Chemistery

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...

A chemistry revision sheet is most useful when you do something with it. Read the explanation, cover it, answer a question, then check where your reasoning broke down. That gives you a specific job for your next study session. Here's a five-minute routine you can try with the free Strong Acids & Bases sheet from 5 Minutes in Chemistry . The sheet has a short explanation, a reference chart, facts to remember and three self-test questions. You only need one printed page, a pen and something to cover the answers. Download the free Strong Acids & Bases sheet The download includes US Letter and A4 PDFs. Choose your paper size and print one copy. The actual free sample. The full series contains 56 revision sheets in this one-page format. 0:00–1:00 — Read one idea Start with the short explanation at the top. On this sheet, the central distinction is what “strong” means in acid–base chemistry. Read it once, then look away and explain it in your own words. If you can only ...

You've got comfortable with pH, and then a question asks for pOH and it feels like a whole new topic. It isn't. pOH is the same idea pointed at the other ion, and the two are locked together by one equation. The short answer: pH measures the concentration of hydrogen ions (H⁺) in a solution, while pOH measures the concentration of hydroxide ions (OH⁻). In water at 25 °C they are always linked by pH + pOH = 14 , so knowing either one gives you the other by subtraction. Want to try a printable revision sheet? The free Strong Acids & Bases sample gives you a one-page reference, a chart and a short self-test before you move on to pH calculations. Quick comparison at a glance Feature pH pOH Measures H⁺ concentration OH⁻ concentration Formula pH = −log[H⁺] pOH = −log[OH⁻] Low value means Acidic Basic (alkaline) High value means Basic (alkaline) Acidic Neutral water at 25 °C 7 7 Typical range 0–14 14–0 Which is quoted in daily life Almost always this one Rarely Rel...