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rates of reaction

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Rates of Reactions Aim: I am going to investigate how the rate of the reaction between sodium thiosulphate and hydrochloric acid depends on the concentration of sodium thiosulphate. The reaction rate of a chemical reaction is the speed of production of products from reactants. Sodium thiosulphate + hydrochloric acid ==> sodium chloride + sulphur dioxide + water + sulphur Na2S2O3 (aq) + 2HCl (aq) ==> 2NaCl (aq) + SO2 (aq) + H2O (l) + S(s) The solid sulphur (S(s)) formed in this reaction makes the colourless solution go cloudy. Factors: The factors I believe that will affect what happens in the investigation are: * Catalyst- A catalyst s a substance which alters the rate of a chemical reaction but is chemically unchanged at the end of the reaction. - A catalyst speeds up a reaction; an inhibitor (a substance) slows it down. * Concentration- The more concentrated the faster the rate (note in some cases the rate may be unaffected by the concentration of a particular reactant provided it is present at a minimum concentration). Remember for gasses, increasing the pressure simply increases the concentration so that's the same thing. * Surface area- greater surface area and since the reaction occurs at the surface we get a faster rate. * Temperature- Usually reactions speed up with increasing temperature ("100C rise doubles rate"). The collision theory: Particles need to collide with each other to react and the collision theory is all about this. The can be affected by the temperature of the particles, the concentration of the particles, whether a catalyst is used or the surface area (if the particles are solid). Temperature affects the rate of a reaction because if particles are cold, they move slowly and there are few collisions between them. ...read more.


Safety: I will be using concentrated acid, so at all times I must be very careful and I must wear goggles. If any spills onto your hands it should be washed off immediately and reported to the teacher. My Investigation: I chose to use sodium thiosulphate as my concentration which I will vary because my preliminary work shows that this concentration was the fastest for the rate of reaction. Preliminary: I have determined to use 5 different concentrations of sodium thiosulphate and water; from 50ml the highest concentration to 10ml the lowest, because during the lessons prior to the start of the investigation we did some trials to choose of which concentration the rate of reaction was fastest. I recognised that the reaction involving sodium thiosulphate and hydrochloric acid took about 6 seconds when I used the ration 50:20. So I have decided to employ this ratio for all my trials. To carry out this investigation I used a conical flask and I poured 50ml's of sodium thiosulphate and 5ml of hydrochloric acid then cover the cross with the conical flask and record the time it looks for the cross to disappear. I then poured 40ml's of sodium thiosulphate and 10ml of water and 5ml of acid until I had five different concentrations. During my trial I also measure the rate of reactions using marble chips and different hydrochloric acid concentrations and then measure the time taken to collect certain amount of gas in a given time. Hypothesis: Rates (chemical) take place out a variety of speeds. The rates of chemical reaction is an of how much of the reactants one by being converted into a given time. ...read more.


When I reduced the amount of sodium thiosulphate to 20ml the time it took nearly doubled. It went up by 8.4 seconds. So the result was 21 seconds. The time for the black cross to disappear started to increase making the rate of reaction slower. The next result was extremely high. The time it took previously doubled not twice but more than four times. When I measured the concentration of sodium thiosulphate it was 10ml and when I did the experiment the time it took to react was very long and slow. It took 84.6 seconds to react. The time for the cross to disappear was very exceptionally high. My graph shows a curve going down from 10ml to 50ml. Meaning the higher the concentration of sodium thiosulphate the faster it took to react so the rate of reaction was extremely fast. If I had to do the experiment again I will probably measured the amount of the concentrated sodium thiosulphate by every 5ml and increasing to 10ml, 15ml until 50ml. So it will go up in 5's instead of 10's. I would also test each result five times and then work out its average rather than doing it three times. This would make my results correct and accurate. Next time I did the experiment I could investigate how the surface area or the temperature affects the rate of reaction. The reason is the surface area of the solid will affect how fast the reaction goes. This is because the two types of molecule can only bump into each other at the liquid solid interface, i.e. on the surface of the solid. So the larger the surface area of the solid, the faster the reaction will be. Smaller particles have a bigger surface area than larger particle for the same mass of solid. ?? ?? ?? ?? Bilal Ahmed 13428 1004 ...read more.

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