Chemistry BMAT Practice Test Questions and Answers

Quantitative chemistry The sum of atomic mass (Ar) values in a molecule is the molecular mass (Mr) Avogadro's constant gives the number of particles in one mole of a substance: Number of particles = Avogadro's constant x number of moles One mole of a substance has a mass (in grams) equal to the Ar or Mr. Mole = mass x Mr The percentage composition of a particular element in a molecule can be calculated by dividing the Ar of the element by the total Mr of the molecule. The empirical formula is the simplest integer ratio of atoms in a compound. The empirical mass can be found when given the reacting masses. These are divided by the Ar of each element and then the ratio between each of these is the empirical formula. Chemical equations can be calculated in the same way from reacting masses. The molecular formula can be calculated using the empirical formula and Mr. Divide the Mr by the Mr of the empirical formula then multiply the empirical formula by this number. Concentration (mol dm^-3) = number of moles x volume Concentration (g dm^-3) = mass / volume One mole of a gas occupies a set volume at a given temperature and pressure. Any gas will occupy 24dm^3 in standard conditions - at room temperature and pressure (rtp). A solutions concentration is determined by the moles/mass of solute in volume of solution. The term saturated solution means that no more solute can be dissolved in the solvent - any additional solute without more solvent results in solid precipitate or let off as gas. In order to neutralise a substance, the same number of moles is needed from each substance (if the ratio is 1:1). To find a concentration of a substance, titrations are performed using a known concentration of acid/alkali to neutralise. n= c x v is used to find the number of moles of the substance being neutralised. This reveals number of moles of the other subs Atomic structure The structure of the atom is a central nucleus (containing protons and neutrons) surrounded by electrons moving in shells/energy levels. The majority of the mass is in the nucleus as it is made up of protons and neutrons. Atomic number is the number of atoms and mass number is the number of protons and neutrons. Neutrons = mass number - atomic number. Electrons in an atom = atomic number. The period represents the number of electron shells (period one has one shell). The group represents how many electrons are in the outer shell (apart from group 0, which represents a full outer shell). Isotopes are atoms of an element with the same number of protons but different numbers of neutrons (different mass numbers).