7. Simple Equilibria and Acid-Base Reactions Flashcards
LaChatelier’s Principle
When a system in dynamic equilibrium is subjected to a change, the position of equilibrium will shift to minimise the change.
Factors that effect Poe
Conc: Increases conc of reactants will move poe to RHS, the products.
Temp:
Increases: Endo favoured
Deacreses - Exo favoured
Pressure (only effects systems involving gases) :
Increases: favours side with fewer gaseous moles
Decreases: favours side with most gaseous moles
Catalysts have no affect on position of equilibrium, but speed up rate of both forward and backward reaction
Conclusions from Kc
Kc = 1, indicates poE is halfway between reactants and products
Kc > 1, indicates poE is towards the product (products predominate)
Kc < 1, indicates poE is towards the reactants (reactants predominate)
Back Titration
Crush 0.5g of tablets and add to weigh boat. Weigh boat indivually and boat after transfer of powder to obtain mass of powder. Transfer powder to conical flask. Add 25cm3 of HCL acid solution. Heat and stir vigoursly. When limestone dissolved take off heat and leave it cool to room temp. Add a few drops of phenlyphatelein and titrate against sodium hyroxide solution. Record value of NaOH needed to neutralise.
Back Titration Calculating
- Calculate the number of moles of NaOH used in the neutralisation reaction with the HCl. This will tell us how much of the HCl was unused in the reaction with the indigestion tablet.
- Calculate how many moles of acid were used to react with the indigestion tablet.
- Calculate the number of moles of calcium carbonate that reacted.
- Calculate the mass of calcium carbonate in the indigestion tablet.
- Calculate the % of calcium carbonate in the indigestion tablet.
Oxidising Agent
A species that accepts electrons; becomes reduced itself in the process
Reducing Agent
A species that donates electrons; becomes oxidised itself in the process
Solubility
All group 1 compounds are soluble
Group 2:
- All nitrates are soluble
- All carbonates are insoluble
Hydroxides are more soluble as you go down the group
Magnesium hydroxide is insoluble; barium hydroxide is soluble
Sulfates become less soluble as you go down the group
Magnesium sulfate is soluble; barium sulfate is insoluble
Thermal stability of hydroxides and carbonates
Group 2 Hydroxides decompose on heating to the oxide and steam
Ca(OH)2 -> CaO + H2O
Group 2 carbonates decmopose on heating to oxide and carbon dioxide
MgCO3 -> MgO +CO2
Thermal stability decreases in both as you go down the group. Trend for carbonates can be shown by heating them and seeing how long it takes for CO2 to formed to turn limewater cloudt.
Trend in Reactivity Gp 7
Halogens react by gaining electrons to form negative halide ions. therefore during reactions halogens are reduced, and they oxidise other substances. As group descends, more shielding for outer electron so its harder to attract electrons. both reactivity and oxidising power decreases.
Chlorine and Flouride in water treatment
Chlorine gas (low concs to be safe) is added to drinking water to kill dangerous bacteria and viruses such as chloera and typhoid
Fluoride is added to water to reduce tooth decay, by preventing cavities.
Reversible reaction
A reaction in which the products can react together to form the original reactants.
Why must the conical flask be swirled during titration?
To ensure all particles react
Why is a white tile used when titration
The white tile is placed under the conical flask so the colour change of the indicator is easy to see
Weak/Strong Acid/Base
Strong acid is an acid that completely dissociates in solution to form H+ ions (e.g HCl -> H+ + Cl-)
Weak acid is an acid that only partially dissociates in solution (CH3COOH <-> CH3COO- + H+)
A strong base is a base that completely dissociates in solution to form OH- ions (NaOH -> Na+ + OH-)
A weak base is a base that only partially dissociates in solution (NH3 +H2O -> NH4+ + OH-)
