My aim for this experiment is to investigate the solubility of salt

Like Hot tea can dissolve more sugar than iced tea, and warm water dissolves less oxygen than cold water. The maximum amount of any solute that can dissolve in a given amount of solvent is called its solubility, and this depends on temperature. The solubility's of gases always decreases with increasing temperature. For liquids and solids, solubility's generally increase with increasing temperature, as is the case with sugar in tea. This should work the same way with hot water and salt the hotter the water the more salt will dissolve.

Variables

For this experiment I would expect to have dependent variables, which are temperature of water, amount of salt before and after and time for each experiment. Fixed variables, the amount of water being heated, the amount of salt at the beginning and the time for each experiment.

Scientific Knowledge

Salts contain positive and negative ions, which are held together by the strong force of attraction between particles with opposite charges.

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When one of these solids dissolves in water, the ions that form the solid are released into solution, where they become associated with the polar solvent molecules.

H2O

NaCl(s)

Na+(aq)

+

Cl-(aq)

We can generally assume that salts dissociate into their ions when they dissolve in water. Ionic compounds dissolve in water if the energy given off when the ions interact with water molecules compensates for the energy needed to break the ionic bonds in the solid and the energy required to separate the water molecules so that the ions can be inserted into solution.

Apparatus

Measuring cylinder, a pair of scales, Bunsen burner, thermometer, stopwatch, spatula, stirring rod, water and salt.

Fair Test

To make this experiment fair I will make sure that the water is always 100 cubic centimetres, the heat of the water is precise; I will make sure of this by reading the thermometer correctly. I will make sure that I use exactly 5 grams of salt each time and I will repeate the experiment 3 times to get an average.

Safety

I will make sure that I wear my glasses throughout the whole experiment to protect my eyes. I will make sure that when I am not using the Bunsen burner I will put it on a yellow flame so that others can see it.

Method

100 ml of water were placed in a beaker.

Salt was added in 5g lots at each temperature.

The solid was stirred in with a stirring rod. When all the 5g had dissolved, another 5g were added. This carried on for 5mins.

When there was solid left on the bottom, which wouldn't dissolve, it meant the solution had become saturated. When the solution had become saturated at a particular temperature, the amount desolved was recorded and another temperature was done.

My results will be recorded like this.

Temp of water...Celsius

Expt

Mass of salt dissolved

1

2

3

ave

Results

Temp of water 20 Celsius

Expt

Mass of salt dissolved

1

5.2

2

5.1

3

5.3

Ave

5.2

Temp of water 30 Celsius

Expt

Mass of salt dissolved

1

5.7

2

5.7

3

5.9

Ave

5.7

Temp of water 40 Celsius

Expt

Mass of salt dissolved

1

6.7

2

6.6

3

6.8

Ave

6.7

Temp of water 50 Celsius

Expt

Mass of salt dissolved

1

13.1

2

8.2

3

8.1

Ave

8.15

I have chosen to ignore this because it is an anonymous result.

Temp of water 60 Celsius

Expt

Mass of salt dissolved

1

9.6

2

9.5

3

9.6

Ave

9.6

This graph shows the amount of salt dissolved at each temperature you can use this graph to find out how much salt would dissolve at different temperatures. E.g. 25 Celsius would dissolve 5.5 grams of salt dissolved in 5mins as I have drawn on the graph.

Conclusion

I believe that my experiments have gone rather well there was only one anonymous result, which was very clear so I felt that I had to ignore it because it would have ruined my results and conclusion. I felt that I did a fair test as I made sure that the water was always 100 cubic centimetres, the heat of the water was precise because I made sure I was reading the thermometer correctly, I made sure that I used exactly 5 grams of salt each time and I did 3 experiments for each temperature to find an average. It was also safe because I wore my glasses throughout the whole experiment to protect my eyes. I made sure that when I am not using the Bunsen burner I put it on a yellow flame so that others could see it.

I could have improved my experiment by doing more tests at each temperature to find a better average e.g. 5 times, this would have given me more precise results. I could have also have done an experiment for sugar and compared the two experiments, which would have made it more interesting to see which one dissolves quicker.