AS Level chemistry

amount of substance is measured using a unit called the mole (mol for short) . one mole is roughly 6 x 〖10〗^23 particles (Avogradro's constant) . It doesn't matter what the particles are . They can be atoms , molecules , electrons or ions

molar mass , M , is the mass of one mole of something . But the main thing to remember is that molar mass is just the same as relative molecular mass M>r (or relative formula mass) . The only difference is you stick a "g mol^-1" for grams per mole on the end

• number of moles = mass of substance
•                            -----------------------
•                            molar mass 
• you can also rearrange the formula and use it to work out either the mass of a substance or its relative molecular mass

how many moles are dissolved per 1 dm^3 of solution . the units are mole dm^-3 or (M)

• number of moles = concentration x volume 
•                                                  (in cm^3)
•                             -----------------------------
•                                               1000 
• or 
• number of moles = concentration x volume
•                                                 (in dm^3)

1000 cm^3 or 1 litre

:)

volume . at room temperature and pressure (r.t.p) this happens to be 24dm^3 (r.t.p. is 298 k (25 degrees centigrade) and 100kPa)

• number of moles = volume in dm^3/24 
• or 
• number of moles = volume in cm^3/24 000

• pV = nRT
• p = pressure measured in pascals (Pa)
• V = volume measured in (m^3)
• n = number of moles 
• R = gas constant whose value is given in the exam 
• T = temperature measured in kelvin (K)

multiply by 1000

add 273

multiply by 10^-6

multiply by 10^-3

balanced equations have the same number of each atom on both sides . You can only add more atoms by adding whole compounds . You do this by putting a number in front of a compound or changing one that's already there . You can't mess with formulas

in ionic equations only the reacting particles are included . You don't have to worry about the rest of the stuff . First you make sure that both sides have the same number of atoms - just like a normal equation . then you balance the charges by adding extra electrons

• 1) write out the balanced equation for the reaction 
• 2) work out how many moles of the reactant you have 
• 3) use the molar ratio from the balanced equation to work out the number of moles of product that will be formed from this much of reactant 
• 4) calculate the mass of that many moles of product

• 1) write out the balanced equation for the reaction 
• 2) work out how many moles of the reactant you have
• 3) use the molar ratio from the balanced equation to work out the number of moles of product that will be formed from this much of reactant 
• 4) put that number of moles into one of the gas equations

• state symbols are put after each compound in an equation . they tell you what state of matter things are in 
• s = solid 
• l = liquid
• g = gas 
• aq = aqueous (solution in water)

when an acid reacts with an alkali you get a salt and water

exactly how much acid is needed to neutralise a quantity of alkali

• measure out some alkali using a pipette and put it in a flask , along with some indicator such as phenolphthalein .
• add the acid to the alkali using a burette - open the tap to run acid into the alkali a little bit at a time .
• every time you add some more acid , give the flask a swirl to make sure that the acid and the alkali are properly mixed .
• first of all do a rough titration to get an idea where the end point is . The end point of the titration is the exact point at which the indicator changes colour - at this point the amount of acid added is just enough to neutralise the alkali .
• now do an accurate titration . run the acid in to within 2cm^3 of the end point , then add the acid dropwise . If you don't notice exactly when the solution changed colour you've overshot and your result won't be accurate .
• record the amount of acid used to neutralise the alkali .
• It's best to repeat this process a few times , making sure you get the same answer each time . this will make sure your results are reliable

:)

• number of moles = 
• concentration x volume (in cm^3)                                                   -----------------------------                                                            1000 
• but this time rearrange it to find volume 
• volume (cm^3) = number of moles x 1000
•                          -----------------------------
•                                       concentration

just the smallest whole number ratio of atoms in a compound

actual numbers of atoms in a molecule . the molecular formula is made up of a whole number of empirical units

• 1) find the empirical mass - that's just the mass of the empirical formula 
• 2) divide the molecular mass by the empirical mass . this tells you how many multiples of the empirical formula are in the molecular formula 
• 3) multiply the empirical formula by that number to find the molecular formula

• 1) [assume you have got 100g of the compound - you can turn the percentages into straight masses] . then you can work out how many moles of each element are in the compound by using number of moles=mass/mr
• 2) divide each number of moles by the smallest number of moles you found in step 1 . this gives you the ratio of the elements in the compound
• 3) apply the numbers from the ratio to the formula

acids that only release one H+ from each molecule

mass of product that should be formed in a chemical reaction . it assumes no chemicals are lost in the process .

• 1) work out how many moles of reactant you have 
• 2) use the equation to work out how many moles of product you would expect that much reactant to make 
• 3) calculate the mass of that many moles of product - and that's the theoretical yield

• less 
• sometimes not all the starting chemicals react fully . And some chemicals are always lost , e.g. some solution gets left on the filter paper , or is lost between transfers between containers

• percentage yield = actual yield 
•                            -------------- x 100
•                            theoretical yield

how efficient a reaction is .

the environment and save the chemical industry money

the percentage yield . This tells you how wasteful the process is - it's based on how much of the product is lost because of things like reactions not completing or looses during collection and purification

how wasteful the reaction itself is . A reaction that has a 100% yield could still be very wasteful if a lot of the atoms from the reactants wind up the in by-products rather than the desired product .

the proportion of reactant atoms that become part of the desired product (rather than by-products) in the balanced chemical equation

chemical companies try to use reactions that have a high atom economy , so they're not producing lots of waste , or spending money making by-products . But reactions with low atom economy may still be used if the waste products can be sold and used for something else (waste products like gases , salts and acids can often be useful reactants for other products)

• % atom economy
•    mass of desired products
• = -------------------------------- x 100 
•    total mass of reactants

add up the molecular masses of the reactants , find the molecular mass of the product your'e interested in and put them both into the formual

100

the number of moles of each compound that is in the balanced equation

balanced equation