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4. Discussion


4.1 Key Findings


We found out that by changing the ratio of water and salt, the results could be drastically different, with the graphs being way different from each other. When pure water is heated, the graph will show an increase in temperature until the water reaches boiling point. As for us, the graph topped at the temperature above pure water, where the temperature leveled off. This tells us that the boiling point is that temperature where the graph leveled off.


For the freezing part, the graph when off the scale, as the water was cooled down so rapidly, the graph did not level out at a certain temperature. Instead, it kept on going down, which means the freezing temperature was greatly affected, or it could mean the sensor node was in contact with the side of the mug, which would have been very cold.

4.2 Explanation of Key Findings

 Water boils when the molecules are able to overcome the force of the air pressure that is keeping them from going into the gas phase. When salt or other impurities is added, sodium chloride for instance, it breaks down into sodium and chlorine ions. These ions change the intermolecular force between the molecules.  In addition to affecting the hydrogen bonding between water molecules, there is an ion-dipole interaction to consider. Every water molecule is a dipole, which means one side (the oxygen side) is more negative and the other side (the hydrogen side) is more positive. The positively-charged sodium ions align with the oxygen side a water molecule, while the negatively-charged chlorine ions align with the hydrogen side of a water molecule. The ion-dipole interaction is stronger than the hydrogen bonding between the water molecules, so more energy is needed to move water away from the ions and into the vapor phase. Even without a charged solute, adding particles to water raises boiling point because part of the pressure the solution exerts on the atmosphere now comes from solute particles, not just solvent (water) molecules. The water molecules need more energy to produce enough pressure to escape the boundary of the liquid. The more salt (or any solute) added to water, the more you raise the boiling point. 

 Freezing point depression occurs when the freezing point of a liquid is lowered by adding another compound to it. The solution has a lower freezing point than that of the pure solvent . For example, the freezing point of seawater is lower than that of pure water. The freezing point of water to which antifreeze has been added is lower than that of pure water.

4.3 Evaluation of Hypothesis

Our hypothesis is that impurities will affect the boiling and freezing point, but only to a certain extent as when water reaches saturation, no more impurities can be dissolved. However, our experiment shows that there is no limit, and it is backed by our background research. The effects of impurities on water’s freezing and boiling point can be recorded and  used as evidence.

4.4 Areas for Improvement
As we were using an induction cooker to heat the water, the heating graph was not consistent as the temperature was always varying. The induction coil was turned on and off overtime automatically to prevent it from damaging itself. Even at the highest setting, the coil was turn off at least 10% of the time. Thus, we got a not so smooth graph. As for the cooling part, the sensor node might be in contact with the cold metal side of the mug, and the temperature recorded might be lower as the mug was in direct contact the nitrogen

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