Enthalpy change of solution is when 1mole of solid solute dissolves to form a solution
Lattice enthalpy is the enthalpy change when one mole of an ionicsolid is formed from its gaseous ions. This is an exothermic quantity.
Enthalpy change of hydration is the enthalpy change when 1mole of a gaseous ion is hydrated by formingbonds to water molecules.
The enthalpy of hydration is more negative/exothermic if the chargedensity of an ion is greater because it forms stronger ion-dipole bonds, so the energy released by bond forming is larger
Lattice enthalpy becomes more exothermic if the ions in the lattice have a greater charge density because there is a greater electrostatic attraction.
Enthalpy change of solution = -Lattice enthalpy + Hydration enthalpies of cation + anion
Explain why ionic substances are soluble in water
Ionic bonds are broken when the ionic substance dissolves, some hydrogen bonds also break between water molecules. Ion-dipole bonds form between water molecules and the ions. The strength of the binds formed is similar to the strength of the bonds broken, so the energy released by bond formation is sufficient to compensate for the energy required to break the bond between ions
Why are ionic compounds insoluble in non-polar solvents?
In order to dissolve, ionic bonds would need to break between the ions in the lattice.ID-ID bonds would also need to break between the organic solvent molecules. They do not have a permanent dipole so only weakion-dipole bonds could form between the ions and the solvent molecules. The energy released by bond formation is not sufficient to compensate for the energy required to break the bond between ions.
Rate of reaction from a concentration-time graph can be found from the gradient. The shape of these curves shows the order:
Zero order = straight line and half-life decreases
1st = curve and half-life is constant
2nd = steeper curve and half-life increases
Rate-concentration graphs:
Zero order = horizontal line,
1st order = straight line through the origin
2nd order = a curve
Rate = k [A]m[B]n
At a highertemperature, the rate constantincreases because the concentrations are constant but the rateincreases.
The Arrhenius equation links rate constant and activationenthalpy. As Ea increases, kdecreases, so a large Ea will mean a slow rate
K= rate constant
Ea= activation enthalpy (Jmol-1)
T= temperature (K)
R= gas constant
If you plot a graph of 1/T against lnk, the gradient is -Ea/R and the y-intercept is A.
Ammonia is formed from N2 and H2, leaving a lone pair on the N which allow it to act as a ligand
Ammonia is soluble in water as it can form hydrogen bonds
The lone pair means NH3 is a base because it forms dative covalent bonds with protons to form the ammonium ion
NO, nitrogen monoxide, is a colourless gas
N2O, dinitrogen monoxide, is a colourless gas with a sweet smell
NO2, nitrogen dioxide, is a brown gas with a sharp odour and is toxic
Nitrate (V) ions are reduced by aluminium in the presence of NaOH when heated to produce NH3 gas.
Nitrate (III) ions to nitrate (V) ions= NO2- + H2O
Nitrate (V) ions to nitrogen gas = 2NO3 + 12H+ + 10e- —> N2 + 6H2O
Nitrogen gas to Nitrogen oxides= x N2 + x O2
The phosphate-sugar backbone in DNA is formed by condensation polymerisation to form phosphate-ester links.
The phosphate -OH groups always attach to the -CH2OH group and the -OH group on the adjacentcarbon.
The bases join via a condensation reaction too, they all have an -NH group in their stricture which loses an H.
The N atom bonds to the sugar, eliminating an -OH group from the sugar to form water. The base always replaces the -OH group on the carbonadjacent to the -O- atom in the ring
The pharmacophore is the part of a drug molecule which binds to the target receptor site and makes it biologically/medicinally active.
You can modify the groups around the pharmacophore to make it more effective or reduce side effects
The molecular recognition of a pharmacophore depends on:
Size and shape: particular structure to fit into the receptor site
Bond formation: functional groups in the pharmacophore form temporary bonds with functional groups in the receptor, for example dipole-dipole, hydrogen bonding e.g amines, alcohols or carboxylic acids, ionic interactions e.g acidic and basic functional groups can donate/accept proteins and become charged
Orentation: only one of E/Z stereoisomers can fit
Amines act as bases because they accept protons to form a cation. An amine has a LP of electrons on the nitrogen atom that can form a dative covalent bond with an H+ ion. You can neutralise an amine by reacting it with an acid to make an ammonium salt: RNH2 + HX —> RNH3 + X-
Amides are carboxylic acid derivatives that can be either primary or secondary (one of H replaced with alkyl group). They are named using the suffix amide, and secondary amides have a prefix N-alkyl-.
To hydrolyse an amide:
Heat with a dilute acid to form a carboxylic acid and ammonium salt (or 2ndary = salt of primary amine)
-CONH2 + HCl + H2O—> -COOH + NH4Cl
Heat with dilute alkali to get a carboxylate ion and NH3 gas (2ndary = an amine)
-CONH2 + NaOH —> -COO-Na+ + NH3
Esters can be hydrolysed to form alcohols
Acid hydrolysis of an ester under reflux with a dilute acid forms a carboxylic acid and an alcohol, it is a reversible reaction which needs a lot of H2O to push the equilibrium to the right
Base hydrolysis of an ester produces a carboxylate salt and alcohol, it is irreversible
Acyl chlorides are named using the suffix -oyl chloride, and you number the carbons from the acyl functional group (same with carboxylic acids)
With esters, you number the carbons out from the ester link in the middle
Acyl chlorides react vigorously with alcohols to form an ester and HCl, and amides to form a secondary amide and HCl
Polyamides are made from dicarboxylic acid and diamine monomers
Polyesters are made from dicarboxylic and diol monomers.
Nylons are a type of polyamide and are named nylon-x,y. Some nylons are made from one type of monomer when molecules have both an amine and carboxylicacid group which can react with themselves in condensation polymerisation reactions, e.g nylon-6
solar energy reaches Earth mainly as visible and UV
Earth absorbs some of this energy, heating up and radiates IR
greenhouse gases in the troposphere absorb some of this IR, in the ‘IR window’, increasing their kinetic energy and raising the temperature
greenhouse gas molecules also re-emit some of the absorbed IR in all directions, some of which heats up the Earth
increased concentrations of greenhouse gases lead to an enhanced greenhouse effect.
absorption of IR by greenhouse gas molecules increases the vibrational energy of their bonds, the energy is transferred to other molecules by collisions, thus increasing their kinetic energy and raising the temperature
In buffer solutions the ethanoic acid only slightly dissociates to H+ and CH3COO-, but the salt fully dissociates into its ions, CH3COO- and Na+.
This equilibrium forms: CH3COOH <—> H+ + CH3COO-
What happens when you add acid to a buffered solution?
the H+ concentration increases, and the extra H+ ions combine with CH3COO- ions to form CH3COOH, which shifts the equilibrium to the left, reducing the H+ concentration.
What happens when you add base to a buffered solution?
If you add base, the OH- concentration increases, so the OH- ions react with H+ ions to form water, removing H+ ions from the solution, causing more CH3COOH to dissociate to form H+ ions, shifting the equilibrium to the right.
In buffer calculations we assume 2 things:
The salt is fully dissociated, so the equilibrium concentration of A- is the same as the initial concentration of the salt
The acid is only slightly dissociated so the equilibrium concentration is the same as the initial concentration.
In weak acid calculations we assume:
It only slightly dissociates, so [HA]>>[H+], so [HA start] = [HA equilibrium]
The dissociation of the acid is much greater than the dissociation of water so all the H+ come from the acid, so [H+]=[A-]
In Ksp calculations we have to assume that the volume of solution does not change when solid dissolves in it
In Kw calculations we assume:
Water only dissociates slightly, and there is so much water compared to the amounts of H+/OH- ions that the concentration of water is considered to have a constant value
Strong bases fully ionise in water
We can find the concentration of MnO4- by titrating against a reducing agent like Fe2+
Reducing agent e.g Fe2+ solution with an unknown concentration in conical flask, add excess dilute H2SO4 to ensure enough H+ ions for reduction
oxidising agent in burette with known concentration e.g MnO4- ions
Carrying out a MnO4- titration:
Add the MnO4- ions in the burette to the conical flask, manganate ions from aqueous potassiumpermanganate solution are purple, they are reduced to colourlessMn2+ ions by the reducing agent until all the reducing agent is used up
End point is when the mixture just becomes tainted by the MnO4-, 1 drop will give it a pink colour
Balancing half equations
write down species before/ after a reaction
Balance any atoms apart from oxygen/hydrogen
Balance any oxygens with H2O
Balance any hydrogens with H+ ions (this and step above may not be needed)
Balance any charges with electrons
In FULL ionic equations there should be NO electrons
The coordination number is the number of coordinate bonds formed with the central metal ion. The complex shape is dependent on the size of the ligands and the coordination number:
small ligands: 6 around a central metal ion (H2O, NH3, CN-)
larger= fits 4 e.g Cl-
only 3 of ethandioate/en can fit
Coordination number of 6= octahedral, 90’, 4= tetrahedral 109.5’ or square planar (specific example of cis-platin which is an anti-cancer drug [Pt(NH3)2(Cl)2](aq), bond angle of 90’