Sodium Thiosulphate in Hydrochloric Acid

[RATE OF REACTION]An investigation on the effect of temperature and concentration on the rate of reaction

2015Dainfern College

Antonio Motta Marques

Antonio Motta-Marques Dr Fowler Rates of Reaction

Chemistry Sodium Thiosulphate and Hydrochloric Acid Reaction Rates

ContentsRates of reaction..................................................1Introduction.....................................................1

Aim..............................................................1Hypothesis.......................................................1

Background Research..............................................2Apparatus list...................................................4

Apparatus Diagram................................................5Method:..........................................................6

Data.............................................................7Controls.........................................................8

Safety Precautions...............................................9Conclusion......................................................10

Evaluation......................................................12Limitations.....................................................14

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Rates of reaction

IntroductionA chemical reaction is a process that leads to the transformation ofone set of chemical substances to another. These reactions only happen if the reacting molecules collide properly. The rate of reaction is the speed of a reaction. When the solution is made more concentrated, there are a greater number of molecules in the same space. This increases the likelihood of reactants colliding properlyand so increases the rate of the chemical reaction.

AimThe aim is to investigate how changing the concentration of reactants can change the rate of reaction between hydrochloric acid and sodium thiosulphate. I will be timing and watching:

How quickly the reactants are used up How quickly a product is formed

The rate of reaction (ROR) describes how fast a reaction takes place.

HypothesisMy prediction is that the reaction between sodium thiosulphate and acid will be fastest whenthe acid is at its highest temperature and concentration. This is because there will be more acid molecules in the same amount of solution and the molecules of both substances will be more dynamic thus ensuring larger amount of more effective collisions with the sodium thiosulphate.

This is because when there are more molecules in the solution, there are more molecules to collide so this will speed up the reaction, and therefore it is more likely they will collide with each other. This causes a quicker reaction.

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Background ResearchChemical reactions are to do with changing the materials that form the base of your experiment. A physical reaction only changes the state of the molecule; the molecule’s chemical structure stays the same.

This is the reaction I will be considering:

Na2 S2O3 (aq) + HCl (aq) NaCl (s) + SO2 (aq) + S + H2O (l)

Sodium thiosulphate + hydrochloric acid sodium + sulphur dioxide +sulphur+ water

Everything before the arrow is a reactant and everything after the arrow is a product

State symbols:

(s) = solid (l) = liquid (g) = gas (aq) = aqueous (dissolved in water)

Traditionally, we have 3 states of matter; solid, liquid and gas. Often a substance’s state of matter can be changed by adding or removing heat energy e.g. ice(s) + heat = water (l).Sodium thiosulphate is a colourless, crystal like compound and is used for dyes and is also a salt. Hydrochloric acid is colourless, poisonous and highly acidic. It is often used as a chemical intermediate and in petroleum production, food processing, pickling, and metal cleaning. It can also be found in the stomach. These chemicals are perfect for my investigation because they are both clear and colourless. This is good because I will instantly be able to see any change in the solution. The state symbol for sulphur dioxide is (aq) not (g) because it is dissolved in water as its original state would be too toxic and corrosive for safe use.

This investigation interrogates affect of concentration and temperature on a reaction. Other factors which may speed up chemical reaction are:

Increasing the pressure (of gases) Using a catalyst Increasing surface area of the reactants

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Rates of reaction vary depending on which chemicals are being used and the activation energy required. Reactions that do not take long to make a product have a high rate of reaction, and reactions that take a longer time have a low rate of reaction.

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Collision theory

Different reactions can happen at different rates. Reactions that occur slowly have a low rate of reaction. Reactions that happen quickly have a high rate of reaction. For example, rusting is a slow reaction; it has a low rate of reaction. Burning and explosions are very fast reactions: they have a high rate of reaction.

Activation energy

Activation energy is the energy required to break the bonds of the reactants, so that new bonds can form to make the products. An input of heat energy is required to start some reactions. This energy gives the reactant particles enough energy to collide with enough force to break apart the bonds so that new products can be made from atoms.

Enthalpy

Enthalpy, in chemistry, is the heat content in a chemical reaction. The enthalpy change is the amount of heat absorbed or released when a chemical reaction occursat a constant pressure.

Use of rate of reaction in industry

The chemical industry makes medicine and many other substances such as;

Limestone - this is used for building

Sulphuric acid – used to make other substances

Ammonia - used to make fertilisers.

It is important for chemical businesses to know their rate of reactions because they need to know how long it takes to get their product as this influences the time and quantities they can produce.

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Apparatus list Hydrochloric Acid (5ml)

Clear colourless solution, this will help me clearly see any colour change and to point out any immediate reactions

Sodium thiosulphate (0.1M) (50ml)

Like hydrochloric acid, sodium thiosulphate is a clear colourless solution; I chose these reactants specifically in order to help me see any chemical reaction and time R.O.R.

Pipette

These helped me to measure and control the amounts of hydrochloric acid and sodium thiosulphate I used thus helping me achieving accurate and consistent concentrations.

Black marker pen

Because my investigation is largely based around me timing how long it takes to cover an ‘X’mark on the paper under conical flask, until it is no longer visible. I decided that it would be best for me to use a bold marker pen to make the mark more visible under the conical flask. This ensures that the solution is completely opaque when I stop the timer.

I used the same marker pen to make sure that

Measuring cylinder (50cm3 & 10cm3)

I used this to ensure that I had the correct measurements for my solution to be just right

Conical flask (250+ml size) clean and sterile

I used a clear conical flask to see any colour change. I also used it to see precipitation and the ‘X’ mark below the conical flask.

The conical flask and all other equipment must be clean as any impurities may contaminate my experiment. Also, it has a narrow top and so it is safer.

White plain Piece of paper

I used a plain white piece of paper to make sure I was able to clearly see the marking when Idrew the black cross on the paper. Using white paper helped the marking to stand out. I used this to gauge when to stop the reaction – when the black x was obscured by the white sulphur precipitate, the timer was stopped.

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Goggles

I had to wear goggles, to protect my eyes because if any chemicals got into my eyes, my eyescould be damaged.

Stopwatch

I used a stopwatch to time how long it took for precipitation to completely cover the mark under the conical flasks/how long it took for the black X to disappear.

Apparatus Diagram

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Method: All the substances needed were gathered and laid out so as to be accessible. The

pages were marked with an “X”. The conical flasks were placed over the papers with the “x”. The chemicals were measured out, in order to find out which ratio of Na2 S2O3 : HCl

yielded the most observable reaction. (50:0 ; 40:10 ; 30:20 ; 20:30 ; 10:40) After the 30:20 ratio was determined to be the most observable; 30mls of that

concentration was reacted with 3mls of HCl. The reaction rate was timed. This reaction was repeated with an increase and decrease of temperature.

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DataVolume of Sodium

Thiosulphate(aq) inml

Volume of Water added(ml)

Time, t, for thecross to disappear

(s)50 0 63,1340 10 73,3730 20 107,5920 30 188,5310 40 483,16

Temperature (°C)Time, t, for the

cross to disappear(s)

0 415.420 107.5940 3860 14,0577 5

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ControlsControls are employed in order to ensure that an accurate test is executed:

•Equally sized beakers were used so that the depth of the solution is the same. This could be a problem because it could take a longer/shorter time for the cross to disappear if there is a bigger “layer” of solution.

•The experiments occurred in the same room on the same day so as to ensure that room temperature was consistent.

•Using the same pen to draw the cross because a different colour could show up better also different thickness of the pen could show up better.

•Using the same piece of paper because graph paper could make the pen show up better than plain/lined paper.

•Using different pipettes for different substances so that none of the chemicals mix together before the experiment has started.

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Safety Precautions Protective goggles wear worn. Loose hair was tied up so as not to obscure vision or complicate the experiment. SO2 can cause is harmful and can cause asthma attacks. It is therefore advisable to

have carried out the experiment near a window or in a fume cupboard.

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ConclusionIn my investigation, my data and my graphs proved that my hypothesis was correct. My hypothesis was that “the reaction between sodium thiosulphate and acid will be fastest when the acid is at its highest concentration” I know that this is correct because looking at my data I can see that there is a clear decrease in the speed of the reaction when the concentration is increased. The experiment had no outliers

Concentration increase speeds up a reaction because there are more particles to collide witheach other, therefore creating more of a possibility of a faster reaction.

Improvements and further investigations:

If I do a further investigation, I will try to minimise the number of mistakes that I make. For example I will;

Repeat my calculations at least 5 times. Do all my measurements at eye level so that my

measurement is as accurate as I can make it.

There isn’t a lot that can be done about human error.

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Limitations Limitations affecting this experiment were:

Human error – Determining when the ‘X’ was fully covered was subject to an individual’s personal interpretation.

Human error – The accuracy with which the stopwatch was operated was not entirely accurate.

The stop watch could have been faulty - the button might not have been working well and may not have stopped the timer whenI pressed it.

Some chemicals may have been left behind in the measuring cylinder/ test tube.

The equipment used might have been contaminated if it wasn’t washed out properly the last time it was used. This could have caused a faster reaction due to any other unwanted chemicals still inside the equipment.

Lastly, there could have been a mistake in the measuring. Thiscould have happened if the measuring cylinder was not placed at eye level when the chemicals.

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Evaluation The investigation was conducted flawlessly – without injury or breakage- and yielded no deviations or outliers. There were howeverminor issues that prevent this research from being fully accurate.

Human error Wrong calculations Wrong measurements Not enough activation energy

I looked at two variables which speed up rate of reaction. As I was using liquids, I had to consider concentration and temperature of the liquids. (If I was using solids, I could investigate surface area and for gases I could investigate pressure)

In concentration I looked at five different concentration of HCl

The volume of HCl stayed the same; also the volume of sodium thiosulphate stayed the same, the concentration of sodium thiosulphate stayed the same. I tried to keep

The temperature constant (room temperature about 20)

This experiment was identified and I looked at margins of error.

I could have use a colorimeter to identify colour changes in the products.

Further tests – if I wanted to take this experiment further, I could conduct an experiment with solids AND liquids such as the marble chip and hydrochloric acid investigation

look at more concentrations, look at different factors that could affect ROR conduct an experiment with solids AND liquids such as the

marble chip and hydrochloric acid investigation There could be lots of improvements in my data if I had

completed the investigation again more accurately. To do this I would make sure that: Keep the temperature the same at all times,

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Use the same clean equipment and fresh chemicals so that mysolutions won’t get contaminated.

Use the same type of marker to draw my ‘X’ and I will make sure is the same thickness. Keep the size of my measuring flask is the same size; this should hopefully make my experiment much fairer and accurate.

I would alter the independent variable to the type of acid I would be using. I would do different trials on sulphuric acid and nitric acid. These two acids react well with the right materials. I would also consider using a wider range of concentrations so I can do in-depth analysis and I can comparethe two acids.

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Sodium Thiosulphate in Hydrochloric Acid

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