## Surface will keep constant during the experiment. To

Surface area of Alka-Seltzer tablet – this variable I will keep constant during the experiment. To ensure that the experiment is fair. I will do this by making sure that when I investigate each temperature, I will keep the surface area of the Alka – Seltzer tablets the same Volume of tap water used – this variable I will keep constant during the experiment. To ensure that the experiment is fair. I will do this by making sure that when I investigate each temperature, I will keep the amount of tap water used the same.  Temperature of the tap water – this is the variable I have chosen to investigate.

Reactions can be made to go faster or slower by changing the temperature of the reactants. I will measure the temperature of the tap water by using a thermometer. Number of Alka-Seltzer tablets used – this variable I will keep constant during the experiment. To ensure that the experiment is fair. I will do this by making sure that when I investigate each temperature, I will keep the number of Alka – Seltzer tablets the same. OUTPUT VARIABLES There are three main output variables that will change as a result of my input variable (temperature). The first one is time.

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This will change, because as the temperature increases, the rate of reaction will speed up making the time less. The second output variable that is changed, as a result of my input variable is the amount of bubbles produced. This will change, because as the temperature increases, the rate of reaction will speed up causing more bubbles more quickly. The last output variable that will change, as a result of my input variable is the amount of heat produced. This will change, because as the temperature increases, the rate of reaction will speed up causing the tablet to produce more heat.

The output variable that I am going to measure is time. I decided to do this, because it is the only one that I will be able to measure with the highest amount of accuracy possible. The other two would be too difficult to measure using only the equipment available to me at school. PRELIMINARY WORK I carried out some preliminary work to help me to decide how to approach the experiment. I decided to investigate the rate at which Alka – Seltzer tablets react in different temperatures of water. In the experiment I used both direct heating of the beaker and a water bath to heat the tap water.

This allowed me to choose the method, which I thought was best. I decided to use the water bath, because I found that it maintained the temperature better. I then had to decide what volume of water to use. I did this by taking one temperature (I chose 40i?? C) and reacting an Alka – Seltzer tablet with it. Here are the results I obtained: TI decided to use 100ml for a couple of reasons.

Firstly because I am using a 250ml beaker, the height of the water has to high enough for the tablet to react properly, therefore 50ml or 20ml is not a sufficient volume. Secondly if I chose 150ml then the reaction may take place too quickly, therefore the results I get may not be very accurate. Now that I have decided what method of heating and what volume of water to use, I can now get 1 reading for each temperature, so that I can plot a graph to help me with my prediction. Here are the results I obtained:

For the actual experiment, I have decided to do five replicates. An Alka – Seltzer tablet will be dropped into the water at different temperatures and the rate of reaction will be timed. For each temperature I have chosen to do five replicates, so that I can get more accurate results. The temperatures that I am going to investigate are 20i?

Rate of reaction is how fast a reaction is going and how long it takes to complete. It is not always just enough to know that a reaction is fast or slow. For example, in a factory that makes products from chemicals, the chemical engineers need to know exactly how fast each reaction is going, and how long it takes to complete. In other words, they need to know the rate of reaction. Rate is a measure of the change that happens in a single unit of time. Rates can be measured in many different ways.

They can be measured at the rate at which a reactant reacts, also at which the product forms. It can also be measured by the time taken for a tablet to dissolve. This is how I am going to measure the rate of reaction in this particular experiment. There are many different variables that can effect the rate of reaction. A reaction can be made to go faster or slower by changing the concentration of a reactant. A reaction can also be made to go faster or slower by changing the temperature of the reactants. In many reactions, one of the reactants is a solid.

Changing the surface area of the solid can also make a reaction go faster or slower. A reaction can also be made to go faster or slower by changing the volume of water used. The rate of reaction depends on how many successful collisions there are in a given unit of time. A collision causes particles to react with each other. The collision must have enough energy for the particles to react together. If there are lots of successful collisions in a given period of time, then the rate of reaction is faster. In other words, the reaction goes quickly, therefore its rate is high. If there are not many, its rate is low.

In a successful collision bonds are broken (this needs energy). Also new bonds are formed (this releases energy). The more successful collisions there are the faster the reaction. The variable I have chosen to investigate is temperature. When reacting substances are heated, the particles take in energy. They move faster, which means they collide more often and with more energy. So there are more successful collisions, therefore the rate goes up. Water can be both hard and soft. Hard water contains calcium hydrogen carbonate. On heating this compound breaks down to form calcium carbonate which is insoluble.

Hardness caused by calcium hydrogen carbonate is called temporary hardness, this is because it can be removed simply by boiling the water. Hardness caused by other compounds is called permanent hardness because boiling does not affect it. Therefore the results from my experiment may be unreliable at the hottest temperatures.

BIBLIOGRAPHY  Complete chemistry (by Rose Marie Gallagher and Paul Jugram) * Internet HYPOTHESIS As the temperature increases so does the rate of reaction. However at higher temperatures the pattern will break down giving unreliable results and the trend in the graph will show this.

Therefore the Alka – Seltzer tablet dropped into the hottest water may give unreliable results. I think this because the water I am using is tap water, which I know contains temporary hardness. Therefore at about 60i?? C the tap water will start to turn to soft water, this may alter the pattern of the results making them unreliable. Also increasing the temperature of the reactants can increase the rate of chemical reactions. This is shown in the results of my preliminary work. PREDICTION From my scientific knowledge I know that as the temperature increases so does the rate of reaction.