GCSE Chemistry Coursework

GCSE Chemistry Coursework

An investigation of how the concentration of hydrochloric acid affects the rate of reaction between hydrochloric acid and potassium carbonate K₂Co₃₍₃₎ + HCl ---à KCl_(0.9) + H₂O(1)+Co₂₍₉₎

Plan:

Introduction

Aim

Independent variables

Equipment

Prediction

Method

Results

Analysing evidence

Evaluation

Introduction:

In my coursework I’m going to investigate the rates of reaction, and the effect different changes have on them. The rate of reaction is the rate of loss of a reactant or the rate of formation of a product during a chemical reaction. There are five factors which affect the rate of a reaction, according to the collision theory of reacting particles: temperature, concentration of solution, pressure, surface area, and catalysts. I have chosen to investigate the effect of the concentration of hydrochloric acid on the rate of reaction. I’ve chosen this factor, because it would be easier to measure the concentration of hydrochloric acid and get more accurate results in my experiment.

Aim:

To investigate how the concentration of hydrochloric acid affects the rate of a reaction between hydrochloric acid and potassium carbonate.

Using my preliminary experiments I decided on using the following equipment:

1. Measuring cylinder

2. Stop clock

3. Measuring tube

4. Stick

5. Scales

Also I used following chemical components:

1. Potassium

2. Hydrochloric acid^-3

Prediction: If I double the concentration of hydrochloric acid, the rate of reaction will double or time will halve. If it won’t halve, I predict that if I increase the concentration of hydrochloric acid, the rate of reaction will increase and time taken for reaction to happen will decreases. In dilute acid, there are not so many acid particles. So there’s not much chance of an acid particle hitting a potassium atom. When the acid is more concentrated, there are more acid particles, so there’s more chance that the reaction will go faster. If solutions of reacting particles are made more concentrated there are more particles per unit volume. Collisions between reacting particles are therefore more likely to occur. For a reaction to occur particles have to collide with each other. Only particles with enough energy to overcome the barrier will react after colliding. The minimum energy that a particle must have to overcome the barrier is called the activation energy, or Ea. The size of this activation energy is different for different reactions. If the frequency of collisions is increased the rate of reaction will increase. However, the percentage of successful collisions will remain the same. An increase in the frequency of collisions can be achieved by increasing the concentration. The more successful collisions there are, the faster the reaction.

Concentration – If the concentration of a solution is increased there are more reactant particles per unit volume. This increases the probability of reactant particles colliding with each other.

Also there are some factors, which can affect the rate of reaction:

1. Temperature

2. Concentration

3. Surface area

4. Catalyst

Effect of a catalyst - A catalyst works by providing an alternative reaction pathway that has lower activation energy. Catalyst provides a reaction route of lower activation energy, however, a greater proportion of particles will have energy greater than the activation energy.

Method:

In my experiment there were some things, which I kept the same:

· Temperature + surface area of K₂CO₃;

· Volume of acid (0-50 cm³)

· Mass of K₂CO₃ (no more than 1g)

The first thing I’m going to do in my experiment is to make sure that everything in my experiment is safe and there’s no risk for me and other students. I’m going to wear white coat, goggles and generally be very careful when using equipment in the laboratory. After this, I will prepare all equipment I need. Then, I’m going to prepare my stop clock and start the experiment. I have decided, that during the experiment I will be changing the concentration of hydrochloric acid from 0.5 mol/dm³ to 2 mol/dm³ . I weighed out 1g of potassium carbonate into a 50cm³ beaker. I then measured out 50cm³ of 2 mol/dm³ acid into a measuring cylinder. I then added the acid to the potassium carbonate balls and at the same time started the stop clock. I then did the same experiment again to repeat and make sure the results were correct. I then varied the concentration of the hydrochloric acid. For 1 mol/dm³ I used 25 cm³ of acid and 25 cm³ of water, for the 0.5 mol/dm³ solution I used 12.5 cm³ of acid and 37.5 cm³ of water. I’m going to record all the results I get in the first experiment and then, I’m going to put them into my results table. Then, I’m going to do the same experiment the second time, in order to make my variables more accurate. Then, I’m going to calculate the average results and, according to them, plot the graph, which will help me to find if there’re any anomalies in my experiment. After all these procedures, I will be able to evaluate my experiment and analyze all mistakes and errors which could occur in the experiment. After this, I’m going to write about how I can improve my experiment.

Results:

The amount of hydrochloric acid (mol/dm^3)	Time taken (s) First experiment	Time taken (s( Second Experiment	Average time Taken (s)
0.5
1.0			36.5
1.5			16.5
2.0			7.5
The amount of hydrochloric acid (mol/dm^3)	The rate of reaction (g/s)
0.5	0.02*
1.0	0.03*
1.5	0.06*
2.0	0.13*

*-on the graph these results will be multiplied by 10, in order to make it easier to show them on the graph.

Analysis

According to the results I’ve gathered in my experiment I have plotted a graph. From my graph I found that as the concentration of hydrochloric acid increases, the time taken for the reaction to take place decreases. Therefore, the rate of reaction increases as the concentration of hydrochloric acid increases. I have proved this by choosing a variety of four concentrations of hydrochloric acid. The average time taken to end the reaction at 0.5 mol/dm³ was 48s. When the concentration was doubled, (1.0) the time taken was 36.5s, at 1.5 mol/dm³ it took 16.5s, and at 2.0 mol/dm³ the time taken was 7.5 seconds respectively. From these results I can see that the time didn’t halve. When the concentration was doubled from 0.5 to 1.0 mol/dm³, the rate of the reaction has changed from 0.02 to 0.03 g/s. This suggests that there was an anomaly in my experiment. There were several factors, which could cause this anomaly to happen:

· Lack of accuracy when measuring the mass of potassium carbonate

· Temperature

· Inaccuracy caused by human reaction

I’m going to explain each of these factors and suggest the ways to prevent them in my evaluation. Although the time of reaction doesn’t quite halve when the concentration of hydrochloric acid increases from 0.5 to 1.0 mol/dm3, when the concentration of hydrochloric acid increases from 1.0 to 1.5 mol/dm3 the rate of reaction doubles from 0.03 to 0.06. Also from 1.5 to 2.0 mol/dm3, the rate of reaction increases from 0.06 to 0.13, which shows that the rate of reaction is more than just doubled. This shows that my prediction was correct. Also, if we look at the graph we can see that from the point 0.5 to 1.0 the rate of reaction doubles. As the concentration of hydrochloric acid increases from 0.5 to 1.0 mol/dm³, the rate of reaction doubles from 0.5 to 1.0 g/s, which suggests, that the rate of reaction is directly proportional to the concentration of hydrochloric acid.

My graph shows, that the rate of reaction increases proportionally to the concentration of hydrochloric acid, and therefore is directly proportional to the concentration. On my graph I used a line of best fit, in order to show that. The line on the graph is straight, which shows this proportion. However, on my graph I have also showed my actual results and points, which came up as anomalies on this graph. Even so, my graph still shows that I was right in my prediction. I have predicted, that if the concentration of hydrochloric acid was doubled, the rate of reaction would double or time would halve. This graph gives me enough evidence to show, that as the concentration of hydrochloric acid doubles, the rate of reaction doubles as well, which proves that my prediction was correct.

Evaluation.

In my opinion the experiment was very successful.

Firstly I want to write about the quality and accuracy of my results. I kept a fair test and made sure I was using correct equipment in the appropriate way. I have also made sure the temperature, the surface area and mass of potassium carbonate (K₂CO₃ ) were kept the same during the whole experiment. I have also made sure I was using appropriate amount of hydrochloric acid for each experiment. Even though, there could be a small error caused by the human reaction, I made sure I was taking the readings from the stop-clock accurately. I’ve repeated my experiment, in order to find out the average results and make them more accurate. Also, when measuring the mass of potassium carbonate, I have always used the same scales and made sure they were always starting at 0g at the beginning. I’ve made sure I was wearing the white coat and goggles and made sure everything was safe.

From the graph and results table it is evident, that the average time of reaction increases as the amount of hydrochloric acid increases. From the results it can be concluded, that the time of reaction is dependent on the amount of hydrochloric acid being produced.

Overall, I have obtained fairly accurate results, which satisfied me, proved my predictions, and which also helped me to plot quite informative graph and results table. Also, I think I gave enough time in my experiment for the reaction to happen. However, as I was carrying out my investigation I noticed, that there were some problems with accuracy in my experiment, and that there were few things, which I could improve. The first thing I think I could possibly improve next time is measuring of the amount of hydrochloric acid more accurately. Slight differences could have caused some changes in time, which could slightly affect the rate of reaction. The second problem which could affect the time of reaction could be my own, human reaction. Although I tried to pay more attention when taking the readings from the stop clock, there were some slight changes. I can still improve on this, but my own reaction is one of the independent variables in this experiment, which I’m not able to change much. Also, my experiment took place in the chemistry laboratory. Although I’ve tried to keep the temperature in my experiment the same, there is a possibility, that during the experiment there were some slight changes in the temperature in the classroom, which could affect the rate of the reaction. As the result of that, the results I’ve gained in this experiment could slightly alter. The solution for this problem is to use a special thermometer, in order to make a control of temperature in the room and to make sure there are no anomalies taking place in my experiment. The third problem, which could occur and cause anomaly in my experiment, was the accuracy in measuring of the mass of K₂CO_3. When measuring the amount of potassium carbonate, I was using special electron scales, but even though I made sure they were always starting at 0g point at the beginning, they could still sometimes be wrong. All these factors have caused some anomalies and inaccuracy in my experiment. However, I will be able to improve it next time.

The data collected from this experiment indicates, that even though there were some slight changes in the experiment, the results I’ve gained were relevant and proved that my prediction was right. From this experiment I have learnt, that next time I do it, I will need to be more accurate when measuring and recording my results. Also, I think that by trying using a wider range of concentrations of hydrochloric acid next time, it will be possible to find a wider range of more varied and accurate results. If all the factors, which caused an anomaly in this experiment don’t occur next time, I’m sure the results will be more accurate and predictable. Making sure that the previous errors don’t take place in the next experiment, will help to maintain higher quality evidence, and as a result, higher quality of experiment.

Overall, I’m satisfied with the results I have gained in my experiment. I think that from my experiment I have gathered enough evidence to prove, what I have predicted before starting it, that as the concentration of hydrochloric acid doubles, the rate of reaction between hydrochloric acid and potassium carbonate doubles and time taken for the reaction to happen halves. Therefore, I think that my experiment was successful.

Дата добавления: 2015-11-05