Chemistery

Keep stirring sugar into a glass of iced tea and at some point it stops disappearing. A little pile settles at the bottom and simply refuses to go. The water hasn't got tired — it's full. The short answer: a saturated solution contains the maximum amount of solute that will dissolve in a given solvent at a given temperature. Add more and it just sits there undissolved, because dissolving and re-crystallising are happening at exactly the same rate. The three kinds of solution Type How much solute What you see Stable? Unsaturated Less than the maximum More solute still dissolves when added Yes Saturated Exactly the maximum Extra solute sits undissolved at the bottom Yes Supersaturated More than the maximum Clear, but crystallises at the slightest disturbance No — metastable What "saturated" really means The undissolved crystals at the bottom of a saturated solution aren't doing nothing. At the microscopic level, two processes are ...

Every solution question starts with the same small decision, and it trips up more students than the calculations that follow: which one is the solute and which is the solvent? Get it backwards and your concentration answer is upside down. The short answer: the solute is the substance that gets dissolved ; the solvent is the substance that does the dissolving . Together they make a solution , and the solvent is normally whichever one is present in the greater amount. Quick comparison at a glance Feature Solute Solvent Role Gets dissolved Does the dissolving Amount present Usually the smaller amount Usually the larger amount State after mixing Takes on the solvent's state Keeps its own state Common state Often solid, but can be any Usually liquid Everyday example Salt, sugar, CO₂ Water, ethanol, acetone In salt water Salt (NaCl) Water Changes when mixed? Broken up into particles/ions Stays as it is What a solute is A solute is wha...

Salt vanishes into water in seconds. Oil sits on top and sulks no matter how hard you stir. Sugar dissolves faster in hot tea than iced tea. All three are the same question wearing different clothes: what makes something dissolve? The short answer: solubility is the maximum amount of a substance that will dissolve in a given amount of solvent at a particular temperature. Whether something dissolves comes down to one rule — "like dissolves like" — because polar solvents pull apart polar and ionic solutes, and nonpolar solvents dissolve nonpolar solutes. What solubility actually measures Solubility is a number, not a yes/no. It's usually quoted as grams of solute per 100 g of water at a stated temperature : Table salt, NaCl: about 36 g per 100 g of water at 25 °C Sugar (sucrose): about 200 g per 100 g of water at 20 °C Chalk, CaCO₃: about 0.0013 g per 100 g of water at 25 °C Notice that chalk isn't strictly insoluble — it's just so poorly soluble that w...

Two concentration units, one letter apart, both pronounced almost identically. The difference comes down to a single word in each definition — solution versus solvent — and that one word changes when you'd use each. The short answer: molarity (M) is moles of solute per litre of solution . Molality (m) is moles of solute per kilogram of solvent . Molarity measures the final mixture by volume; molality measures only the solvent, by mass. Quick comparison at a glance Feature Molarity (M) Molality (m) Definition mol solute ÷ L of solution mol solute ÷ kg of solvent Units mol/L mol/kg Denominator measures The whole mixture Only the solvent Measured by Volume Mass Changes with temperature? Yes — liquids expand No — mass is fixed Best used for Titrations, everyday lab work Boiling point and freezing point problems How you prepare it Dissolve, then top up to the mark Weigh solute and solvent separately What is molarity? Molarity is the concentration unit you'll use...