Lab Experiment 3 (Heat of Neutralization) PDF

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nullnullnullUNIVERSITI TEKNOLOGI MARA FAKULTIKEJURUTERAAN KIMIA ENGINEERINGCHEMISTRY LABORATORY (CHE485)NAME & STUDENT NO.:1. KHAIRUL AKMAL HAZIQ BIN SAMSUDIN (2020628258)2. MIRZA ADRIANA BINTI MURAD (2020860262)3. AMIRUL RASYID BIN ZULKARNAIN (2020859494)4. NURUL ATHIRAH BINTI MAT SUKRI (202049...

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UNIVERSITI TEKNOLOGI MARA FAKULTI KEJURUTERAAN KIMIA ENGINEERING CHEMISTRY LABORATORY (CHE485) 1. KHAIRUL AKMAL HAZIQ BIN SAMSUDIN (2020628258) NAME & STUDENT NO. : 2. MIRZA ADRIANA BINTI MURAD (2020860262) 3. AMIRUL RASYID BIN ZULKARNAIN (2020859494) 4. NURUL ATHIRAH BINTI MAT SUKRI (2020496544) 5. NURUL SHARIFAH AINA BINTI MOHAMMAD (2020816592) GROUP : GROUP 4 EXPERIMENT : THERMODYNAMIC EXPERIMENT- HEAT OF NEUTRALIZATION DATE PERFORMED : 13RD NOVEMBER 2020 SEMESTER : OCTOBER 2020-FEBRUARY 2021 PROGRAMME / CODE : BACHELOR OF ENGINEERING (HONS) CHEMICAL/ EH220 SUBMIT TO : DR. SAFARI ZAINAL No. 1 2 3 4 5 6 7 8 9 10 11 12

Title Abstract/Summary Introduction Aims Theory Apparatus Methodology/Procedure Results Calculations Discussion Conclusion Recommendations Reference / Appendix TOTAL MARKS Remarks: Checked by :

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Allocated Marks (%) 5 10 5 10 5 10 10 10 20 5 5 5 100

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Table of Content 1

Abstract ....................................................................................................................................... 3

2

Introduction ................................................................................................................................. 4

3

Literature review ......................................................................................................................... 5

4

Methodology ............................................................................................................................... 8 4.1

Chemical.............................................................................................................................. 8

4.2

Apparatus ............................................................................................................................ 8

4.3

Experimental Procedure ...................................................................................................... 8

4.4

Mathematical equation ........................................................................................................ 8

4.4.1 Formula for number of moles, n ...................................................................................... 8 4.4.2 Formula of weight, m ...................................................................................................... 8 4.4.3 Formula of heat of neutralization, q ................................................................................ 9 4.4.4 Formula of Heat of Neutralization, 𝚫𝐇 ........................................................................... 9 5

Result......................................................................................................................................... 10

6

Discussion ................................................................................................................................. 11

7

Conclusion and recommendation .............................................................................................. 13

8

References ................................................................................................................................. 14

9

Appendices ................................................................................................................................ 15

1 Abstract The enthalpy of neutralization can be defined as the change in enthalpy that occurs when one equivalent of an acid and one equivalent of a base undergo a neutralization reaction to form water and salt. It also can be defined as energy released with the formation of 1 mole of water. In this experiment, hydrochloric acid (HCl) is the acid and sodium hydroxide (NaOH) is the base. The purpose of this experiment is to determine the molar heat of neutralization between the base, NaOH and the acid, HCI, and also to identify the classification of reaction (exothermic or endothermic) by the reaction of NaOH and HCI. Energy changes always accompany chemical reactions. If energy, in the form of heat is liberated, the reaction is exothermic and if energy is absorbed the reaction will be endothermic. The equation for any strong acid being neutralized by a strong alkali is essentially just a reaction between hydrogen ions and hydroxide ions to make water. The experiment was conducted by both acid and base were added in the insulated vessel and the final temperature is recorded. When two highly reactive substances such as HCl and NaOH were reacted together, it will produce a neutral solution where neutralization reactions occur during the process. The heat of neutralization reaction between acid and base will be higher if the amount of alkali used is more than acid. Based on the research from the previous experiment, the result obtained for the neutralization reaction between a weak acid and a strong alkali has been recorded it shows that the heat of neutralization for weak acid and strong base is lower than the heat of neutralization for strong acid and strong base. Heat of neutralization for each trial had been determined and the energy change for every trial had also been observed. Throughout the experiment, we can conclude that when these two reacted together, it showed that were no excess hydrogen ions left.

2 Introduction The enthalpy of neutralization can be defined as the change in enthalpy that occurs when one equivalent of an acid and one equivalent of a base undergo a neutralization reaction to form water and salt. It also can be defined as energy released with the formation of 1 mole of water. In this experiment, hydrochloric acid (HCl) is the acid and sodium hydroxide (NaOH) is the base. The equation below is the chemical reaction for the both substances.

HCl + NaOH → NaCl + H2O In this reaction, HCL will react with NaOH to produce sodium chloride (NaCl) and water (H2O). In this process, ion Cl- from HCl will be neutralized with ion Na+ from NaOH which will form NaCl. When an acid has been neutralized, there will be no excess amount of the acid left in the solution. The process is exothermic because the reaction between both substances release heat. Heat can be measured by conduct the experiment in calorimeter and the data will be recorded. The heat release released by the reaction will be absorbed by surrounding and the calorimeter. A calorimeter is an object used for calorimetry, or the process of measuring the heat of chemical reactions or physical changes as well as heat capacity. The calorimeter measured the change of temperature during the reaction. After that, heat can be calculated by using below formula,

Q = mCp ∆T

In this formula, Q stands for heat of neutralization in Joule unit (J), m stands for mass in gram (g), Cp stands for specific heat (J/g ºC) and ∆T stands for changes in temperature (ºC). Since the process is exothermic, Q in this formula will be negative. Hydrochloric acid in this reaction is a strong acid while sodium hydroxide is strong base. The changes of enthalpy in this reaction is expected to be -57.30 kJ/mol (standard enthalpy change). The objective of this experiment is to determine the molar heat of neutralization between the base, NaOH and the acid, HCl. Next, it is also to identify the identification of reaction between NaOH and HCl and to evaluate the strength of acid and alkali, respectively by varying the volume of strong alkali.

3 Literature review A chemical reaction is accompanied by an energy change described as a change in heat content: energy is absorbed (endothermic reaction) or released (exothermic reaction). In general, the breaking of bonds in reactants requires the consumption of energy, and the creation of new bonds in products involves the release of energy. The potential energy that is stored in chemical bonds can be thought of as the heat content of a system, enthalpy. When these chemicals react, a change in energy (absorb or release of energy) will result in a change in enthalpy, ∆H. The overall change in energy will depend on the unique properties of the reactants and products.

Energy changes always accompany chemical reactions. If energy, in the form of heat is liberated, the reaction is exothermic and if energy is absorbed the reaction will be endothermic. Thermochemistry is concerned with the measurement of the amount of heat evolved or absorbed. The heat (or enthalpy) of neutralization (∆H) is the heat evolved when an acid and a base react to form a salt plus water.

Sodium hydroxide solution consists of sodium ions and hydroxide ions in solution. The equation for any strong acid being neutralized by a strong alkali is essentially just a reaction between hydrogen ions and hydroxide ions to make water. The other ions present (sodium and chloride, for example) are just spectator ions, taking no part in the reaction.

The full equation for the reaction between hydrochloric acid and sodium hydroxide solution is: NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l) + Q

The reaction actually happening is:

OH−(aq)+H+(aq)→H2O(l)

Q in the above equation is -∆H and is expressed in J/mol of water. Neutralization reactions are generally exothermic and thus ∆H is negative.

Calculating the limiting reactant, the change in enthalpy of the reaction, ∆Hrxn, can be determined since the reaction was conducted under conditions of constant pressure.

∆Hrxn = qrxn / moles of limiting reactant Calorimetry is the study of heat transferred in a chemical reaction. The amount of heat absorbed or released during this thermochemical process is measured by a change in temperature. The device used to measure the change is called a calorimeter, where ideally, the calorimeter would not absorb any heat from its surroundings and at the same time not allow any heat from the reaction to escape. (1) q = msΔT where q = heat , m = mass, s = specific heat (J g-1 ºC-1 ) , ΔT = Temperature change. The specific heat of a substance, s, is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius (an intensive property). Heat measurements are performed by carrying out the reaction in a calorimeter. The heat (Q) given off by the neutralization reaction is absorbed by the reaction solution and the calorimeter. Both the solution and calorimeter increase in temperature due to the absorbed heat and this increase can be measured with a thermometer. ∆H is negative if heat is released and positive if heat is absorbed.

The heat released during a reaction is given by the expression: 𝐇𝐞𝐚𝐭 𝐨𝐟 𝐍𝐞𝐮𝐭𝐫𝐚𝐥𝐢𝐳𝐚𝐭𝐢𝐨𝐧, 𝐪 = 𝐌𝐚𝐬𝐬 × 𝐒𝐩𝐞𝐜𝐢𝐟𝐢𝐜 𝐇𝐞𝐚𝐭 × 𝐂𝐡𝐚𝐧𝐠𝐞 𝐢𝐧 𝐓𝐞𝐦𝐩𝐞𝐫𝐚𝐭𝐮𝐫𝐞 The molar heat of neutralization is the amount of heat each mole of base added to the acid (or vice versa) causes the reaction to give off. (A mole is a unit chemists use to represent large numbers of molecules). Molar heat of neutralisation (molar enthalpy of neutralization) is the energy liberated per mole of water formed during a neutralisation reaction usually given in units of J mol-1. The formula given by:

𝐌𝐨𝐥𝐚𝐫 𝐇𝐞𝐚𝐭 𝐨𝐟 𝐍𝐞𝐮𝐭𝐫𝐚𝐥𝐢𝐳𝐚𝐭𝐢𝐨𝐧, 𝚫𝐇 = (

−𝐪 (𝐍𝐞𝐮𝐭𝐫𝐚𝐥𝐢𝐳𝐚𝐭𝐢𝐨𝐧) ) 𝐧

In a weak acid, such as acetic acid, at ordinary concentrations, something like 99% of the acid is not actually ionized. That means that the enthalpy change of neutralization will include other enthalpy terms involved in ionizing the acid as well as the reaction between the hydrogen ions and hydroxide ions. And in a weak alkali like ammonia solution, the ammonia is also present mainly as ammonia molecules in solution. Again, there will be other enthalpy changes involved apart from the simple formation of water from hydrogen ions and hydroxide ions. For reactions involving acetic acid or ammonia, the measured enthalpy change of neutralization is a few kJ less exothermic than with strong acids and bases.

For example, one source which gives the enthalpy change of neutralization of sodium hydroxide solution with HCl as -57.9 kJ mol-1:

NaOH(aq)+HCl(aq)→Na+(aq)+Cl−(aq)+H2O(l)

The enthalpy changes of neutralization for sodium hydroxide solution being neutralized by acetic acid is -56.1 kJ mol-1:

NaOH(aq)+CH3COOH(aq)→Na+(aq)+CH3COO−(aq)+H2O(l)

For very weak acids, like hydrogen cyanide solution, the enthalpy change of neutralization may be much less. A different source gives the value for hydrogen cyanide solution being neutralized by potassium hydroxide solution as -11.7 kJ mol-1, for example:

NaOH(aq)+HCN(aq)→Na+(aq)+CN−(aq)+H2O(l)

4 Methodology 4.1 Chemical 3M sodium hydroxide, 3M hydrochloric acid and acetic acid 4.2 Apparatus Insulated vessel, thermometer 4.3 Experimental Procedure An insulated vessel equipped with a magnetic is prepared and then the volume of acid is measured. Next, the step continued by the acid is added to the insulated vessel and then the vessel is covered while the thermometer is inserted at the same time. After that, the thermometer reading is being recorded. Next procedure is the volume of base is measured, followed by the base then is added to the vessel. Lastly, the final temperature is recorded. The experiment is repeated three times and the data is tabulated as shown below.

4.4

Mathematical equation

4.4.1 Formula for number of moles, n Number of moles, n = Molarity × Volume o Number of moles HCl, n o =(

3 mol L

) × 0.049 L

o = 0.147 mol 4.4.2 Formula of weight, m Weight, m = Mole × Molecular weight o Weight, m

g

o = 0.147 mol × 36.46 mol

o = 5.36 g

4.4.3 Formula of heat of neutralization, q Heat of Neutralization, q = Mass × Specific Heat × Change in Temperature o Heat of Neutralization, q

o = 11.36 g × 4.184

o = 1026.65 J

J

g°C

× (53.3 − 31.7)°C

4.4.4 Formula of Heat of Neutralization, 𝚫𝐇 Molar Heat of Neutralization, ΔH = ( o =(

−1026.65 J 0.147 mol

) = −6984.01

J mol

−q (Neutralization) ) n

5 Result Based on the experiment, this is the result for Trial 1, Trial 2 and Trial 3.

Trial 1 Number of mol HCl = 0.147 mol Number of mol NaOH = 0.150 mol Total mass of the solution = 11.36 g Heat of neutralization, q = 1026.65 J Molar heat of neutralization, ΔH = -6984.01 J/mol

Trial 2 Number of mol HCl = 0.150 mol Number of mol NaOH = 0.150 mol Total mass of the solution = 11.47 g Heat of neutralization, q = 940.61 J Molar heat of neutralization, ΔH = -6270.73 J/mol

Trial 2 Number of mol HCl = 0.150 mol Number of mol NaOH = 0.147 mol Total mass of the solution = 11.35 g Heat of neutralization, q = 964.01 J Molar heat of neutralization, ΔH = -6426.73 J/mol

6 Discussion When two highly reactive substances such as HCl and NaOH were reacted together, it will produce a neutral solution where neutralization reactions occur during the process.[1] When a strong acid is neutralized by a strong base, there will be no excess hydrogen ions left in the solution.[2] The chemical equation below shown the neutralization reaction between HCl and NaOH in water:

The pH of the solution will be close to a value of 7 but the exact pH value is dependent on the temperature of the solution. It can be categorized as a neutral solution as it is neither acidic nor alkaline. On the other hand, when weak acid react with a strong base, it will produce an alkali solution with pH value which more than 7. Table below shows the pH levels at equivalence point:

Based on the result obtained, the initial temperature of Trial 1 was 31.7℃ and final temperature was 53.3℃. The initial temperature of the experiment was the temperature of HCl and final temperature was when the HCl react with NaOH. The change in temperature of Trial 1 was 21.6℃. Molarity or concentration of HCl and NaOH were the same which is 3M. Volume HCl and NaOH were 49 ml and 50 ml, respectively. The total mass of solution was 11.36g. Number of moles for HCl is 0.147 mol and number of mol NaOH is 0.150 mol. Number of mol of NaOH is higher than number of mol HCl. HCl was the limiting reagent for this experiment. Heat of neutralization, q for Trial 1 was 1026.65 J and the value of molar heat of neutralization, ΔH was -6984.01 J/mol. For Trial 2, the initial temperature was 33.2℃ and the final temperature was 52.9℃. The temperature different was 19.7℃. Molarity or concentration of HCl and NaOH were the same as Trial 1 which is 3M. Volume of HCl and NaOH were equal which is 50 ml. Total mass of the solution 11.47g. Number of mol for HCl and NaOH trial 2 were the same which is 0.150 mol. Heat

of neutralization, q for Trial 2 was 940.61 J and the value of molar heat of neutralization, ΔH was 6270.73 J/mol. For Trial 3, the initial temperature was 31.9℃ and the final temperature was 52.2℃. the temperature different was 20.3℃. Molarity or concentration of HCl and NaOH for Trial 3 is the same as Trial 1 and Trial 2 which is 3M. Volume of HCl and NaOH were 50 ml and 49 ml, respectively. The total mass of the solution was 11.35g. Number of mol for HCl was 0.150 mol and number of mol for NaOH was 0.147 mol. Heat of neutralization, q for Trial 3 was 964.01 J and the value of molar heat of neutralization, ΔH was -6426.73 J/mol. From this experiment, the neutralization reaction for all trial were an exothermic reaction as it has released heat to the surrounding. In an exothermic reaction, the energy is released to the surrounding in the form of heat or light because the total energy of the product from the reaction is less than the total energy of the reactants. Thus, the change in enthalpy, ΔH for an exothermic reaction will always give a negative value. In this experiment, the Trial 1 has given the highest heat of neutralization value and the highest molar heat of neutralization value because it had a greater quantity or volume of an alkali to react with an acid compared to the volume of reactant in Trial 2 and Trial 3. In general, the heat of neutralization reaction between acid and base will be higher if the amount of alkali used is more than acid. The heat of neutralization for all trial can be compared based on the volume of reactant as the reaction only consumed a reactant with the same strength. While, Trial 2 and Trial 3 had a lower heat of neutralization value than Trial 1 because the reaction was conducted with a lesser amount of alkali. Neutralization reaction also can be conducted by reacting a weak acid with a strong alkali. As example, the neutralization reaction between Acetic Acid and NaOH in water. Based on the research from the previous experiment, the result obtained for the neutralization reaction between a weak acid and a strong alkali has been recorded it shows that the heat of neutralization for weak acid and strong base is lower than the heat of neutralization for strong acid and strong base. It is because weak bases does not ionized completely in aqueous solution. Therefore, some energy is required for their complete ionization and that is why net energy released is less. It can be concluded that a strong acid and weak acid give a quite similar heat of neutralization changed. This is because all types of acid and base will have the same kind of ions which is Hydrogen ion and Hydroxide ion respectively. Besides that, an acid with different level of strengthen still had the same number of ions that will react with any kind of base to produce water and salt. Theoretically, only hydrogen ion and hydroxide ion will react between each other during neutralization reaction.

7 Conclusion and recommendation As a conclusion, heat of neutralization for each trial had been determined and the energy change for every trial had also been observed. Heat is the energy change involved throughout this expe...