Extended Experimental Investigation Essay
Extended Experimental Investigation
Abstract: Cold packs are based on the principle of endothermic reactions, which means a reaction that absorbs heat from the surrounding resulting in a temperature drop. Due to this temperature drop, cold packs have many benefits when it comes to injuries such as sprains and strains. It cools the local tissue and reduces bleeding, swelling and pain. It also aids in a speedy recovery.
The most commonly used chemical in instant cold packs is ammonium nitrate which will be tested in the investigation along with four other chemicals in water. These other chemicals include potassium nitrate, potassium chloride, sodium acetate and sodium chloride. The two lowest chemicals will then be mixed together at different concentration ratios to see if this drops the temperature further. The chemical/s the produce the lowest temperatures will be tested and compared against a normal frozen cold pack.
A chemical reaction is the process of altering the composition and structure of one set of chemical substances to another.1 Two or more elements react forming a chemical compound. These changes occur due to the movement of electrons breaking and forming new chemical bonds.2 Factors can influence the rate in which the reaction occurs, these include catalyst, concentration, temperature and particle size. All chemical reactions result in changes of energy whether that it through light, sound and of course heat. When energy (heat) is released from a reaction into its surroundings, it is called an exothermic reaction. However, on the hand when heat is absorbed it is called an endothermic reaction.
3 The extended experimental investigation requires one to “design and make a pack which when operated will produce hot or cold temperature.” The group chose to attempt to produce an instant cold pack for the experiment. An instant cold pack does not require refrigeration and can be stored for months and be able to produce cold temperatures anywhere, anytime. They are quick and easy to use, consisting of two or three compartments separated by breakable barriers.
The compartments contain various chemicals which when the barriers are broken combine together resulting in an endothermic reaction. Instant ice packs are commonly made from ammonium nitrate and water.4 The reaction is not reversible and therefore can only be used once.5 Ice packs in generally are used as a technique to care for pain, injury and the discomfort of joints and muscles. They play a crucial part in the first step of the treatment for sprains, strains, muscle pulls and other such injuries. 6 Ice packs are also commonly used in the rehabilitation of injuries and other long term chronic problems (eg. arthritis). If used correctly and immediately after an incident occurs, it can reduce swelling as well as tissue damage, blood clots, inflammation and muscle spasms.
The pack can also assist in the reduction of pain by numbing the affected area. The cold temperatures increase the flow of nutrients, assist in waste removal, increases strength and encourage healing; essentially, it means one will heal faster. Furthermore, they constrict blood vessels round the affected area and cools surrounding tissue. This slows blood flow as well as cell metabolism, which can decrease the chance of hemorrhage and even cell death in serious cases. To ensure a quick recovery follow the R.I.C.E.R principle: Rest – Avoid movement to reduce further damage.
Ice therapy – Cools tissue, and reduces bleeding, swelling and pain. Ice for 20minutes every 2 hours. Compression – Reduces bleeding and swelling.
Elevant injury – Reduces bleeding and swelling. Refer to a doctor/physiotherapist – full recovery more likely7
Normal frozen gel cold packs and the ordinary bag of ice can range anywhere between -17-0°C. This can actually be causing the body more harm than good resulting in freezing of the skin. In extreme cases where the ice pack has been let on for extended periods of time, the cold temperatures can possibly lead to frostbite and nerve palsy.
To ensure this does not occur it is recommended that the ice pack is wrapped in something such as a towel to create a barrier between the skin and the pack. It is also recommended that the pack does not stay on for longer than 20 minutes and to allow the skin to recovery between treatment a 1-2 hour break be is necessary. It is said that the safest temperature for treatment ranges between 7-11°C8,9. Therefore to create an effective instant cold pack it must reach between 7-11°C and stay at a reasonable temperature for 20 minutes. Aim:
To design and create an effective instant cold pack by using selected chemicals to produce an endothermic reaction. The reaction is required to produce cold enough temperatures to support an injury and remain cold over a period of time. To be classified as an effective instant cold pack it needs to remain at a reasonable temperature (safely regulated output: 7-11°C) for 20 minutes. 10,11 Hypothesis:
It was hypothesised that ammonium nitrate would generate and remain at the lowest temperature out of the five different chosen chemicals. This was supposed as various sources suggested ammonium nitrate as a common instant cold pack ingredient; however, the concentration and chemical to water ratio required was
The various risks were taken into consideration and appropriate action was put into practice. All equipment was collected and calculations regarding the amount (0.05 moles) of the required chemicals were made (see next page). The 0.05 moles of each chemical was weighed using a glass dish, spatula and electronic scales. Breakers were then filled with 20 millilitres of water and the temperature of the water was taken. The room temperature was also recorded. The chemicals were added into separate breakers and the temperature was recorded every two minutes over a 30-minute period. After performing the tests, the two best outcomes (seen in graph 1 and table 1) were ammonium nitrate and potassium nitrate. These two chemicals were tested further by being mixed together at different ratios, including 1:1, 3:1, 1:3. The same method was used however, temperatures were recorded every two minutes over a 20-minute period and 40 millilitres of water was used instead of 20.
Calculating amounts of Ammonium Nitrate and Potassium Nitrate for the various ratios. 1:1 = 0.05 molar concentration of Ammonium Nitrate: 0.05 molar concentrate of Potassium Nitrate4 grams of NH4NO3: 5.05 grams of KNO3 3:1 = 0.075 molar concentration of Ammonium Nitrate: 0.025 molar concentration of Potassium Nitrate6 grams of NH4NO3: 2.5 grams of KNO3 1:3 = 0.025 molar concentration of Ammonium Nitrate: 0.075 molar concentration of Potassium Nitrate2 grams of NH4NO3: 7.6 grams of KNO3
Ammonium nitrate (NH4NO3) as previously stated is the most common chemical to be used in the making of an instant ice pack.13 It is obvious from the results of the experiment that this would be practical as ammonium nitrate remained at the lowest temperature for the longest period (see graph 1). This can also be seen in graph 2 where the ratios with more or equal amounts of ammonium nitrate compared to potassium nitrate remain the lowest. When there was three parts of potassium nitrate and only 1 part of the ammonium nitrate is was at least 2°C higher at any given time compared to the other two ratios. Therefore, it is evident that a reaction with ammonium nitrate absorbs the most heat resulting in the coldest temperatures.
Ammonium nitrate is a salt, just like many other chemical including sodium chloride (common table salt) which was used in the first tests of the experiment. Salts contain ions, which are charged particles. When a positive ion is attracted and comes into contact with a negative one it forms crystals. The reaction of ammonium nitrate and the absorption of heat can be broken down into two step, both of which include energy changes. The first step requires a lot a heat which is used to break the bond between the ions separating the solid crystal. The energy (heat) required is absorbed from the surroundings. The first step can be seen below. Step 1: NH4NO3 + Heat NH4+ + NO3-
The second step involves the water. The water molecules are attracted to the positive and negative ions and therefore attach themselves. This process releases energy (heat) into the surrounding. The second step can be seen below. Step 2: NH4+ + NO3- +H2O NH4+ (H2O)x + NO3- (H20)x + Heat Even though during the second step heat is released into the surroundings the reaction is still considered to be endothermic. This is because more heat is involved in the first step, absorbing energy from the surroundings. Approximately six kilocalories per mole of ammonium nitrate is absorbed. This leaves the environment colder.
The concept called entropy is what is believed to be the reason why when ammonium nitrate reacts with water it spontaneously gets cold. Endothermic reactions such as NH4NO3 + H2O happen spontaneously when the reaction permits a large increase in entropy.14Entropy is the measure of the disorder of a system.15 Commonly chemical arrangements change from being orderly to “unorderly”. Nature can tend to change and increase the amount of disorder and therefore entropy. When this occurs it has the trend to release heat.
When entropy is at a high enough level, it can overrides driving the heat flow essentially backward. In terms of instant cold packs, the ingredients are waiting patiently in separate compartments in a highly ordered state. The water is clean and pure and the ammonium nitrate ion solid crystals are in an ordered pattern. However, this all changes when the barriers are broken and the ammonium nitrate dissolves in the water. The charged ions scatter and dissolve throughout the water. The water is now said to be impure and polluted and the system went from being ordered to disordered. The reaction is therefore considered to be partly driven by this increase in entropy.16 To compare the created instant cold pack against a traditional cold pack the temperature was recorded of a normal frozen cold pack in a wet towel over a period of 20 minutes on 2 minute intervals.
The results can be seen in table 3 and graph 3. There is also a comparison graph (graph 4) to highlight the differences between the normal cold pack and the ammonium nitrate and potassium nitrate with the 3:1 ratio. It can be seen from that graph that the created cold pack did not reach as low of temperatures as the normal cold pack with an approximate average difference of 10°C. Even though the instant cold pack may not have been as cold it is convenient and can be used when ice/freezer may not be available.
As previously mention in the introduction just because the normal cold pack is the coldest does not mean it is the best. Just like the commercial cold packs (one shown figure 1, appendix 3 which reaches -4°C in 5 seconds) the normal pack falls into the temperature range that may do more harm than good (-17-0°C). The normal cold pack does not come out of
this range until approximately the 12 minute mark. On the other hand, the created instant cold pack is in the safe output temperature range (7-11°C) and remains at a reasonable temperature for the required time period.
Furthermore it is seen in graph 4 that both the temperatures of the normal and instant cold packs increase in a similar trend. There were possible errors that could have occurred during the experiment and if it was to be conducted again more overall care would be taken. When measuring amounts, weighing the various chemicals and taking temperatures there is room for marginal human error.
Also due to there only being three members of the group and five beakers containing water and the chemical that all needed temperatures to be recorded at the same time; this caused two members to be juggling to record two beakers each as well as someone taking the time. This would have had an effect on the results. Furthermore, the person reading the thermometer was not constant as different people read the thermometer slightly different. However, it would have only been a very little difference and have no significant effect on the recordings although it is worth noting.
There are various aspects that could be changed to improve the final results. The main one includes providing the reaction with some kind of packaging and insulation as well as breakage inner compartments. During the experiment, the reaction took place in a glass beaker which theoretically is only an endothermic reaction and not a instant cold pack. To transform it into a usable instant cold pack an outer bag made of thick, strong plastic containing water has a smaller, second weaker bag encloseing the chemical inside.
When done correctly the inner bag should break when a force is appealed (eg. a punch) causing the inter bag to break releasing the chemical into the water. The reaction can then take place. Further testing could go into finding if changing the substance in the big and small bag has an effect on the temperature outputted. Further testing and future investigations could go into discovering the effects and outcomes between using group one elements compared to group two. In addition, the concentrations of the chemicals could be further investigated alongside varying the amount of water. Research could also go into making it into a gel instant cold pack so it could be easily mounded to the patients affected area. The effect of room temperature could also be studied.
In conclusion, the aim was met in designing and creating an effective instant cold pack by using selected chemicals to produce an endothermic reaction. Even though the pack did not remain within the safety regulated output temperature of 7-11°C for the whole 20 minutes, it still was at a reasonable temperature to be beneficial; essentially, it would be better than doing nothing.
The created instant cold pack was compared to a normal frozen cold pack. The normal pack reached colder temperatures averaging approximately 10°C colder than the created pack over the period of time. However, it was discovered that just because it is the coldest does not necessarily mean it is the best. There are potential risks with cold packs reaching temperatures below 0°C. The combination of ammonium nitrate and potassium nitrate at a ratio 3:1 was found to produce the coldest temperatures for the longest. Overall ammonium nitrate proved to be the most effective individual chemical.
The process in which it absorbs heat involves two steps; one being that is breaks into ions and the second that the water molecules are then attracted to these charged ions. Even though the second step outputs heat, the first step absorbs more energy causing it to be an endothermic reaction and therefore cold to touch. If the experiment was to be conducted again more care would be taken to preventing possible errors. Further investigation would focus on packaging and insulation as well as the effects of the groups of elements and the concentrations of the chemicals compared to amount of water.
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Wear safety glasses. Do not allow the solid to come into contact with combustible materials. Wear safety glasses. If the solid is very finely powdered you may need to use a fume cupboard to prevent any powder being inhaled; otherwise it should be safe to handle this material in the open lab. Wear safety glasses.
Wear safety glasses.
Wear safety glasses if local rules require them.
Eye contact: Flush the eye well with water. If irritation persists, call for medical help. Skin contact: Wash off with water. If swallowed: Wash out the mouth with water, if conscious, and call for medical help, Eye contact: Immediately flush the eye with water. If irritation persists, call for medical help. Skin contact: Wash off with soap and water.
If swallowed: Call for medical help if the amount swallowed is not trivial.