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# reactant concentraction and rate of reaction

By Christine Carpenter,2014-11-06 15:10
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reactant concentraction and rate of reaction

Alex Deng

Reactant concentration and rate of reaction Aim: this experiment is to study if the concentration of reactants influence rates of reaction.

Hypothesis: the higher the concentration of Na2S2O3 is the faster the reaction will be. Equipment:

; Sodium thiosulfate solution

; Hydrochloric acid

; Distilled water

; Stop clock

Variables: Depended: The rate of the reaction

Independed: The concentration of the reactant

Controlled: The volume of the reactant

The temperature

The way to measure how soon the reactants take to fully ractant

The same containers for the reaction. Method:

1. Place 45 mL of 0.25 mol LNa2S2O3 in a 100 mL conical flask. Put the flask over a

cross marked on a piece of white paper.

2. Add 5 mL of 2 mol L HCl and briefly agitate to ensure mixing of the reactants. Start

a stop clock at the moment of the adding.

3. Note and record the time taken for the cross to ‘disappear’ when it is viewed through

the solution from directly overhead. The formation of solid sulfate causes the cross to

be obscured.

4. Repeat the experiment using various sodium thiosulfate concentrations.

Results

Vol. of 0.25 mol O Total Concentration Vol. of HTime for cross to Average 1Time 2-1(s) L NaSO(mL) added volume of NaSOon disappear (s), 3 time (s) 223 223 -(mL) after mixing (mol Ltimes taken; 1mixing (mL) )

45mL 0mL 50mL 0.225 21s, 17s, 18s, 18.66s 0.054

35mL 10mL 50mL 0.175 22s, 21s, 21s, 21.33s 0.046

25mL 20mL 50mL 0.125 32s, 31s, 30s, 31.00s 0.032

15mL 30mL 50ml 0.075 52s, 51s, 45s, 49.33s 0.020

5mL 40mL 50mL 0.025 364s, 360s, 360s, 361.33s 0.0027

Alex Deng

concentraction and the rate of the

reaction

0.054

0.046

0.032

0.02

0.0027

0.225 0.175 0.125 0.075 0.025

系列1 系列2

In the graph, the five number underneath the black bar are the concentrations of sodium thiosulfate in the reaction and the numbers in the blue circles are the rate of the reaction.

Discussion:

This experiment is aim to find out the connection between concentration of the reactants and the rate of the reaction. As have been mentioned in the method and the variables, this experiment only have two variables which is the independed variable concentration of the

reactants and the depended variable the rates of the reactions. The experiment and the

hypothesis are made base on the collision theory. The collision theory states that when suitable particles of the reactant hit each other a successful chemical reaction occur. Based on the collision theory, the hypothesis is that the higher the concentration of Na2S2O3 is the

faster the reaction will be. We made this hypothesis because as in the collision theory says, if there are more collisions happened at the same time, the faster the reaction is, therefore if the number of the reactants’ Molecular in the solution increase which means the

concentration of the two reactants increase the chance of the Molecular of the two reactants will surely increase which will increase the rate of the reaction. In this experiment we use water to control the concentration of the reactant. For example, if we want the concentration -1of the sodium thiosulfate be 0.225, we will add 45 mL of 0.25 mol L sodium thiosulfate

solution. In my opinion this hypothesis is reasonable and logical and the method of this experiment is also possible and reliable.

The result of this experiment has strongly support the hypothesis. As the result table and the graph show, it is very easy to see that, as the concentration of two reactants and the rate of the reaction are the only two variables, concentration is certainly related to the rate of the reaction. From the result table we can see that as the concentration of the sodium thiosulfate decrease from the o.225 to 0.175 the rate of the reaction decrease from 0.054 to 0.046. When the concentration decrease from 0.175 to 0.125 the rate of the reaction decrease again which is from 0.046 to 0.032. The same situation happened to the following results, as the conclusion, the rate of the reaction will decrease. If we view this conclusion oppositely we can see it is exactly the same to the hypothesis. However as we study even more about the data we can find out that the concentration of the reactants and the rate of the reaction is not proportional although it seems to be. In the experiment results, as the concentration decrease from 0.225 to 0.075 which means the concentration decrease to one third and the

Alex Deng

rate of the reaction also decrease from 0.054 to 0.02. Many people think this pair of data can be used to prove the conclusion that the rate of the reaction and the concentration of the reactants are proportional. However if we review the experiment result table there are another pair of data that can prove their theory is wrong. When the concentration of reactants decrease from 0.075 to 0.025 which decrease to one third, the rate of the reaction doesn’t decrease as less, the rate of the reaction decrease to 0.0027 from 0.02 which is about one seventh. But fortunately, this can be also explain by the collision theory. As the collision theory says, the rate of reaction increase when the number of the collisions between reactants increase, therefore we can know the rate of reaction is proportional to the number of collision. From the experiment we are unable to tell that the concentration of the reactant and the collisions are proportional, therefore both the theory and the experiment results don’t support the conclusion that concentration of the reactants and the rate of the reaction is proportional.

Conclusion:

As the conclusion, I think our hypothesisi has be well support by the collision theory and the experiment data. In this experiment we have prove there is a connection between cincentration of the reactants and the rate of the reaction which is the rate of reaction will increase if the concentration of the reactants increase and if the concentration of the reactants decrease the rate of the reaction will decrease as well but concetraction of the reactants and the rate of reaction won’t increase or decrease in the same rate. As the result I think this experiment is a successdul

experiment.

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