indicators

what are the colour ranges for universal indicator?

from red, yellow, green, blue and violet (showing PH 0-14)

what is the most accurate form of PH measurement?

a PH meter

what are the colours of bromothymol blue?

yellow in the acidic solutions and blue in the basic solutions. In a neutral PH of 7 the indicator is green- a midway between yellow and blue.

At what PH does bromothymol blue change colours?

between PH 6- 7.6

what type of acids and bases are indicators?

weak bronsted and Lowry acid or bases

why do indicators change colour?

the conjugate acid from the indicator and the conjugate base is another colour

indicators are…… molecules that…

large organic molecules that change colour in response to the changes in PH of a solution

what is the equation for an indicator?

HIn(aq) + H20 (l) —→ In-(aq) + H3O+ (aq)

the posistion of equilibrium of the indicators expression is dependant on what?

the PH of the solution, as changing the PH changes the relative concentrations of the acidic and basic forms

what is the equation of the ionisation of bromothymol blue?

HBB +H20 —> BB- +H30+

what would happen if a few drops of bromoythmol blue is added to a HCl solution?

the additional H3O+ ions from the HCl cause the indicator equilibrium system to shift to the left to oppose the increase in the concentration of the H3O+ ions. The concentration of HBB molecules becomes much greater than the concentration of BB- ions- and therefore the solution presents as a yellow colour

what is the transition point?

is the midpoint of the indicator change

what is the transition point for bromoythmol blue?

7 (this is when the concentrations of HBB and BB- molecules are equal)

what are the colours of methyl orange?

it is red in acidic solutions and yellow in basic solutions

at which Ph does methyl orange change colours?

3.1 and 4.4 in which it is orange

is methyl orange a weak acid or base?

acid

methyl orange is used in the analysis of what?

weak bases

phenophalein is used int he analysis of what?

weak acids

what are the colours of phenophalein?

colourless in acidic solutions and pink in basic solutions

what is the PH range that phenolphthalein chnages colour?

8.3- 10.0

what is the indicator range?

the range of PH values over which an indicator changes colour

what is a neutralisation reaction?

a reaction with a acid and base to form water and a salt

what is the equivalence point?

is the point during a neutralisation reaction when the acid and a base are in the stoichiometric ratio represented by thee reaction equation

why are indicators commonly used in volumetric analysis?

this is to help visualise the equivalence point of a reaction.

what is volumetric analysis?

is a quantitative technique in whihc the volumes of solution of known concentrations are added to unknown concentrations

what is a titration?

is a form of analysis in which a base of a known concentration and volume is reacted with an acid of unknown concentration. the volume needed to neutralise the base can be used to determine the concentration of the acid by stoichiometric calculations

what is the end point of an indicator?

is the point of the titration when the indicator changes in colour

why is it vital that the indicator chosen changes colour sharply in the region of the equivalence point?

so that accurate concentrations are added to the unknown concentration solution

where is the equivalence point on a titration curve?

when the gradient is the steepest

what happens near the equivalence point?

the addition of a small amount of the known concentration solution produces a very large change in the pH

what is the transition point?

is the point at which the concentrations of both the indicator and its conjugate are equal.

how can the transition point be calculated?

fining PH from minus log and using concentration go hydronium ions