The aim of this investigation is to find out the factors that affect the rate of reaction between limestone (calcium carbonate) and hydrochloric acid.
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Becki miller Rates of reaction coursework Aim The aim of this investigation is to find out the factors that affect the rate of reaction between limestone (calcium carbonate) and hydrochloric acid. Background information Rain water once was the purest form of water available but now it is often contaminated by pollutants in the air. Factories and power stations give out oxides of nitrogen and sulphur as pollution, this combined with atmospheric moisture creates acid rain and over a period of time dissolves things made of marble such as statues and building fronts, this is because the acid dissolves the calcium carbonate in the stone and when the solution evaporates it forms crystals in the stone, as the crystals grow they break apart the stone and the structure crumbles. This is called chemical weathering. The investigation will be a laboratory based version of chemical weathering to determine how different concentrations of acid affect the rate of reaction. Plan The following is the chemical equation for the reaction between calcium carbonate and hydrochloric acid. Calcium + hydrochloric -> Calcium + water + Carbon Carbonate acid chloride dioxide CaCO + 2HCl -> CaCl + H O + CO There are a few ways of measuring the rate of this reaction as shown in the following... 1. Measuring the mass of calcium carbonate lost. 2.
Powdered calcium carbonate Hydrochloric acid molecules are able to get to the calcium carbonate more easily and can collide with each molecule far more quickly, this speeds up the rate of reaction. Lump of calcium Carbonate Hydrochloric acid molecules have to break down the lump of calcium carbonate layer by layer which takes much longer and slows down the reaction speed. Method You will need... - 5 concentrations of hydrochloric acid ... * 0.10 molar * 0.50 molar * 1.00 molar * 1.75 molar * 2.00 molar - 75mg of medium sized calcium carbonate (5mg per experiment) - 1 gas syringe with rubber bung - 1 conical flask - measuring cylinder - electronic scales (to measure the mass of calcium carbonate) - Stopwatch - Clamp Stand Step 1- Set up the equipment in the list above as shown in the diagram on the following page. Step 2- Measure 20ml of hydrochloric acid and pour into conical flask. Step 3- Weigh 5mg of calcium carbonate and add it to the hydrochloric acid in the conical flask and quickly put the rubber bung in the top of the conical flask and start stopwatch. Step 4 - Time the reaction for 1 minute and read the measure on the gas syringe after 1 minute.
The line of best fit shows that as the acid concentration increases so does the rate of reaction this is because the ratio of acid to water is increasing, therefore increasing the number of acid particles in the solution. The graph also shows a positive correlation. Evaluation As I mentioned in my evaluation I had one anomalous result, this was the rate of reaction between 1.0 and 1.75 molar acid concentrations, in comparison to my other results the reaction rate should have shown a larger difference than what it did as there is a greater difference between the concentrations of acids used than the rest. For better accuracy there should be a larger range of acids used between 1.0 and 1.75, for example: 1.0, 1.1, 1.2, 1.3, 1.4 and so on. This could be done throughout in order to give far more accurate results. I think that there are many possible reasons for the anomalous result that I got, such as, tampered with acids, larger surface area of limestone (the different sizes of limestone may have become muddled up), there may have been a slight leak in the rubber bung and gas could possibly have dispersed into the surrounding atmosphere. The experiment could have been more accurate by using an electronic balance to measure the loss of mass rather than using a gas syringe to measure the gas given off by the hydrochloric acid and limestone.
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