OCR A-level chemistry amount of substance Questions and answer

OCR A-level chemistry amount of substance Questions and answer What is a mole? the amount of a substance that contains as many particles of that substance as there are atoms in exactly 12g of carbon-12. 1 mole contains the Avogadro number of particles. what is avogadro's number? 6.02 x 10^23 moles= Mass / Mr what is water of crystallisation? water molecules that form an essential part of a crystalline compound what is a hydrated compound? a crystalline compound that contains water molecules what is an anhydrous compound? a compound that does not contain water molecules concentration= moles/volume what is an empirical formula? the simplest whole number ratio of atoms of each element in a compound what is a molecular formula? The actual number of atoms of each element in a compound equation for moles of a gas at RTP ideal gas equation volume = m3 pressure= Pa temp = K gas constant= 8.314JK-1mol-1 what is stoichiometry? the ratio of the amount, in moles, of each substance in a balanced equation what is concentration? a measure of the amount of solute dissolved per unit of solvent (moldm-3) equation for atom economy equation for percentage yield when would you use a titration? -when finding an unknown concentration -identifying unknown substances -finding purity of a substance what is a standard solution? a solution with a known concentration how do you prepare a standard solution? -solid is weighed by difference -solid is dissolved in beaker using less distilled water than needed to fill the volumetric flask to the mark the solution is transferred to a volumetric flask. the last traces of solution rinsed into the flask with distilled water -fill flask to graduation line by adding distilled water drop by drop using a pipette. bottom of meniscus must be on the line. -invert the volumetric flask several times