C7 flashcards
(12 cards)
Combustion of Heptane (in excess oxygen)
When heptane combusts in the presence of excess oxygen, it undergoes a complete combustion reaction, producing carbon dioxide and water as products:
C7H16+11O2→7CO2+8H2OC
7 H
Combustion of Pentane (limited oxygen)
In restricted oxygen conditions, pentane undergoes incomplete combustion, resulting in the formation of carbon monoxide and water or even carbon (soot) and water, depending on the oxygen availability:
C5H12+5O2→5CO+6H2OC
5
State at Room Temperature – Mercury (C)
Substance C is identified as mercury, which is metallic and exhibits metallic bonding due to the presence of delocalised electrons around a lattice of positive ions.
Reaction: C (metallic) + D (covalent molecular) → B (ionic)
When the metallic element mercury (C) reacts with a covalent molecular compound (D), they form an ionic compound (B) through electron transfer. This is notable because it involves a metallic element and a molecular compound forming an ionic product, suggesting that D acts as an electron acceptor.
Silicon Carborundum in Sandpaper
Silicon carborundum, or silicon carbide (SiC), is a covalent network solid where each silicon atom is bonded to four carbon atoms in a rigid, three-dimensional lattice. This structure results in extremely strong covalent bonds throughout, giving SiC its exceptional hardness, high melting point, and resistance to wear. These properties make it ideal for sandpaper, as it stays sharp under pressure and does not react easily with other substances. Its thermal and chemical stability also allow it to perform well in harsh conditions.
Explaining Covalent Bonding from Given Elements
When given two non-metals, such as hydrogen and chlorine, they form a covalent bond by sharing one pair of electrons, allowing both atoms to attain stable electron configurations. The resulting molecule, HCl, involves equal or unequal sharing depending on the electronegativity difference.
Saturated vs Unsaturated Reactions
Saturated hydrocarbons (alkanes) undergo substitution reactions, which are relatively slow and require UV light to break the strong C–H bonds and initiate the reaction. In contrast, unsaturated hydrocarbons (alkenes/alkynes) undergo fast addition reactions at the site of the double or triple bond without needing a catalyst or light.
Four Allotropes of Carbon
Diamond
Graphite
Fullerene
Graphene
Valence Electrons
Valence electrons are the electrons located in the outermost shell of an atom. They are responsible for chemical bonding, as atoms tend to gain, lose, or share valence electrons to achieve a full outer shell, usually corresponding to the stable noble gas configuration.
Ductility of Metals
Metals are ductile because the layers of metal cations in the metallic lattice can slide over each other without breaking the metallic bond. The delocalised electrons act as a cushion, allowing the metal to be drawn into wires without fracturing.
Volatility of Gases
Gases are volatile and easily evaporate because their particles have a lot of energy and are far apart, with very weak forces holding them together. This means the particles move freely and can escape into the air easily. Substances that become gases at low temperatures (like perfume or alcohol) have low boiling points, so they evaporate quickly — that’s what makes them volatile.
What makes mercury unusual
What makes mercury unusual is that, unlike most metals, it is a liquid at room temperature. Despite this, it still retains the ability to conduct electricity, which is characteristic of metals in all physical states, due to the presence of mobile delocalised electrons.
