# The two independent variables - Sample Essay

Contents Introduction Variables Equipment Preliminary experiment The results for the preliminary experiment. Evaluation of preliminary Justification of Method: Main experiment – changing the surface area. Results for surface area. Graphs for surface area. Conclusion Main experiment – changing concentration. Tables for concentration. Graphs for concentration. Scientific explanation Evaluation of Range Bars: Gradients Surface area Concentration – Evaluation Evaluation of procedures Evaluating data Reliability of Conclusion Introduction.

The rate of a reaction is a measure of how slow or fast the reaction happens. If the chemical reaction is too slow, it would be harder to see a reaction. The rate is measured from the change, which happens in a single unit of time. To find out the rate of reaction one needs to: 1. Look how quickly a product is formed 2. Increase the concentration 3. Work out the collision theory 4. Increase the surface area, and 5. Increase the temperature There are several ways to measure the rate of reaction. You can measure the rate at which a product is formed; or you can measure the rate at which a reactant is used up.

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The PH, concentration of reactants, surface area, and enzymes, such as the use of catalysts, are all factors which may change or affect the rate of a reaction. I have decided to change the mass of the calcium chips, and the concentration of the hydrochloric acid, as we have adequate equipment to carry out this experiment safely and accurately. The reaction between hydrochloric acid, and calcium carbonate (marble chips) is one example of which carbon dioxide gas is produced: CaCO3 (s) + 2HCl (aq) i CaCl2 (aq) + H2O (l) + CO2 (g).

In this reaction, carbon dioxide is the easiest substance to measure. This is because it is the only gas in the reaction. It bubbles off, and can be collected in a gas syringe, where its volume is being measured. Other reasons why the reaction is right, is that we can change the surface area of the calcium carbonate, and change the concentration by changing the hydrochloric acid. By changing these two factors, we can see how fast these reactions take place. If a reaction is too fast, it will become too difficult to read, such as a firework exploding.

Other reactions are far too slow; these will also be difficult to read, as reading them will be too time-consuming. However, this reaction happens at a correct speed; not too fast or too slow. This is ideal as you can get the reading, and repeat the investigation again to make it more reliable. Variables The two independent variables of this study are concentration and surface area. The dependent variable is the volume of gas. The control variables are the mass of calcium carbonate, as it could affect the speed; because it can increase or decrease the speed of the gas.

We changed this by changing the control variables such as the volume of acid, and the mass of calcium carbonate. The concentration of the acid is a control variable, as it might affect the rate of a reaction. We measured how much hydrochloric acid for each experiment, and we measured it on eye level. We also controlled the temperature by using a thermometer, this is done to make sure that the temperature of the hydrochloric acid for every experiment was consistent. We also used the same scientists to fulfil the same roles to ensure that no variations in the experiment.

Equipment The equipment I used to carry out the experiment was: 1. Measuring Cylinder: -This equipment was the best choice for my experiment, because we had to measure the exact amount of hydrochloric acid to get accurate results. It is accurate because, it measures to 100ml. 1. Pipette -To make sure the volume of acid used was as accurate as possible. The way we measured the acid was at eye level from the bottom of the meniscus. 1. gas syringe -To measure the volume of carbon dioxide gas produced.

The syringe was precise because it measured volume in 1ml divisions. Throughout this reaction, the carbon dioxide is colourless so without it I would have problems measuring and observing the reaction, so if a substance was added to give the carbon dioxide a colour, my final results might not be reliable. I have researched that using a gas syringe is a lot more efficient, than using a measuring cylinder as problems may occur with the air bubbles. 1. The electronic balance – We used to measure the amount of calcium carbonate we would need for each experiment.

The balance is measured in grams (g) We used this equipment to ensure the experiment is precise, because the electronic balance is measured to 3 decimal places. This is helpful as I am using a mass of 0. 5grams. 1. The digital stop clock -We used the stop clock to time the length of the experiment and to make sure that we didn’t go over the amount of time set to do each repeat. There is a start and reset button to start the timer and a stop button to stop the timer, which makes it more easy to use.

The digital stop watch is also precise because it measures to hundredth seconds which helped us accurately record the volumes of gas at our set intervalsand making the experiment a fair test as every measurement was taken at certain time. 1. Stand clamp: -We used the stand clamp for safety reasons. We must ensure that the gas syringe and the flask, with the hydrochloric acid are connected to each other. They must be stable so they do not tip over. This is because it may affect the results, and if the acid spills, it could be expensive to replace a new one and same goes with the gas syringe.

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