Unit 1: Section 2 - Amount of Substance

Number of particles = Number of moles x Avogadro’s constant

Number of particles/atoms/ions in one mole of a substance

Mass of substance = Number of moles x Mr

Number of moles = Concentration x Volume

pV=nRT p - pressure in Pa V - volume in m^3 n - number of moles R - gas constant in JK^-1mol^-1 T - temperature in K

25°C/298K 1 atm/ 101kPa 1 moldm^-3

• Write the balanced symbol equation • Identify the soluble compounds using the solubility rules or the aqueous state symbol • Split up the soluble compounds into ions • Cancel ions that appear on both sides of the equation • Write out the resulting ionic equation

• Work out how many moles of NaOH you need using moles = concentration x volume • Work out how many grams of NaOH you need using mass = moles x Mr • Use weighing by difference to find the precise mass of the solid used and add to beaker making sure to rinse the washings • Add distilled water to the beaker and stir until all NaOH has been dissolved • Tip the solution into a volumetric flask using a funnel • Rinse the beaker and stirring rod with distilled water, making sure there’s no solute left over • Use distilled water to fill the flask up to the line, making sure the bottom of the meniscus is lined up • Stopper and invert the flask a few times to ensure it’s all been mixed

• Use a pipette to measure a set volume of the solution you want to know the concentration of, and put it in a flask • Add a few drops of indicator • Then fill a burette with a standard solution of the acid that you know the exact concentration of • Use a funnel to carefully pour the acid into the burette, always doing this below eye level

• Do a rough titration to get an idea where the end point actually is • Take an initial reading to see exactly how much acid is in the burette, then run the acid within 2cm^3 of the rough titre, then add it dropwise, swirling the flask until the colour just changes • Work out the amount of acid required to neutralise the alkali • Repeat until you have three concordant results • Calculate a mean value

Methyl orange - red in acid and yellow in alkali Phenolphthalein - colourless in acid and pink in alkali Use a white tile to be able to see the colour change easier

The simplest whole number ratio of atoms of each element in a compound

Gives the actual numbers of atoms of each element in a compound

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

Percentage Yield = Actual Yield / Theoretical Yield x 100

Tells you how wasteful a process is, based on how much product is lost during the process

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

Percentage Atom Economy = Molecular mass of desired products / Sum of molecular masses of all reactants x 100

• Better for the environment because they produce less waste • They make more efficient use of raw materials, so they’re more sustainable • They are less expensive because they need to spend less time separating the desired product from the waste products, and less on treating waste