- Concentration of the reactants -The more concentrated the solvent, the more particles are present and the greater the chance of a collision taking place. In diluted acids, they are fewer particles so the chance of collisions occurring is reduced meaning it will take more time for a reaction to take place. Therefore if concentration is increased, the reaction rate also increases. Amount of the reactants -It is important to keep the amount of reactants constant in the experiment because as the reactant is used up, so the reaction is slowed down. For instance if you use 50ml in the first experiment and 53ml in the second it would not be a fair test there would be more liquid for the solid to react with in the second experiment causing the reaction time to increase.
Calcium carbonate (CaCO3)
Calcium carbonate is a white solid, found in nature as limestone, marble, and chalk. It is a valuable resource, used in the making of iron, steel, cement, glass, slaked lime, bleaching powder, sodium carbonate and bicarbonate, and many other industrially useful substances.
Hydrochloric acid (HCl)
Hydrochloric acid is a highly corrosive solution of hydrogen chloride (a colourless, acidic gas) in water. It has many industrial uses, including recovery of zinc from galvanized scrap iron and the production of chlorine. It is also produced in the stomachs of animals for the purposes of digestion.
Rate of reaction
During a reaction at constant temperature the concentration of the reactants decreases and so the rate of reaction decreases.
The rate of reaction is at its greatest at the beginning of the reaction and it gradually slows down
Collision Theory
Collision theory explains how chemical reactions take place and why rates of reaction alter. For a reaction to occur the reactant particles must collide. Only a certain fraction of the total collisions cause chemical change these are called fruitful collisions. The fruitful collisions have sufficient energy (activation energy) at the moment of impact to break the existing bonds and form new bonds, resulting in the products of the reaction. Increasing the concentration of the reactants and raising the temperature bring about more collisions and therefore more fruitful collisions, increasing the rate of reaction.
Prediction
Using my preliminary experiment and my background knowledge I came up with a prediction. I think that the less concentrated the hydrochloric acid is the longer it will take for it to react with the calcium carbonate. I think this because the higher the concentration of the hydrochloric acid is, the higher the chance of the bonds breaking because the stronger the hydrochloric acid is the more energy the molecules have so they travel with more force which means the bonds break. If the molecules do not have much energy they will just bounce of the bonds harmlessly. The energy is needed to break the bonds and get the reaction started. Rates of reaction can be changed not only by catalysts but also by changes in temperature and by changes in concentrations. Raising the temperature increases the rate by increasing the kinetic energy of the molecules of the reactants, thereby increasing the number of collisions per second and the likelihood of transition states being achieved. Increasing the concentration can also increase the reaction rate by increasing the rate of molecular collisions. Concentration of the acid is higher so there is more chance of the particles colliding.
Fair Test
To make this a fair test I will need to keep all other variables the same apart from the concentration of the hydrochloric acid. This means the weight of marble chips should stay the same as well as using the same number of chips used; the temperature of the experiment should be the same throughout the experiment so that there is an equal amount of energy in each separate test; the amount of hydrochloric acid should also stay the same; the same measuring equipment should be used when measuring out thing so that there is no change in volume.
Method
I am going to change the concentration of the hydrochloric acid to 5 different concentrations 100%, 80%, 60%, 40% and 20%.
100% = 50cm3 hydrochloric acid
80% = 40cm3 hydrochloric acid and 10cm3 water
60% = 30cm3 hydrochloric acid and 20cm3 water
40% = 20cm3 hydrochloric acid and 30cm3 water
20% = 10cm3 hydrochloric acid and 10cm3 water
I am going to time how long it takes for each different concentrated acid to react with the calcium carbonate with a stopwatch. I am going to try and make my investigation as fair as I possibly can by repeating the process as many times as I can and get an average by adding them all together and dividing by the number of results I get. Also I will use the same amount of calcium carbonate which is 2.0grams and the same amount of liquid which is 50cm3. Each time I start my experiment I will make sure the beaker is clean and dry. Hopefully it will be safe because I will wear safety spectacles and take as much care as possible while walking with any beaker, substance etc. in my hands so the calcium carbonate or hydrochloric acid will not come into contact with anything else than each other. I am going to
Measure 50cm3 hydrochloric acid, add it to 2.0g of calcium carbonate then time the reaction rate.
I will measure 40cm3 of hydrochloric acid and 10cm3 of water add the calcium carbonate and time the reaction rate.
I will measure 30cm3 of hydrochloric acid and 20cm3 of water add the calcium carbonate and time the reaction rate.
I will measure 20cm3 of hydrochloric acid and 30cm3 of water add the calcium carbonate and time the reaction rate.
I will measure 10cm3 of hydrochloric acid and 40cm3 of water add the calcium carbonate and time the reaction rate.
I will repeat this process as many times as I can.
During the preliminary experiment I came across some difficulties. When I added the calcium carbonate some fell over the side so it was not a very accurate 2.0g. Due to the time of our lesson I had to complete the practical over 3-4 lessons so the room temperature may have been different so that may have changed the reaction rate a little.
Main Experiment Results
Graphs to show results are in the graphs section of this coursework
Conclusion
My graphs show a “strong positive correlation”, as the concentration on the x-axis is increases so does the amount of gas on the y-axis this means that when there is a higher concentration of acid in the tube there is more gas produced, this shows my prediction:
‘The higher the concentration or the hydrochloric acid
Quicker the rate of reaction will be.’
proved to be true, as the higher concentrations produced more gas, if there is more gas being produced over a certain period of time then the rate of reaction must be increasing also.
Evaluation
In my opinion my experiment was conducted well and I received fairly accurate results. There are a few things that could have been improved in my experiment; the first was the fact that I may have got trapped air bubbles in the measuring cylinder, which would have given some tests a slight advantage. Also the fact that I had to stop and start the stopwatch while taking the readings made it hard to get accurate results each an every time. An improvement to my experiment would be to have some help from a partner. The accuracy of my experiment was not great, it is hard to add the marble chips, hold the tube and start the time watch all at once. This would have affected the accuracy of my results. My results aren’t very reliable because I can’t do three things at once. Another improvement to make my results more reliable and accurate would be to pick another variable like temperature and see the result that has on the rate of reaction.