Unit 1.3 - Chemical equations Flashcards
How many cm3 are in 1dm3?
What is 1 cm3 equal to?
1dm3 = 1000cm3
1 cm3 = 1 ml
How many mg are in 1g?
1g = 1000mg
How many g are in 1kg?
1kg = 1000g
How do you convert temperature to kelvin?
°C + 273
Relative isotopic mass
Mass of an atom of an isotope relative to 1/12th the mass of an atom of carbon - 12.
Relative atomic mass
Average mass of one atom of the element relative to 1/12th the mass of one atom of carbon - 12.
Relative formula mass
Sum of the relative atomic masses of all atoms present in its formula.
Relative molecular mass
Mr of an element is defined as the mass of one molecule divided by 1/12th the mass of one atom of carbon 12.
Mole
Mass of a substance that contains the same number of particles (atoms/molecules/ions) as there are atoms in 12g of the carbon-12 isotope.
Isotope
Atoms of the same element which have the same number of protons but a different number of neutrons.
Molecular ion
The positive ion formed in a mass spectrometer from the whole molecule.
Fragmentation
Splitting of molecules, in a mass spectrometer, into smaller parts.
Avogadro’s constant
Number of atoms per mole (same no. particles in 12g of C-12).
Stoichiometry
Molar relationship between the amounts of reactants and products in a chemical reaction.
Empirical formula
Simplest formula showing the simplest whole number ratio of the number of atoms of each element present.
Molecular formula
Shows actual number of atoms of each element present in the molecule.
Molar volume
Volume per mole of a gas. Only use if temp is between 0°C-25°C, pressure 1 atm.
Solute
Dissolved substance.
Solvent
Liquid in which the solute dissolves
Concentrated
Solution with large quantity of solute in a small quantity of solvent.
Error
Skilled worker would find difficult to avoid due to consequence of the way the apparatus has been constructed and how readings can be made using it.
Mistake
Skilled operator can avoid by being careful.
How do you calculate the number of moles?
n= m (g)/Mr
How do you calculate the concentration?
C= n/V (dm-3)
How do you calculate the number of moles in a given volume of gas at given temperature and pressure?
n= Vol./Molar Vol.
How do you calculate the concentration in g dm-3?
Concentration (mol dm-3) x Mr
Describe how to make a solution (5).
1) Accurately weigh the solute on a balance.
2) Dissolve the weighed mass in water in a beaker using a stirring rod.
3) Add to a volumetric flask washing through the beaker using a wash bottle.
4) Carefully add more water to the solution until it reaches the mark.
5) Mix the solution throughly by using a stopper and shaking it.
Ideal Gas Equation
PV=nRT
Ideal gas equation
1) What is pressure measured in?
2) What is volume measured in?
3) What is temperature measured in?
4) What does R stand for?
1) Pa
2) m3
3) K
4) Gas constant
1) How many Pa are in 1kPa?
2) How may dm3 are in 1m3?
1) 1000Pa = 1kPa
2) 1000dm3 = 1m3
How do you calculate the percentage yield?
actual yield/theoretical yield x 100
How do you calculate atom economy?
theoretical mass of required product/total mass of reactants used x 100
What are the 3 main steps in calculating reacting masses?
1) Work out number of moles (n= M/Mr)
2) Ratio of n:n
3) M= n x Mr
What are the 3 main steps in titration calculations?
1) Work out number of moles (n= c x v)
2) Ratio of n:n
3) C = n/v
What is back titration?
Amount of excess reactant unused at the end of a reaction is found and so the amount used can be calculated.
What is the method for titration? (4)
1) Place an acid/alkali in a burette.
2) Measure 25cm3 of an acid/alkali using a pipette and place in a conical flask.
3) Add a few drops of indicator to the flask.
4) Titrate (add from burette) until there is a colour change.
Why is atom economy important?
High atom economies produce less waste, which means more profit.
How do you calculate the empirical formula?
Divide mass by atomic number, then divide by the lowest number.
How do you calculate the molecular formula?
Actual Mr/Mr of empirical formula.
Multiply the formula by the calculated value.
Mass spectrometry
1) What happens at vaporisation?
1) Elements are injected directly into the instrument just before the ionisation chamber. Less voliate solids must be preheated and vaporised.
Mass spectrometry
2) What happens at ionisation?
2) Why will most of them carry a charge of +1?
2) Stream of vaporised element enters the ionisation chamber. Electrically heated metal coil gives off electrons which are attracted to the electron trap (positively charged plate). Particles become bombarded with a stream of electrons and some of collisions are energetic enough to knock electrons making positive ions.
2) More difficult to remove further electrons from an already positive ion.
Mass spectrometry
3) What happens at acceleration phase?
3) What is the need for the vacuum?
3) Electric field accelerates the positive ions to high speeds.
3) Ions need to have a free run through the machine without hitting air molecules.
Mass spectrometry
4) What does the amount of deflection depend on?
4) Mass of ion - lighter ions are deflected more than heavier ones
Charge of ion - Ions with 2 or more positive charges are deflected more.
5) What happens at the detection stage?
Beams of ions passing through are detected via current. Only ions with the correct mass/charge ratio will make it through to the ion detector.
The other ions collide with the walls where they will pick up electrons and become neutralised.
State 3 uses of mass spectrometry.
Identifying unknown compounds, identifying trace compounds in forensic science and analysing molecules in space.
How do you calculate the relative atomic mass/abundance of an isotope?
Isotope number x length / all lengths added together
Describe how the mass spectrum is formed (3)
Molecular ion forms from an electron being knocked off to give a positive ion.
They are energetically unstable and some will break into fragments.
Different fragmentations form causing a wide range of lines in the mass spectrum.
What happens to chlorine when it is passed through the ionisation chamber?
Electron is knocked off cl2+ which undergoes fragmentation to cl+ which is more stable.
How do you calculate percentage error?
% error = error/reading x 100
State 3 sources of error in titrations.
Leaving funnel in burette, not reading the meniscus at eye level and over-shooting the end point.
