The Effect Of Concentration On Reaction Rate

02 Nov 2017

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Rohan Daniel

Class: 10C

John Paul College http://upload.wikimedia.org/wikipedia/en/a/ac/John_Paul_College_(Brisbane)_logo.pnghttp://chemistry.skola.edu.mt/wp-content/uploads/2012/07/chemistry.jpg

Instructor: Dr. Van Slyke

Team Members: Rohan Daniel, Seth Gibson and Shannon Flood

Table of Contents

Abstract

An experiment which involves marble chips (calcium carbonate) and hydrochloric acid will be conducted and analysed to observe the effect of concentration on reaction rate. It is hypothesised that if the molarity of hydrochloric acid (independent variable) is increased; then higher volumes of carbon dioxide (dependent variable) will be produced. To prove this theory, the concentration of 30mL of hydrochloric acid will be altered and its effect on 4g of marble chips will be studied under a constant temperature. When marble chips react with hydrochloric acid, calcium chloride, carbon dioxide and water and produced. This acid-base chemical reaction is given by the formula CaCO3(s) + 2HCl (aq) → CaCl2 (aq) + CO2 (g) + H2O (l). The carbon dioxide produced when the two reactants react is then measured every 20 seconds until 3 mins and recorded in a table which is averaged and graphed. To further research the effect of catalysts on reaction rates, the effect of pressure on a reaction can also be studied.

Introduction

A chemical reaction is the process in which one more substances is chemically converted into one or more different substances by breaking pre-existing chemical bonds and forming newer bonds. The rate at which a chemical reaction proceeds depends on various factors such as the temperature, pressure of catalyst, physical state of reactants, reactant structure and the concentration of reactants (Graham, 1978). This report will investigate the influence of the concentration of reactants on the reaction rate by discussing an experiment which involves the reactants marble chips and hydrochloric acid. Marble chips, also known as calcium carbonate is a chemical compound with the molecular formula CaCO3. The formation of this ionic compound involves a Ca2+ cation and a CO32- polyatomic anion that attracts one another because of the equal opposite charge (Carolina Biological Supply Company, 2010). On the other hand, hydrochloric acid (hydrogen chloride) is a highly corrosive, strong mineral acid which is formed when a hydrogen atom shares one electron with a chlorine atom to form a polar covalent bond. In this type of bonding, electrons are not shared equally between the hydrogen and chlorine atom but are more strongly attracted to the chlorine. Due to this unequal sharing, the chlorine atom possesses a slightly negative character and the hydrogen atom a slightly positive character, a condition described by the term polar (The Chemical Bond, 2009). In this experiment, the two reactants stated above are combined to form a salt, calcium chloride. In this case, the calcium (Ca2+) ion displaces the hydrogen atom and ionically bonds with two chlorine (Cl-) ions. In addition, carbon dioxide and water are also formed. This acid and base reaction is expressed through the chemical equation CaCO3(s) + 2HCl (aq) → CaCl2 (aq) + CO2 (g) + H2O (l).

The collision theory states that when particles of two or more reactants collide, only a certain percentage of the reacting particles have enough energy, also known as activation energy at the moment of impact to break the pre-existing bonds and form a new bond (Mahajan, n.d). To prove this theory, this experiment was designed to demonstrate the influence of concentration over reaction rate by measuring the volume of carbon dioxide produced when five different molarities (0.5, 1.0, 1.5, 2.0 and 2.5) of hydrochloric acid measuring 30ml react with 4g of marble chips. The reliability of the experiment was ensured by repeating the test six times with each molarity of hydrochloric acid. Furthermore, the controlled variables (volume of hydrochloric acid and the mass of marble chips) were maintained throughout the experiment by using a funnel to pour the hydrochloric acid from a measuring cylinder to a conical flask to confirm there was no spillage and that the acid measured 30mL. However, no measurement can be entirely accurate; therefore, the volume of hydrochloric acid measured was within a range of uncertainty of ±1mL. The mass of marble chips were also maintained by sifting the marble chips to weigh precisely 4g and by cleaning the weighing scale after the completion of each assessment. Alike the uncertainty of the volume of hydrochloric acid, when reading the measuring cylinder the weight of the marble chips also lied within a range of ±0.01g as the mass of gases in the air and the grade of the equipment may also contribute to the accuracy when mass is measured.

Aim

The aim of this experiment is to investigate how different concentrations of one type of reactant (Hydrochloric acid) affect the rate of reaction between marble chips (CaCO3) and hydrochloric acid (HCl) by measuring the volume of carbon dioxide (CO2) produced.

Hypothesis

It is hypothesised that if the molarity of hydrochloric acid (independent variable) is increased; then higher volumes of carbon dioxide (dependent variable) will be produced because the reacting bodies must possess enough energy at the moment of impact to break pre-existing bonds and form a new bond. Thus if the independent variable is of a higher concentration there is a greater chance of particles colliding, increasing the rate of the reaction.

Variables

Variables are any factor that can be controlled or changed in an experiment. The dependent variable describes what will be measured or observed, the independent variable elucidates what is varied during the experiment and the controlled variable is the factor that is held constant during an experiment (Martin, 2011). In the fundamentals of combining hydrochloric acid (HCl) and marble chips (CaCO3), the independent variable was the concentration of hydrochloric acid; the dependent variable was the volume of carbon dioxide produced and the controlled variables included the volume of hydrochloric acid, the mass of the marble chips and the environmental conditions.

4.1 Dependent Variable

The volume of carbon dioxide produced was measured using a measuring cylinder and a bee hive. The acid-base reaction taking place in the conical flask produces carbon dioxide as a product which displaces the water in the measuring cylinder. The volume of carbon dioxide produced is therefore measured by determining the volume of water displaced.

4.2 Independent Variable

The concentration of the hydrochloric acid was varied throughout the experiment. 0.5, 1.0, 1.5, 2.0 and 2.5 molarities were used. In this experiment, 4g of marble chips reacted with 30mL of one molarity of hydrochloric acid to prove that concentration has strong correlation with reaction rate.

4.3 Controlled Variable

The controlled variables in this experiment include the volume of hydrochloric acid, the mass of the marble chips and environmental conditions. 30mL of hydrochloric acid was measured and reacted with the marble chips. The consistency of the volume of hydrochloric acid is therefore important to ensure the fairness of this test and so that the data generated at the conclusion of the experiment is accurate. The equilibrium of the volume of hydrochloric acid was maintained by accurately measuring 30mL and by using a funnel to transfer the acid from a measuring cylinder to a conical flask. This would verify that the solution was not spilled. In addition to this variable, the mass of the marble chips should also be consistent throughout the experiment as it would affect the rate of the reaction. For example, if the mass is higher than 4g, then the reaction would proceed at a faster rate because more collisions would take place between the particles. To maintain the mass of the marble chips, they were sifted to exactly weigh 4g and the weighing scale was cleaned after each weigh up so that there was no residue. Finally, environmental conditions such as the temperature and the pressure should also be maintained throughout the experiment as they are factors affecting a reaction rate. To maintain stable environmental conditions, this experiment was conducted under an average temperature of 26o and normal pressure on 15/04/2013 and on 17/04/2013 (AccuWeather, 2013).

Materials

120g Marble Chips(Calcium Carbonate)

180mL 0.5M Hydrochloric acid

180mL 1.0M Hydrochloric acid

180mL 1.5M Hydrochloric acid

180mL 2.0M Hydrochloric acid

180mL 2.5M Hydrochloric acid

(1) Sieve

(1) Beehive

(1) 100mL Conical flask

(2) 100mL Measuring cylinder

(1) Funnel

Cleaning cloth or recycled paper

(1) Rubber stopper with glass tube to fit conical flask

(1) 1cm x 6cm Plastic tubing

(1) Measuring scale

(1) Trough/ Tub

(1) Stopwatch or clock with second hand

4.0L Tap water

(1) Heatproof mat

Safety glasses

Lab coat

Gloves (If required)

500mL Distilled water

Hazard Identification for Science Practical

Outline of the proposed experiment:

An investigation on how different concentrations of one type of reactant (Hydrochloric acid) affect the rate of reaction between marble chips (CaCO3) and hydrochloric acid (HCl) by measuring the volume of carbon dioxide (CO2) produced.

Hazardous nature of the Reactants:

Tick the Yes or No box

Chemical

Hydrochloric Acid

Marble Chips

Risk

Concentration

30mL - 0.5, 1.0, 1.5, 2.0, 2.5

4g

Irritant

Yes [ ✓ ] No [ ]

Yes [ ] No [ ✓ ]

Yes [ ] No [ ]

Yes [ ] No [ ]

Corrosive

Yes [ ✓ ] No [  ]

Yes [  ] No [ ✓ ]

Yes [ ] No [ ]

Yes [ ] No [ ]

Toxic

Yes [ ] No [ ✓ ]

Yes [ ] No [ ✓ ]

Yes [ ] No [ ]

Yes [ ] No [ ]

Harmful

Yes [ ✓ ] No [ ]

Yes [ ✓ ] No [ ]

Yes [ ] No [ ]

Yes [ ] No [ ]

Flammable

Yes [ ] No [ ✓ ]

Yes [ ] No [ ✓ ]

Yes [ ] No [ ]

Yes [ ] No [ ]

Oxidising

Yes [  ] No [ ✓ ]

Yes [  ] No [✓ ]

Yes [ ] No [ ]

Yes [ ] No [ ]

Dangerous to the environment

Yes [ ✓ ] No [ ]

Yes [ ] No [ ✓ ]

Yes [ ] No [ ]

Yes [ ] No [ ]

Other:

Yes [ ] No [ ✓ ]

Yes [ ] No [ ✓ ]

Yes [ ] No [ ]

Yes [ ] No [ ]

Hazardous nature of the Products:

Tick the Yes or No box

Chemical

Calcium Chloride

Carbon Dioxide

Water

Risk

State

Aqueous

Gas

Aqueous

Irritant

Yes [ ✓ ] No [ ]

Yes [ ] No [  ✓]

Yes [ ] No [ ✓ ]

Yes [ ] No [ ]

Corrosive

Yes [ ] No [ ✓ ]

Yes [ ] No [ ✓ ]

Yes [ ] No [ ✓ ]

Yes [ ] No [ ]

Toxic

Yes [ ] No [ ✓ ]

Yes [ ] No [ ✓ ]

Yes [ ] No [ ✓ ]

Yes [ ] No [ ]

Harmful

Yes [ ✓ ] No [ ]

Yes [ ] No [ ✓ ]

Yes [ ] No [ ✓ ]

Yes [ ] No [ ]

Flammable

Yes [ ] No [ ✓ ]

Yes [ ] No [ ]

Yes [ ] No [ ✓ ]

Yes [ ] No [ ]

Oxidising

Yes [ ] No [ ✓]

Yes [ ] No [ ]

Yes [ ] No [ ✓ ]

Yes [ ] No [ ]

Dangerous to the environment

Yes [ ] No [ ✓ ]

Yes [ ] No [ ✓ ]

Yes [ ] No [ ✓ ]

Yes [ ] No [ ]

Other:

Yes [ ] No [ ]

Yes [ ] No [ ]

Yes [ ] No [ ]

Yes [ ] No [ ]

Is the Reaction:

[ ✓] Exothermic [ ] Endothermic [ ✓] Gas formed

Equipment Required:

Score with Yes, No or Possible

Equipment

Hydrochloric Acid

Marble Chips

Risk of

Score

Score

Score

Score

Cuts

No

No

Burns

Yes

No

Fire

No

No

Electrical Shock

No

No

Moving parts

No

No

Other

What Personal Protective Equipment is Required to safely carry out the Experiment based on sections 1 to 4:

[ ✓ ] Lab coat [ ✓ ] Safety glasses [ ] Gloves

What Additional Safety Measures if any are Required to be able to safely carry out the Experiment based on sections 1 to 4:

[ ] Fume Cupboard [ ] General Ventilation [ ] Safety Screen

[ ] Audible/visual warnings [ ] Safety Induction

Please ensure that you are familiar with the location and access to the Emergency Facilities:

[ ✓ ] Spill Kit [ ✓ ] Eye wash station [ ✓ ] First aid kit [ ✓ ] Safety Shower

[ ✓ ] School Nurse

Final Check List based on the answers from 1 to 7 of this form:

The Estimated Risk is considered to be

[ ✓ ] Low [ ] Medium [ ] High

[ ✓ ] All recommended controls will be implemented and the emergency facilities are available.

[ ✓ ] I/we have read the MSDS and am familiar with the hazards and first aid procedures.

[ ✓ ] I/we have been trained on the use of any specialised equipment which is required.

[ ✓ ] All waste material will be placed in the waste containers provide, not down the drains.

Approval:

Approved by your teacher: _________________________________ Date:__________________

Approved by HOD if required: _______________________________ Date:__________________

Method

Caution: Wear safety glasses, gloves and lab coat to protect the body from harmful chemicals and irritants during the experiment. Do not inhale or consume any chemicals.

First and most importantly, safety glasses, gloves and a lab coat were worn. Subsequently, a trough was approximately ½ filled with tap water and set aside. A beehive was then submerged into the trough filled with water. 30mL of 0.5M Hydrochloric acid was measured in a 100mL measuring cylinder and was then poured into a 100mL conical flask through a funnel. The conical flask was then placed on a heat proof mat. Following this, 4g of marble chips (Calcium Carbonate) was weighed on a weighing scale and set aside. If the weight of the marble chips did not measure 4g, a sieve was used to sift the marble chips. After the completion of weighing the marble chips, the weighing scale was cleaned using a cleaning cloth or recycled paper to ensure that there was no remainder of marble chips on the scale. Succeeding this, a tube that led to the bottom of the beehive was connected to the glass tube of a rubber stopper. A 100mL measuring cylinder was then completely filled with water and was placed on the top of the beehive so that the hole on the top was completely covered (see diagram 1.1 in appendix for the setup of the experiment). Then, the 4g of marble chips measured earlier was added to the conical flask and almost instantly the stopwatch was started and the rubber stopper was tightly attached to the opening of the conical flask. As the reaction took place in the conical flask, the carbon dioxide produced was determined by measuring the volume of water that had been displaced in the measuring cylinder. Recordings of the volume of carbon dioxide produced were taken at eye–level every 20 seconds until 3 minutes; until all the water in the measuring cylinder had been substituted by carbon dioxide or until the reaction had stopped completely, whichever occurred first. After the recordings were taken, the remaining reactants were then safely disposed in a large beaker and the conical flask was emptied and cleaned using a cleaning cloth. This procedure was repeated 6 times in total with 5 different concentrations of hydrochloric acid. Finally, an average result was generated at the conclusion of the experiment and a graph was drawn.

Results

7.1 Quantitative Observations

Table 1.1 - Raw data of the volume of CO2 produced when a 0.5M Hydrochloric acid solution was used

Table 1.2- Raw data of the volume of CO2 produced when a 1.0M Hydrochloric acid solution was used

Table 1.3 - Raw data of the volume of CO2 produced when a 1.5M Hydrochloric acid solution was used

Table 1.4 - Raw data of the volume of CO2 produced when a 2.0M Hydrochloric acid solution was used

Table 1.5 - Raw results of the volume of CO2 produced when a 2.5M Hydrochloric acid solution was used

Volume of CO2 produced (mL)

Time (seconds)

0.5M

1.0M

1.5M

2.0M

2.5M

20

40

60

80

100

120

140

160

180

Table 1.6 – Average calculations of the raw data recorded when experimenting hydrochloric acid and Calcium Carbonate7.2 Analysis of Results

Volume of CO2 produced (mL)

Time (seconds)

0.5M

1.0M

1.5M

2.0M

2.5M

20

3

12

25

46

63

40

7

34

64

100

121

60

14

61

103

123

125

80

24

85

125

125

125

100

33

108

125

125

125

120

43

118

125

125

125

140

50

125

125

125

125

160

58

125

125

125

125

180

65

125

125

125

125

Table 1.7 – Average of the results recorded whilst experimenting with hydrochloric acid and Calcium Carbonate

Graph 1.1 – Volume of carbon dioxide produced with 5 different molarities of HCl

In this experiment, hydrochloric acid and marble chips (calcium carbonate) react to form calcium chloride, carbon dioxide and water. This acid and base reaction is formulated through the equation: CaCO3(s) + 2HCl (aq) → CaCl2 (aq) + CO2 (g) + H2O (l). When the marble chips were added to the hydrochloric acid, the volume of carbon dioxide produced was measured and recorded every 20 seconds until 3 minutes (see tables 1.1-1.5). It was observed that when the molarity of hydrochloric acid was increased more carbon dioxide was produced. This can be seen in table 1.7 and graph 1.1; when a 0.5M hydrochloric acid was used, 3mL of carbon dioxide was produced at 20 seconds. As the molarity increased to 1.0M, the volume of carbon dioxide produced at 20 seconds simultaneously increased to 12mL. In addition, it was observed that as the molarity increased, the time taken for the reaction to produce 125mL of carbon dioxide decreased significantly. This can be seen in graph 1.1 in which the time taken for 125mL of carbon dioxide to be produced when 1.0M hydrochloric acid solution was used recorded 140 seconds. Whereas the time taken for 125mL of carbon dioxide to be produced when a 1.5M hydrochloric acid solution was used recorded only 60 seconds. These results prove that concentration is a factor that significantly affects the reaction rate.

7.2 Qualitative Observations

When 4g of marble chips were added to the 30ml of hydrochloric acid, a clear but an effervescent reaction took place. It was noticed that as the molarity of hydrochloric acid increased, the effervescences produced also increased at a steady pace. Thus it is believed that the quantity of bubbles emitted during a reaction is directly linked to the concentration of reactants. It was also observed that at the completion of the reaction the outside of the conical flask was cold which conveys that an exothermic reaction took place.

Discussion

When marble chips (calcium carbonate) and hydrochloric acid react; calcium chloride, carbon dioxide and water are produced. When conducting this experiment which involved 30mL of five different molarities of hydrochloric acid (0.5, 1.0, 1.5, 2.0, and 2.5) and 4g of marble chips (calcium carbonate), the volume of carbon dioxide produced was measured to study the influence of concentration over reaction rate. From the results of this experiment (see table 1.7), it can be comprehended that the volume of carbon dioxide produced is directly related to the molarity of hydrochloric acid. In other words, as the molarity of hydrochloric acid increased, the volume of carbon dioxide produced also increased at a rapid rate. Making reference to table 1.6, when a 0.5M hydrochloric acid solution was used, at 60 seconds 14 mL of carbon dioxide was recorded. In comparison, when a 1.0M hydrochloric acid solution was used, 61 mL of carbon dioxide was produced at 60 seconds and when a 1.5M hydrochloric acid solution was used, 103 mL of carbon dioxide displaced the water in the measuring cylinder over the same period of time. These results link to the collision theory which states that the reacting particles must possess enough activation energy at the moment of impact to break the pre-existing bonds and form a newer bond (Mahajan, n.d). Thus if the molarity of hydrochloric acid solution is increased, the reacting bodies will possess a greater extent of energy at the moment of impact which in return will shorten the amount of time required for the reaction to proceed. This can also be observed in graph 1.1, when a higher molarity of hydrochloric acid solution is used, less time is required for the reaction to produce 250mL of carbon dioxide. This explains the results recorded for a 1.0M hydrochloric acid solution, where 140 seconds were required for 250mL of carbon dioxide to be produced. Whereas, only 80 seconds was required for the same volume of carbon dioxide to be produced when a 1.5M hydrochloric acid was used. From these results it can be seen that the concentration of reactants have a significant influence over the rate of reaction. Consequently, the hypothesis was proven correct that if the molarity of hydrochloric acid (independent variable) was increased; then higher volumes of carbon dioxide (dependent variable) would be produced because there is a greater chance of particles colliding, increasing the rate of the reaction.

In the process of this experiment, there may have been some sources of error that led to inconsistencies in the results. These errors are believed to have occurred when readings were taken from the measuring cylinder and the weighing scale. During this experiment, the measuring cylinder was used to measure out 30ml of hydrochloric acid and also to calculate the volume of carbon dioxide produced. However, measuring equipment have different classes and different levels of accuracy and in this experiment a ‘B’ class measuring cylinder was used and the observers’ precision was always one or two values off because of the alternation of height at which the measurements were taken. In addition, the position of the plastic tubing always alternated because of the short size and there was nothing supporting it to keep it in a constant position. The effect of this error on the results can be seen in table 1.1, where the volume of carbon dioxide produced for trial 3 of 0.5M hydrochloric acid at 20 and 40 seconds is much less than the other trials. This was caused because the tube was not supported and the carbon dioxide was released into the trough instead of the measuring cylinder. Therefore random errors were made and the recorded measurements were not constantly accurate but lied within a range of uncertainty of ±1mL. This error affects the volume of hydrochloric acid and carbon dioxide measured. If the volume of hydrochloric acid was greater or lower than 30mL, then the reaction would occur at various rates and the final results would not be as reliable because no reactants were controlled. The weighing scale was also used for measuring the marble chips and if the weight did not equal to 4g then a sieve was used to sift the chips. Conversely, the air contains of many gases that affect the weight projected on the weighing scale and hence causes a systematic error associated with the measuring instrument. The measurements of the marble chips thereby were always positioned between a range of uncertainty of ±0.01g (Bakke, n.d.). To improve this experiment, better class measuring instruments with more accurate increments should be used so that the readings would be consistent. In addition, the plastic tubing should be longer and supported so it remains in a fixed position (at least 2mL into the measuring cylinder) and produces consistent levels of carbon dioxide. If the tubing was not led into the measuring cylinder, the results would be lower as carbon dioxide would escape. Evaluating the method of this experiment, when 4g of marble chips react with 30ml of greater molarities of hydrochloric acid solution, the reaction proceeds instantly which reduces thereby reduces the number recordings that can be taken. To improve this method and to show a strong correlation between the reaction rate and the molarity, either the volume of hydrochloric acid should be reduced or the mass of the marble chips should be increased. A possible further investigation to observe how a catalyst affects the rate of reaction is to study the effect of pressure on reaction rate. If high amounts of pressure are applied to the molecules, then the number of collisions will increase thus decreasing the time required for a reaction to complete. Investigating this catalyst will back up the results generated from this experiment and will show strengthen the collision theory.

Conclusion

The collision theory states that when particles of two or more reactants collide, only a certain percentage of the reacting particles have enough energy, also known as activation energy at the moment of impact to break the pre-existing bonds and form a new bond. The aim of this experiment was to investigate how different concentrations of one type of reactant (Hydrochloric acid) affect the rate of reaction between marble chips (CaCO3) and hydrochloric acid (HCl) by measuring the volume of carbon dioxide (CO2) produced. The experiment went as expected with no unusual events other than some random and systematic errors. The results to this test proved that when greater molarities of hydrochloric acid were used, higher volumes of carbon dioxide was produced. Thus the results support the hypothesis that the concentration has a positive correlation with the rate at which a reaction proceeds.

Diagram 1.1 – Setup of the Experiment

Appendices



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