IB HL Chemistry Internal
Assessment
What is the rate law expression of the reaction between sodium thiosulphate
(Na2S2O3) and hydrochloric acid (HCl), by measuring the time taken for the
reaction to complete at varying concentrations of sodium thiosulphate (mol dm-3)?
, Research Question: What is the rate law expression of the reaction between sodium
thiosulphate (Na2S2O3) and hydrochloric acid (HCl), by measuring the time taken for the
reaction to complete at varying concentrations of sodium thiosulphate (mol dm-3)?
Introduction
My idea to conduct this investigation began when we learned about chemical kinetics and the
different factors that affect the rate of a chemical reaction. We have learned from our textbooks
that there are seven factors that affect the rate of reaction: (1) temperature, (2) concentration, (3)
surface area, (4) agitation/stirring, (5) catalysts, (6) pressure and the (7) phase of reactants. The
real-life applications of chemical kinetics are universal and important.
For example, Scientists use chemical kinetics as a diagnostic tool. They use it to slow down a
fast reaction or speed up a slow reaction, so that they are able to observe it more carefully. There
are also plenty of industrial applications of chemical kinetics. For instance, to slow down the
deterioration of bagged or canned goods, companies add chemicals that help slow down the
growth of mold so that they can increase their shelf life. That is, we use chemicals to slow down
the chemical reactions from food being spoiled. More commonly, we use chemical kinetics when
cooking. Food cooks faster at high temperatures due to the increase in the reaction rate. For
instance, cooking using different food sizes, refrigerating food to slow down the rate of decay,
and using a pressure cooker (Talib and Harun, 2016). The potential use of chemical kinetics in
the real world is endless and is very relevant in fields such as pharmaceuticals. Moreover, the
investigation between the varying concentrations of sodium thiosulphate (Na2S2O3) and
hydrochloric acid (HCl) will help me determine the rate law expression of the reaction. This
experiment is commonly used worldwide to help with the understanding of reaction kinetics,
mainly due to the simplicity of measuring the reaction time. This has to do with the precipitate
that forms and will be further discussed in the next section.
Investigation
Reaction under study
Na2S2O3(aq) + 2HCl(aq) → S(s) + SO2(g) + 2NaCl(aq)
Background Information
In the investigation of the reaction between sodium thiosulphate (Na2S2O3) and hydrochloric acid
(HCl), it is known that as the concentration of sodium thiosulphate increase, the rate at which it
reacts with hydrochloric acid will also increase. The reason for this hypothesis has to do with the
collision theory. It explains the reaction rates with respect to the fact that reacting particles must
have an effective collision with one another in order for a reaction to occur. An effective
collision will have:
1. Correct orientation of reactants (also known as the steric factor or collision geometry)
2. Sufficient collision energy (activation energy)
Assessment
What is the rate law expression of the reaction between sodium thiosulphate
(Na2S2O3) and hydrochloric acid (HCl), by measuring the time taken for the
reaction to complete at varying concentrations of sodium thiosulphate (mol dm-3)?
, Research Question: What is the rate law expression of the reaction between sodium
thiosulphate (Na2S2O3) and hydrochloric acid (HCl), by measuring the time taken for the
reaction to complete at varying concentrations of sodium thiosulphate (mol dm-3)?
Introduction
My idea to conduct this investigation began when we learned about chemical kinetics and the
different factors that affect the rate of a chemical reaction. We have learned from our textbooks
that there are seven factors that affect the rate of reaction: (1) temperature, (2) concentration, (3)
surface area, (4) agitation/stirring, (5) catalysts, (6) pressure and the (7) phase of reactants. The
real-life applications of chemical kinetics are universal and important.
For example, Scientists use chemical kinetics as a diagnostic tool. They use it to slow down a
fast reaction or speed up a slow reaction, so that they are able to observe it more carefully. There
are also plenty of industrial applications of chemical kinetics. For instance, to slow down the
deterioration of bagged or canned goods, companies add chemicals that help slow down the
growth of mold so that they can increase their shelf life. That is, we use chemicals to slow down
the chemical reactions from food being spoiled. More commonly, we use chemical kinetics when
cooking. Food cooks faster at high temperatures due to the increase in the reaction rate. For
instance, cooking using different food sizes, refrigerating food to slow down the rate of decay,
and using a pressure cooker (Talib and Harun, 2016). The potential use of chemical kinetics in
the real world is endless and is very relevant in fields such as pharmaceuticals. Moreover, the
investigation between the varying concentrations of sodium thiosulphate (Na2S2O3) and
hydrochloric acid (HCl) will help me determine the rate law expression of the reaction. This
experiment is commonly used worldwide to help with the understanding of reaction kinetics,
mainly due to the simplicity of measuring the reaction time. This has to do with the precipitate
that forms and will be further discussed in the next section.
Investigation
Reaction under study
Na2S2O3(aq) + 2HCl(aq) → S(s) + SO2(g) + 2NaCl(aq)
Background Information
In the investigation of the reaction between sodium thiosulphate (Na2S2O3) and hydrochloric acid
(HCl), it is known that as the concentration of sodium thiosulphate increase, the rate at which it
reacts with hydrochloric acid will also increase. The reason for this hypothesis has to do with the
collision theory. It explains the reaction rates with respect to the fact that reacting particles must
have an effective collision with one another in order for a reaction to occur. An effective
collision will have:
1. Correct orientation of reactants (also known as the steric factor or collision geometry)
2. Sufficient collision energy (activation energy)
