The Properties Of Acids And Bases
Visão Geral
Swallow an indigestion tablet and something quietly dramatic happens in your stomach. A powder that would do nothing at all in a glass of water goes to work on a liquid strong enough to strip paint, and within a few minutes the burning stops. That rescue is the same event that farmers buy by the lorry load to repair sour fields, that power stations engineer into their chimneys to keep sulfur out of the sky, and that a technician performs a hundred times a week at a laboratory bench with a burette. One reaction, four completely different settings.
This lesson gets underneath it. You will find out what a base actually is and why only some bases earn the name alkali, why every acid you meet owes its behaviour to one particular ion, how a strip of paper dipped in a mixture of dyes can report the acidity of a solution in a colour you can read across a room, and why the salt that appears at the end of a neutralisation has one half of its name donated by the acid and the other half by the base. By the end you will be able to look at any acid and any base in the specification and name the product before you mix them.
Objetivos
- Metal oxides and hydroxides are bases. Soluble hydroxides are called alkalis.
- Acids react with bases to form salts. These reactions are called neutralisation reactions.
- The particular salt produced in any reaction between an acid and a base or alkali depends on: the acid used (hydrochloric acid produces chlorides, nitric acid produces nitrates, sulfuric acid produces sulfates); the metal in the base or alkali.
- Ammonia dissolves in water to produce an alkaline solution. It is used to produce ammonium salts.
- A solution of calcium hydroxide in water (limewater) reacts with carbon dioxide to produce calcium carbonate.
- Hydrogen ions, H+ (aq), make solutions acidic and hydroxide ions, OH- (aq), make solutions alkaline. The pH scale is a measure of the acidity or alkalinity of a solution. Students should be familiar with the pH scale from 0 to 14, and know that pH 7 is a neutral solution. Students should be able to describe the use of universal indicator to measure the approximate pH of a solution.
- In neutralisation reactions, hydrogen ions react with hydroxide ions to produce water. This reaction can be represented by the equation: H+ (aq) + OH- (aq) → H2O (l)
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- Which of these substances is an alkali? A. copper(II) oxide B. calcium carbonate C. potassium hydroxide D. sulfuric acid Answer: C
- Which salt is produced when magnesium oxide reacts with nitric acid? A. magnesium chloride B. magnesium nitrate C. magnesium sulfate D. magnesium nitride Answer: B
- Which statement about a solution of pH 12 is correct? A. It contains no hydroxide ions. B. It contains more hydroxide ions than hydrogen ions. C. It turns universal indicator red. D. It is neutral. Answer: B
- Which equation represents the neutralisation of an acid by an alkali? A. H+ (aq) + OH- (aq) -> H2O (l) B. H2 (g) + O2 (g) -> H2O (l) C. Na+ (aq) + Cl- (aq) -> NaCl (s) D. CaCO3 (s) -> CaO (s) + CO2 (g) Answer: A
- Carbon dioxide is bubbled through limewater. What is observed? A. The colourless solution turns cloudy white. B. The solution turns blue. C. A gas is given off that relights a glowing splint. D. A yellow precipitate forms. Answer: A
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