All Units Flashcards
What is Gravimetric Analysis?
Discovering the mass of a chemical that is isolated from a mixture or precipitated in a reaction
2 common examples of an appropriate time to use Gravimetric Analysis
Percentage of water in bread Concentration of salt in baby food
What is the sign that the Gravimetric Analysis has reached its end?
The measured mass is constant
What does a desiccator do?
Absorbs moisture
When measuring the mass of the precipitate, what do you have to consider?
The degree of solubility of the compounds
How do you calculate the mass of the product precipitate?
Step 1: Balance equation
Step 2: calculate mol of the compounds mass you are given
Step 3: Use ratios to work out the mol of the compound whose mass you are trying to work out
Step 4: n=m/GFM
Step 5: If percentage is required final/initial mass x100
What is volumetric Analysis?
A process using volumes of liquids to analyse a concentration (basically titration)
What is a primary standard solution?
A substance so pure that the amount of substance, in moles, can be calculated accurately from their masses
List 4 possible characteristics of a primary standard solution
- Readily available 2. Available in pure form 3. Not readily react in the atmosphere 4. Be easily stored 5. Have high molar mass 6. Be inexpensive
Give three examples of primary standard solutions
- Sodium carbonate 2. Sodium borate 3. Hydrated oxalis acid
What formula is likely to be used when calculating volumetric analysis?
C1V1= C2V2
Describe the process of preparing a standard solution
- Work out mass needed - Dissolve the weighed sample in a small beaker and transfer to the volumetric flask - wash the small beaker at least three times and add to flask - half fill the water, shake to dissolve sample - add water up to the calibration line then shake again
Why aren’t common acids generally used as standard solutions?
Often absorb water in the atmosphere when they react with CO2, leaving them impure or have unknown exact concentration
In titrations, what is meant by Aliquot and equivalence point?
Aliquot - volume measured out by the pipette
Equivalence point - the point in the reaction which the reaction is just complete (the reactants are in their exact mole proportions)
Name the four types of volumetric analysis
- Acid base (neutralisation) 2. Redox 3. Back titration 4. Complexometric titrations
What does %w/w , %v/w mean?
Percentage of : weight in weight and volume in weight
How do you calculate ppm?
What is a weak acid?
A weak acid is an acid which partially dissociates in solution
Describe a back titration
Stage 1- Reactant A of unknown concentration is reacted with excess reactant B of known concentration Stage 2- A direct titration is then performed to determine the amount of reactant B in excess
When do we use back titrations?
-A reactant is volatile -Acid or base is insoluble -A particular reaction is slow -The end point is very difficult to observe if you use a weak acid or base
What is light?
Light is waves of energy which consists of photons
Equation to find the speed of light where; speed of light= c, frequency=v and wavelength=λ
c=λv
Equation of wave number
Equation for frequency
- v=vc
Equation for energy of a photon
E=hv
Energy for one mole of a photon
E=Lhf
When does the continuous spectrum occur?
When visible light passed through a glass prisim
When does the emission spectra occur?
When electrical energy is passed through a gaseous sample, consists of narrow lines of colour
What are excited electrons?
Electrons with a high amounts of energy. These electrons jump between energy levels and once they fall back to the ground state light is emitted
What is the emission spectra?
The different wavelengths of light that are produced when elements release energy
Which parts of the electromagnetic spectrum can emission lines be detected?
In both UV and infrared
How do you calculate the wavelength of any line?
1/lamda=R(1/n21 - 1/n22)
From the wavelength equation, what does n1 equal when dealing with a line in the Lyman series?
1
From the wavelength equation, what does n1 equal when dealing with a line in the Balmer series?
2
What is the infinity level?
The highest possible energy an electron can have as part of an atom
What is lambert’s law?
A=Elc
What does each of E,l and c refer to in Lamberts law?
E= Epsilon l=length of solution the light passes through c= concentration of solution
What does Heisenberg’s Uncertainty Principle state?
You cannot determine the position and momentum of an electron at the same time
What does Aufbau’s Principle state?
Electrons enter at the lowest available energy level
What does Pauli’s Exclusion Principle state?
No two electrons can have the same four quantum numbers
What does Hund’s Rule of Maximum Multiplicity state?
When in orbitals of equal energy, electrons will try to remain unpaired
What is an orbital?
A region of space where one is likely to find an electron
What shape and occurrence is seen with the orbital s?
Spherical and one in every principal level
What shape and occurrence is seen with the orbital p?
Dumb-bell and three in level 2 upwards
What shape and occurrence is seen with the orbital d?
Various shapes and seen 5 times in level 3 upwards
What shape and occurrence is seen with the orbital f?
Various and seen seven times in level 4 upwards
Which significant orbital over laps another?
4s overlaps 3d
Which elements are exceptions to the configuration rules and why?
Chromium and copper To achieve a more stable arrangement of lower energy, one of the 4s electrons is promoted into the 3d to give six unpaired electrons.
What is a positive ion called?
Cations
What are negative ions called?
Anions
Where are electrons removed from when being oxidised or reduced?
Removed from the highest occupied orbital, excluding transition metals
What transitional metals are exceptions to the rule that transition metals don’t remove electrons from the highest occupied orbital?
First row transitional metals
What are orbitals called if they have the same energy level?
Degenerate orbitals
Which is more stable, half filled or partially filled orbitals?
Half filled
Which of half filled or partially filled has the highest ionisation energy?
Half filled because it is more stable
What does VSEPR stand for?
Valence Shell Electron Pair Repulsion
What shape corresponds to an atom with two electron pairs?
Linear, 180 degrees
What shape corresponds to an atom with three electron pairs?
Trigonal Planar, 120 degrees
What shape corresponds to an atom with four electron pairs?
Tetrahedral, 109.5 degrees
What shape corresponds to an atom with five electron pairs?
Trigonal bipyramidal, 120 and90 degrees
What shape corresponds to an atom with six electron pairs?
Octahedral, 90 degrees
Which is strongest, an electron non-bonding pair or an electron bonding pair?
Non-bonding
What shape occurs when a compound has two bonding pairs?
Linear
What shape occurs when a compound has three bonding pairs?
Trigonal planar
What angle between electron pairs occurs when a compound has four electron pairs, one of which is a lone pair and three are bonding?
107 degree
What angle between electron pairs occurs when a compound has four electron pairs, two of which are lone pairs and the other two are bonding pairs?
104.5 degrees
What shape occurs when a compound has five bonding pairs?
Trigonal bipyramidal
What shape occurs when a compound has six bonding pairs?
Octahedral
What are d block transition metals?
Metals with an incomplete d subshell
When a transitional metal is oxidised where does the electron come from?
The outermost sub shell
What is the oxidation state similar to?
The valency that an element has when it is part of a compound
What is the oxidation number of an uncombined element?
0
What is the oxidation number of a single ion?
The same as the charge given
What is fluorine’s oxidation number?
-1
What does the sum of all the oxidation numbers in a compound?
0
What must the oxidation number add up to in a polyatomic ion?
The charge of the ion
What are ligands?
Ligands are negative ions or uncharged molecules with one or more non-bonding electrons.
What is dative covalent bonding in relation to transition metals?
When ligands donate their non-bonding electrons into unfilled metal orbitals.
What are monodentate ligands?
Ligands that only donate 1 pair of electrons
What are bidentate ligands?
Ligands that donate two pairs of electrons
What are multidentate ligands?
Ligands that donate more than two electron pairs
A common example of a monodentate
H20
A common example of a bidentate
Oxalate ion
A common example of a multidentate?
EDTA
What is the coordination number?
The number of bonds from the ligand to the central metal ion
How do you write the formula of the central metal ion and its ligand
1) Metal ion is first 2) Next, negatively charged ligand 3) Then enclosed with brackets and the overall charge
How do you write the name of complexes?
Ligands are named first in alphabetical order, followed by the name of the metal and its oxidation state If the ligand is negative and it’s ending is ide, it’s end changed from ide to o
What is ammonia’s ligand name?
Ammine
What is water’s ligand name?
Aqua
What is the ligand name for CO
Carbonyl
What is the name of the ligand for the nitrate ion?
Nitrito
What happens if the overall ion (inclusive of ligands and central ion) is negative?
If the whole compound is negative then the ion ends in ‘ate’
When would a split in the D orbitals occur?
When the metal is approached by a ligand and some d orbitals gain more energy so are no longer degenerate
What is the energy difference dependant on in a splitting d orbital?
The position of the ligand in the spectrochemical series. The larger the energy difference, the stronger the ligand’s energy field
What is the short form of the spectrochemical series?
Cyanide ion> Ammonia> Water> Hydroxide ion>Fluorine ion> Chlorine ion>Bromine ion> Iodine ion
What colour are copper solutions usually?
Blue
What colour are nickel solutions usually?
Green
What causes the emission of colours from metals?
The electrons in lower orbitals gaining energy and then moving to higher orbitals
How do you tell which colour a metal will emit?
The colour absorbed is opposite of the colour emitted
What method can you use to study colour emission?
UV and Visible Spectroscopy
In which wavelength region will d-d transitions occur if the ligand has a strong field?
UV- 200-400nm
In which wavelength region will d-d transition occur when the ligand has a weak field?
Visible light- 400-700nm
What are catalysts called when they are in the same state as their reactants?
Homogeneous catalysts
What are catalysts called when they are in different states than their reactants?
Heterogeneous catalysts
How do transition metals act as a catalyst?
The unpaired electron in the d-orbital (or vacant d orbital) forms a weak bond with the reactant. This puts the reactant in a favourable position as it’s covalent bond is weakened thus allowing the other reactant to attack.
What is chemical equilibrium?
When the rate of the forward reaction is equal to the rate of reverse reaction.
What three factors can influence the position of the equilibrium?
Concentration Pressure Temperature
What equation is used to find the equilibrium constant Kc?
What happens to the equilibrium equation if the reaction is heterogenous?
The pure solid(s)/liquid(s) present at equilibrium are given the value 1
What effect has changing the concentration or pressure of the reaction on the equilibrium constant.
None
What is the equation for the ionisation of water?
What term is given to the equilibrium constant of the ionisation of water.
Ionic Product
What are substances called when they act as both a base and an acid?
Amphoteric
What is the equation for the equilibrium constant of water?
What are the pH ranges for acids, alkalis and water?
7<
7>
=7
What is the relationship between pH and hydrogen ion concentration?
What is the relationship between pH and hydroxide ion concentration?
pH= -log10[OH-]
What are acids called if they have either one or two hydrogen ions?
Monoprotic and Diprotic
What is common among weak bases?
They contain an amine group
What is common among strong bases?
They contain oxides and hydroxides of alkali metals
What is the relationship between conductivity and pH of acids and alkalis?
As the pH moves further away from 7, in either direction, the conductivity increases
