The Burning of Primary and Secondary Alcohols Extended Experimental Investigation

December 1, 2017 Chemistry

The Burning of Primary and Secondary Alcohols Year 11A Chemistry By Jarrod Ahern Abstract The aim of the investigation was to determine whether primary alcohols use less energy than secondary alcohols for fuel. The hypothesis is if primary alcohols are heated and results are taken, they produce a lesser heat of reaction then secondary alcohols. The method used was to find the average bond energies of three relating primary and secondary alcohols and compare it with the average theoretical values. Hence the primary alcohols produce less energy most of the time and this was tested by using the correct methods. Contents Pg 1 – Aim

Pg 1-2 – Theory Pg 2 – Hypothesis Pg 2-3 – Variables Pg 3 – Apparatus Pg 3 – Procedure Pg 4 – Results Pg 5-6 – Analysis Pg 7 – Discussion Pg 8 – Conclusion Pg 9 – Appendices Pg 11 – Bibliography Aim There are many different purposes for fuel around the world right now. The use of fuels has increased and we are investigating to find the most essential fuels for various things. Using the most effective fuel source is essential. Hence, various primary and secondary alcohols will be tested to see which uses the lesser energy. The investigation is aimed to determine whether primary alcohols use less energy than secondary alcohols for fuel.

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Theory An alcohol is referred to as groups of organic chemical compounds. Alcohols occur when a hydroxyl (-OH) functional group replaces one or two of the hydrogen atoms. There are many types of alcohols but they are classified by their structure. Primary, Secondary and Tertiary depending on how many carbons are attached to the OH group. Primary and Secondary structures will be the main focus of this assignment. Primary alcohols are when the carbon atom that carries the –OH group is only attached to one alkyl group. A secondary alcohol is when the OH is directly linked to two of the alkyl groups.

The tertiary is the final alcohol group this occurs when the OH molecule is attached to three alkyl groups. When chemical reactions occur they require energy to break and form bonds which is released in the form of heat. There are two different types of enthalpy reaction, endothermic and exothermic. Endothermic is when a system absorbs the heat and turns cold, and when it produces heat it is known as an exothermic reaction. However, this investigation will only analyse exothermic reactions. Enthalpy cannot be measured directly, it is calculated as the heat added or lost in the reaction which is the change in enthalpy, or ?

H. ?H shows the difference between the enthalpy at the start of the reaction compared to what it is at the end of the reaction. Hess’s Law is a method used to find enthalpy change within a reaction. Hess’s law is the sum of the heats of formation of the products minus the sum of the heats of formation of the reactants is equal to the enthalpy change of the reaction. It is very important as it determines the enthalpy change of a reaction even if it’s not easily measured directly. Combustion is a key factor that is looked at in this report.

Combustion is a form of exothermic chemical reaction in which a reaction between two or more chemicals produces heat. For combustion to take place a fuel source and oxygen is needed and this can take place anywhere in the atmosphere or in a closed system. When an exothermic reaction occurs involving a fuel heat is created, as well as carbon dioxide and water. When a substance is completely broken down and transformed into oxygen and carbon dioxide the combustion is complete but it is almost impossible to accomplish. In this experiment, combustion took place when the alcohols where being burnt.

The bonds broke and the fuel completely disappeared and turned into oxygen and carbon dioxide. There wasn’t enough time for the combustion to complete and this would result in soot on the bottom of the test tube. Hypothesis If primary alcohols are heated and results are taken, they produce a lesser heat of reaction then secondary alcohols. Variables Independent variable * Primary and secondary alcohols used in the experiment. Dependent variable * The amount of energy lost during the burning of related primary and secondary alcohols. Controlled variables * Wick type * Height of test tube above flame (4 cm) Volume of water heated (30 mL) * The temperature increase (70 degrees Celsius) * Controlled environment (The same) * The scale type * The distilled water used * Same containers Uncontrolled variables * Different initial temperatures of the distilled water ranging from 24- 25 degrees Celsius. However, this should not affect the end results. * Extinguishing the flame exactly on 70 degrees Celsius. As this would make a slight variation it should also not affect the end result by a large amount. Apparatus * Test tube * Thermometer * Retort stand * Clamp x2 * 1-propanol * 2-propanol * 1-pentanol * 2-pentanol * 1-butanol * 2-butonal

Procedure 1. Gather apparatus equipment- also collect required materials: -Thermometer, retort stand, test tube/s, clamps, matches, metal can, burner with wick and particular alcohol, 30mL of water for each experiment. 2. Weigh the burner on the scale, make sure ‘tare’ is taken into consideration and record weight of the burner without the lid. 3. Set up the experiment area, burner around the metal and several clamps on retort stand to hold the test tube and thermometer in place. 4. Fill test tube with 30mL of distilled water 5. Measure initial temperature of water which will always be approximately room temperature and record. . Light burner wick and center the flame. 7. Make sure there are no variables affecting the flame. 8. When temperature rises to the desired level of 70 degrees Celsius, extinguish flame by putting the lid back on the burner. 9. Reweigh the burner without the lid and record the final weight, also taking ‘tare’ into consideration. Analysis Table 7: Energy Released in Reactions (kJ/mole) Alcohol| Trial 1| Trial 2| Trial 3| Average| Propan-1-ol| 387| 420| 374| 393. 67| Propan-2-ol| 509| 454| 235| 399. 33| Butan-1-ol| 773| 657| 573| 667. 67| Butan-2-ol| 861| 524| 434| 606. 33| Pentan-1-ol| 526| 896| 588| 670|

Pentan-2-ol| 877| 877| 655| 803| ? = c x m x ? T This equation is used to find the number of Joules, then J/g = Joules ? Initial weight of burner – Final weight of burner will find the joules per gram. Then J/mol = Joules per gram (J/g) x Molar mass of the alcohol will find the joules per mole. Full Working out for Propan-1-ol: ? = c x m x ? T = 4. 2 J/g x 30mL x 46°C = 5796J J/g = Joules ? Initial weight of burner – Final weight of burner = 5796 ? 237. 44 – 236. 54 = 5796 ? 0. 9 = 6440 J/g J/mol = Joules per gram (J/g) x Molar mass of the alcohol = 6440 J/g x 60. 1 = 387044 J/mol ? 387 kJ/mol Average (387 + 420 + 374) ? 3 = 1181 ? 3 = 393. 67 kJ/mol This process is repeated for all primary and secondary alcohols. (See appendices) Graph 1: Comparing Bond Energies of Primary Alcohols (kJ/mol) Graph 2: Comparing Bond Energies of Secondary Alcohols (kJ/mol) Discussion This investigation about burning primary and secondary alcohols was intended for finding the correct fuel source that should be used for everyday objects such as motors and various things. Fuels undergo exothermic reactions that result in the release of energy. The energy released is that stored in the bonds of the fuel substances.

The aim of this investigation was to see if primary alcohols used a lesser energy than secondary alcohols The primary and secondary fuels used in this investigation went through a serious of test and the results were recorded into individual tables in the results section of this report. As you can see in Table 1 for propan-1-ol there is the data needed to find the average kJ/mole on each of the three trails. It clearly shows the temperature change or ? T from the initial to the final temperature and the initial and final masses of the burners. Also there is the obvious result like amount of distilled water used which was always 30mL.

All of these results were an essential part of equation to find the kJ/mole. The process of finding the result was repeated for the other types of alcohols and put into the equations. Once this was completed a final table was completed to get the average bond energies of the experiments. This table was table 7 in the analysis section of this report and it also evidently shows each trial’s bond energy in kJ/mole for each type of alcohol. The average of the three trials for every alcohol was calculated and used in comparison with the theoretical average bond energy values.

Out of the three related primary and secondary alcohols bond energy averages, two related primary alcohols used less energy than their relating secondary alcohols. Therefore, the results collected and analyzed has indeed supported the when the hypothesis states that when primary alcohols are heated, they produce a lesser heat of reaction then secondary alcohols. After researching the theoretical bond energy values for each alcohol it was noticed that the average bond energies of the alcohols used in the experiment had an excessive different to the theoretical values of the same alcohol.

This was discovered as, for propan-1-ol, in the data collected was 393. 67kJ/mole where as the theoretical value was 4410kJ/mole. This was an incredible different to the average bond energy we collected and this is all because of incomplete combustion. When alcohols are burnt it is best that complete combustion occurs. The efficiency of the alcohol is dependent on the percentage of the alcohol that is burnt. When the experiments were conducted, complete combustion did not take place. The theoretical bond energies are higher because they have been fully combusted, however in the xperiment done by us the alcohols were not fully combusted and as a result black soot would appear on all of the test tubes used. There were several problems and scientific errors involved in the experiment when it was taking place. Firstly, when gathering the temperature from thermometer, it had air bubbles which separated the red substance. Therefore, this was most likely to affect the end temperature results as the water was getting to hot when the thermometer read 70 degrees Celsius. Also for the second trial during the experiment, there was bad environment issue.

The set up was under an air conditioner and as a consequence the flame was abnormally large and wasn’t directly on under the test tube for the whole experiment. This was counteracted by stacking two heat proof can on top of each other to stop the flow of the air conditioner to the flame. This was a controlled variable that should’ve been controlled, next it will be turned off to achieve more accurate results. Another problem during the experiments was the ‘parallax error’. Before the investigation and in-depth explanation this was unheard of be me and my group member.

Parallax error is when the temperature level on the thermometer is not read properly, the scale on the glass and the eye reading the temperature are not horizontal causing the scientific error in the reading of the thermometer causing a slight variation in the ? T. This was stopped after hearing about this. To stop this error the thermometer should be read in line with the red substance. When burning any substance that gives off fumes in the process, it should be done in a fume cabinet. The risks of the alcohols we were burning have certain risk involved that should be taken into consideration for it to be a safer experiment.

For example, Propan-1-ol is harmful if swallowed, it can cause lung damage if swallowed the vapours may cause dizziness and drowsiness and discomfort of respitory system and skin though there is limited evidence of this. Pentan-1-ol is harmful by inhalation, the vapours may cause dizziness and drowsiness though there is limited evidence of this also, may cause lung damage if swallowed and irritating to lung system. Butan-1-ol may cause lung damage if swallowed, has a risk of serious damage to eyes, vapours may cause dizziness or suffocation, skin contact may produce health damage and harmful if inhaled or swallowed.

There are many ways to stop all of these from causing harm and most were all practice during the experiment. When the investigation was undergoing, all of the variables were tried to keep control of so that all the experiment are as similar as possible. Some of these variables included height of the boiling tube above the wick. It is essential to put the test tube in the hottest part of the flame to ensure accurate results. This was done as accurately as possible every time to ensure that there was the right amount of heat going through the water for every test. Another variable was the type of wick used.

All of the wicks were the same but if it wasn’t it would have distorted the size of the flame dramatically, even though the flame was bigger in some experiments but this could not be controlled. Something that could be changed for next could be an increase in the size of the heat can so no heat is lost to the surrounding environment. Each primary alcohol used less energy to its relating secondary alcohol. However, according to the results, pentan-2-ol has the best burn rate. The average bond energy from our experiment is the highest and the theoretical is the highest as well. 2-ol could be used in everyday necessities like motors. Conclusion The aim of the investigation was to determine whether primary alcohols use less energy than secondary alcohols for fuel. The aim could get approximate results for each alcohol tested as the variable were controlled and the apparatus was done correctly with minor errors mentioned in the discussion such as the air bubbles in the thermometer, parallax error on the thermometer, the air-conditioning affect that flame and the safety of the experiment which doesn’t affect the results.

The average of the three trials for every alcohol was calculated and used in comparison with the theoretical average bond energy values. Out of the three related primary and secondary alcohols bond energy averages, two related primary alcohols used less energy than their relating secondary alcohols. Therefore, the results collected and analyzed has indeed supported the when the hypothesis states that when primary alcohols are heated, they produce a lesser heat of reaction then secondary alcohols.

To make the hypothesis more true, I would modify it to be when most primary alcohols are heated they produce a lesser heat of reaction then secondary alcohols as of the butan-1-ol and butan-2-ol defying the hypothesis. Instead of using the bond energy equation I could have used Hess’s Law as it is a more accurate method of finding the average kJ/mole and it might have had an effect on the butan-1-ol and butan-2-ol results to make them support the hypothesis. Bibliography Anne Marie Helmenstine (2011) About Chemistry, retrieved August 27 from ;http://chemistry. about. om/od/workedchemistryproblems/a/bondenergyexmpl. htm; Author unknown (2011) Combustion Training, retrieved August 31 from ;http://www. e-inst. com/combustion/; Author Unknown (n. d) Definition of Hess’s Law, retrieved August 23 from http://www. cramster. com/definitions/hesss-law/244 Author Unknown (n. d) Stoichiometric Combustion, retrieved August 23 from http://www. engineeringtoolbox. com/stoichiometric-combustion-d_399. html Dortmund Data Bank Software ; Seperation Technology (2009) HFO (Std. Heat of Formation) Data for Propanol, Retrieved September 6 from ;http://onlinelibrary. iley. com/doi/10. 1002/recl. 19700891208/abstract; Jim Clark (2003) Introducing alcohols, retrieved August 5 from ;http://www. chemguide. co. uk/organicprops/alcohols/background. html; Michael Blaber (1996) Energy Relations in Chemistry: Thermochemistry retrieved August 19 from ;http://www. mikeblaber. org/oldwine/chm1045/notes/Energy/Enthalpy/Energy02. htm; Nigel Saunders (2005) Combustion of alcohols, retrieved September 11 from ;http://www. creative-chemistry. org. uk/gcse/documents/Module7/N-m07-24. pdf;

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