SA-Vol Ratio Cheat Sheet

SA:Vol Ratio Introduction In order to survive, cells must exchange materials with the environment to fuel essential metabolic processes. Diffusion is the passive movement of particles (gases and liquids) from an area of high concentration to an area of low concentration (down a concentration gradient). Diffusion is one of the main processes a cell undertakes to obtain vital substances (such as nutrients and oxygen) and remove cellular wastes (such as urea and carbon dioxide). In this experiment, agar cubes will be used to represent a cell. A pH indicator (phenolphthalein) has been added to the cubes, causing them to turn pink. When phenolphthalein is exposed to acid, the indicator loses its colour and the cube will turn clear. Thus, when a cube is placed in an acid solution, the inside of the cube will gradually turn clear as the acid diffuses into the agar. Aim To investigate how the size of a cube affects the rate at which it turns clear when exposed to an acid solution for a period of 3 minutes (or until the smallest cube turns completely colourless). Materials • • • Block of agar / indicator 3 ´ 100 ml beakers Ruler (in millimetres) • • • Cutting board and knife Stopwatch 200ml of 0.1M H2SO4 solution Method 1. Cut the agar block into three cubes of the following dimensions: 3cm3 cube, 2cm3 cube and 1cm3 cube 2. Pour 60ml of sulfuric acid solution into three beakers 3. Immerse one cube in each of the three beakers, start the stopwatch and leave for 3 minutes (180 seconds) 4. Periodically stir the solution – or turn the cubes over 5. After 3 minutes, remove the cubes from the beakers 6. Blot softly with paper towel to remove acid from cube 7. Cut each cube in half to measure the colour change 8. Record all measurements in the data table provided • • • Paper towels Spoon / Tongs Measuring cylinder