1 - Stoichiometric Relationships

• Knowing the molecular mass of acid 1, we can now find out the mass of acid 1, given by: (mass)acid1=(n)acid1×(Mr)acid1.
• A chemical element is a single pure substance, made of only one type of atom.
• A compound is a chemical combination of different elements, containing a fixed ratio of atoms.
• A mixture is composed of two or more substances in which no chemical combination has occurred.
• Temperature is a measure of the average kinetic energy of the particles of a substance.
• Relative atomic mass, Ar, is the weighted average of the isotopes of one atom of an element relative to 1/12 of an atom of carbon-12.
• Relative formula mass, Mr, is the sum of the weighted average of the masses of the atoms in a formula unit relative to one-twelfth of an atom of carbon-12.
• The molar mass of a substance, M, is its relative atomic mass, Ar, or its relative formula mass, Mr, expressed in grams.
• One mole is the mass of substance that contains as many particles as there are atoms in 12 g of carbon-12.
• Molecular mass/empirical mass = x; where x is a positive integer.
• % by mass of element E in a compound = Mr of element / Mr of compound x 100.
• % yield = experimental yield /theoretical yield x 100.
• Boyle’s Law: P ∝ 1/v at constant temperature.
• Avogadro’s Law: V ∝ N at constant pressure.
• Gay-Lussac’s Law: P ∝ T at constant volume.
• Charles’s Law: V ∝ T at constant pressure.
• Ideal gas law equation: PV = nRT.
• Pressure (P) is measured in Pascals (Pa) and can be converted to KPa by multiplying by 10^3.
• Volume (V) is measured in m^3 and can be converted to dm^3 or cm^3 by dividing or multiplying by 10^3 respectively.
• Number of moles (n) is measured in moles and can be converted to m^3 by dividing by the gas constant (R).
• Gas constant (R) is 8.31 J mol K.
• Conversely, at high altitude, where the atmospheric pressure is lower, the boiling point of water is reduced so it takes much longer to cook food.
• Freeze drying is an effective process for the preservation of food and some pharmaceuticals, depending on the sublimation of ice.
• In freeze-drying, the substance to be preserved is first frozen, and the water inside the substance turns to ice.
• The frozen substance is then warmed gently at very low pressure which causes the ice to change directly to water vapour, a process known as sublimation.
• The freeze-dried product is stored in a moisture-free package that excludes oxygen, and can be reconstituted by the addition of water.
• Dew point is the atmospheric temperature (varying according to pressure and humidity) below which water droplets begin to condense and dew can form.
• As the air temperature drops below its saturation point, known as the dew point, the familiar condensed water called dew forms.
• The temperature of the dew point depends on the atmospheric pressure and the water content of the air, also known as the relative humidity.
• A relative humidity of 100% indicates that the air is maximally saturated with water and the dew point is equal to the current temperature.
• The process of refrigeration is usually based on energy changes during the evaporation and condensation cycle under changing pressure of a volatile liquid known as the refrigerant.
• At low pressure the liquid vaporizes and absorbs heat, causing cooling of the surroundings.
• Back titration can be used to analyse excess acid or alkali after a reaction has occurred, and can also be used to measure the amount of limiting reactant in a reaction.
• If we are given volume and concentration of the base and volume and concentration of the acid, and need to find the mass of acid used, we can react the remaining volume of base total with another acid: acid2.
• Since we know the volume and concentration of acid2 and the ratio between acid2 and base excess, we can find the moles of base excess.
• Using that, we can find the volume of base excess.
• We know the total volume of base used: (V)base total, and now we know the excess volume of base: (V)base excess.
• Using this and concentration of the base, we can find out the moles of the base used in the first reaction: (n)base used.
• Since we know the ratio between acid 1 and base used, we can use that to find the moles of acid 1 in the first reaction.
• Temperature (T) is measured in Kelvin and can be converted to °C by subtracting 273.15.