Acids and Alkalis

• Indicators are substances that change colour when they are added to acids and alkalis. • Litmus is the most well-known indicator. • It turns red in acid and blue in alkalis.
• Universal indicator is most commonly used in the laboratory. When added to a solution, it changes to a colour that shows the pH of the solution
• Acids contain H+ ions e.g. HCl or H2SO4.
• When an acid is added to an alkali (or base) the H+ ions combine with the OH- ions forming water, neutralising the pH.
• When acids react with water they form ions. The degree to which they do this determines whether they are strong or weak acids. Strong acids are essentially 100% ionised whereas weak acids ionise very little in solution.
• Concentration is distinct from strength. A concentrated acid contains a large amount of acid in a given volume; a dilute solution contains a small amount.
• Strong and weak acids produce the same type of products but we react more slowly. Ethanoic acid is a weak acid so it reacts slowly. Hydrochloric acid is a strong acid so it reacts quickly.
• When an acid is neutralised a salt is formed and all products are neutral, so they are called neutralisation reactions.
• A neutralisation reaction is exothermic
• The highest temperature reached in a neutralisation reaction is at the point of neutralisation.
• Metal + Acid -> Salt + Hydrogen
• Metal Oxide + Acid -> Salt + Water

  (base)
• Metal Hydroxide + Acid -> Salt + Water

  (alkali)
• Metal Carbonate + Acid -> Salt + Water + Carbon Dioxide
• • Hydrochloric acid = chloride salt
  • Sulfuric acid = sulfate salt
  • Nitric acid = nitrate salt
  • Ethanoic acid = ethanoate salt
• In thee reaction of an acid and a metal, hydrogen gas (H2) is produced which means you will see bubbles (fizzing). The more bubbles you see, the more reactive the metal is.
• Order of reactivity = Ca, Mg, Zn, Fe, + Cu

  (number of bubbles of hydrogen gas produced)
• Test for hydrogen

  -Ignites with a squeaky POP!