Stoichiometry & acids/bases - Co-ordinated Sciences IGCSE Study Notes

Let's break down these fancy words!

Stoichiometry (pronounced: stoy-key-AH-muh-tree) is just a super-smart way of saying 'chemical recipe'. Imagine you're making a sandwich. You need 2 slices of bread and 1 slice of cheese. If you want to make 5 sandwiches, you'll need 10 slices of bread and 5 slices of cheese, right? Stoichiometry is exactly like that, but for chemicals. It helps us figure out how much of each ingredient (reactant) we need to get how much of the final product we want.

Acids and Bases are like the 'flavors' of chemistry – sour and bitter/slippery.

• Acids are substances that taste sour (like lemon juice or vinegar) and can be corrosive (meaning they can eat away at things, like strong cleaning products).
• Bases (also called alkalis if they dissolve in water) are substances that feel slippery (like soap) and taste bitter. They can also be corrosive.

Think of it like a balancing act. Acids and bases are opposites, and when you mix them, they can cancel each other out in a process called neutralisation (making them less harmful). This is super useful, like when you take an antacid for an upset stomach – that's a base neutralising the acid in your tummy!

Let's imagine you're making a delicious batch of cupcakes (our chemical reaction!).

1. The Recipe (Balanced Chemical Equation): Your recipe says: 1 cup of flour + 1 egg + 1/2 cup sugar --> 12 cupcakes. This is our 'balanced equation' – it tells us the exact ratios.
2. Stoichiometry in Action: If you only have 2 eggs, how many cupcakes can you make? Using the recipe, you know 1 egg makes 12 cupcakes, so 2 eggs will make 24 cupcakes! You also know you'll need 2 cups of flour and 1 cup of sugar. Stoichiometry helps you scale your recipe up or down perfectly.
3. Acids and Bases in the Kitchen: Ever added baking soda (a base) to a recipe that has lemon juice or buttermilk (acids)? When they mix, they create bubbles (carbon dioxide gas) that make your cupcakes light and fluffy! This is a mini neutralisation reaction making something useful. If you add too much acid, your cupcakes might be too dense; too much base, and they might taste soapy. Knowing about acids and bases helps you get the texture and taste just right!