in this video we're going to run through the different food tests and we're going to cover all the ones that you need to know for your gcsc biology practicals so we'll cover the Benedicts test which is for sugars the iodine test for starch the buet test for proteins and the Sudan 3 test for lipids and for those of you doing the edexel course we'll cover the Emulsion test for lipids as well now one thing that all of these tests have in common is you need to prepare your food sample for this you first need to get your piece of food and break it up using a Mor and pessel then you need to put this crushed food into a beaker with some distilled water and stir it with a glass WOD and some of it dissolves the last thing we need to do is filter out the solution using a funnel that's been LED with Filter paper to get rid of all the solid bits of food that we don't need and this solution that we end up with will be our sample that we can use for the food tests sugars are the small units that all carbohydrates are made of and they can be split into two types reducing sugars and non-reducing sugars now you don't really need to know the difference between these two but just remember that the Benedicts test only tests for reduced sugars so to do this test you first prepare your food sample like we did a minute ago and transfer 5 cm cubed of that sample to a test tube you also need to prepare a water bath and set it to 75° C once your water bath is ready you can add about 10 drops of Benedict solution to your test tube and place it in the water bath for 5 minutes for safety reasons though you should use a test tube holder to place it in the water bath and point the tube away from you and anybody else now if no reducing sugars are present think your solution will stay blue but if there are reducing sugars present it should change to green yellow or even brick red depending on the concentration just like sugars starch is a type of carbohydrate but it's a much larger and more complex molecule luckily though the test for it is much simpler all you do is take 5 C of your food sample and add a few drops of iodine solution this will turn the solution a browny orange color next you give it a gentle shake and if the sample did contain starch the solution will change from that brownie orange color to a blue black color and as all we did here was add iodine we simply call this the iodine test the buet test meanwhile is a test for protein in this one you add two rather than 5 cm cubed of your sample to a test tube and then add another two cm of the buet solution to your sample turning it blue before gently giving it a shape and at the food sample did contain protein the solution would change from Blue to pink or purple now if you're doing the Ed XL course you might need to be a bit more specific and instead of just adding Petri agent add potassium hydroxide followed by copper sulfate when it comes to lipids we do something called the Sudan 3 test for this you need 5 cm cubed of your food sample but importantly you don't need to have filtered it then you add three drops of the sidan 3 stained solution to the test tube and gently shake it if the lipid was present it should get stained by the Sudan 3 solution and as the lipid separates from the water because it's not soluble you'll see there's a bright red layer at the Top If you're doing the edexel course then you might need to know about the Emulsion test F lipids instead in this case all you do is take your food sample add 2 cm cubed of ethanol and Shake It vigorously then you add an equal volume of distilled water and if it goes a cloudy white color it means that lipid was present if there is isn't any cloudy white color then there wasn't any lipid if you haven't heard yet you can find all of our videos on our website Cognito dog you'll also find questions flash cards exam style questions and pass papers and we track all of your progress so that you always know what to study next so sign up for free by clicking here or browse our playlist here on YouTube