1. INTRODUCTION1.1 BACKGROUND”Have you ever used a hot pack to warm yourhands or a cold pack on an injury? How can something produce heat or coldwithout any microwaving or refrigeration involved? The answer is: chemistry.Chemical reactions that produce heat are called exothermic. The burning of gasoline in a car engine is anexample of an exothermic reaction.Reactions that are accompanied by the absorptionof heat are called endothermic. Asan example of an endothermic reaction, when the chemical ammonium nitrate is dissolved inwater, the resulting solution is colder than either of the starting materials.
This kind of endothermic process is used in instant cold packs. These coldpacks have a strong outer plastic layer that holds a bag of water and achemical, or mixture of chemicals, that result in an endothermic reaction whendissolved in water. When the cold pack is squeezed, the inner bag of waterbreaks and the water mixes with the chemicals. The cold pack starts to cool assoon as the inner bag is broken, and stays cold for over an hour. Many instantcold packs contain ammonium nitrate.
Ammonium nitrate is a white crystallinesubstance. When it is dissolved in water, it splits into positiveammonium ions andnegative nitrate ions. In the process of dissolving the crystal, the watermolecules “donate” some of their energy. As a result, the water coolsdown. How much heat energy is”lost” when ammonium nitrate dissolves in water? You can measure theamount of heat that is involved using Equation 1.” (Source: http://www.sciencebuddies.org ) Equation 1: q = c m (T1 -T2) q = energy, measured in joules (J) c = heat capacity, measured in joules per gram per degree Celsius, J/(g°C) m = mass of solution, measured in grams (g) T1 = initial temperature, in degrees Celsius T2 = highest/lowest temperature, in degrees Celsius J = joules (J), unit of energy °C = degrees Celsius”Equation 1 states that “the amount of heatenergy that is lost when water changes from temperature T1 to the lowertemperature, T2, equals the difference in the two temperatures, times the heatcapacity, times the mass of the solution.
“The heat capacity of a substance tells you howmuch the temperature will change for a given amount of energy exchanged. Forwater at 25°C, the heat capacity is 4.18 J/(g°C).” (Source: http://www.sciencebuddies.org )Equation 2: c (water) = 4.18 J (g°C) c = heat capacity, measured in joules per gram per degrees Celsius, (J/g°C) J = joules (J), unit of energy g = grams (g) of water °C = degrees Celsius”Equation 2 says that”the heat capacity of water is 4.18 joules per gram of water per degreeCelsius.
” What this means is that if you add 4.18 J of heat energy to 1 gof water, its temperature will increase by 1.0°C. Substances other than waterhave different heat capacities.
” (Source: http://www.sciencebuddies.org )Throughoutmy life, I did once use the cold pack and once use the hot pack.
It is allbecause I had sprained my ankle when I was about to lift a heavy box and itswollen right after the accident. My family got a cold pack at home since mybrother is a practical Physical Education teacher just somewhere near my house.Even though the cold pack did not cure the swollen totally, but it reduced theinflammation faced by me.Therewas once again, my leg’s muscle suddenly got stiff and I could not move eveninch. All I could do was just held the pain while waiting for my brother to geta hot pack.
It was a relieve though for having him as a brother. After someminutes, the stiffness reduced and eventually lost.WhatI knew about those two packs is they are made from calcium chloride andammonium nitrate. But I did learn that there are many other chemicals thatproduced exothermic and endothermic reactions.
By investigating the effect ofother chemicals on the temperature of water, I can identify any other chemicalsthat can be use for these reactions. 1.2 RESEARCH QUESTIONHowdoes the effect on temperature of solution over time determine the suitabilityof a salt to be used in cold pack or hot pack while the temperature changeswere recorded constantly for 4 minutes? 1.3 AIM Toinvestigate the relationship between the effects on temperature of solutionover time and the suitability of a salt to be used in cold pack or hot pack. 1.4 HYPOTHESIS In making hot pack, the salts thatare suitable to be used are the one which can increase the temperature ofsolution after being mixed with water in short time, as well as maintaining thetemperature for a long time or having only little decreases from time to time.The maximum temperature reached by the salt solution should also relevant to behold by skin to avoid scald. As for cold pack, the salts used inmaking it can cause decrease in temperature of solution in short time afterdissolve in water.
The temperature able to maintain for sometimes and increasesonly bit by bit for minutes until it reaches the room initial temperatureagain. 2. METHODOLOGY2.
1 SAFETY PRECAUTION1. Wear indirectly vented chemical-splash goggles andchemical-resistant gloves and apron while in the laboratory.2. Handle all glassware with care.3. Wash your hands with soap and water before leavingthe laboratory. 2.2 VARIABLES VARIABLE HOW TO CONTROL a) Independent: The type of salts Use different type of salts which are ammonium nitrate, ammonium chloride, calcium chloride, sodium chloride, magnesium sulphate and copper(II) sulphate b) Dependent: The temperature of solution over time Measure the temperature of the solution for every 15 seconds.
c) Controlled: I) The weight of salt II) The volume of water III) The time taken Use same weight of salt which is 5 g for each trial. Mix salt with 25mL of distilled water for each trial. Record the temperature changes for 4 minutes for each trial. 2.2.
1 APPARATUSAND MATERIALS APPARATUS MATERIALS Distilled water Copper (II) sulphate Spatula Magnesium sulphate 25mL measuring cylinder ± 0.25 Dehydrated calcium chloride Digital stopwatch, ± 0.01s Sodium chloride Digital weighing scale, ± 0.01g Ammonium chloride Thermometer, ± 0.
25º Ammonium nitrate Calorimeter with lid Small bowl 2.2.2 PROCEDURE1. Measure 20mL of distilled water using measuring cylinder.2. Pour the measured distilled water into the calorimeter.3. Measure the initial temperature of the water using thermometer andrecord it.
4. Put small bowl on the digital weighing scale.5. Zero the scale and slowly put down 5g of copper(II) sulphate using the spatula.6. Pour the salt into the water-filled calorimeter and immediatelyclose it as well as start the stopwatch.
7. Stir the solution gently throughout the process.8. For each 15 seconds in 4 minutes period, measure the solution’stemperature using the thermometer and record the value.9.
Dispose of the copper(II)sulphate solution down the sink.10. Repeat steps 1 to 8 fourmore times to get five trials.11. Calculate the average temperatureover times and the average amount of energy involved to be included in therecord.12. Repeat the steps 1 to 10by using different salt which are ammonium nitrate,ammonium chloride, dehydrated calcium chloride, sodium chloride and magnesium sulphate.
3. RESULTS AND ANALYSIS3.1 QUANTITATIVE Type of salt Average temperature of solution over time (ºC) Average amount of energy involve (J) 0 15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240 Copper (II) sulphate, CuSO4 30.8 36.7 37.1 36.8 36.
2 35.8 35.3 34.9 34.8 34.4 34.
2 34.0 33.9 33.8 33.4 33.4 33.4 -526.68 ± 21.
07 Magnesium sulfate, MgSO4 29.8 38.5 39.
6 39.5 39.1 39.1 38.
9 38.7 38.4 38.0 37.5 37.4 36.9 36.7 36.
4 36.2 35.9 -819.28 ± 32.77 Dehydrated calcium chloride, CaCl2 29.8 35.
6 35.1 34.4 33.9 33.4 33.0 32.8 32.
4 32.3 32.2 32.0 31.
8 31.8 31.8 31.7 31.
5 -484.88 ± 19.40 Sodium chloride, NaCl 28.6 27.8 27.8 27.7 27.7 27.
7 27.7 27.7 27.9 27.9 28.1 28.1 28.
1 28.1 28.1 28.1 28.2 75.
24 ± 3.01 Ammonium chloride, NH4Cl 27.9 19.1 19.
1 19.2 19.8 20.6 21.0 21.
4 22.1 22.5 22.9 23.1 23.3 23.6 23.
7 24.0 24.2 735.68 ± 29.43 Ammonium nitrate, NH4NO3 28.8 21.
9 19.6 20.3 21.4 22.
2 22.8 23.4 23.7 24.2 24.6 24.9 25.1 25.
2 25.4 25.7 25.8 769.12 ± 30.76 3.2 QUALITATIVE Type of salt Observation Copper (II) sulphate, CuSO4 Solution turns from colourless to blue Blue precipitate formed Magnesium sulfate, MgSO4 No changes Dehydrated calcium chloride, CaCl2 White precipitate formed Sodium chloride, NaCl White precipitate formed Ammonium chloride, NH4Cl No changes Ammonium nitrate, NH4NO3 White precipitate formed 3.3 PROCESSINGAND ANALYSIS3.
3.1 Example of calculationi. Average temperature of solutionover time (ºC), copper(II) sulphate at 0s= = = 30.8ii. Amount ofenergy involve (J), copper(II) sulphate= c m (T1 -T2)= 4.18 × 20 × (30.
8 – 37.1)=- 526.68Where q =energy, measured in joules (J), c = heatcapacity, measured in joules per gram per degree Celsius, J/(g°C), m =mass of solution in grams (g), T1 = initial temperature in degrees Celsius, T2 =highest/lowest temperature in degrees Celsius, J = joules (J) unit of energy and °C = degrees Celsius iii. Uncertainty, average amount of energy involved in copper(II)sulphatePercentageof uncertaintya. Digital weighing scale = × 100% = 0.2%b. Measuring cylinder = × 100% = 1.
25%c. Digital stopwatch = 16( × 100%) = 1.07%d. Thermometer, initial temp = × 100% = 0.81%e.
Thermometer, initial temp = × 100% = 0.67%Total percentage uncertainty = 0.2 + 1.25 + 1.07 + 0.81 +0.
67 = 4%Absolute uncertainty = × 526.68J = ± 21.07 J?, theaverage amount of energy involved is (- 526.68 ± 21.07) J 3.3.2 GraphGraph 1: Average temperature ofsolution over time (exothermic)Graph 2: Average temperature ofsolution over time (endothermic) 3.
4 DISCUSSIONFor theGraph 1, all three solutions from different types of salt had a rapid increasefor the first 15 seconds. Starting at 30 seconds period, the temperature ofsolution of dehydrated calcium chloride decreased until the third minute beforehad a plateau for 45 seconds and continued to decrease. As for solutions ofcopper (II) sulphate and magnesium sulphate, they still had a little incrementof temperature after 15 seconds and reached its peak when the time is 30seconds. Copper (II) sulphate solution’s temperature started to declinethroughout the experiment, except for the last 45 seconds, where they alreadyreached constant temperature. Different with magnesium sulphate solution whichthe temperature of the solution decreased for 30 seconds after that and becomeconstant the next 30 seconds. From 90 seconds period, the temperature of thesolution kept on decreasing until the forth minute. All three types of salthave the same trend of changes but among them, the temperature changes of magnesiumsulphate solution was the highest, followed by copper (II) sulphate solution andthe lowest was dehydrated calcium chloride solution.While from the Graph 2, it can beseen that the three salt solutions all reflect the trend occurs in Graph 1.
They decreased in temperature first before gradually increased again to reachthe room temperature. Sodium chloride solution was clearly shown to have verysmall changes of temperature throughout the 4 minutes period. Ammonium nitratesolution was continuously decreased in temperature for the first 30 seconds andafter that increased steadily till the experiment ended. For the temperature ofammonium chloride solution, it declined sharply and been constant for 15seconds. Then, the solution temperature started to increase gradually until theforth minute.The changes of temperature werecaused by the loss and gain of energy of the particles of the solution whenthey reacted to each other to carry out the reactions. Every substance hastheir own heat capacity, and every atom bonding forces are different. Becauseof that, the amount of energy involved in a reaction and maximum temperature aredifferent as well.
4. EVALUATION4.1 LIMITATIONSAND WAYS TO OVERCOME LIMITATION WAYS TO OVERCOME 1. The heat may escape from the calorimeter just before the lid is placed. Close the calorimeter immediately right after the salt is poured into it to minimize the amount of heat escaped. 2. Some salts need more water to allow them to dissolve completely. Carry out the experiment using much more distilled water to ensure that all salts dissolved.
5. CONCLUSIONToidentify if a salt is suitable to be used in making hot pack or cold pack, weneed to consider the increment or decrement of the temperature of solutionwhich reflect the amount of energy involved to complete the reaction.As for exothermic reaction, allthree types of salt are suitable to be used in making hot pack since they showincrement in temperature when get dissolved in water. They also decrease slowlyby time which is good for hot pack in maintaining the temperature for a longertime. But, for magnesium sulphate, the temperature it can reach almost 40°C andthe patient may not be able to stand such temperature.
To overcome the problem,a layer of insulator should be placed inside the hot pack to lower down thetemperature.In making cold pack, the mostsuitable salts to be used are ammonium nitrate and ammonium chloride becauseboth of them showed the same trend of temperature changes. They released energyrapidly to decrease the temperature but take some time to back to roomtemperature. The minimum temperatures are also suitable to be hold by our body.Sodium chloride showed only very little changes in its temperature after beingmixed with water so it is not really suitable to be used in cold pack.Therefore, the hypothesis was supported.