Acids, Bases & Chemical Analysis

Acids are proton donors that release H+ ions when dissolved in water, whilst bases are proton acceptors that neutralise acids. Think of it as acids giving away hydrogen ions and bases grabbing them up.

The key difference between bases and alkalis often trips students up, but it's actually straightforward. Alkalis are just bases that dissolve in water to form OH- ions - so all alkalis are bases, but not all bases are alkalis.

Strong acids and bases almost completely break apart in water (like HCl), whilst weak ones only partially split up (like ethanoic acid in vinegar). This doesn't mean weak acids are less dangerous - it's just about how much they dissociate!

Titrations are your go-to method for finding unknown concentrations. You'll use a burette to add one solution drop by drop to another until you reach the endpoint - that's when your indicator changes colour to show the reaction is complete.

Quick Tip: Always do a rough titration first to get close to your endpoint, then do precise ones. Your results should be within 0.1 cm³ of each other.

Polyprotic acids like sulfuric acid (H₂SO₄) can donate multiple protons, which affects your calculations. Remember to account for how many H+ ions each acid molecule can release.

Redox Reactions & Oxidation Numbers

Redox reactions involve the transfer of electrons between substances, and they're happening around you constantly - from rusting metal to your body's metabolism. The trick is learning to spot when electrons are moving.

Oxidation means losing electrons (remember: OIL RIG - Oxidation Is Loss, Reduction Is Gain). When something gets oxidised, its oxidation number increases. The substance that causes this is called an oxidising agent, and it gets reduced in the process.

Reduction is the opposite - gaining electrons and decreasing oxidation numbers. Reducing agents donate electrons and get oxidised themselves. It's like a chemical exchange system where one substance's loss is another's gain.

Oxidation numbers follow specific rules that make them predictable. Uncombined elements are always 0, Group 1 metals are always +1, and oxygen is usually -2 (except in peroxides). These rules help you track electron movement and balance equations.

Memory Hook: Think of oxidation numbers as keeping score of electrons. When the number goes up, electrons have been lost (oxidation). When it goes down, electrons have been gained (reduction).