21 Acids, Bases and Buffers Flashcards
Symbol of concentration
Square brackets
pH
-log10(H+)
(H+)
10^-pH
How to find the alkaline solution
Calculate [H+]
Use kw = 1.00x10^-14 to calculate [H+]
Convert [H+] to pH using -log10[H+]
Difference between a strong and weak acid
Strong acid is fully desiccated
HCl — H+ + Cl-
NA ⇌ H+ + A-
What type of acid is ethanoic acid
Weak acid
Water
Little bit of water is ionised at any one time at a constant
(Water is slightly dissociated.)
pH scale
Made by Danish biochemist Soren sorenson ( 1909 )
Control of activity
Bronsted-lowry acid
An acid is a substance that can donate a proton and base can accept a proton
explain how a solution containing sodium hydrogen carbonate and sodium carbonate can act as a buffer as small amount of acid or alkali are added
small amount of acid
-the HCO3- reacts with the added H+, shifting the equilibrium shifts to the left
small amount of alkali
-H+ reacts with the OH- ions shifting equilibrium to the right
the overall amount of H+ stays pretty much the same
state the meaning of the term weak acid as applied to carboxylic acids
partially dissociated (partially ionised)
write an equations for the reaction of propanoic acid with sodium carbonate
2CH3CH2COOH + Na2CO3 —- 2CH3CH2COOHa + CO2 + H20
suggest what substance might be present in the air to cause the pH to change. Explain how and why the pH of the pH 9.00 solution
Carbon Dioxide
The pH was decrease as it has reacted with the H+ ions in solution
suggest a suitable piece of apparatus that could be used to measure out the sodium hydroxide solution. Explain why this apparatus is more suitable than a pipette for this purpose.
Buret
you can measure out exactly the right amount of liquid but also you can added it drop by drop
Explain why the end point of this reaction would be difficult to judge accurately using an indicator
the pH gradually increase so would be difficult to find the point at which it changes because the indicator could change over a range of values
suggest why choroethanoic acts is a stronger acid than ethnic acid
chlorine is more electronegative than hydrogen so withdrawn electrons which weaken the O-H bond
the dissociation of methanol acid in an aqueous solution is endothermic.
Deduce whether the pH of a solution of methanoic acid will increase, decrease or stay the same if the solution is heated. (explain your answer)
decrease the pH
if the forwards reaction is endothermic then more product is made to oppose the increase in temperature. the equilibrium shifts to the left.
buffer
a buffer solution resist the changes in pH when adding a small amount of acid and alkali
control the pH in living systems
made of weak acid and conjugate base
(A buffer solution maintains an approximately constant pH, despite dilution or addition of small amounts of acid or base.)
Acidic buffer
adding alkali
-removes the OH-
adding acid
-equilibrium shifts to the left
half-netrlisation
pH = pKa
measures of how strong a weak acid is
half way between the starting point and equivalence point
HA + OH- —- H2O + A-
acid-base titration
titration is used to find the concentration of a solution by gradually adding it to a second solution which it reacts with
titration curve
- the pH doesn’t change in the linear manner as a base is added
- each curve has almost horizontal sections where lots of base is added
- equivalence point = the point in a titration at which the reaction is just complete
Adding an acid (equations)
-calculate the pH of the buffer
-calculate the number of moles of acid added
-add the original number of moles of acid
-take this away from the original number of base
-calculate new concentration of acid and salt
-work out the pH
(ignore the small volume as it has little effect on the total volume)
Adding a base (equations)
-calculate the pH of the buffer
-calculate the number of moles of base added
-add the original number of moles of base
-take this away from the original number of acid
-calculate new concentration of acid and salt
-work out the pH
(ignore the small volume as it has little effect on the total volume)
