Chemistery

The first time you meet a titration curve it looks like a lazy S lying on its side, and the obvious question is why anyone would plot it at all. The answer is that almost every number you need from a titration — the concentration, the pKa of the acid, which indicator to use — is sitting somewhere on that curve, if you know where to look. The short answer: a titration curve is a graph of the pH of the flask against the volume of titrant added . It is nearly flat for most of the titration and then jumps almost vertically over a fraction of a millilitre; that steep section is the equivalence point , where the acid and base have reacted in exactly the ratio the balanced equation demands. What the axes actually mean The x-axis is the volume of titrant delivered from the burette, usually in cm³ or mL. The y-axis is the pH measured in the conical flask, either with a pH meter or inferred from an indicator. Every point on the curve is one snapshot of the flask. You start at the far lef...

Dissolve table salt in water and the pH stays at 7. Dissolve the same amount of ammonium chloride and the pH drops to about 5. Both are salts, both came from a neutralisation, and neither contains an obvious acid. The explanation is that "neutralisation" does not always produce something neutral. The short answer: a salt's solution is acidic if it came from a strong acid and a weak base , basic if it came from a weak acid and a strong base , and neutral if both parents were strong . The reason is hydrolysis — ions left over from a weak parent react with water and shift the pH. Quick comparison at a glance Parent acid Parent base Resulting solution Example Approx. pH of 0.10 M Strong Strong Neutral NaCl, KNO₃ 7.0 Strong Weak Acidic NH₄Cl, NH₄NO₃ 5.1 Weak Strong Basic CH₃COONa (8.9), NaF (8.1) 8–9 Weak Weak Depends on Ka vs Kb CH₃COONH₄ ≈ 7.0 Why any salt changes the pH A salt dissolves into two ions, and the question is wheth...

Ask what water is and the honest answer is "it depends what you put it with". Drop in hydrogen chloride and water behaves as a base. Bubble in ammonia and the same water behaves as an acid. Substances that can go either way have a name, and they turn up far more often than most students expect. The short answer: an amphoteric substance can act as either an acid or a base , depending on what it meets. Water is the classic example — it donates a proton to ammonia and accepts one from HCl — and so are bicarbonate, HCO₃⁻, and oxides such as Al₂O₃ and ZnO. What "amphoteric" actually means The word comes from the Greek amphoteros , "both of two". A substance is amphoteric if it has a reaction available in both directions: something it can give away to a proton-hungry partner (a base), and something it can take from a proton donor (an acid). There is a narrower term you will meet alongside it. Amphiprotic means specifically that the substance can both don...

Acetic acid, CH₃COOH, contains four hydrogen atoms and donates exactly one. Phosphoric acid, H₃PO₄, contains three and donates all three — but not equally, and not at the same pH. Counting acidic hydrogens correctly is the difference between a titration answer that works and one that is out by a factor of two or three. The short answer: a monoprotic acid can donate one proton per molecule; a polyprotic acid can donate more than one , losing them one at a time in separate steps with steadily smaller Ka values. Acidic hydrogens are the ones attached to an electronegative atom — most often O , sometimes N , S or a halogen — and never the ones on a plain C–H bond. Quick comparison at a glance Feature Monoprotic Polyprotic Protons donated Exactly 1 2 or more — diprotic (2), triprotic (3), and beyond Ionisation steps One One per proton, sequentially Ka values A single Ka Ka₁ > Ka₂ > Ka₃ Equivalence points in titration One Up to one per ionisable prot...

Pure water is supposed to be the definition of neutral. So why does a pH meter dipped into boiling distilled water read about 6.1 — and why is that water still neutral? The answer is one small constant that quietly underpins the entire pH scale. The short answer: Kw is the ion product of water , the equilibrium constant for water reacting with itself: Kw = [H₃O⁺][OH⁻] = 1.0 × 10⁻¹⁴ at 25 °C . Because that product is fixed at a given temperature, knowing either ion concentration always gives you the other. Water reacts with itself Water is amphiprotic — it can donate a proton and accept one. Given enough molecules, some of them do both to each other: 2 H₂O ⇌ H₃O⁺ + OH⁻ This is called autoionisation (or self-ionisation). It happens in every sample of water, and in every aqueous solution, all the time. It is just extremely rare: at 25 °C only about one water molecule in 555 million is ionised at any instant. The equilibrium constant for that reaction, with the solvent water fold...

Everyone learns "NaOH is strong, ammonia is weak" and then hits a question about 0.010 M NaOH versus 6 M ammonia and freezes. Which one has the higher pH? The answer needs the difference between strength and concentration — and this is the pair of words that decides it. The short answer: a strong base produces hydroxide ions essentially completely in water, so its OH⁻ concentration equals its concentration. A weak base only partly reacts, sitting at an equilibrium described by Kb , so its OH⁻ concentration is far lower than its concentration. Quick comparison at a glance Feature Strong base Weak base Behaviour in water Reacts/dissociates essentially completely Partly reacts; equilibrium Arrow used Single, → Double, ⇌ Kb Not applicable — it dissociates, it does not equilibrate with water Small and measurable [OH⁻] ≈ the base's concentration Much less than its concentration Typical pH of 0.10 M 13.0 ~11.1 Examples NaOH, KOH, Ba(OH)₂...