laura.burgess
Note by , created almost 6 years ago

Chemistry Note on F325, created by laura.burgess on 11/28/2013.

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laura.burgess
Created by laura.burgess almost 6 years ago
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Page 1

An ACID is a PROTON DONORA BASE is a PROTON ACCEPTOR

Acid + METAL ---> SALT + H2Acid + BASE ---> SALT + H20Acid + ALKALI ---> SALT + H20Acid + CARBONATE ---> SALT + H20 +CO2

A conjugate acid-base pair is a pair two species that transform into each other by the gain or loss of a proton

Strong acids dissociate completely in aqueous solution. HCl, HNO3, H2SO4, HBr, HI and HClO4 are the only strong acids. The equilibrium position lies to the right.Weak acids dissociate partially in aqueous solution. Many naturally occurring acids are weak. The equilibrium position lies to the left.

The acid dissociation constant ( Ka) is an equilibrium constant which measures the extent of dissociation.If there is a larger Ka value, there is a large extent of dissociation and it is a strong acid. If there is a small Ka value there is a small extent of dissociation and it is a weak acid.

Ka = ([H+]*[A-])/[HA] moldm-3Kw = Kc x [H+] = [H+][OH-] = 10^-14 mol2dm-6

STRONG ACID[H+]=[HA]

WEAK ACID[H+]=sqrt(Ka x [HA])

pH = -log[H+]

STRONG BASE[H+] = Kw / [OH-]

BUFFER[H+] = Ka x ([HA]/[A-])

A BUFFER SOLUTION is a mixture that minimises the pH changes on the addition of small amounts of acids/bases.It is a mixture of a weak acid and its conjugate base and is formed by mixing the acid and a salt of the acid.

When an acid is added:- [H+] increases- the conjugate base reacts with the H+- equilibrium shifts to the left

When an alkali is added:- [OH-] increases- H+ reacts with OH-- Acid dissociates to  replace H+- equilibrium shifts to the  right

Rate of reaction = change in concentration/timeFor reaction A+B => C, Rate = k[A]^n[B]^mwhere n and m are the order of the reaction with respect to the reactantsk = rate/[A][B]When temp increases, k increases and reaction goes faster. When temp decreases, k decreases and reaction slows down

Conc- time graphs:  For a 0 order reactant, gradient is constant. For a 1st order reactant, half life is constant. For 2nd order, half life increases

For reaction aA +bB cC +dDKc = [C]^c[D]^d / [A]^a[B]^bKc > 1 means high yield of products. Kc means low yield of products.If endo, temp increases = Kc increasesIf exo, temp increases = Kc decreasesKc value is not affected by pressure/conc

Enthalpy change of neutralisation is the enthalpy change when and aqueous acid is neutralised by an aqueous base to form one mole of H20 under standard conditions

LATTICE ENTHALPY is the enthalpy change when 1 mole of a solid ionic compound is formed from its gaseous ions under standard conditions

Lattice enthalpy is EXOTHERMIC so is always negative. This is because new ionic bonds are being formed.

Two factors can affect lattice enthalpy:· IONIC SIZE: the smaller the ion, the stronger the attraction between ions. Therefore, the smaller the ionic size, the more negative the lattice enthalpy value and the stronger the ionic bond.· IONIC CHARGE: the higher the charge, the stronger the attraction between ions. Therefore the higher the ionic charge, the more negative the lattice enthalpy value

SOLUTION ENTHALPY is the energy change during the dissolution of an ionic compound in water

Two step process:1) Energy is put in to overcome attraction between ions, ionic bond breaks to form gaseous ions. Endothermic.2) Hydration of ions: +ve ions bond with O2-, -ve ions bond with H+. Exothermic

STANDARD ENTHALPY CHANGE OF HYDRATION is the enthalpy change when 1 mole of isolated gaseous ions is dissolved in water forming 1 mole of aqueous ions under standard conditionsSTANDARD ENTHALPY CHANGE OF SOLUTION is the enthalpy change that takes place when 1 mole of a compound is completely dissolved in water under standard conditions.

Two factors can affect hydration enthalpy:- IONIC SIZE: The smaller the ion, the greater the attraction. The smaller the ionic size, the more negative the hydration enthalpy-IONIC CHARGE: The higher the charge, the greater the attraction and the stronger the hydration  The higher the ionic charge, the more negative the hydration.

A transition metal is a d-block element that forms an ion with an incomplete d subshell

All transition metals have 4s2 apart from Cr and Cu which have 4s1

The main properties of transition metals are that they:- form coloured compounds- have variable oxidation states- can act as catalysts

Transition metals will react with NaOH to form coloured precipitates:- Fe(II) - pale green soln => green ppt- Fe(III) - yellow soln => brown ppt- Cu(II) - pale blue soln => pale blue ppt- Co(II) - pink soln => dark blue ppt

In solution will form complex ions, consisting of a TM ion coordinate bonded to ligandsA ligand is a molecule or ion that can donate a pair of e- to the TMI to form a coordinate bond. Monodentate donates 1 pair, bidentates donate 2 etcThe coordination no. is the total number of coordinate bonds in a complex ion. 

Complex ions can come in a number of shapes:- Octahedral - 6 bonds - 90o- Square planar - 4 bonds - 90o- Tetrahedral - 4 bonds - 109.5o- Linear - 2 bonds - 180o

Stereoisomers are species with the same structural formula but different arrangement of atoms in spaceCis-trans isomers can occur in octahedral (2 next to each other (cis) , or atom opposite sides (trans)) or in square planar (same side (cis) or opposite (trans))Optical isomers are non-superimposable mirror images of one another. In order to occur there must be a complex with 3 bidentate ligands, 2 bidentate and 2 mondentate, or one hexdentatre

Ligand substitution reactions are where one ligand is replaced by another.

The stability constant, Kstab, is the equilibrium constant for an equilibrium existing between a TMI surrounded by water ligands and the complex formed after it has undergone ligand substitution.

H20 is left out of the Kstab equation as it is virtually constantA large Kstab value indicates that equilibrium lies to the right. It also indicates that the ion is easily formed. 

In redox titrations, an oxidising agent can be titrated against a reducing agent. Sometimes an indicator is used, but often a colour change occurs when a TM changes oxdn state. e.g. MnO4- => Mn2+, Purple => v. pale pink

Redox titration equations -1) Calculate moles of ions added using n=CV2) Deduce moles of ions reacted using ratio from balanced equation3) Calculate conc of ions in soln

Entropy is the quantitative measure of the degree of disorder in a system. 

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