Brush Up Flashcards
How do you calculate pH of a buffer solution by mixing an acid and a base?
|>Calculate initial n
|>smallest reactant n is used up
|>[H⁺] = Ka x ([HA]/[A⁻])
|>[H⁺] = Kw / (n(OH⁻)/total v.)
An Acidic Buffer is a mixture of?
weak acid, HA & one of its salts, A⁻
Two ways of making Acidic buffers?
|>Add together weak acid & one of its salts
|>Partially neutralise some weak acid by adding a base
When OH⁻ is added to a basic buffer, what occurs?
|>OH⁻ reacts with BH⁺
|>Equilibrium shifts left
|>pH changes are minimised
When acid is added to a basic buffer, what occurs?
|>H⁺ reacts with OH⁻
|>Equilibrium shifts right
|>pH changes are minimised
A Basic buffer is a mixture of?
weak base, B & one of its salts, BH⁺
Equation for [H⁺] of a buffer?
[H⁺] = Ka x ([HA]/[A⁻])
When OH⁻ is added to a acidic buffer, what occurs?
|>OH⁻ reacts with H⁺
|>Equilibrium shifts right
|>pH changes are minimised
Two ways of making Basic buffers?
|>Add together weak base & one of its salts
|>Partially neutralise some weak base by adding an acid
When acid is added to a basic buffer, what occurs?
|>H⁺ reacts with A⁻
|>Equilibrium shifts left
|>pH changes are minimised
Method to make a buffer?
|>Weigh accurately Xg of salt (A⁻) |>In a beaker, dissolve in its acid (HA) |>Using a funnel, transfer to volumetric flask |>Include washings |>Make up to mark with acid |>Invert multiple times to mix
Define: Kw, ionic product of water
Kw = [H⁺][OH⁻]
When mixing strong acid & strong alkali
where Base is in excess, [H⁺] = ?
[H⁺] = Kw / (n(OH⁻)/total v.)
When mixing strong acid & strong alkali
where Acid is in excess, [H⁺] = ?
[H⁺] = n(H⁺)/total v.
the Most Reactive Metals have the
____ Eᶿ values?
Most Negative
if Concentration of Ions in the Left Half-Cell
Increases, equilibria ____
E¹⁄₂cell becomes ____
Ecell ____ because ____
Shifts Right
Less Negative
Decreases
Cell has smaller difference in E
if Concentration of Ions in the Right Half-Cell
Decreases, equilibria ____
E¹⁄₂cell becomes ____
Ecell ____ because ____
Shifts Left
Less Positive
Decreases
Cell has smaller difference in E
if Concentration of Ions in the Right Half-Cell
Increases, equilibria ____
E¹⁄₂cell becomes ____
Ecell ____ because ____
Shifts Right
More Positive
Increases
Cell has bigger difference in E
if Concentration of Ions in the Right Half-Cell
Increases, equilibria ____
E¹⁄₂cell becomes ____
Ecell ____ because ____
Shifts Left
More Negative
Increases
Cell has bigger difference in E
the Most Reactive Non-metals have the
____ Eᶿ values?
Most Positive
Define: Standard Electrode Potential
e.m.f of a half cell compared with a standard hydrogen half-cell
Measured under standard conditions
Reduction occurs at the ____ electrode?
Positive
Equation for: mole fraction of a gas
Mole fraction = moles of gas in mixture/
of a gas total n of all gases in mixture
Equation for: Partial Pressure of a gas
Partial Pressure = mole fraction of gas x Total Pressure
of a gas
Equation for Gibbs free Energy Change, ΔG?
ΔG = ΔH - TΔS
Charge density increases if:
Charge Increases & Size Decreases
Charge Increases & Size is Constant
Charge density decreases if:
Charge Decreases & Size Increases
Charge is Constant & Size Increases
As Charge Density Increases, ΔhydH ____?
becomes less Exothermic
Define: Enthalpy of Lattice Formation ΔLFHᶿ
Enthalpy Change when
One mole of Ionic Substance
is formed from its Gaseous Ions
Forming bonds is ____ ?
Exothermic
Energy is Given out
As Charge Density Increases, ΔLDH ____?
becomes less Exothermic
Lattice Dissociation Enthalpies are ____ because bonds ____?
Endothermic
Bonds are being Broken
As Charge Density Decreases, ΔLDH ____?
becomes more Exothermic
As Charge Density Decreases, ΔLFH ____?
becomes less Exothermic
As Charge Density Increases, ΔLFH ____?
becomes more Exothermic
Why are ionic compounds w/ Exothermic
Enthalpy Changes of Solution
more likely to Dissolve?
More energy is Released when Ions are Hydrated than is needed in
Dissociation
Define: Enthalpy of Hydration ΔhydHᶿ
Enthalpy Change when
One mole of Aqueous Ions is formed from
One mole of Gaseous Ions
For Born-Haber cycles, Endothermic reactions are represented by ____?
Arrows pointing up
As Charge Density Increases, ΔhydH ____?
becomes less Exothermic
As Charge Density Decreases, ΔhydH ____?
becomes more Exothermic
Why is a Compromise temp of 450°C used?
High for Fast Rate
Low for Increased Yield
As a reaction occurs, the rate ____ as conc. of reactant ____?
Decreases
Falls
Why is using Mean Bond Enthalpies less accurate than Hess’ Law?
Mean average is used
Assumption all reactions are gaseous
Two examples of Endothermic reactions?
Thermal decomposition of CaCO₃
Photosynthesis
Equation to calculate ΔH in KJmol⁻¹
ΔH = q(x10⁻³ if q in J) / mol
What is Calorimetry?
Method to determine Enthalpy changes by experiment, converting temp. change of water to quantity of heat energy
Define: Bond Enthalpy
Energy Required to break
One mole of a given Covalent bond in gaseous molecules
Define: Enthalpy
Heat energy stored in a chemical system
How much does Hydrogen Bonding increase water’s b.p.t by?
about 200°C
Charge of Sulfate(IV) ion?
SO₃²⁻
Charge of Nitrate(III) ion?
NO₂⁻
Charge of Nitrate(V) ion?
NO₃⁻
Charge of Sulfate(VI) ion?
SO₄²⁻
Shape and Bond Angle: Water?
Trigonal Pyramidal
107°
Steps to find conc. of a solution of a base?
|>Fill a burette w/ standard solution of acid
|>Pipette known volume of base into conical flask
|>Add a few drops of indicator
|>Add solution until indicator changes colour
|>Record volume to the nearest 0.05cm³
|>Perform rough titration, then accurate ones to calculate mean from concordant values
Steps for making a standard solution?
|>Dissolve a known mass of solid in Deionised Water
|>Using a funnel, transfer into a volumetric flask, including washings
|>Make up to a certain volume
|>Invert to mix contents
Stages of Electron Bombardment Ionisation
|>Vapourise
|>Fire high energy Electrons at sample using electron gun
|>knocks off electron
Stages of Electrospray Ionisation?
|>Dissolve sample in volatile solvent
|>Pass through a fine needle to create mist
|>Apply high voltage to tip of needle
|>Sample gains H⁺
How to calculate no. of moles of water of crystallisation?
|>Need to know mass of hydrated & anhydrous salts
|>Mass of water = mass hydrated - mass anhydrous
|>Work out no. of moles of anhydrous salt
& of water
|>Find simplest ratio
Equation for Ar?
Σ(mass x abundance of each isotope)/
total abundance
