S2 Science Environmental Chemistry - Summary Notes 1. Acids and Alkalis pH is a measure of how much Hydrogen (H+) is in a solution. This means how acidic or alkaline it is. 0 Acid (red-yellow) Neutral (green) Alkali (blue-purple) Cleaning products such as bleach are usually alkalis. Some foods and drinks can be acidic. They should be dissolved in water before testing. 2. pH indicators Some chemicals change colour to show the pH of a solution - pH indicators. Universal indicator and pH paper turn red in acids, green in neutral solutions and dark blue in alkalis. Some vegetables such as red cabbage make good pH indicators Dilution causes acids to become weaker – pH increases towards 7. Dilution causes alkalis to become weaker – pH decreases towards 7. pH probes can also be used to measure the pH of a solution. This is the most accurate method of measuring pH as it gives an exact digital readout. 3. Fertilisers In order to increase the production of plants we need to add nutrients to the soil. Fertilisers are substances that we add to soils that contain one or more of the elements - Potassium, Nitrogen or Phosphorus. Most fertilisers are made by the reaction of an acid and an alkali. 4. Rocks The whole earth is made of rocks & minerals. A mineral is composed of the same substance throughout – one single chemical. A rock is made up of 2 or more minerals. 1. Igneous - formed when hot liquid rock (magma) cools and hardens. 2. Sedimentary - rocks get worn down, form layers as sediments, get buried and squashed together. In time they harden to form new rocks. 3. Metamorphic - a metamorphic rock is formed from other rocks that are changed because of heat or pressure. Metal Ores are rocks containing compounds of metals Unreactive metals such as gold are found in the Earth’s crust uncombined. Other metals such as copper or iron need to be extracted by: 1. heating alone 2. heating with carbon Copper can be extracted from malachite by first heating then heating again with carbon. malachite (copper ore) lime water (turns from clear to cloudy in carbon dioxide) 5. Displacement Reactions Some metals can displace (remove) other metals from solutions they are in. More reactive metals can displace less reactive metals. Order of reactivity (most to least): Magnesium, zinc, iron, copper 6. Corrosion This is the deterioration of a metal, which results from a chemical reaction with its environment. Rust is the term used specifically for the corrosion of iron. Ferroxyl Indicator is used to test for rust: yellow to blue. Rusting is caused by the reaction of iron metal with oxygen and water. It is speeded up in salt water and in acidic solutions like acid rain Protection against rusting can be done by painting the metal, coating the metal in plastic or galvanising (which is coating the metal in a layer of Zinc metal).