double titration method

the british university in egypt
Experiment: Analytical Chemistry Lab
Acid-base titrations using Method of Double Indicators

Osama Hassan Shaikh Idris Nasr 117796






TABLE OF CONTENT
Abstract 2
Introduction 3
Equipment 4
Experimental procedures 4
Result 5
Treatment of data 6
Discussion 7






























Abstract

The aim of this experiment is to determine the amount and the composition of NaHCO3 (aq) and Na2CO3 (aq.) by using two indicator method. We use phynolphynthaline and methyl orange indicator to detect the endpoint of titration. The first step in this experiment is to clean up all the equipment we will use in this experiment. Secondly we add 10ml of the unknown mixture in the conical flask, then we fill the burette with HCL with known volume and molarity. Thirdly, add two or three drops of phenylphinthaline in the mixture, after that we open the valve of the burette till the pink color be dilute then record the volume of HCL using. Forth, add three or four drops of orang methyl then repeat the previous step and take the reading.
























Introduction

Titration method uses to measure the molarity of unknown mixture. Titration is technique by adding a fluid with known concentration to another fluid till all solute react with the first fluid. The reactant fluid that utilized named standard solution. In this experiment we utilize a strong acid HCL as a standard solution. When we add a base like NaOH the strong acid and the base will react to form finally salt and water. This kind of reactions named neutralization.

HCL+NaOH NaCL+ H2O

We use indicators to measure the end point or equivalent point of the reaction. The indicator change the color of the solution to know that the reaction reach the end point. We use two kinds of indicators in this experiment. The first indicator we are going to use is phnylphnthalin which is turning the base to pink color with basic solution and colorless with acidic solution. The second indicator is methyl orange which turn orang with acidic solution. When the color of the mixture starts to change, this mean that we reach the end point of the reaction "neutralization". In this experiment we use HCL to titrate a solution of Na2CO3 and NaHCO3 the reaction of HCL with Na2CO3 take place by two steps:
HCl(aq) + Na2CO3(aq) NaHCO3(aq) + H2O(l) …………………. (1)
HCl(aq) + NaHCO3(aq) NaCl(aq) + CO2(g) + H2O(l) …………… (2)

While the recation between HCL and NaOH finished only with one step:
HCL + NaOH NaCL + H2O



Equipment
phenolphthalein indicator,
methyl orange indicator
0.2 M standard HCl(aq).
a mixture of NaHCO3(aq) and Na2CO3(aq).
deionised water.
Beaker.
conical flask.
Funnel.
Burette.
stand and burette clamp.


Experimental procedure
Put 10ml of the unknown mixture in the conical flask.
Fill the burette with the HCL.
Put 2 to 3 drops of phynilepenthalin indicator.
Titrate HCL in the mixture till the color change, then record the volume as (V1).
Add 2 to 3 drops of methyl orange indicator to the mixture.
Complete titration using HCL and then recorde the volume of HCL as (V2).
Repeat the procedure three times and note the recordes.

Result
First attempt


Phenolphthalein indicator
V1
Methyl orange indicator
V2
Final burette reading/cm3
5.2
15.2
Initial burette reading/cm3
0
5.2
Volume of 0.2 M HCl used/cm3
5.2
10


Second attempt

Phenolphthalein indicator
V1
Methyl orange indicator
V2
Final burette reading/cm3
5.1
14.9
Initial burette reading/cm3
0
5.1
Volume of 0.2 M HCl used/cm3
5.1
9.8

Third attempt

Phenolphthalein indicator
V1
Methyl orange indicator
V2
Final burette reading/cm3
5.3
14.65
Initial burette reading/cm3
0
5.3
Volume of 0.2 M HCl used/cm3
5.3
9.35

Treatment of data
Average volume of HCL:
Average volume= V1+V2+…..Vnno. of recordes

Average Phenolphthalein indicator
V1.avg
Average Methyl orange indicator
V2.avg
5.2
9.7

Standard deviation of HCL:
St.dev. of Phenolphthalein indicator
St.dev. of Methyl orange indicator

0.0067
0.0742

Standard errors of all of the devices used during the experiment:
standard error=smallest measurable unitthe device's total measuring capacity×100
Standard error of Phenolphthalein
%
Standard error of Methyl orange indicator
%
5.1
9.35

Write an equation describing the reaction between HCl and the mixture in the presence of phenolphthalein.
NaOH+H2O NaCL+H2O
Calculate the difference in volume between V2-V1=V3?
V1= volume of HCL used in 1st titration with phenolphthalein.
V2 = volume of HCL used in 1st titration with methyl orange.
V3=V2-V1 Volume of NaOH in the first titration.

Trail #1
Trail #2
Trail #3
Volume of NaOH
4.8
4.7
4.05


Complete the following questions:
a. V1 corresponds to volume of HCL used in titration with phenolphthalein.
b. V2 corresponds to volume of HCL used in titration with methyl orange.
c. V2-V1 corresponds to volume of NaOH.

Discussion

in this experiment the reaction have to step in the first reaction the solution would be basic so we need to be detect by an indicator react with a base , and in the second step the indicator should be react with acidic solution. For example we can use Thymolphthalein or Alizarin yellow instead of phenolphthalein and methyl red instead of methyl orange.









Multi steps titration that mean there are more than one equivalent point in the ph curve.















The indicator change the color of the solution to know that the reaction reach the end point. The ph indicator is a weak acidity dye or colored paper used to detect the proton ion in the solution by the change in the color of the dye or the paper when its dipped or added in the solution.










Rang of phenolphthalein is between pH 8.3 - 10.0. While rang of methyl orange between 3.1 - 4.4.



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