let's see how quickly we can cover the required practicals for Ed Exel pson GCSE chemistry first some tips remember that in many of these investigations there's an independent variable the thing you change a dependent variable the other thing that changes as a result which you measure and controls variables that could change but we keep them the same throughout in order to ensure that results are accurate always say what piece of equipment you use for each measurement don't just say measure the length of the object also add with a ruler or whatever you're using that's a mark in itself when it comes to safety we always use goggles and off and gloves when working with chemicals State the flipping obvious if you think surely they don't want me to put that put it down anyway you never know what marks you might pick up talk about the accuracy of measurements how will you reduce errors and uncertainties for example you get your eye in line with the measurement when using a ruler or measuring cylinder to reduce Parallax error another classic thing you should put down is multiple or repeat measurements or readings to calculate a mean from finally it's okay to write your answers in bullet point format in fact I recommend it as it helps you and the examiner keep track of how many different points are being made because I'm trying to fit lows in here you might see me write abbreviated points for the sake of brevity but when you write a point do it in full make sure you use proper English don't start going all tazan like saying heat liquid with fire more like heat the water gently on a Gau on a tripod over a buns and burner flame also don't forget that you can see me and others from mansbury science doing these practicals for Reales on mansbury education link is in the description let's go chemistry one chromatography this allows us to separate the different solutes or other particles found in a mixture we put the spot of the solution or another kind of mixture just above the bottom of a piece of chromatography paper filter paper also works this is our stationary phase we also draw a line across the paper at the same point in pencil this will not move up the paper with the water and acts as our reference point for measurements later we secure the paper to A rod so it hangs down in a test tube or Beaker with a bit of distilled water in so the bottom of the paper just touches the water the spot must not touch the water directly we then wait for the distilled water to move to diffuse up the paper by capillary action hence why it's called the mobile phase this pulls particles in the mixture upwards too with lighter particles moving further up the paper than heavier ones so they separate out we can then calculate the RF value retention Factor by dividing the distance the solute moves by the distance the mobile phase the water moves by again these are both measured from the pencil line we can then compare these RF values with known values for different substances which helps us identify what's in our mixture chemistry 2 investigating pH all we do is measure the end pH of a reaction between different masses of a powdered base an alkalite like calcium hydroxide or calcium oxide and a fixed volume of a dilute acid say hydrochloric acid after mixing thoroughly we can take a pet or glass capillary tube to take a drop and put it on a small bit of universal indicator paper in the dimple of a spotting tile we can then compare the color produced against the charts and determine the mass needed to neutralize the acid that will be once it gets to a ph of 7 of course we could then use moles to calculate the concentration of the acid if needed chemistry three preparing copper sulfate salt crystals nice and easy we just take a base like copper oxide and an acid like concentrated sulfuric acid a base essentially just means something that can neutralize an acid we heat the acid first in a beaker then add excess copper oxide you can tell it's in excess when there's some of the unreacted powder at the bottom of the beaker the neutralization reaction makes copper sulfate solution we filter the unreacted copper oxide out then gently heat the solution in an evaporating Basin over a beaker of water that's on a tripod above a Bunton burner flame and you're left with solid crystals of copper sulfate chemistry for electrolysis we want to electroly copper sulfate solution twice once with inert graphite electrodes and again with copper electrodes with the inert electrodes copper is produced at the cathode and oxygen is produced at the anode here's the half all ionic equations for those we're left over with hydrogen and sulfate ions so that makes sulfur acid if you use copper electrodes then the copper atoms in the anode well they will lose electrons to make cu2 plus ions that go into the solution at the cathode the opposite happens the cu2 plus ions in solution they move to the cathode and they gain electrons to turn back into copper atoms they've been reduced so we should see the mass of the anode decrease while the mass of the cathode increase you might be thinking what's the point in this it's a bit of a zero sum game but this can be used to purify by copper and other metals in a similar way if we have an impure copper anode that means there's copper and other bits in it the other bits will not move to the cathode once we start the electrolysis the impure bits will just fall to the bottom of the beaker and it's just pure copper atoms that are deposited on the cathode So in theory we should end up with pure copper on the cathode chemistry five titration we can carry out a titration to determine the concentration of an acid if we know the concentration of The Alkali is neutralizing or vice versa we use a glass pet to measure out a specific volume of the alkal and put in a conical flask then add an indicator like methy orange which turns pink in the presence of an acid then we fill the buet up to the 0 CM Cube Mark at the top and open the tap you can do a rough tighter or rough titration first by adding the acid quickly while swirling the flask once it turns pink you know The Alkali has been neutralized you've likely overshot it but this is just to give you an idea of what the volume needed is repeat this process but close the tap so the acid is only being added a drop at time when you get close to the volume from your rough tighter after each drop swirl the flask if it turns pink but returns to Orange after swirling it's not done it's only once it stays pink does that give you the volume that was needed to neutralize The Alkali you need to use your knowledge of moles in stochiometry of H+ to O minus ions in the acid and Alkali respectively in order to then calculate the unknown concentration in moles per decim cubed of course this is just the moles of the acid or alkco used divided by the volume of the solution or water in decim cubed here's a sample calcul ation for sodium hydroxide and sulfuric acid to see this explained check out my separate titration video chemistry 6 rates of reaction there are two practics we can do to observe the rate of reaction the first is fairly simple if a gas is made from a reaction we can do it in a conical flask with a tube leading to an inverted measuring cylinder filled with water allowing us to measure the volume of gas made every 10 seconds say we can plot this against time to see the reaction curve the gradient at any time is the rate at that time we can then change a variable say temperature or concentration of reactant to be our independent variable and we can plot multiple curves on the same axes to compare them the other PRACK involves a reaction between sodium thy sufate and hydrochloric acid which produces a product that causes the mixture to go cloudy we can say the turbidity increases we carry out the reaction in the chical flask over a piece of paper with a cross drawn on it we use a STP clock to time how long it takes for the cross to disappear when we look from above the flask that's our dependent variable we can then change a condition say temperature or concentration for our independent variable then plot the times again this chemistry 7 identifying ions we need to be able to identify various metal and non-metal ions found in compounds these five metals can be identified using a flame test we dip a piece of nichrome wire in a solution or a powder of the compound or in a sample of water from prax and place it at the edge of a Bunton flame next we can test for non-metal ions to test for carbonate ions add hydrochloric acid if bubbles are made we can collect the gas with a tube or pipet and put it in lime water if it turns cloudy it's carbon dioxide showing that there must be carbonate ions present to test for halide hallogen ions we add silver nitrate solution and nitric acid if chloride ions are present a white precipitate will form cream precipitate is a result of bromide ions yellow iodide adding hydrochloric acid and berium chloride will result in a white precipitate formed if there are sulfate ions present if you've done a good job purifying your water from pra six then you shouldn't see the positive tests for sodium or chloride ions chemistry 8 combustion of alcohols we put a volume of an alcohol like ethanol in a spirit burner under a copper calorimeter held above it using a retor stand which has a known volume or mass of water in we measure the start and end temperature of the water to calculate the temperature difference we can then compare this result for different alcohols like propanol Etc leave a like and a comment if you found this helpful click on the cast to go to the malsbury science playlist all the other card to go to the videos covering whole papers see you next time