in combustion, producing energy, carbon dioxide, and water.

Coordination Compounds

Coordination compounds consist of a central metal atom or ion surrounded by molecules or anions called ligands. These compounds form complex structures due to coordinate covalent bonds. Iron pentacarbonyl, represented by the formula Fe(CO)_5, is a coordination compound with an iron atom bonded to five carbonyl groups.

• Features of coordination compounds: They exhibit a wide range of colors and magnetic properties due to the metal-ligand interactions.
• These compounds have distinct geometries, depending on the number and arrangement of ligands.
• Coordination compounds play crucial roles in various chemical processes, including catalysis and biochemistry.

Chemical Nomenclature

Chemical nomenclature is the systematic naming of chemical compounds. It ensures clear and easy communication in the scientific community. Names give information about the structure and composition of a compound. For instance, potassium hydrogen carbonate (KHCO_3) indicates the presence of potassium, hydrogen, and carbonate ions in the compound.

• Basic principles: In ionic compounds, the metal is named first, followed by the non-metal with an 'ide' suffix, like sodium cyanide (NaCN).
• For organic compounds, nomenclature indicates the number and types of atoms or groups involved, such as alkanes and alkynes.
• Coordination compounds often include the metal's oxidation state in their names, and ligands are named preceding the metal. For example, iron pentacarbonyl.