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calcium hydorxide in water experiment

By Hasan-Rabab-11S Oct 22, 2014 1848 Words
In this experiment I will investigate the temperature of 50cm³ of water before and after I have added calcium chloride, I will gradually increase the amount of calcium chloride by 1 gram to see if there is a significant change.

When Calcium Chloride is mixed with water it performs an exothermic reaction which makes new bonds between the salt (Calcium Chloride) and the water. This will therefore make the solution of the reaction increase in temperature.

Exothermic reactions transfer energy to the surroundings. Endothermic reactions take in energy from the surroundings. Reversible reactions are where the products can react to remake the original reactants. If the forward reaction is exothermic, the reverse reaction is endothermic.

Energy is absorbed to break bonds. Bond-breaking is an endothermic process. Energy is released when new bonds form. Bond-making is an exothermic process. Whether a reaction is endothermic or exothermic depends on the difference between the energy needed to break bonds and the energy released when new bonds form. If more heat energy is released when making the bonds than was taken in when they broke, the reaction is exothermic.

Endothermic reactions are reactions that transfer energy to the surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to become hotter. The temperature increase can be detected using a thermometer. Some examples of exothermic reactions are: burning

neutralisation reactions between acids and alkalis

These are reactions that take in energy from the surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to get colder. The temperature decrease can also be detected using a thermometer. Some examples of endothermic reactions are: electrolysis

In this experiment the calcium chloride will be my independent variable as I will start by using 1 gram and go up to 5. The dependant variable is the temperature of water used before and after adding the salt. The control factors are the amount of water I use, size of the beaker, size of the polystyrene cup, the room I do the experiment in and weather or not the windows are open.

Hypothesis

My hypothesis is that as the amount of calcium chloride is increased the temperature of the water will and that all the calcium chloride will dissolve, also that when I draw my graph there will be a positive correlation. I know this because when Calcium Chloride is mixed with water it performs an exothermic reaction which makes new bonds between the salt (Calcium Chloride) and the water. This will therefore make the solution of the reaction increase in temperature.

Factors

Factors that could affect this experiment are whether or not the room is well ventilated, this could affect the experiment because if the windows are open during one reading and are closed during another it will change the room temperature and the temperature of the water, this can be prevented by making sure that the room is well ventilated during all the readings. Another factor that could affect the temperature of the salt solution is the temperature of the water before you add the salt, if the water is cooled or heated it could have an effect on the temperature after I add the salt, this is why I used distilled water that was at room temperature. Finally the amount of salt that is used is very important, if I accidentally measure more than I am meant to, for example 1.2g instead of 1g the results would be different and it would not be a fair test. That is why I used he electric weighing scale that is to 2 decimal point and very accurate to ensure a fair test. Equipment list

Glass beaker (150cm³)
Weighing boat
thermometer
polystyrene cup
measuring cylinder
weighing scale
spatula
weighing scale
calcium chloride
distilled water
electric weighing scale
thermometer

Equipment justification

The measuring cylinder is used to measure 50cm3 of distilled water and then pouring it into the polystyrene cup, I chose to use this because it is very accurate as it has many dashes to show you how much water there is. The weighing boat is to ensure that none of the salt is spilled when I am weighing the amount that I need. The thermometer is what I used to take the temperature of the water before and after I added the salt and I also used it to stir the salt. I will put the polystyrene cup into the beaker so it help the beaker balance and not tip over due to the weight of the thermometer, this made the experiment a lot easier and safer, it also stopped the thermometer from sliding around in the beaker. I used the spatula to scoop the calcium chloride and place it into the weighing boat. The electric weighing scale is very accurate as it is to 2 decimal places and can ensure that you measure exactly the amount of salt that you need. I chose to use calcium chloride because it will have exothermic reaction which will create heat which means that temperature change will be a positive number, but the other salt would have created and endothermic reaction and the temperature change would be negative so I would have to be dealing with negative numbers when making my tables and graphs and finding out the average change in (J) and because it is in negative it would be a lot easier to make a mistake. That is why I chose calcium chloride. 1. Firstly I measured 50cm³ of distilled water using a measuring cylinder and poured it into a polystyrene cup which I then placed into a beaker. 2. Next I took a thermometer and took the temperature of the water which was around 22 degrees. 3. After that I used a measuring boat and a electric scale to measure exactly 1 gram of calcium chloride and then tipped it into the same cup of water. 4. I used the thermometer to stir the water with the calcium chloride in it until all of it had dissolved and it hard turned into brine. 5. Then I had to keep a close eye on the thermometer and record the highest temperature that the brine reached. 6. After I recorder the before and after temperatures I took the polystyrene cup out of the beaker and rinsed it out and repeated the same test again doing exactly the same thing and still using 1 gram of calcium chloride. 7. Now that I had done this twice with one gram I would do the same but now with 2 grams of salt and then going up by one gram until 5 grams, still repeating each measurement of salt twice. 8. I then took all my results and put them into a table and found the average temperature change and used it to make a graph. 9. Finally if I had any outliers I would do the experiment a third time for that specific measurement of salt.

Diagram

Risk assessment

Risk
Hazards
Probability
Prevention
Getting a salt in your eye
Could irritate eye and cause severe problems.
,4/10
Wear goggles at all time and do not throw the salts around or try to throw it at others. Thermometer or glass beaker breaks
Glass could cut someone and injure them.
,8/10
Be careful with the equipment and don't place the beaker or thermometer on the edge of your desk or anywhere unstable. Mixing chemicals
Could spill a chemical on another and make a harmful reaction. ,2/10
Make sure there are no other harmful chemicals nearby that could create a reaction and don't mes around in the lab. Salt (calcium chloride) on skin
Could irritate skin and cause a rash and itchiness.
,7/10
Some one could have a cut or very sensitive skin and the salt or brine could be irritant to them and harm them, be careful and thought full around other people, don't play with the salt. Water spillage

Easy for someone to slip on while walking.
,9/10
Ground could get slippery and become a hazard. Always keep paper towels around and be sensible while walking around with liquids. Results

Temperature change (°C)

Mass of salt (g)
Test 1
Test 2
Test 3
Average temperature (°C)
1
1.5
1.5

1.5
2
4
4

4
3
6
10
6
6
4
8
7.5

7.75
5
9
8.5

8.75

In my second experiment while using 3g I got 10, this seems very out of place compared to the rest of my results. This result is an outlier, that is why I had to do it a third time and when I did it a third time I got 6 which fits the pattern. When I got 10 I must have done something wrong such as added too much salt or too much water or too little, also I could have not read the temperature correctly.

Mass off salt (g)
Volume (cm³)
Average temperature change (ºc)
Energy (J)
1
50
1.5
315
2
50
4
840
3
50
6
1260
4
50
7.75
1627.5
5
50
8.75
1837.5

Energy change in (J) = 4.2J/g/ºc x mass of water in (g) x temperature change in (ºc) This is the formulae that I used to calculate the temperature change in (J)

Preliminary work

Results table

Formulae
Water cm³
Mass g
Initial temperature ºc
Final temperature
ºc
Temperature change
NaCl
25

25
1

3
21

21
21

20
0

-1
NH4Cl
25

25
1

3
21

21
20

18
-1

-3
CaCl2
25

25
1

3
21.5

21
23

25
1.5

4

In my preliminary I only used 1g and 3g of my salt and I also only did each experiment once. In my real experiment I used from 1g to 5g of my chosen salt and repeated each one 3 times to make sure my results were reliable and that I had a lot of results to make my graph more detailed and also to make it easier for me to identify any outliers.

I chose to use Calcium Chloride because when it is mixed with water it creates and exothermic reaction which means it creates heat unlike the other which create an endothermic reaction. The fact that the reaction made heat makes it a lot easier for me because it meant that I do not have to deal with negative numbers where I can easily make a mistake because the average temperature change will always be positive. Also my graph will be very simple as it will have a positive correlation and only be made up of positive numbers. Another reason why I chose calcium chloride is because the salt is made up of little balls and would make it easier for me to get and exact one digit measurement on the scale by just add or removing single balls of the salt, unlike the other salts that where powders and would not be as easy to handle and measure. That is why I carried on using Calcium Chloride and not one of the other salts provided.

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