The variable that I will change will be the temperature of the water that the Alka Seltzer is put in.

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SKILL P: PLANNING             Ibrahim Abu-Abdo

Statement of the problem:

The variable that I will change will be the temperature of the water that the Alka Seltzer is put in.

For my results I will measure the time taken for the Alka seltzer tablet to completely dissolve in water at different temperatures.

Input variables:

  • Varying surface area of Alka-Seltzer tablet, i.e. if cut into smaller pieces or crushed it will increase the surface area. (If the surface area is increased (more powdered) the rate of reaction also increases. This means that there are more collisions between the solid and liquid.)

  • Amount of tap water H2O used, i.e. volume (ml).

  • Amount of Alka-Seltzer tablets used, i.e. quantity of tablets. (one is used)

  • Number of times the solution is stirred. (If the solution is stirred more there are more collisions between the particles therefore the reaction is speeded up.)

  • Temperature of Water-°C. (As the temperature increases so does the rate of reaction. By increasing the temperature, particles move faster, i.e. they have more energy. So, they collide with more energy and more frequently.)

  • pH of Solution: Water has pH of 7 at 25°C. As the pH decreases, i.e as the solution increases in acidity, the rate of the reaction increases as well.

Output Variables:

Rate of reaction depends on all the 6 points I have stated above:

  • If the surface area of the tablets is increased by crushing, the particles around it in the solution will have more area to work on, and the rates of reactions will increase because there will be more collisions. Complete reaction will finish faster.

  • The more amount of water used as we increase the temperature, the quicker the tablets will dissolve because there will be more water particles to collide with. So the rate increases.

  • If the amount of tablets being used is increased for the same amount of water, i.e as concentration increases, rate will increase as well because there will be more collisions between particles.

  • If the water with Alka-Seltzer tablets are stirred during the reaction, then the rates of reactions will increase because the particles will be forced to make contact with each others and react much quicker, rather than take their time to make contact, and therefore the number collisions will increase.

  • If the temperature is increased, then the particles will move much faster because they have more energy in them and therefore vibrate a lot and they tend to collide with more energy, and so the number of collisions will increase.

  • As pH decreases, acidity in solution is high. This makes H+ ions in solution readily available for HCO3- ions in the tablets, hence making it fizz quickly forming carbon dioxide and water. So as pH decreases, the rate of reaction increases as well.

Preliminary Work:

I did this preliminary work using the following apparatus. The results obtained are tabulated below:

Apparatus:

  • 300ml beaker

  • Tap water

  • Alka-Seltzer Tablets

  • Thermometer
  • Bunsen Burner
  • Tripod
  • Heat mat
  • Gauze
  • Goggles

Diagram of the experiment:

                         

Method:

  • I set up the apparatus as shown in the diagram. I then placed a thermometer into the beaker which I already filled with 150ml of water. I then set the water to the required temperature by heating it (although I did not have to do this for the first temperature which was 20°C, where I just kept the water as it was without heating it). When the water reached the required temperature I placed an alka seltzer tablet into it, and as I did so I started the timer. When Alka seltzer tablet dissolved (just until the actual tablet was not visible anymore, even though there was still some white scum in the water) I stopped timing and wrote down the time gained in my results table.

  • A thermometer was placed in the beaker of water to measure the temperature (°C) of the water until the required temperature is reached. I made sure not to place it in the beaker while being heated.
  • The experiment will be carried out at different temperatures. A Bunsen on a roaring flame will be placed directly underneath the beaker to heat it with it being supported by a tripod and gauze.
  • One Alka-Seltzer tablet was dropped into the beaker at the required temperature. The time taken for the tablets to dissolve was timed and recorded. This was done as follows: The beaker will be removed from the gauze at a certain temperature and then an alka seltzer tablet was dropped slowly in the water in one hand and the stopwatch was set on in the other at exactly the same time. The time taken for it to dissolve was recorded.                                                                                                                             After doing so the beaker filled with alka seltzer solution was emptied and cleaned out thoroughly to make sure that it was not contaminated from previous attempt.
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  • This process of heating the water, dropping the alka seltzer tablet into it, timing how long it took to dissolve, cleaning out the beaker and re-filling it was repeated for each temperature twice.

  • Because of the beakers high temperature at some parts of the experiment I had to handle it using a clamp.

Here are the results that I obtained from this preliminary experiment:

Things I shall change for my final experiment

  • Instead of just measuring the water in the beaker, I shall measure water in a measuring cylinder to increase accuracy. I ...

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