CHEMISTRY EXTERNAL REVISION Flashcards
What happens if more nitrogen is added?
N2 (g) + 3H2 (g) -> 2NH3 (g)
If more nitrogen is added, the equilibrium will shift to the right favouring the forward reaction and more collisions occur between N2 and 3H2. Therefore, the concentration of NH3 will increase until a new equilibrium is reached.
What happens if pressure is doubled/ volume halved?
2SO2 (g) + O2 (g) -> 2 SO3 (g)
If the pressure is doubled / volume halved, the reaction will favour the direction with the least moles. Therefore, the position of equilibrium will shift to the right, favouring the forward reaction
What happens if it is diluted?
Fe3+ (aq) + SCN- (aq) FeSCN2+ (aq)
2 particles in solution 1 particle in solution
Dilution by adding water reduces the number of particles by volume. (This is shown by a sharp decrease, not gradual). This results in a shift in the position of equilibrium towards the side that produces the greater number of dissolved particles. The addition of water momentarily lowers the concentration of each substance. In terms of Le Chat’s principle, a net reverse reaction will occur, increasing the total number of particles in solution.
What is - ∆H?
exothermic (heat lost to surroundings)
What is + ∆H?
endothermic (heat absorbed from surroundings)
What happens if you increase the temp of an exothermic reaction?
Shifts to the left (to absorb some of the added energy).
All molecules have more energy and move faster. The direction of the endothermic reaction is favoured because it requires more energy to occur. Hence, the reverse reaction is favoured.
What happens if you increase the temp. of an endothermic reaction?
Sifts to the right (to absorb some of the added energy)
All molecules have more energy and move faster. The direction of the endothermic reaction is favoured because it requires more energy to occur. Hence the forward reaction is favoured
what does a catalyst do?
Adding a catalyst to an equilibrium system speeds up the rate of the forward and reverse reactions equally. As a result, the catalyst does not change the equilibrium concentrations of the reactants or products.
A catalyst lowers the activation energy of the forward and reverse reactions equally.
Doubling coefficients will? (to Kc)
square original value of Kc
Halving the coefficients will? (to Kc)
Kc will be square rooted
Reversing the reaction will? (to Kc)
Kc will have the inverse value: 1/Kc
Increasing the temp of a reaction will do what to Kc
Kc will:
- increase for an endothermic reaction
- decrease for an exothermic reaction
Strong acids…
readily donate protons and completely dissociates in water
Weak acids….
Do not readily donate protons and incompletely dissociate in water
Strong bases…
Readily accept protons and completely dissociate in water
Weak bases…
Do not readily accept protons and incompletely dissociate in water
Explain strength vs concentration
The strength of an acid or base is determined by its ability to dissociate in solution, whereas the concentration of an acid or base refers to the amount of acid or base present in a given volume of solution.
What is the Bronsted-Lowry model of acids and bases?
In an acid-base reaction, the acid donates a proton to form its conjugate base and the base accepts a proton and becomes its conjugate acid.
primary standard:
A substance so pure that the amount can be accurately calculated from its mass. Has a known formula.
standard solution:
A solution with an accurately known concentration. A standard solution is made from a primary solution
titre:
the volume delivered by a burette
aliquot:
the volume delivered by a pipette
end point:
the point at which the indicator changes colour
equivalence point:
The point in the titration where the stoichiometric proportions of the reactants have been mixed
What is a titration curve?
a graphical representation of the pH of a solution
during a titration
What is the half-equivalence point / pKa?
The half equivalence point or
pKa is the point on a titration curve that represents when half the neutralisation reaction is complete. That is, it is the half way to equivalence or neutralisation
To calculate it you find the volume of NaOH (mL) at equivalence point the half equivalence point is half the volume of the volume equivalence point
n = C x V
n= moles C= concentration, in mol/L V= volume, in L
What is a redox reaction?
Involves the transfer of electrons
Oxidation:
Loss of electrons (OIL)
Reduction:
Gain of electrons (RIG)
Reducing agent:
A reactant that causes another reactant to gain electrons during a redox reaction. This reactant is oxidised and loses electrons.
Oxidising agent:
A reactant that causes another reactant to lose electrons during a redox reaction. This reactant is, itself, reduced and gains electrons
Steps in balancing complex redox reactions:
- Balance all elements except hydrogen and oxygen
- Balance oxygen atoms using H2O
- Balance hydrogen using H+
- Balance charge using electrons and add states
Assigning Oxidation numbers:
- Elements=0
- For monatomic ions, the ON= charge on that ion except for where rule 3 and 4 determine otherwise
- H=+1
- O=-2
- The sum of ON = overall charge for a compound/ polyatomic ion
A decrease in ON means an element has been…
reduced
An increase in ON means an element has been…
oxidised
Which cell has spontaneous reactions?
galvanic
Which cell has non-spontaneous reactions?
electrolytic
Galvanic cell energy:
chemical -> electrical
Electrolytic cell energy:
electric -> chemical
Oxidation occurs at the…
anode
AN OX
Reduction occurs at the…
cathode
RED CAT
In a galvanic cell, anode is…
negative
In an electrolytic cell, anode is…
positive
saturated hydrocarbons:
- only carbon-carbon single bonds
- alkanes
- chemical formula rule: CnH2n+2
Unsaturated hydrocarbons:
- carbon-carbon double or triple bonds
- alkene chemical formula rule: C2H2n
- alkyne chemical formula rule: C2H2n-2
stereoisomers:
All the atoms in stereoisomers are connected in the same order, but the orientation in space of some of the atoms is different
Trans-isomer
2 identical groups at the ends of the double bond, which are on the opposite side of the plane of the C=C bond
Cis-isomer
2 identical groups at the ends of the double bond, which are on the same side of the plane of the C=C bond
Difference between class and functional group:
for OH, hydroxyl is the functional group whereas alcohol is the class
haloalkane suffix:
fluoro, chloro, bromo, iodo
anime suffix:
amine
nitrile suffix:
nitrile
aldehyde suffix:
al
ketone suffix:
one
carboxylic acid suffix:
oic acid
ester suffix
-yl then -oate
amide suffix:
amide
prioritised functional groups (highest to lowest):
carboxylic acid ester amide nitrile aldehyde ketone alcohol amine alkene alkyne alkane haloalkane
as the chain length of molecules increase…..
the dispersion forces increase, and this increases the MP and BP further. The trend is opposite for volatility.
As the hydrocarbon chain increases in length, the solubility…
the solubility decreases, due to the disruption of hydrogen bonding between water molecules by the long non-polar hydrocarbon chains, which can only form dispersion forces. In organic solvents, the opposite trend in solubility is observed. The longer the non-polar hydrocarbon chain of an alcohol, the more soluble it is in organic solvents.
substitution reaction:
Replacement of an atom or group of atoms by another atom or group of atoms. At least 2 new products are formed
addition reaction:
Addition to both ends of a C=C bond. 1 product is formed (so there are no by-products)
combustion reaction:
A type of oxidation reaction involving oxygen
reactions of alkanes:
combustion: the reaction of an alkane with oxygen
substitution: a reaction that involves exchanging one or more atoms on a molecule with other atoms
reactions of haloalkanes:
substitution: halogens, cyanide ions, ammonia and hydroxide ions are substituted for the halogens that are attached to the carbon chain of the haloalkane
elimination: a pair of atoms in a molecule being removed to form a double bond
reaction of alkene:
addition/ reduction reaction: a small molecule is added to the carbons around the double bond converting this to a single bond and different organic compound
reactions of alcohols:
Primary alcohols- oxidised to aldehydes then carboxylic acids
Secondary alcohols- oxidised to ketones
reactions of esters:
esters are formed from the condensation of a carboxylic acid and an alcohol
hydrolysis of esters results in the formation of an alcohol and a carboxylic acid from an ester
condensation reaction:
involves reacting two molecules together that result in elimination of a small molecule such as water
hydrolysis reaction:
involve the use of water to reverse a condensation reaction
carboxylic acid+ alcohol =
ester
reactions of nitriles:
undergo reduction reactions to become amines in the presence of heat and a metal catalyst
a reduction reaction involves a unsaturated compound becoming saturated, i.e. nitrile to amine
reaction of amides:
formed from condensation reactions of carboxylic acids
carboxylic acid + amine -> amide + H2O
proteins are…
polymers made from monomers called a-amino acids
a-amino acids are…
small molecules containing a carboxyl functional group and amino functional group bonded to the same carbon atom
secondary protein structures:
a-helix or B-pleated sheets
what are the bonds that form secondary protein structures?
hydrogen bonds, between a hydrogen and oxygen
primary protein structure:
The order in which the amino acids making up the protein are joined together. The chains of amino acid units are often referred to as polypeptides
secondary protein structure:
Folding and twisting of the chain, held in place by hydrogen bonds between CO and NH groups in adjacent parts of the chain. Some proteins form a 3-D a-helical shape. Other sections can form a shape called a B-pleated sheet.
tertiary protein structure:
Overall 3-D structure of the protein. The different functional groups in the R (side chain) part of the amino acids have different polarities and they create shapes that are held in place by disulfide (S-S) covalent bonds, ionic bonds between -NH3+ and -COO- groups, dipole-dipole forces, hydrogen bonds and dispersion forces.
quaternary protein structure:
Some proteins, such as haemoglobin, are composed of 2 or more polypeptide chains, forming a quaternary structure. Haemoglobin, for example, consists of 4 protein molecules. There is a section on each molecule with non-polar R groups, creating a hydrophobic (water hating) region. Dispersion forces between adjacent and non-polar sections of the protein molecules are the major reason for the attraction between them.
how is a triglyceride formed?
condensation reaction between 1 molecule of glycerol and 3 fatty acid molecules
how are soaps made?
base hydrolysis reaction between a triglyceride and sodium hydroxide in a process called saponification
triglyceride + sodium hydroxide -> soap and glycerol
Common strong acids:
HNO3 -> Nitric Acid
HI, HF, HBr, HCl -> Halogen acids
H2SO4 -> Sulphuric acid
Common strong bases:
NaOH
KOH
Ba(OH)
Weak bases, any other OH based
Chromatography separates….
proteins
In chromatography, the moving liquid is referred to as the ____ phase
mobile
The solvent and the components pass over a solid material, the _____ phase
stationary
The more strongly a component bonds to the stationary phase….
…the slower the rate of movement of the component over the stationary phase.
The time taken for the component of a mixture to pass through a HCPL column is called the…..
retention time, Rt of the component
Compounds that absorb strongly to the stationary phase in the column….
…move slowly and have high Rt values.
Electrophoresis is used to separate and identify the components in mixtures of….
amino acids, polypeptides or proteins
When an electric current is applied to the gel in electrophoresis…
…the negatively charged molecules move towards the positive terminal and are separated according to their mass and charge
In a mass spectrum:
Base peak/ highest peak =
Highest peak to the right=
most abundant ion
molecular mass
Mass spectrometry vs Infrared spectroscopy
Mass spectrometry= straight lines
Infrared spectroscopy= curved lines from the top
X Ray crystallography determines the….
atomic and molecular structure of a compound. Allows the position of atoms in a compound to be known precisely
atom economy =
(molar mass of desired product / molar mass of all reactants) x 100 %
Process of addition polymerisation:
- Produces long chain polymers
- Monomers are small unsaturated molecules containing a double bond
- = bond is broken during the polymerisation process
Condensation polymerisation:
Can occur when monomers contain 2 functional groups. Unlike addition polymerisation, in which all of the monomer becomes part of the polymer, a small molecule (usually H2O or HCl is also formed.
How are disaccharides formed?
from a condensation reaction that involves the hydroxyl groups on 2 monosaccharide molecules
Steps in volumetric analysis:
- Balanced Equation
- Moles of known calculated
- Use stoichiometric ratio to calculate n of base
- Calculate molarity of base using c= n/v
- Calculate M1 (original molarity) using M1 x V1
Monosaccharide empirical formula:
CH2O
What bond is formed between 2 amino acids?
peptide bonds
Bonds in a disaccharide
glycosidic
