Making Soluble Salts & Electrolysis

Salt-making is all about combining positive ions (from metals or metal compounds) with negative ions to create new compounds. You'll use copper oxide and sulfuric acid as your limiting reactant to make beautiful blue copper sulfate crystals.

The trick is heating your acid gently, then adding copper oxide bit by bit until there's powder left over - this tells you the reaction has stopped and your solution is neutral. After filtering out the excess powder, you'll evaporate half the water and wait 24 hours for crystals to form.

Electrolysis splits compounds using electricity and graphite electrodes. With copper chloride solution, you'll get copper coating the cathode (negative electrode) and chlorine gas bubbles at the anode. Sodium chloride behaves differently - you get hydrogen gas at the cathode instead because sodium is too reactive.

Top Tip: Always test gases safely - use damp litmus paper for chlorine and a lit splint for hydrogen. Never let your electrodes touch or you'll create a dangerous short circuit!

Temperature Changes & Titrations

Temperature change experiments measure how much heat reactions produce or absorb. You'll mix hydrochloric acid with different volumes of sodium hydroxide in a polystyrene cup (which prevents heat loss) and record the maximum temperature each time.

Start with 30cm³ of acid, then gradually add 5cm³ portions of alkali whilst stirring with your thermometer. The temperature will rise to a peak, then start dropping - that peak shows you the neutralisation point.

Titrations help you find unknown concentrations by carefully adding acid to alkali until neutralisation occurs. You'll use phenolphthalein indicator, which changes from pink to colourless when the solution becomes neutral. The key is adding acid drop by drop near the end point.

Read your burette at eye level using the bottom of the meniscus (the curved bit). You need concordant results within 0.1cm³ of each other, so expect to repeat this several times until your readings are consistent enough for accurate calculations.

Remember: Always place your conical flask on a white tile - it makes colour changes much easier to spot during titrations.