Chris Harris: 'hello and welcome to this video on formula equations and amount of substance my name is Chris Harris and I'm from a Larry tutors comm and this video the whole point of this video is to give you an overview of this part of the elements for life topic for OCR be Salters and basically it's just designed provision to give you an idea of an overview and because it's revision and the slides that I'm using here you can have access to them as well and you can purchase them you just click on the link in the description box below and you can get ahold of them there they're really good value for money and and and can really kind of compliment your revision and help you to get that a star or a in chemistry okay so like I say this is dedicated to the Psalter specification and it meets these points taken from the syllabus to okay so just have a quick look at the atom and structure of the atom and because we're going to talk about obviously moles and and and and the like so we need to know a little bit more about the structure of the atom so just a nutshell we have a nucleus it's really small it contains protons and neutrons we have electrons that sit in orbitals and these obviously orbit the nucleus around it we need to know the charges of these things as well protons have a relative charge of plus one so that positive a massive one neutrons are neutral and they have a massive one electrons are minus one the relative charge is minus one and their relative mass is one over two thousand so we can't say it's zero because they do have a mass it's just very very light or very low and obviously in the periodic table you'll see your elements and have written are like this the bigger number is the mass number tells number of protons and neutrons in the nucleus and the bottom number is called the atomic or proton number and this tells us the number of protons in the nucleus and remember in elements the number of protons equals the number of electrons so this can also be the number of electrons in elements okay so we need to know that with our ions and isotopes so I on to have a different number electrons and protons see here oxygen has got gained two electrons this is a negative ion and it would then combine with the positive ions to form a stable compound but if you have a look at the number of protons in here number protons is eight in oxygen and as a charge of plus eight neutrons is eight but they don't have a charged electron this has 10 electrons a charge of minus two so overall it has a charge of minus a minus 10 sorry so overall it has a charge of minus T and which is this is why it's owed to minus looking at positive ions something like sodium sodium has 11 protons in the in the middle of it which is a charge of plus 11 12 these others which have a charge of zero and it has 10 electrons which means it has a charge of minus 10 so overall the overall charge is +1 so positive ions actually lose an electron to form the positive ion that they are here and this is an example which is sodium isotopes these are elements with the same number of protons but they have a different number of neutrons so you can see here that we've got a set of 3 isotopes here these are all carbon isotopes and if we have a look here with the same number of protons here across all of them and so we've got 6 protons and each cousin so you see the program at the bottom is the same but the number of neutrons is different you can see here that we've got because it's gone 12 13 14 we've got extra neutrons obviously in these isotopes up here so these ones are the isotopes of each other because they have the same number of protons but a different number of neutrons okay you've got to know your definitions as well you'll see and these might see these crop up in you exam so the relative atomic masses the AR this is the weighted mean mass of an atom of an element compared to 1/12 of the mass of an atom of carbon-12 so make sure you know that definition make sure you know the definition of relative isotopic mass as well this is just the mass not amine mass is just a mass of an atom of an isotope compared to 1/12 of the mass of an apple carbon-12 so it's always this same bit at the end here and relative molecular mass or formula mass so this is the mean mass of a molecule compared to on 12 of the mass of an atom of carbon-12 so it's a molec'
Work out the theoretical mass, balance the equation, determine the molar masses of the species involved, convert masses to grams, divide the mass of the desired product by the molar mass of the reactant, and calculate the maximum amount of product that can be produced
Write out the elements involved, convert percentages to masses, divide by the relative atomic mass to get the number of moles, find the ratio of moles, and write the final formula using the smallest ratio
In a reaction involving the complete combustion of calcium, if 32.6 grams of calcium oxide was produced and the theoretical mass is 47.6 grams, the percentage yield is calculated as 32.6 / 47.6 * 100 = 68.5%
Readings in titrations should be taken from the bottom of the meniscus and at eye level, recorded to two decimal places, and repeated for concordant results