Chemistery

If a catalyst speeds a reaction up, an inhibitor must be its mirror image and slow it down, right? Half right — and the half that's wrong is exactly where exam marks get lost. The short answer: a catalyst speeds a reaction up by offering an alternative route with a lower activation energy, and is regenerated unchanged at the end. An inhibitor slows a reaction down — usually by blocking or removing something the reaction depends on — and is very often used up in the process. Quick comparison at a glance Feature Catalyst Inhibitor Effect on rate Increases it Decreases it How it works Provides a lower-activation-energy pathway Blocks a site, removes a reactive intermediate, or poisons a catalyst Consumed overall? No — always regenerated Depends on the type; many are used up Amount needed Tiny, often catalytic traces Usually far more than a catalyst Effect on equilibrium position None None (it changes only how fast equilibrium is reached, if at all) Effect on activation ene...

Rust takes years. A firework takes milliseconds. Both are chemical reactions, and the only difference your exam actually asks about is how fast . That question has a name. The short answer: the reaction rate is how quickly reactants are used up or products are formed, measured as a change in concentration per unit time — usually in mol dm⁻³ s⁻¹ . A fast reaction has a large rate; a slow one has a small rate. What reaction rate actually measures Rate is a speed , and like any speed it's an amount divided by a time: rate = change in concentration ÷ time taken Written with symbols, for a reactant that's being consumed: rate = −Δ[reactant] / Δt and for a product being made: rate = +Δ[product] / Δt The minus sign is bookkeeping, not physics. Reactant concentration falls, so Δ[reactant] is negative; the minus flips it so the rate itself comes out positive. Rates are always quoted as positive numbers. You don't have to use concentration. In the lab you measure whatever...

Ammonia turns red litmus blue, neutralises acids and behaves like a base in every way you can test. It also contains no OH group whatsoever. That awkward fact is the reason chemistry has more than one definition of a base. The short answer: the Arrhenius definition says an acid produces H⁺ ions in water and a base produces OH⁻ ions in water. The Brønsted–Lowry definition is broader: an acid is any proton donor and a base any proton acceptor , which works outside water and explains substances like ammonia that have no hydroxide to give. Quick comparison at a glance Feature Arrhenius Brønsted–Lowry Proposed 1884 1923 Acid is A substance producing H⁺ in water A proton (H⁺) donor Base is A substance producing OH⁻ in water A proton (H⁺) acceptor Requires water? Yes No Covers ammonia as a base? Not under the original definition Yes Covers gas-phase reactions? No Yes Introduces conjugate pairs? No Yes Scope Narrower Broader — includes all Arrhenius acids and bases What the Ar...

You're handed a beaker of acid and told to work out how concentrated it is. You can't weigh it — it's already dissolved. You can't see it. What you can do is find out exactly how much base it takes to cancel it out, and work backwards. That's a titration. The short answer: a titration is a lab technique for finding the unknown concentration of a solution by reacting it with a solution of known concentration, added drop by drop until the reaction is exactly complete. An indicator signals that moment, and the volume used lets you calculate the answer. What a titration actually is The setup is always the same three pieces of glassware: The burette holds the solution you know — the titrant — and lets you add it in measured drops. The conical flask holds the solution you don't know — the analyte — measured out precisely with a pipette. A few drops of indicator go in the flask to signal the finish. You run titrant in slowly, swirling. Near the end you g...

Both sit in the same drawer in every school lab, both change colour in acid, and both get called "indicator paper". But one of them answers a yes/no question and the other gives you a number — and using the wrong one costs marks. The short answer: litmus only tells you whether a solution is acidic or basic — red in acid, blue in base — while universal indicator is a mixture of dyes that produces a whole range of colours, telling you approximately how acidic or basic it is on the pH scale. Quick comparison at a glance Feature Litmus Universal indicator What it tells you Acid or base (yes/no) Approximate pH value Number of indicators One (a lichen extract) A mixture of several Colours Red and blue only Red → orange → yellow → green → blue → purple In acid Red Red/orange/yellow In neutral No reliable colour Green In base Blue Blue/purple Precision None — just a category About ±1 pH unit Best used for A quick yes/no check Estimating pH Use in titrations Rarely No...

Add one drop of strong acid to a glass of pure water and the pH crashes from 7 to about 3. Add the same drop to your bloodstream and nothing happens — your pH shifts by maybe a hundredth of a unit. The difference is a buffer, and without it you would not survive lunch. The short answer: a buffer is a solution that resists changes in pH when small amounts of acid or base are added. It works because it contains a weak acid and its conjugate base side by side, one ready to mop up added OH⁻ and the other ready to mop up added H⁺. What a buffer actually is A buffer needs two components present in comparable amounts: a weak acid (call it HA), and its conjugate base (A⁻) — the same species minus its proton. The classic laboratory buffer is acetic acid (CH₃COOH) with sodium acetate (CH₃COONa) . The acetic acid supplies HA; the sodium acetate dissolves to supply A⁻. The pair works because a weak acid sits in equilibrium rather than committing one way: CH₃COOH ⇌ H⁺ + CH₃COO⁻ Having...