acids and bases

Question 1

what are branstead lowry acids

Answer 1

proton donors

Question 2

what are branstead lowry bases

Answer 2

proton acceptors

Question 3

what is produced when you mix acids with water?

Answer 3

HA + H2O ⇌h3O+ + A-

the h3o+ is where the h+ ions are as they

Question 4

what is produced when you add water to bases?

Answer 4

B + H2O ⇌ BH+ + OH-

Question 5

how do strong acids disassociate?

Answer 5

strong acids are HCL,H2SO4 ect
they disassociate completely
it is an equilibrium reaction but the forward reaction is strongly favoured
HCL⇌H+ + Cl-

Question 6

how do weak acids disassociate ?

Answer 6

weak acids are usually carboxylic acids and they disassociate badly
in the equilibrium reaction the backward reaction is favoured and therefore not much H+ is produced
CH3COOh⇌ H+ + CH3COO-

Question 7

How do strong bases disassociate?

Answer 7

they disassociate strongly examples such as NaOH,KOH
in the equilibrium reaction the forward reaction is strongly favoured so a lot of OH- is produced
NaOH⇌Na+ + OH-

Question 8

how do weak bases disassociate ?

Answer 8

weak bases are such as NH3 they disassociate badly
and not much OH- is produced
in the equilbirum the backward reaction is favoured
sometimes water is needed
NH3 + H2O ⇌ Nh4 + OH-

Question 9

how does water disassociate?

Answer 9

It disassociates very weakly
so the backeards reaction is favoured this meams their is a very small amount of OH- and H3O+

2H2O⇌ H3O+ + OH-

we can assume the Kc of water is constant

Question 10

what is Kw

Answer 10

the ionic product of water

Kw= [OH-][H+]

and it is the same in a given temperature

Question 11

what is the value of Kw?

Answer 11

1.00x10^-14

Question 12

what can be said about the formula for Kw in pure water?

Answer 12

as H2O⇌H+ + OH- the amount of H+ produced is the same as OH-

Kw=[H+]^2

Question 13

what is the pH equation?

Answer 13

pH = -log10[H+]

Question 14

how to calculate the pH of strong acid?

Answer 14

1 molecule of strong acid dissociates to form 1 molecule of H+
therefore we can assume that the concentration of acid is conc of H+
sub this into -log10[H+] to get the pH
the inverse can be done if you have the pH by doing 10^-pH to get the conc of H+

Question 15

how to calculate the pH of strong base?

Answer 15

1 molecule of strong base form 1 molecules of H+ use this and kW constant to work out h+ sub in to -log10[H+]

Question 16

what is Ka

Answer 16

a constant used to work out the pH of weak acids as the amount of molecules of acid is not equal to the molecules of H+

ka=[H+]^2/acid

Question 17

how to calculate the pH of a weak acid?

Answer 17

use Ka constant and acid concentration to work out [H+]^2
square root it and sub into -log10{H+} to get pH

Question 18

what is pka?

Answer 18

pka=-log10[Ka]

Question 19

what are the 4 titration curves?

Answer 19

all s shaped curves
strong acid strong base starts at 1/0 ph and finshes at 14/15
strong acid weak base starts at 1/0 ph and finished at 7/8
weak acid strong base starts at 6/7 ph and finishes at 14/15
weak acid weak base starts at 6/7 ph finishes at 7/8

Question 20

what is the equilavence point /end point in titration?

Answer 20

its when the acid has been fully neutralised by the base and vice versa
it is the steap part of the graph

Question 21

what is the half neutralisation point?

Answer 21

halfway point between equiavlence point and 0
it is the point where HA= A-
therefore it can be used to calculate the pH of a weak acid as
ka=[H+][A-]/HA

the HA and A- cancel out leaving
Ka=[H+]
take - log 10 of both sides
pKa=pHyo

Question 22

what indicators are best for a strong acid and weak/strong base titration?

Answer 22

methyl orange turns from red to orange at 3-4.5
this is good as it coves the neutralisation point

Question 23

what indicator is best used for weak acid and strong base?

Answer 23

phenolphthalein turns from colourless to pink at 8.2-10
this is good as it covers the neutralisation point

Question 24

what is a buffer

Answer 24

something that resists the change in pH

Question 25

what are acid buffers?

Answer 25

they are buffers that resist the change in pH to keep it under 7.They are made up of a weak acid and its salt

Question 26

how does acid buffer work?

Answer 26

their are 2 equations disassociation of weak acid (dissociates weakly) equilibirum favours back) CH3COOH ⇆ CH3COO- + H+ disassociation of salt (disassociates strongly ) equilibrium favours right CH3COONa ⇆ CH3COO- + Na+ If an acid is added to this buffer the H+ will react with CH3COO- (high conc formed salt disassociation) reforming CH3COOH pushing equilibrium to the left if base is added to this buffer OH- reacts with H+ the removal of H+ from the disassociation of weak acid causes the equilbrium to shift to the right to produce more H+ hence making it more acidic

Question 27

what is a basic buffer

Answer 27

resist the pH change and keep the pH above 7.they are made from weak base and its salt

Question 28

how does a basic buffer work?

Answer 28

there are 2 equations disassociation of weak base disassociates weakly (equilibirium favours left) NH3 + H2O ⇆ NH4+ +OH- disassociation of salt disassociates strolngly equilibrium favours right NH4CL⇆NH4+ +CL- If OH- is added it reacts with the NH4+ shifting equilbrium to the right producing more NH3 + H2O if H+ is added it reacts with the OH- the removal of H+ causes the equilbirum to shift to the right to reaplace it

Question 29

how to calculate the pH of a buffer?

Answer 29

write out the Ka equation [H+][CH3COO-]/[CH3COOH] rearrange to get [H+] on one side [Ka][CH3COOH]/CH3COO- = [H+] calculate the [H+] sub into -log10 [H+]

Question 30

how to calculate the pH change in a buffer?

Answer 30

calculate moles work out increase and decrease in moles after adding acid/base work out new concentrations with new volume rearrange Ka to get H+ subinto -log10[H+]

Question 31

what are the uses of buffers?

Answer 31

shampoo washing powder blood

Question 32

Suggest why chloroethanoic acid is a stronger acid than ethanoic acid.

Answer 32

cl is electronegative so pulls electrons this makes the OH bond weaker

Question 33

State the meaning of the term weak as applied to carboxylic acids

Answer 33

partially disassociated /ionised

Question 34

Give two additional instructions that would improve this method for making up the salicylic acid solution

Answer 34

use a flask to transfer solution and rinse the flask rinse beaker and add washings to the flask

Question 35

Explain why the expression for Kw does not include the concentration of water

Answer 35

very few H+ and OH- H2O is effectively constant

Question 36

Explain why the value of Kw increases as the temperature increase

Answer 36

breaking bonds is in endothermic the equilbrium moves to the left to oppose increaese temperature

Question 37

State why calibrating a pH meter just before it is used improves the accuracy of the pH measurement.

Answer 37

over time the pH meter becomes less accurate

Question 38

Describe how you would obtain the pH curve for the titration

Answer 38

measure pH of acid add alkali in small quantities eg 2cm3 after every addition measure the pH stirring the mixture continue to do this until nearly reaching the end point near the endpoint reduce interval size of measuring pH e.g 0.5cm3 continue to do this until alkali is in excess

Question 39

how to calculate the pH of a buffer after an acid is added?

Answer 39

work out moles of acid added + mol to acid in buffer -mole from base in buffer work out new volume by adding all volumes work out new conc for acid/base in buffer using new moles calculate H+ calculate pH

Question 40

calculating ph in an acid base reaction

Answer 40

work out moles of acid work out moles of base larger moles- smaller moles do moles/vol to work out conc use kw equation

Question 41

Ph of buffer made from weak acid & strong base?

Answer 41

moles of acid moles of base work out xs acid moles= moles of HX moles of base = moles of x- add vols