Calorimetry cooling curve assignments PDF

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Keeping up the standards Cooling curve of stearic acid by Haris Iqbal Aim: The aim of the experiment is to determine physical changes and temperature change and study cooling curves using both stearic acid and Paraffin wax

Introduction: Stearic acid is a substance that has been used over a long period of time for different types of stuff to adding to cosmetics and hygiene products such as soap or shampoo. Stearic acid is often referred to as ‘fatty acid’ that is extracted from animal fats or vegetables. In this experiment the calorimeter technique will be used to study the cooling curve of a solid substance. A calorimeter is a glass beaker that can be used with a thermometer to measure the temperature during the reaction which heat is exchanged with the outer environment. There are two different types of thermometers we are going to use throughout this experiment (digital based and alcohol based). Each one of the thermometers has its own principle and function.

Equipment: -250ml beaker -0-110°C Thermometer -Retort stand, clamp and boss -Tripod -Mat -Boiling tube with solid Stearic Acid -Stop clock -Bunsen Burner -Gauze -Digital thermometer -Alcohol based thermometer

Diagram 1: digital thermometer

Diagram 2: alcohol-based thermometer

https://www.amazon.co.uk/Thermometers-Kitchen-Home/b?ie=UTF8&node=10707731 http://www.allafrance.com/products/precision-alla-france-r-thermometers-red-liquid-c-11_17.html

Health and safety: -Chipped or broken glassware can cause students to scratch and cut themselves therefore, it should be cleaned up as soon as possible -Wear lab coats to prevent staining on clothes -Wear goggles to prevent eye damage -Kettle containing boiling water so handle with care -Report any damaged equipment to tutor -Handle glassware very carefully -Read instructions thoroughly before starting the experiment

Risk assessment Equipment/Chemical hazard

Risk

Prevention

Treatment

Boiling water

Burns

Wear correct lab gear e.g. Wash the burned Lab coat and area with plenty of cold water and seek goggles medical help if the case is very serious

Bunsen burner

Burns

Wear proper lab gear such as lab coat

Glassware

Cut and bleeding

Wear gloves Get the first aid kit and proper lab and put a plaster gear on the cut

Stearic acid

Irritant to the eyes and skin

Wash the affected area with plenty of water and seek medical attention if gets worse

Seek medical help and wash the burned area with plenty of cold water

Method: -Pour 150㎤ of water into the beaker -Heat it on a tripod and gauze until the water just starts to boil -Set up the apparatus as shown in the diagram on the below however keep the water boiling -Use the clamp stand to lift the tube from the hot water. By using a results table, record the temperature of the stearic acid each minute until it reaches 40 °C. (You can also record on your results table when you see the stearic acid start to solidify again). Before I started with this experiment, I made sure I washed and calibrated all the equipment properly. After that I started to set up the apparatus as shown in the diagram below. I then placed a digital thermometer into the boiling tube containing stearic acid and was used to calculate the drop-in temperature as the stearic acid started to cool down. I used a stopwatch because I took readings of the thermometer

every minute until the liquid converted back into a solid state or when the temperature reached 40 °C. After that I produced a cooling curve graph and I put temperature on the y-axis and time on the x-axis. I then plotted my results and drew a curve of best fit and calculated the rate of cooling by drawing gradients on the graph.

Thermometer

Clamp and stand

150ml water 250ml beaker

Tripod and gauze

Heat-proof mat

Bunsen burner

Image taken by me at 12/11/19 at 11:30

Results: Stearic acid in air (Digital thermometer) Time (s)

Temperature (°C)

60

94

120

85

180

77

240

72

300

68-opaque

360

66

420

65

480

65

540

64

600

64

660

64.5

720

63

780

62.5

840

62.2

900

62

960

61.9

1020

61

1080

60

1140

59.8

1200

59

1260

58

1320

57

1380

55.9

1440

54.7

1500

53.4

1560

52.7

1620

51.3

1680

50.2

1740

49

1800

48.4

1860

47.7

1920

46

1980

45

2040

44.2

2100

43.6

2160

42.5

2220

41.4

Stearic acid in water (alcohol-based thermometer)

Time (in minutes)

Temperature of stearic acid ( C)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

83 81 78 71 70 68 68 67 67 67 67 67 67 67 67 67 67 66 66 66 66 65 64 64 62 61 59 57 54 51 45 45 43 41 40 39

Calculations: Calculation of the rate of cooling for stearic acid in air (digital thermometer based)= 1)change in y ÷ change in x 2) 40÷1325= 0.03°C/per min

Calculation of the rate of cooling for stearic acid in water (Alcohol based thermometer) =

1) Change in y ÷ change in x 2) 13 ÷ 7 = 1.86°C/per min

Analysis of the cooling curves: Stearic acid in air (digital based thermometer): The result of the rate of cooling for stearic acid in air was 0.03°C/per min. This is the first graph shown above with the digital thermometer used to record the readings. As you can see on the graph it starts to decrease temperature gradually for the first 200 seconds. This part of the graph explains how the temperature starts to decrease and liquid starts to cool down that however after that it decreases a faster and at about 275 seconds it decreases slower and gradually. The part where its almost flat and is decreasing very slowly is the time it took for stearic acid to change its physical state from liquid to a solid and when it decreases a little bit more it then shows the stearic acid is completely solidified

Evaluation: If I look at the aim, it says I must construct cooling curves for stearic acid using a digital and alcohol-based thermometer. My attempt with stearic acid in air was good and was done with a digital thermometer however I done my graph on Microsoft Excel which was accurate but was hard to calculate the gradient because the the space between the time units were very far apart. Furthermore, the practical work for constructing the graph was done with care and I was very cautious because I wanted to

reach the highest accuracy. A concern was that the digital thermometer kept kept resetting at times and we had to calibrate it again which delayed our experiment. Another thing that was concerning was that according to another student in my class, she got 2°C/per min and she used a digital thermometer therefore my results weren’t that far off, and this gave me confidence that my experiment went well.

Furthermore, the rate of cooling curve has a very important link with intermolecular forces and the state of substances the reason to this is that molecular gases, liquids and solids most effective exists due to the stability among their intermolecular forces this is retentive them collectively and the kinetic electricity in their molecules riding them far from each different. The cooling and heating of liquids and solids can as well decide their bodily nation. Both the liquids and solids have special traits. Some of the characteristics are: -Liquids have volume that is not dependent on the container of the shape -Liquids are less dense than solids -The intermolecular forces for liquids are too strong for the atoms to hold together, whereas the intermolecular forces for solids holds the molecules together -In liquids the attractive forces do not hold the molecules together, however for solids, the attractive forces provide a rigid structure It can be said that intermolecular forces make up the repulsive and attractive forces between molecules. The intermolecular forces also dominate the melting and boiling points, pressure and viscosity The greater the intermolecular forces means that higher temperature will be needed to lower the forces of attraction binding the molecules. This means that the change of state from a solid to a liquid needs a lot of energy and even more energy for liquid to a gas.

This theory was applied in the experiment as I melted solid to a liquid by using heat energy. My calculations of the cooling curve were all dependant on how quickly the temperature decreased so that I could draw the gradient accurately

Lastly, as the experiment went successful and there were less errors that I had expected, there was still some improvements that could have been made to get more accurate and reliable results. One improvement that could have been made is the amount of times I repeated the experiment, I think I should have repeated it more to get more reliable results. Another improvement is using proper and working equipment because my digital thermometer kept resetting and I had calibrated it again each time that happened. Lack of time for the experiment lead to the temperature not being cooled down to room temperature and this maybe the reason for anomalous results or gradients not calculated properly.

Cooling curve of paraffin wax Aim: Be able to construct a cooling curve for paraffin wax

Introduction: Paraffin wax is a colourless hard wax that is a mixture of straight chain hydrocarbons and it has a melting point at around 48°C – 66°C. Paraffin wax is found in petroleum. It is used in many products such as candles, wax paper and electrical insulators.

Apparatus -250cm3 beaker -Digital thermometer -Stop clock -Retort stand and clamp -Bunsen burner -Gauze -Tripod

-Heat resistant mat -Boiling tube -Paraffin wax (chemical)

Health and safety -Handle the glassware carefully -Put all bags under the table and keep chairs tucked in -Wear proper goggles and a lab coat before starting the experiment

Risk assessment: Equipment / chemical hazard

Risk

Prevention

Treatment

Paraffin wax

Inhalation

Wear proper lab gear such googles and try to keep the distance of the substance from inhaling it

Drink plenty of water and seek medical help if the case is very serious

Bunsen burner

Burns

Wear proper lab gear such lab coat, googles and gloves, follow the instructions with great care

Seek medical help and wash the burned area with plenty of cold water

glassware

Cut and bleeding

Wear gloves and proper lab gear

Get the first aid and plaster the cut, seek medical help if the case is very serious

Method: Before starting the experiment, I made sure I washed all the equipment properly and calibrated the equipment. I got my digital thermometer that I had calibrated and put it into beaker containing 10g of paraffin wax and freshly boiled water. This was used to record the temperature drop as the paraffin wax started to cool down. After that I started to look at how paraffin wax started to heat up then melt. I then recorded the temperature of the liquid paraffin wax at its highest temperature and I removed the boiling tube from the beaker and allowed the liquid to cool down

Results: Time (in seconds) 60 120 180 240 360 420 480 540 600 660 720 780 840 900 960 1020 1080 1140 1200 1260 1320 1380 1440 1500 1560 1620 1680 1740 1800 1860 1920 1980 2040 2100 2140 2200

Temperature (°C) 103 100 98 94.6 82 74.5 71.3 68.5 66.2 65.7 65 63.5 62.3 62 61 61 60.6 59.3 58.9 58 57.8 56.4 55.7 55 54.2 53.5 53 52.1 51 50.5 49.7 49 48.3 48 47 46.1

2260 2320 2380 2440 2500 2560 2620

45 45 44.8 43.4 42.5 41.7 40.4

Calculations: Digital based thermometer 1) change in y ÷ change in x 2) 40 ÷ 2400 = 0.016 °C/min

Analysis: In my attempt of this cooling curve graph it went successful. At the start of the graph the temperature starts to decrease gradually however at about 800 seconds the digital thermometer reset, and this caused an anomaly in my graph and results therefore this was an error from the thermometer. I calculated the gradient to be 0.016 °C/min. After the anomaly the temperature carries on decreasing gradually and starts to solidify again

Evaluation: My cooling curve of the paraffin wax was done with a digital thermometer. I noticed as the time increases the temperature decreases. I compared my results with my class mate, and he got 1.67 °C/min with a digital based thermometer also. Therefore, this indicates my results aren’t reliable because they weren’t close to his. In my attempt of the rate of cooling from the graphs was not accurate due to some experimental errors as you can see on the graph, the anomalous result. This was due to the digital thermometer not working properly and this had a big impact on the experiment. As I mentioned for stearic acid, the intermolecular forces had a big impact on the rate of cooling and with this experiment it didn’t have much impact. It was mostly affected by the

decreasing of temperature and decreasing of kinetic energy. Furthermore, for me this experiment did not go as expected and I believe if I had done one more attempt, I would’ve gotten more reliable results. In future experiments I would try my best to stop using digital as they can have malfunctions and mess up your experiment and, I would try to use alcohol-based thermometers because they are sensitive to heat

Conclusion for both experiments: If we look back at the aim for this investigation, I was supposed to construct cooling curve for both stearic acid and paraffin wax. My cooling curve of stearic acid was done successfully, and I feel that the alcohol thermometer gave me more reliable results. In contrast, the other experiment with paraffin wax did not go as well due to lack of time and equipment failure. I think that with more improvement and better planning future experiments will give me more reliable results because I will know exactly what to do and how to do it....