To analyze the consequence of reactant concentration on the rate of the reaction between Na thiosulphate and hydrochloric acid AND to find the order of Na thiosulphate.
The reaction used in this experiment is between dilute hydrochloric acid and Na thiosulphate ( formula Na2S2O3 ) . You can see from the chemical equation below that one of the merchandises is sulfur, which does non fade out in H2O.Order now
As the reaction returns, a all right precipitate of sulfur signifiers, which makes the H2O go cloudy. If the reaction is carried out in a beaker standing on a piece of paper marked with an Ten, the precipitate finally becomes thick plenty to halt the Ten from being seen. We can clip how long it takes for the X to vanish for different concentrations of the Na thiosulphate solution. This will demo us how the reaction rate alterations with concentration.
I will be increasingly altering the concentration of Na thiosulphate by adding increasing sums of H2O each clip in order to thin the substance. The volume of H2O will be increased by 20cm3 and volume of Na thiosulphate decreased by 20cm3 each clip, maintaining the entire volume fixed at 120cm3.
- 1 Dependant Variable:
- 2 Controlled Variable:
- 3 Procedure:
- 4 Volume of 2M HCl
- 5 ( cm3 )
- 6 Volume of 0.15M Na2S2O3 ( cm3 )
- 7 Volume of distilled H2O
- 8 ( cm3 )
- 9 Look down at the X through the solution in the beaker. Equally shortly as the X disappears wholly, halt the clock and enter the clip taken in seconds in the consequences tabular array.
- 10 Consequence:
- 11 a?z
- 12 a?z
- 13 a?z
- 14 a?z
- 15 Initial Rate Method
- 16 So Reaction rate = Fixed sum of reaction
- 17 Time taken
- 18 Decision:
- 19 Evaluation:
I will be detecting the rate of formation of sulfur atoms from the reaction between Na thiosulphate and hydrochloric acid, which will do the solution to travel cloudy as the reaction progresses. This will be measured by clocking how long it takes for the cross on the sheet of paper to go vague.
The temperature of the solution will hold to be kept changeless as it will impact its rate of reaction. Temperature is nil but the step of kinetic energy and if the temperature were to alter it would intend that there would be more or less molecules with sufficient energy to respond. This is a major job which will bring forth some anomalousnesss in the consequences and is rather difficult to rectify without proper equipment but to be certain it did non impact the consequences I measured the temperature before and after the experiment and found no drastic alteration in the temperature of the room. The concentration of hydrochloric acid will besides be kept changeless in order to keep a just trial as we will be detecting the effects of the alteration in concentration of Na thiosulphate. The volume will besides be kept changeless, to guarantee that the is relative to the volume of its solution used.
Volume of 2M HCl
( cm3 )
Volume of 0.15M Na2S2O3 ( cm3 )
Volume of distilled H2O
( cm3 )
1. Label one of the 400cm3 beakers ‘THIO ‘ and collect in it about 320cm3 of 0.15M Na thiosulphate solution.
2. Label the other 400cm3 beaker ‘WATER ‘ and collect in it about 310cm3 of distilled H2O.
3. Label one of the 250cm3 beakers ‘ACID ‘ and collect in it about 140cm3 of 1M hydrochloric acid.
Use the ( 100cm3 ) mensurating cylinder to mensurate out 100cm3 of 0.15M Na thiosulphate and pour this into the staying EMPTY 250cm3 beaker and stand it on the paper marked with an Ten.
Use the 2nd ( 100cm3 ) mensurating cylinder to mensurate out 20cm3 of 1M hydrochloric acid. Quickly pour the acid into the beaker standing on the cross and get down the clock.
Look down at the X through the solution in the beaker. Equally shortly as the X disappears wholly, halt the clock and enter the clip taken in seconds in the consequences tabular array.
7. Rinse out the beaker good and dry it. Reset the clock. Repeat the experiment with different concentrations of Na thiosulphate – brand these up harmonizing to the instructions given in the above tabular array.
Quantitative altogether & A ; processed informations
HCl/cm3 ( A±0.5cm3 )
Water/cm3 ( A±0.5cm3 )
Sodium Thiosulphate/cm3 ( A±0.5cm3 )
Time/sec ( A±1s )
Average Time/sec ( A±1s )
During the reaction between the two clear solutions, Na thiosulphate and hydrochloric acid, produced a xanthous precipitate of sulfur, which caused the solution to travel opaque and vague the black cross drawn on the white sheet of paper. After wholly responding, the black cross was no longer seeable.
Successfully garnering the informations, now I will seek to happen the order of the reaction with regard to Na thiosulphate through
Initial Rate Method
The initial rate method is handily employed for clock reactions in which one or more constituents exhibit periodic alteration. For each experiment ( matching to each initial concentration of reactant ) the clip taken for a definite, little sum of a merchandise to be formed at the start of the reaction ( when its rate is most rapid ) is measured. This gives a step of the initial rate of the reaction because the shorter the clip taken for it to organize, the faster the rate.
So Reaction rate = Fixed sum of reaction
As we can see rate and clip are reciprocally related, or rate i‚µ 1/time. A rate against concentration curve is obtained by plotting 1/t against volume, uncovering the order of reaction with regard to the reactant concerned as in fig.1
Volume/cm3 ( A±0.5cm3 )
Initial Rate /s-1 ( A±4 % )
1.8 x 10-2
1.4 x 10-2
1.1 x 10-2
0.7 x 10-2
0.3 x 10-2
( Graph in separate sheet. )
After plotting the graph and pulling a line of best tantrum, the order of reaction with regard to sodium thiosulphate will be apparent.
The graph shows a additive secret plan, which means that the order of reaction with regard to sodium thiosulphate is one. Thus our rate jurisprudence will look like this
Rate a?? , which can besides be written as Rate = k 1
Although there are a few complications with the grade of truth of the collected information which is largely down to random instead than systematic mistake as the disappearing of the cross was reasonably judged by sight and besides the hold in halting the clock. I would state that the entire random mistakes generated a tolerance of A±3 % . Still I stand by my tabular array of consequences which show that the reaction proceeded much slower when the concentration was decreased due to the less figure of atoms per unit volume, take downing the opportunity of a successful hit between molecules. As the frequence of hits decreased, the rate of reaction decreased, decelerating down the rate of formation of sulfur, thereby increasing the sum of clip measured. My graph besides verifies this as there is a positive correlativity between concentration and rate, significance that if the concentration were to lessenings by half the rate would besides diminish by half, therefore increasing the clip measured for the formation of sulfur.
Not all of my consequences were reliable, I believe that the experiment was successful but there were some undependable or anomalous consequences which were non expected, which is due to the fact that there was a higher concentration than the one noted. I repeated the experiment three times and took an mean value to guarantee the consequences were accurate but although most of the consequences from each experiment were similar, there were still some abnormalities.
If I were to make the experiment once more, I would utilize a burette to mensurate the right volumes of Na thiosulphate and hydrochloric acid. I realised that I may non hold been precise plenty when utilizing the measurement cylinder. To farther better quality and preciseness of the consequences, I would utilize a light metre to mensurate the sum of light left in the reaction instead than visually judging when the cross has disappeared.
The lone anomalousness was during the 3rd experiment where the readings were manner off from the first two, which could be due to the fact that I did non utilize a stock solution of hydrochloric acid or possibly from improper cleansing of the equipment on reuse.