Chemistry in our world

Acids metal + Acid-> salt + hydrogen Magnesium + hydrochloric acid -> magnesium chloride + hydrogen We can test for hydrogen by holding a lighted splint over the test tube and listening for a pop

Neutralisation Acid + alkali (e.g. Calcium carbonate) makes a neutral substance Calcium carbonate + hydrochloric acid -> calcium chloride + water + carbon dioxide Limewater turns cloudy when carbon dioxide reacts with it

Temperature changes The reaction between citric acid and sodium hydrogen carbonate feels cold – it takes heat in from the surroundings We can speed up a chemical reaction by heating it up

Atmosphere The early atmosphere on Earth was mostly carbon dioxide The early atmosphere was produced by volcanic activity The oceans were made when water vapour condensed Today, there is 20% oxygen in the atmosphere

Fossil fuels Crude oil is a mixture of compounds Crude oil is found in underground deposits Some greenhouse gases make the Earth’s temperature rise Sulfur dioxide makes acid rain, kills plants and damages buildings

Water To make water safe to drink we need to sterilise it We do this to kill the bacteria in it