Autumn chemistry: TLC of Fall Leaves (What's inside an autumn leaf скачать в хорошем качестве

Autumn chemistry: TLC of Fall Leaves (What's inside an autumn leaf

In this episode of "Science Inside the Lab", I'll be investigating the colours of autumn leaves. 0:00 - Introduction and leaf collection Why do leaves change colour during autumn/fall? 1:55 - Overview of Thin-Layer Chromatography separation technique involving a solid and liquid (mobile) phase pigments move up the solid phase (silica plate or filter paper) with a liquid phase (mix of nonpolar and polar solvents) different pigments move at different speeds based on their polarity (whether or not they have + or - charges at their ends, like a battery) This movement up the solid phase with the liquid creates a pattern of colored bands Non-polar pigments travel farther (Usain Bolt); polar pigments stay lower (closer to the starting line) TLC works like a race, where pigments move at different speeds based on their chemical nature 4:20 - Prepare the extraction chamber Line a large glass container with filter paper pour a small volume (~5 mL) of mobile phase (polar and non-polar solvent) into the beaker Cover the opening of the beaker and place it into a well-ventilated area until it's time to separate the pigments 5:55 - pigment extraction Cut the leaves into small pieces add a pinch of sand to the mortar add ~1-2 mL of solvent (mix of nonpolar and polar) Use a pestle to grind the leaves keep grinding until a concentrated liquid is extracted collect into clean tubes/vials 9:30 - Prepare the TLC plate Cut the TLC plate, e.g., silica plate or filter paper, to the appropriate size Use a pencil (it contains no pigments) to draw two horizontal lines ~1 cm from the top and 1 cm from the bottom of the plate/paper. This line represents the "line of origin" or starting block the line of origin is where the pigments will line up to start the separation race 10:35 - Spotting the extracted pigments Use a micropipette tip, capillary tube or tiny straw to place small dots of each pigment along the line of origin 16:35 - Expected results Each pigment band = a specific pigment molecule; together they show the chemistry behind autumn colours the typical order of separation: fastest to slowest (top to bottom) (more nonpolar to less nonpolar or less polar to more polar) carotenes - orange Beta-carotene - bright yellow xanthophylls - yellow (pale yellow) chlorophyll a - blue-green chlorophyll b - yellow green pheophytin - olive/brown anthocyanins - red/purple TLC helps us see the hidden pigments and understand the chemistry of the Fall season