acids, alkalis and titrations UPDATED

p46 - 48

what does the pH scale go from

0 to 14

pH of strongly acidic

0-3

pH of weakly acidic

4-6

pH of neutral

7

pH of weakly alkaline

8-10

pH of strongly alkaline

11-14

what is an indicator

one or more substances

that change colour

depending on the pH of a solution

what is universal indicator do

a mixture of indicators

changes colour

in a gradual way

over a range of pH values

how do u find the pH of an aqueous solution using universal indicator

- add indicator to the solution

- compare the colour formed to a pH chart

limtus indicator results

- red in acidic solutions

- purple in neutral

- blue in alkaline solutions

methyl orange indicator results

- red in acidic

- yellow in neutral and alkaline

TELL IF ACIDIC

phenolphthalein indicator results

- colourless in acidic and neutral

- pink in alkaline

TELL IF ALKLAINE

describe acids (3)

- acid is a source of H+ ions

- they are proton donors

- acidic solutions have a pH of less than 7

describe alkalis (3)

- alkali is source of OH- ions

- they are proton acceptors

- alkaline solutions have a pH of more than 7

what is a base and what is it in terms of protons

- a substance that can neutralise an acid

- they are proton acceptors

what are alkalis in terms of bases

alkalis are soluble bases

neutralisation

the reaction between an acid and a base/alkali

show neutralisation in terms of ions

H+ (aq) + OH-(aq) -> H2O(l)

describe a neutralisation reaction in terms of proton transfer

- the acid donates protons

- these are then accepted by the base

what is a strong acid

HCl

what is a weak acid

vinegar

what is a weak alkaline

ammonia solution

what is a strong alkaline

sodium hydroxide solution

what is a neutral (2)

water and sodium chloride solution

what is formed during a neutralisation reaction

a salt (an ionic compound)

acid + base ->

salt + water

acid + metal oxide ->

salt + water

acid + metal hydroxide ->

salt + water

acid + ammonia ->

ammonium salt

acid + metal carbonate ->

salt + water + carbon dioxide

what do titrations allow you to do

to find out exactly how much acid it needed to neutralise a quantity of alkali

describe titration method

- rinse a 100cm3 conical flask with distilled water

- wash a pipette with alkali u are using

- transfer alkali to conical flask using 25cm3 pipette

- add 2-3 drops indicator

- rinse burette with acid

- re-fill burette with acid using a funnel, to below eye level/ 0 mark

- record the initial volume to nearest 0.05 cm3

- add acid thru tap quickly to conical flask with constant swirling until indicator changes colour

- record final value on burette

- repeat steps 5-9 but add acid drop by drop as end point approaches

- continue repeating until concordant results (0.10 cm3)

- rinse conical flask 3x between titrations

how could there be diff versions of a titration

u could do a titration where u add acid to alkali or the other way around

what equipment do u need for a titration

burette

burette holder

clamp stand

25ml glass pipette

pipette filler

2 plastic pipettes

100ml conical flask

white tile

plastic funnel

wash bottle

why do u fill the acid to below eye level

so acid can't spill in your eyes

what formula triangle would u use to do calculations from a titration

conc (mol/dm3) = mol/ vol (dm3)