Amount of Substance Flashcards
What does the formula unit show?
The ratio of each type of atom in an ionically bonded lattice
What is the mass of the formula unit called and what’s its symbol?
The relative formula mass
Symbol: Mf but sometimes Mr is still used
How do you work out relative formula mass?
Average mass of one formula unit of an element of compound/ 1/12 the mass of one atom of carbon-12
How many particles does a mole contain? And what is this number called?
6.023 x 10▪23 particles. The avagadro constant.
What is the mass of a mole of atoms of an element in grams?
The relative atomic mass in grams
What was amedeo avagadros hypothesis?
That at the same temperature and pressure equal volumes of different gases contain the same number of particles
How do you work out How many atoms are there in 0.200 mol helium gas?
You times it by the avagadro constant
What is the formula for Mr mole lives under the hill?
Mass= Mr x mol
How do you get the number of moles from the number of atoms or molecules?
You divide by the avagadro constant
What are the assumed properties of an ideal gas?
- It is made up of identical particles in continuous random motion
- the particles can be thought of as point like with position but with zero volume
- the particles do not react when they collide
- collisions between particles are perfectly elastic- the total kinetic energy if the particles after the collision is the same as before
- the particles have no intermolecular forces
Which gases behave most like ideal gases?
Hydrogen, nitrogen, oxygen and the noble gases
What is Boyle’s law in words and formula
At constant temperature T, the volume V of a fixed mass of gas is inversely proportional to the pressure P applied to it
P x V =constant
What happens to gases as the temperature is increased?
The gases expand because their molecules move faster and are further apart so their density decreases and vice versa if the temperature decreases.
What is Jacques Charles law?
At constant pressure the volume of a fixed mass of gas is proportional to its temperature
V= constant x T
What happens at absolute zero temperature (-273.15 ° c)
Gases reach zero volume
How do you convert °c to Kelvin?
Add 273
What is the ideal gas equation?
pV= nRT
P= pressure of the gas in Pascals (pa) V= volume of the gas in m3 n= number of moles of the gaseous particles R = molar gas constant (8.31 J K-1 mol -1) T = temperature in Kelvin (K)
What is the empirical formula?
The simplest whole number ratio of atoms of each element that are in a compound
What is the molecular formula?
The actual number of atoms of each element used to make a molecule of formula unit
How do you work out the empirical formula?
Convert the masses of each element to moles to get the ratio of each element and then divide by the smallest number.
What is a chemical equation?
A shorthand way of writing a chemical reaction. It uses chemical formulae for the reactants and products. Formulae use letter symbols to represent the elements and numbers to show how many atoms or each element are involved
What are the different state symbols and what do they mean?
(S) solid
(l) liquid
(g) gas
(Aq) aqueous
What does it mean to balance an equation?
Make sure that there are the same amount of each element on both sides of the reaction
What is the calculation for percentage yield and what is it used to Express?
It is used to Express how close the actual yield is to the theoretical yield
Percentage yield = actual yield/ theoretical yield x100
What is the calculation for percentage atom economy and what is it used for?
It is a way to compare the maximum mass of a product that can be obtained with the mass of the reactants
Percentage atom economy = molecular mass of desired product/ sum of molecular masses for all reactants x 100
What benefits will chemical processes with high atom economies have?
They will have economic, ethical and environmental benefits for industry and the society it serves
What is the use of an ionic equation?
They provide a shorthand way to show the essential chemistry involving the ions in a reaction
How do you work out an ionic equation?
1) write out the full equation
2) write the equations as ions and cancel the ions that appear on both sides
Remember that covalently bonded molecules dont form ions
What are the ions that appear of both sides of an equation known as?
Spectator ions
What are common solvents?
Water and ethanol
What is concentration measured in?
Mol dm-3 and g dm-3
What is the calculation for concentration?
Concentration (mol dm-3) = moles of solute/ volume of solution (dm3)
C = n/v
What practical do chemists do to determine unknown concentrations?
A titration
How do you make a volumetric solution?
1) a known number of moles in a solute must be dissolved in demonised water and the solution made up to a known volume
2) weigh a weighing boat and measure the required mass of compound into it. The number of moles can be calculated from the mass and the relative molecular or formula mass of the compound.
3) the compound needs to be transferred quantitavely (all transferred) which is done by putting a small funnel in the neck of a volumetric flask. The compound is tipped in and any remaining in the container is washed in using a wash bottle containing demonised water
4) start to fl thrlask adding demonised water and swirling the contents to make sure the compound dissolves. Do this until the solution is about 1 cm below the flasks graduation mark. Deionised water is then added drop by drop until the bottom of the meniscus is just level with the graduation mark.
How do you carry out an acid base titration?
1) pour some of the solution to be analysed into a beaker
2) use a clean dry pipette with a safety filler to draw the solution to just above the graduation line. Make sure the pipette is below the solution at all times.
3) controlling the release with the safety filler the solution is drained out until the bottom of the meniscus is level with the graduation line on the pipette.
4) the filler is then removed and the solution is emptied into the conical flask.
5) the brunette is then clamped. Before use the burete rinsed a few times with the volumetric solution
6) the volumetric solution is poured in through a funnel and then the volume is recorded.
7) the volumetric solution is added from a burette in tests and as the end point gets closer the colour takes longer to change.
8) the titration is then added drop by drop when it is close to the end titration. The burette reading is recorded when there is a colour change..
9) you should start by doing a rough titration and repeat until 3 concordant results are obtained
