Chemistery

"Strong" and "weak" are useful words right up to the moment someone asks how weak. Is hydrofluoric acid weaker than formic acid? By how much? That is what Ka is for: it turns a vague adjective into a number you can calculate with. The short answer: Ka , the acid dissociation constant , is the equilibrium constant for an acid giving up its proton to water. A larger Ka means a stronger acid — at the same concentration, more of it is ionised at equilibrium — and because the numbers are tiny, they are usually quoted as pKa = −log Ka , where a smaller pKa means a stronger acid . What Ka actually is Every weak acid in water sets up an equilibrium: HA + H₂O ⇌ H₃O⁺ + A⁻ Write the equilibrium expression for it and you get Ka: Ka = [H₃O⁺][A⁻] ÷ [HA] Water does not appear, even though it is a reactant. It is the solvent, present in enormous excess, and its concentration barely changes — so by convention it is folded into the constant rather than written out. Read th...

You write out a reaction, the mark scheme says "identify the conjugate base", and suddenly every species on the page looks like a candidate. The good news is that the answer is never a judgement call. There is a mechanical test, and it takes about three seconds. The short answer: a conjugate base is what is left of an acid after it donates a proton (H⁺); a conjugate acid is what a base becomes after it accepts one. The two members of a conjugate pair always differ by exactly one H⁺ — one hydrogen and one unit of charge — and nothing else. Quick comparison at a glance Feature Conjugate acid Conjugate base Formed by A base gaining H⁺ An acid losing H⁺ Change in formula One H added One H removed Change in charge More positive by 1 More negative by 1 Where to find it Opposite the base it came from Opposite the acid it came from Example NH₃ → NH₄⁺ CH₃COOH → CH₃COO⁻ Its own role Can donate that H⁺ back Can accept an H⁺ back What ...

Before 1892 the same compound might be called four different things in four different countries, and chemists genuinely could not be sure they were discussing the same substance. IUPAC nomenclature fixed that: a set of rules that turns any structure into exactly one name, and any name back into exactly one structure. The short answer: IUPAC nomenclature is the international system for naming chemical compounds unambiguously. For organic molecules it builds every name from three parts — a prefix listing the substituents, a root giving the longest carbon chain, and a suffix naming the main functional group — so the name is a set of assembly instructions. The anatomy of a name Take 2-methylbutan-1-ol and cut it apart: Piece What it says 2-methyl Prefix — a CH₃ branch on carbon 2 but Root — the main chain is 4 carbons long an All single bonds 1-ol Suffix — an –OH group on carbon 1 Read backwards and you can draw it without ever having seen the compound. That is the en...

Once you accept that one molecular formula can describe several compounds, the next question arrives immediately: how many kinds of difference are there? Two molecules can be built from the same atoms and differ in the wiring, or they can have identical wiring and differ only in how they sit in space. That split is the whole of isomer classification. The short answer: structural isomers have their atoms bonded together in a different order , while stereoisomers have exactly the same bonding order but a different arrangement in three-dimensional space. The quick test: list which atom is bonded to which for both molecules — if the lists differ it's structural, if they match it's stereo. Quick comparison at a glance Feature Structural isomers Stereoisomers Also called Constitutional isomers Configurational isomers What differs Which atom is bonded to which Spatial arrangement only Connectivity Different Identical Subtypes Chain, position, functional group Geometric...

Here is a fact that quietly breaks a rule you learned early on. Two bottles on a shelf: one holds a gas that boils at −0.5 °C, the other a gas that boils at −11.7 °C. They are different compounds with different properties. And both have the molecular formula C₄H₁₀ . The short answer: isomers are compounds with the same molecular formula but different arrangements of atoms . Because chemical behaviour depends on how atoms are connected and positioned in space — not merely on how many of each there are — isomers are genuinely different substances with different physical and chemical properties. What a molecular formula leaves out A molecular formula is an inventory: C₄H₁₀ says four carbons and ten hydrogens. It says nothing about which carbon is joined to which. Once a molecule has four or more carbons, there is usually more than one legal way to wire them up. For C₄H₁₀ there are exactly two: Butane — a straight chain, CH₃–CH₂–CH₂–CH₃. Boils at −0.5 °C. 2-methylpropane — a th...

Cyclohexane and benzene look almost like the same molecule: both are six-carbon rings, differing by six hydrogens. Yet cyclohexane is a forgettable solvent and benzene is a whole separate branch of organic chemistry with its own rules and its own reactions. The word that separates them is aromatic . The short answer: aromatic compounds contain a flat, fully conjugated ring whose π electrons are delocalised around the whole ring, giving unusual stability; aliphatic compounds are everything else organic — chains, branches and non-aromatic rings. The practical consequence is that aromatic rings undergo substitution to preserve their delocalisation, while unsaturated aliphatic compounds undergo addition . Quick comparison at a glance Feature Aliphatic Aromatic Structure Open chains, branches, non-aromatic rings At least one aromatic ring Includes Alkanes, alkenes, alkynes, cycloalkanes and cycloalkenes Benzene, toluene, naphthalene, pyridine π electrons Localised in individua...