Atoms and reactions Flashcards
Defintion of relative molecular mass, Mr
This compares the mass of a moleculewith 1/12th of the mass of an atom of carbon-12. It’s calculated by adding together the relative atomic masses of the elements making up the molecule.
Defintion of relative formula mass
This compares the mass of a formula unit with 1/12th of the mass of an atom of carbon-12. It is calculated by adding together the relative atomic masses of the elements making up the empirical formula.
Definition of the mole
The amount of (any) substance containing as many particles as there are carbon atoms in exactly 12g of carbon-12.
Defintion of the Avogadro’s constant
The number of particles in one mole of any substance. It has the value of 6.02 x 10^23 mol^-1.
Avogadro’s equ
Total number of particles = total number of particles in substance x Na x n
Definition of an empirical formula
The simplest whole number ratio of atoms of each element in a compound.
Definition of molecular formula
The actual number of atoms of each element in a compound.
Defintion of hydrated
A complex staructure which has water moelcules (water of crystallisation) incorporated.
Definition of anhydrous
The compound which remains when the water of crystallisation is removed from a hydrated salt.
Definition of water of crystallisation
Water molecules which make up the part of the crystal structure of a compound, that can be removed by heating.
Method for hydrated salts
- Weigh an empty crucible.
- Add the hydrated salt into the weighted crucible.
- Weigh the crucible and the hydrated salt.
- Using a pipe clay triangle to support the crucible containing the hydrated salt on a tripod.
- Heat the crucible and contents gently (to prevent spitting of solution and loss of mass = inaccurate measurement) for around one minute, then heat it strongly for a further three minutes. Repeat until continuous mass.
- Leave the crucible to cool.
- Weigh the crucible and anhydrous salt.
% mass =
(Total mass of desired chemical / total mass of the compound) x 100
Definition of Avogadro’s law
At the the same temperature and pressure, equal volumes of different gases contain the same number of gas molecules.
Definition of molar gas volume
The volume per mole of gas molecules at a stated temperature and pressure (dm^3mol^-1).
Gas equ
Volume in dm^3 = n x 24
Volume in cm^3 = n x 24,000
Equ for reactions not carried out at RTP
Pv = nRT
Unit changes for Pv = nRT
Pressure: KPa –> Pa x1000
Temperature: degree –> K +273
Volume: m^3 –> dm^3 x10^6
Concentration =
moles / volume
Definition of solution
This is made when a solute (solid) is completely dissolved in a solvent.
Definition of concentration
The amount of solute, in mol, dissolved in 1dm^3 of solvent. The units are moldm^-3.
Definition of standard solution
A solution of known concentration. They are prepared by dissolving an exact mass of the solute in a solvent and making up to an exact volume using a volumetric flask (more precise).
Why is it important to ensure the measuring of the solute is accurate?
If the solvent fills up above the meniscus on the volumetric flask, the volume would increase, so the moles of the solute remian the same meaning the concentration would decrease.
Method for making up a standard solution
- Accurately measure the mass of the solid carefully using a balance to an appropriate number of decimal places.
- Dissolve the solid carefully in about 100cm^3 of distilled (or de-ionised) water, stirring with a glass rod.
- Transfer the solution to a clean 250cm^3 volumetric flask, using a funnel.
- Rinse the beaker, glass rod and funnel with distilled water and include the rinsings into the volumetric flask.
- Make up to just below the mark with distilled water.
- Make up the solution to the mark, using a dropping pipette.
- Insert the stopper, and invert slowly several times to mix thouroughly.
Uncertainty equ
(Uncertainty / measurement) x 100
Definition of a titration
A technique to accurately measure the volume of one solution that reacts exactly with another solution so that the concentration of the unknown can be found.
Burettes have an uncertainty of…
+/- 0.05cm^3
Percentage yield =
(actual mass / theoretical mass) x 100
OR
(actual moles / theoretical moles) x 100
Definition of percentage yield
How much product you actually made compared to how much you could have made in theory.
Atom economy =
(sum of Mr of desired products / sume of Mr of all products) x 100
