The effect concentration of hydrochloric acid has on the rate of reaction -- A* - page 3
Keywords: Rate of reaction hydrochloric acid sodium thiosulphate concentration
By georgie1 on 31/12/2009
Level: GCSE Key Stage 4 (Years 10-11)
Page Number: 3 of 8 pages: 1 2 3 4 5 6 7 8
the 2 reactants in a clean holder and I can see through the glass bottom for when the X marked on the card disappears.
- Stand and clamp. This holds burette at a safe level, so that substances can be poured in below eye level [to avoid spillages into eyes] and measure at eye level for accuracy.
- Card with X marked on. This is so I can place it underneath the conical flask and wait until the solution becomes opaque. When this happens, I know the reaction has taken place.
- Stopwatch. This is so I can efficiently time how long each reaction takes until products go cloudy and opaque, and therefore can calculate rates of reaction.
- Plastic Goggles. This is for safety so that no chemicals can easily get into the eyes.
Preliminary Experiment
Firstly, I completed a preliminary experiment to understand exactly what I needed to do in order to achieve the best results in my final investigation. I completed a similar experiment to see if the instructions that I had originally planned for my final investigation were going to be appropriate. This way, I would be able to refine my final investigation and see if any factors needed to be changed. I used 6 different concentrations of 5cm³ hydrochloric acid [0.0M, 0.2m, 0.4M, 0.6M, 0.8, 1.0M] and added them with 50cm³ of sodium thiosulphate. My results were as follows:
Concentration/M Time/secs Rate of reaction
1.0M [5cm³ HCl, 0cm³ H₂0 ] 33.00 3.03
0.8M [4cm³ HCl, 1cm³ H₂0 ] 44.00 2.27
0.6M [3cm³ HCl, 2cm³ H₂0 ] 41.00 2.44
0.4M [2cm³ HCl, 3cm³ H₂0 ] 48.00 2.08
0.2M [1cm³ HCl, 4cm³ H₂0 ] 71.00 1.41
0.0M [water] [0cm³ HCl, 5cm³ H₂0 ] Solution does not turn opaque n/a
From looking at this table, it is clear that there is a general pattern in the rates of reaction, being that the more concentrated the hydrochloric acid, the higher the rate of reaction. Although my result for 0.6M does not exactly fit this pattern, I assume that this must be an outlier. As a result, I am only making minor adjustments to my final investigation. I am definitely going to repeat the experiment more than once so I can clearly distinguish anomalies, and for reliability. I am going to measure the time to a greater degree of accuracy and up to 2 decimal places, so that the rate of reaction will be more accurate. I am also going to use distilled water rather than tap water when diluting the hydrochloric acid, because this way there are definitely no impurities
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