why we are use the indicators(ie phenopthalene,methylered,...etc)?

Answer 1

the indicators show colour change at different pH. an acid-base indicator is usually a weak organic acid or base(eg: phenolphthalein and methyl orange, respectively). so depending on the solution being acidic or basic its degree of dissociation will change. taking the eg: of phenolphthalein, its a colourless organic acid.( HPh). it dissociates into H+ and Ph- ions.the latter is pink in colour. if the soln is acidic then [H+] increases , so dissociation of HPh is restricted(common ion effect). so the equilibrium shifts to the left and the indicator remains colourless. if a base is added / soln is basic then OH- reacts with H+ and decreases[H+]. therefore the equilibrium will shift to the left. so more dissociation occur and and the [Ph-] c increases. as Ph- is pink in colour, an increase in its concentration will turn the soln. pink . Hence in acidic soln phenolphthalein is colourless and in basic solution it turns pink.
Now if we take the case of an organic basic indicator like methyl orange, its the opposite.MeOH dissociates into Me+ and OH- .MeOH is orange while Me+ is pink. n acidic soln the OH- and the H+ will react shifting the equilibrium to the right and the [Me+] will increase turning the colour of the soln. pink. i basic soln, due to the common ion effect, the equilibrium Will shift to the left and the soln will turn orange.
that's how the indicators work. now.. as to why we use it (in acid-base titration). at the end point of a titration, the acid and base is being neutralised. bt depending on the strength of the acid and base the ed point need not be at pH 7. it can lie aboveor below that value. that's where the different indicators come in. these indicators have a pH range, ie, a range in which they show the colour change. to be exact 'pH range is the interval btw the first detectable colour change and the point at which the transition is apparently complete'. depending on whether the equivalence point occurs in acidic or basic pH we can use the different indicators.

Answer 2

Indicators are used generally in titrations but they are not just restricted to titrations indicators may also be used for biological staining or chromatographic staining Indicators have the property to change colour depending on the pH level like phenolphthalein is colourless in acidic medium but pink in basic or alkaline medium in acid base titrations the end point can be determined by using instruments like a pH meter a potentiometer a conductometer and if you are just doing a normal titration then indicators are the perfect choice after the end point is reached the next drop of the titrant that is added reacts with the indicator added and the indicator undergoes transition to emit the colour indicating the neutalisation point

Answer 3

when you do titrations to see how acid or basic something is, one way you do so is by adding an indicator that will change color as the pH changes.

When you reach the color/non color you are looking for, you know approximatly how much acid or base was required for the solution in question.

Answer 4

Indicators are uses to determine the end point by color change.

Answer 5

to know to end of the titration that is to know the end of neutralising of acid and base

Answer 6

JST A ONE LINE ANSWR... TO CHK FR THE EQUIVALENCE POINT IN THE ACID BASE REACTIONS.

Answer 7

to see wether titration is over i.e to identify equivalence pt