thermometric titration experiment report

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A Thermometric Titration-Part B

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Jonniel Vince Cruz

— This experiment aimed determining the enthalpy of neutralization for the strong acid-strong base and weak acid-strong base reactions. Coffee-cup calorimetry was applied to equimolar concentrations of both hydrochloric acid and acetic acid with sodium hydroxide. From the calculated heat capacity of solution, it was found out that the reaction of strong acid-strong base reaction had a mean enthalpy of neutralization of-74844.25 kJ/mol, yielding a percentage error of 28.18%. W eak acid neutralization yielded a value of –73.60 kJ/mol-a percentage error of 12.43%. In the analysis it is assumed that a linear relationship exists in the extrapolation of the final temperature, necessitating stabilities in temperature determinations.

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This lab utilizes the principles to Acid-Base Titration in order to standardize a solution of sodium hydroxide and then use this newly standardized solution to determine the total acidity of acetic acid in vinegar sample and then compare it to the commercial value. The two brands vinegar used in the lab were EHP and Umani.

Jeffren Chong Tat Loon

Atharva Kulkarni

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Practical Science

Table of Contents

Enthalpy – Thermometric titration

Introduction:

Thermometric titration is a method used to determine the unknown concentration of a solution by measuring the heat produced or absorbed during a chemical reaction. The process involves titrating the solution of unknown concentration with a standard solution of a known concentration and monitoring the temperature change during the reaction.

The purpose of this experiment is to determine the concentration of two acids, hydrochloric acid (HCl) and ethanoic acid (CH 3 CO 2 H), by thermometric titration. The enthalpy change of neutralization for each reaction will also be calculated.

To perform the thermometric titration, a 50.0 cm 3 of standard sodium hydroxide solution is transferred into a polystyrene cup using a pipette and filler. The temperature of the solution is recorded before adding 5.0 cm 3 of HCl solution from a burette. The mixture is stirred with a thermometer, and the temperature is recorded. The process is repeated for successive 5.0 cm 3 portions of HCl solution until a total of 50.0 cm 3 of HCl solution is added. The same procedure is followed for titrating ethanoic acid with standard sodium hydroxide solution.

The results are recorded in a table, with the volumes of the acid added and the corresponding temperatures recorded after each addition.

Results table for the titration of HCl.

Results table for the titration of ethanoic acid.

Calculation:

The temperature (y-axis) is plotted against the volume of acid added (x-axis) for each acid on the same graph. The line is extrapolated in both the positive and negative gradients of the graph, and the point where these two lines intersect is used to determine the maximum temperature achieved during the neutralization. This process is repeated for both HCl and ethanoic acid. From the maximum temperature rise, the quantity of energy released in each titration is determined. Assuming the specific heat capacity of the solutions is the same as that for water (4.18 J g -1 K -1 ) and that the heat capacity of the cup is zero, the standard enthalpy change of neutralization for each reaction is calculated.

• The enthalpy change of neutralization for a very dilute strong acid reacting with a very dilute strong base is constant at -57.6 kJ mol -1 (where mol -1 refers to one mole of water produced) because the heat of neutralization is the same for any acid and base combination that produces one mole of water.
• Two reasons for the experimental results for HCl being a little less negative than -57.6 kJ mol -1 could be due to: Imperfect insulation of the calorimeter resulting in heat loss to the surroundings. Incomplete dissociation of the acid and the base in the solution resulting in less energy being released during the reaction.
• The heats of neutralization for reactions involving weak acids and/or weak bases are always less negative than for strong acids and bases because weak acids and bases are only partially ionized in solution. As a result, the number of ions produced during the reaction is smaller than that produced by strong acids and bases. The production of fewer ions means that less energy is released during the reaction, resulting in a less negative enthalpy change of neutralization.

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Titration is a well-established analysis technique taught to each and every chemistry student. It is carried out in nearly every analytical laboratory either as  manual titration ,  photometric titration , or  potentiometric titration . In this blog entry, I would like to present an additional kind of titration you may  not have heard of before –  thermometric titration  – which can be considered the missing piece of the titration puzzle.

Here, I plan to cover the following topics:

What is thermometric titration?

Why consider thermometric titration, practical application examples.

At first glance, thermometric titration (TET) looks like a normal titration and you won’t see much (or any) difference from a short distance. The differences compared to potentiometric titration are in the details.

TET is based on the principle of  enthalpy change (ΔH) . Each chemical reaction is associated with a change in enthalpy which in turn causes a temperature change. During a titration, analyte and titrant react either  exothermically  (increase in temperature) or  endothermically  (decrease in temperature).

During a thermometric titration, the titrant is added at a constant rate and the  change in temperature  caused by the reaction between analyte and titrant is measured. By plotting the temperature versus the added titrant volume, the endpoint can be determined by a break within the titration curve.  Figure 1  shows idealized thermometric titration curves for both exothermic and endothermic situations.

What happens during a thermometric titration?

During an  exothermic  titration reaction, the temperature increases with the titrant addition as long as analyte is still present. When all analyte is consumed, the temperature decreases again as the solution equilibrates with the atmospheric temperature and/or due to the dilution of the solution with titrant ( Figure 1 , left graph). This temperature decrease results in an exothermic endpoint. 

On the contrary, for an  endothermic  titration reaction, the temperature decreases with the titrant addition as long as analyte is still available. When all analyte is consumed, the temperature stabilizes or increases again as the solution equilibrates with the atmospheric temperature and/or due to the dilution of the solution with titrant ( Figure 1,  right graph). This temperature decrease results in an endothermic endpoint.

Knowing the absolute temperature, isolating the titration vessel, or thermostating the titration vessel is thus not required for the titration.

In order to measure the small temperature changes during the titration, a  very fast responding thermistor  with a  high resolution  is required. These sensors are capable of measuring temperature differences of less than 0.001 °C , and allow the collection of a  measuring point every 0.3 seconds  ( Figure 2 ).  

Learn more about our fast, sensitive Thermoprobe products below – available even for aggressive sample solutions.

Metrohm Thermoprobe

If you would like to learn more about the theory behind TET, then download our free comprehensive monograph on thermometric titration.

Monograph: Practical thermometric titrimetry

Potentiometric and photometric titration are already well established as instrumental titration techniques, so why should one consider thermometric titration instead?

TET has the same advantages as any instrumental titration technique:

• Inexpensive analyses: Titration instruments are inexpensive to purchase and do not have high running and maintenance costs compared to other instruments for elemental analysis (e.g., HPLC or ICP-MS).
• Absolute method: Titration is an  absolute method , meaning it is not necessary to frequently calibrate the system.
• Versatile use: Titration is a universal method, which can be used to determine many different analytes in various industries.
• Easy to automate: Titration can be easily automated, increasing reproducibility and efficiency in your lab.

Find out more information about how automating titrations can help your laboratory workload in our previous blog article.

Why consider automation – even for simple titrations

In comparison to classical instrumental titration, thermometric titration has several additional advantages:

• Fast titrations:  Due to the constant titrant addition, thermometric titrations are very fast. Typically, a thermometric titration takes 2–3 minutes.
• Single sensor:  Regardless of the titration reaction (e.g., acid-base, redox, precipitation, …), the same sensor (Thermoprobe) can be used for all of them.
• Maintenance-free sensor:  Additionally, the Thermoprobe  is maintenance free. It requires  no calibration  or electrolyte filling and can simply be stored dry.
• Less solvent:  Typically, thermometric titrations use 30 mL of solvent or even less. The small amount of solvent ensures that the dilution is minimized, and the enthalpy changes can be detected reliably. As a side benefit,  less waste  is produced.
• Additional titrations possible:  Because enthalpy change is universal for any chemical reaction, thermometric titration is not bound to finding a suitable color indicator or indication electrode. This allows the possibility of additional titrations which cannot be covered by other kinds of titration.
• Easier sample preparation:  As TET uses higher titrant concentrations it is possible to use larger sample sizes, reducing weighing and dilution errors. Tedious sample preparation steps such as filtration can be omitted as well.

Learn more about the 859 Titrotherm system for the most reliable TET determinations below.

859 Titrotherm complete with tiamo™ software

In this section I will show some practical examples where TET can be applied.

Acid number and base number

The acid number (AN) and base number (BN) are two key parameters in the petroleum industry. They are determined by a nonaqueous acid-base titration using KOH or HClO 4 , respectively, as titrant.

During such determinations, very weak acids (for AN analysis) and bases (for BN analysis) are titrated with only small enthalpy changes. Using a catalytic indicator, these weak acids and bases can also be determined by TET.

ASTM D8045   describes the analysis of the AN by thermometric titration. The benefits of carrying out this titration are:

• Less solvent  (30 mL instead of 60 or 120 mL), meaning  less waste
• Fast titration  (1–3 minutes)
• No conditioning  of the sensor

If you wish to learn more about how well the results of the AN determination according to  ASTM D8045  correlate with  ASTM D664 , download our free White Paper as well as our brochure below.

White Paper: Avoid corrosion—A new method for TAN determination in crude oil and petroleum products

Brochure: Determination of AN in crude oil and in petroleum products in accordance with ASTM D8045 – Precise and reproducible results in 60 seconds

For more detailed information about the titration itself, download the following free Application Bulletins.

AB-427: Acid number in raw oils and petroleum products through thermometric titration in accordance with ASTM D8045

AB-405: Determination of the total base number in petroleum products

Using conventional titration, the salt content in foodstuff is usually determined based solely on the chloride content. However, foods usually contain additional sources of sodium, e.g. ,monosodium glutamate (also known as «MSG»). With TET it becomes possible to titrate the sodium directly, and thus to  inexpensively determine the true sodium content in foodstuff , as stipulated in several countries.

If you wish to learn more about the sodium determination, watch our Metrohm LabCast video: 

For more detailed information on the titration itself, download the free Application Bulletin here.

AB-298: Automated sodium determination in various foods with 859 Titrotherm

Fertilizer analysis

Fertilizers consist of various nutrients, including phosphorus, nitrogen, and potassium, which are important for plant growth. TET enables the analysis of these nutrients by employing classical gravimetric reactions as the basis for the titration (e.g., precipitation of sulfate with barium). This allows for a  rapid determination , without needing to wait hours for a result, as with conventional procedures based on drying and weighing the precipitate.

which can be analyzed by TET include:

• Ammoniacal nitrogen
• Urea nitrogen

Want to learn more about the analysis of fertilizers with thermometric titration? Download our free White Paper below on this topic.

White Paper: Multiparameter analysis in fertilizers – Fast and easy via thermometric titration

For more detailed information regarding the different fertilizer applications, check out the Metrohm Application Finder:

Metrohm Application Finder: TET applications for fertilizers

Metal-organic compounds

Metal-organic compounds, such as  Grignard reagents  or butyl lithium compounds, are used for synthetizing active pharmaceutical ingredients (APIs) or manufacturing polymers such as polybutadiene. With TET, the analysis of these sensitive species can be performed  rapidly and reliably  by titrating them under inert gas with 2-butanol.

If you wish to learn more about this topic, check out our free corresponding Application Note.

Determination of metal-organic compounds

These were just a few examples about the possibilities of thermometric titration to demonstrate its versatile use. For a more detailed selection, have a look at our Application Finder.

Download free TET applications here

To summarize:

• TET is an alternative titration method based on  enthalpy change
• A  fast and sensitive  Thermoprobe is used to determine exothermic and endothermic endpoints
• Thermometric titration is a  fast analysis technique  providing  results in less than 3 minutes
• Thermometric titration can be used for various analyses, including  titrations which cannot be performed otherwise  (e.g., sodium determination)

I hope this overview has given you a better idea about thermometric titration –  the missing piece of the titration puzzle.

Your knowledge take-aways

Determination of AN in crude oil and in petroleum products in accordance with ASTM D8045 – Precise and reproducible results in 60 seconds

White Paper: Multiparameter analysis in fertilizers – Fast and easy via thermometric titration

Lucia Meier

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How to Write a Lab Report About Titration

How to Calculate & Mix Chemical Solutions

Titrations are standard chemistry laboratory procedures usually used to determine the unknown concentration of a substance. They involve slowly adding a reagent to a reaction mixture until the chemical reaction is complete. The completion of the reaction is usually marked by the color change of an indicator substance. The volume of reagent required to complete the reaction is precisely measured using a burette. Calculations can then be carried out to determine the concentration of the original substance.

Complete your titration ensuring you achieve concordant results. You should have three results within 0.1 cubic centimeters of each other in order to be concordant.

Write your introduction. For a titration, the introduction should include information about what you hope to find out and what substance or product you will be analyzing. Write about the reaction you will be using, including the equation and the conditions required. Include details of the indicator stating the expected color change and writing a brief explanation of the suitability of the chosen indicator.

Describe details of your experimental method in the next section. Include a description of how you made up your solutions, if applicable. State the volume and concentration of any reagents used.

Draw a table to represent the results of your titration. It is customary to write the final burette volume in the first row, the initial burette volume in the second row and the titre in the third row. The titre is calculated by subtracting the initial volume from the final volume. To indicate precision, write all your results in cubic centimeters to two decimal places, adding a zero to the end of the number if necessary. Most standard burettes allow measurement to the nearest 0.05 cubic centimeters. Include all your repeat readings in the table, and indicate which are the concordant results to be used in the calculation of the mean titre. Calculate the mean titre using the concordant results only and record it below your results table.

Calculate your unknown using the mean titre and standard volumetric analysis methods. Lay out your calculations clearly, writing them down in a step-by-step format. This will help you to avoid mistakes, and will also ensure you are given credit for method if you make a minor error. Ensure you add the appropriate units to your answers, and use a suitable degree of precision: usually two decimal places. For guidance on completing the calculations, there are a number of online resources.

Write your conclusion. In a titration, the conclusion is often a simple statement of the experimentally determined parameter. Depending on the aim of the titration, more detail may be required. For example, a brief discussion on whether the results fall within the expected range may be appropriate.

Things You'll Need

Related articles, how to calculate melting & boiling points using molality, acid base titration sources of error improvements, definition of endpoint titration, how to make a 20% sugar solution, how to know when a titration is complete, steps in finding percent yield, the effects of water during a titration experiment, how to calculate the ph titration, how to determine the concentration of a titration, how to make a calibration standard for an hplc, how to calculate the calculations for spectrophotometers, what type of reaction produces a precipitate, how to test for sodium bicarbonate, errors in titration experiments, the advantages of potentiometric titration, titration of sodium carbonate with hydrochloric acid, titration explained, how to identify if a solution is neutral, base or acidic.

• UCLA Chemistry Department: Some Tips on Writing Lab Reports
• Germanna Community College: Writing a Formal Lab Report

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Veronica Mitchell has been a freelancer since 2010, writing mainly in biomedical and health fields, but also covering lifestyle and parenting topics. She has a Master of Arts in veterinary and medical sciences from Cambridge University and is a qualified high-school science teacher.

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A thermometric titration - determine the concentrations of hydrochloric acid and ethanoic acids by thermometric titration and find the enthalpy of neutralization.

E xperiment   12                              

~ A thermometric titration ~

To determine the conecentrations of hychloric acid and ethanoic acis by thermometric titration and find the enthalpy of neutralization.

• Titration of HCL with standard NaOH:
• 50cm 3 of NaOH solution is pipetted and transfer to the polystyrene cup, It was allow to stand for a few minutes.
• The initial temperature was recorded. 5.0 cm 3 ofHCL was burette to the cup.
• The mixture was stirred well by using the thermometer, the temperature was recorded.
• Sucessive 5.0 cm 3 portions of HCL was added and the mixture was stirred, the temperature was recorded after each addition.
• The adding and recording process was continued till the addition of 50 cm 3 of acid.
• Titration of CH 3 COOH with standard NaOH:

• The procedure was the same as HCL except CH 3 COOH was used.

Results and Calculations:

(I)   Titration of HCL

 (II)   Titration of CH 3 COOH

Calculations:

Concentration of HCl:

(1)(50) = m (25)

    m = 2M

Concentration of CH 3 COOH:

(1)(50) = m (5)

    m = 10M

By E=mc Δ T

E = [(100)/1000](4180)[(32) – 25]

This is a preview of the whole essay

E = 2926 J dm -1 K -1

∴ Heat energy released = 2926 J dm -1 K -1

For CH 3 COOH:

E = [(100)/1000](4180)[(24.5) – 23]

E = 627 J dm -1 K -1

∴ Heat energy released = 627 J dm -1 K -1

Standard enthaply change of neutralization:

Δ H f o  = − E / no.of moles of water formed

By the equation:

 2NaOH + 2HCl ⇔  2NaCl + H 2 O

As NaOH is limited reagent,

∴  no. of mole of H 2 O = (1)(50/1000) = 0.05 mol

Δ H o neu  = 2926/0.05

Δ H o neu   = −  58.52 kJ

(Calculations)

CH 3 COOH + NaOH ⇔  CH3COOH - Na +  + H 2 O

Δ H o neu  = 627/0.05

Δ H o neu   = −  12.54 kJ

∴The standard enthaply change of neutralization of using HCl and CH 3 COOH are − 58.52kJ mol -1  and − 12.54kJ mol -1  respectively.

• [H 2 O] is a constant when it acts as a solvent. The equilibrium will shifts to the left or shift to the right and [H 2 O] remanins unchanged. As the [acid] and [base] is very low though it is strong, [H 2 O] remanins unchanged.
• (I) Some heat is lost to the surrounding. (II) We assume that the heat capacity of the cup is zero.
• As they are not completely ionized in water, the equilibrium shifts to the right. Hence, less portion of weak acids/bases has reacted with the bases/acid. Thus, it’s heat of neutralization is less negative than the strong ones.

Discussion:

We must stir the solution throughly after each addition of the acid, so as to measure a temperature with higher accuracy. Moreover, we must replace the lid before stirring which can minimize the heat lost to the surrounding. We should stir gently or the plactic lid will break as a result of our volience.

After all, after the experiment we will plot a graph to determine the highest temperature, it is unwise to add the last drop of acid from the burette drop by drop, as it is time consuming and we cannot get the most accurute temperature after adding. We should add the acid with care and about 5.0cm 3  each time.

(discussion)

We should try hard to make sure whether the rise in temperature is logical, if the temperature have no willing to increase for a degree after a few times of the addition of the strong acid. We should once report it to the teacher to find if the given reagent has a different concentration from given.

As sodium hydroxide is very corrosive, we must use the pipette filler supplied, and we must wear lab coat and safety spectacles in the laboratory.

The last drop of the pipette should be dipped into the solution.

We should fill the burette with a filter funnel and under eye sight for safety reasons. The filter funnel should be removed after filling.

The burette should be placed upright to the vertical.

Conclusion:

The value from experimential result of neutralizatin using HCl and CH 3 COOH are − 58.52kJ mol -1  and − 12.54kJ mol -1  respectively. The one using HCl is more negative than − 57.6 kJ mol -1 , as the maximum temperture attained may be higher estimated.

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