Chemistry Practical PDF

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Chemistry Required Practical 1: Hypothesis: As the temperature rises, the rate of reaction increases, as there is a proportionally large increase in the number of energetic particles. Explanation of Hypothesis: The higher the temperature, the more kinetic energy the particles will obtain. Therefore the particles will move faster and therefore collide with other atoms more frequently. This in turn increases the rate at which the reaction occurs. The most important factor is activation energy; collisions only occur if the colliding particles interact with sufficient energy to commence the reaction. If the numbers of particles with the minimum activation energy increase, through the increasing temperature (in the Maxwell-Boltzmann distribution, one can see there are more particles to the right of the activation energy), the reaction speeds up, due to the presence of more energetic particles. Hence a combination of the increase in the number of high-energy collisions and particles that possess the minimum activation energy, results in more successful reactions. Variables: The independent variable, the one we change, is the varying temperature of the sodium thiosulfate and hydrochloric acid, whilst the dependant variable, the one we measure, is the time taken for the reaction to occur. This directly links to the rate of reaction as the lower the time taken, the faster the rate of reaction. Sodium thiosulfate and HCl and their corresponding volume and concentration must be controlled to conduct a fair test and avoid anomalies, as excess will distort the results of the experiment, preventing valid results. The same batch of equipment will be used to minimise systematic errors, making sure the trials are as repeatable as possible. Equipment: Volumetric Conical flask (250 cm3) – to hold the measured volume of sodium thiosulfate solution and water  Measuring cylinder (10 cm3)- to measure the volume of the hydrochloric acid  Measuring cylinder (50 cm3)- to measure the volume of water and sodium thiosulfate solution together  0.25 mol dm-3 sodium thiosulfate solution- base used in this experiment as a control variable  2 mol dm-3 hydrochloric acid- an acid which causes a precipitate of sulfur to form during the experiment  2 Test tubes- to hold the measured hydrochloric acid and sodium thiosulfate solution in  2 Thermometers- to measure the temperature of sodium hydroxide solution and HCl, which is the changing factor, in each experiment  5 water baths with test tube holders at 20,30,40,50,60(°C)- this is used to investigate the independent variable of temperature as accurately as possible and will keep the water’s temperature constantly at each temperature  Plain paper marked with a cross- this is the indicator of the experiment- once visible, the stopwatch must be stopped  Stopwatch- to measure time taken for the reaction to occur 

Risk Assessment: 1. Sulfur dioxide forms as a by-product of this reaction and therefore one must wear eye protection and ensure there is good ventilation as it can cause breathing problems. This is the reason why a smaller volume of sodium thiosulfate is being used. 2. HCl may spill onto skin or there may be eye contact, causing burns, and since HCl is very irritant, it must be removed instantly. Flush your skin/eyes with plenty of water for at least 15

minutes. If this does not help, apply anti-bacterial cream over the contaminated skin and seek medical attention. To avoid such a circumstance in the first place, one must wear gloves and goggles at all times and be careful whilst transferring solutions. 3. The conical flasks, beaker and measuring cylinders are made of glass and may fall and break; causing cuts, and therefore must be handled carefully. Method: 1. After measuring 10 cm3 of the 0.25 mol dm-3 sodium thiosulfate solution and 40 cm3 of water in the 50 cm3 measuring cylinder, pour this mixture into a test tube. 2. Using the 10 cm3 measuring cylinder, measure out 5 cm3 of dilute hydrochloric acid of 2 mol dm-3 and pour into the test tube provided. 3. Arrange both the test tubes into a water bath, thermostatically controlled at your first desired temperature (in this case 20 °C) 4. Place a thermometer in each test tube to ensure that the solutions have met the set temperature of the water bath. Once the required temperature of the sodium thiosulfate and water solution and the hydrochloric acid is reached, remove the test tubes from the water bath. 5. Quickly empty the sodium thiosulfate and water solution into a conical flask and place it over the paper, marked with a distinct cross, and immediately add the hydrochloric acid from the test tube into the conical flask. Start the stopwatch. 6. Swirl the flask, with a thermometer, to ensure the two solutions are mixed and record the initial temperature of the mixture. 7. Carefully observe the cross from directly above the solution and when the cross disappears from sight, stop the stopwatch. Record the time taken for the cross to disappear in your results table. 8. Using the thermometer, record the final temperature of the mixture. 9. Pour the solution in the fume cupboard if possible, or down the sink, and rinse the equipment. 10. In your results table, record initial and final temperatures and work out a mean temperature of each reaction mixture. Use this to calculate the rate of reaction to 3 significant figures. 11. Repeat the entire experiment, at least 3 times for concordant results, for each of the five temperatures and record all your results. Results Table: Experiment Trial Number numbe r 1 1

Initial Final Average Time taken for temperature/ temperature/ temperature/ the cross to °C °C °C disappear/ms−1

Rate of reaction 1/Time Taken

2 3 Overall Average

This table can be continued for the remaining 4 experiments using different temperatures. References: 1. http://www.chemguide.co.uk/physical/basicrates/temperature.html -Date accessed: 06/11/16 2. http://filestore.aqa.org.uk/subjects/AQA-2420-W-TRB-PSA06.PDF - Date accessed: 07/11/16 3. http://www.rsc.org/learn-chemistry/resource/res00000448/the-effect-of-temperature-onreaction-rate?cmpid=CMP00000518- Date accessed: 07/11/16 4. http://filestore.aqa.org.uk/subjects/AQA-2420-W-TRB-PSA06.PDF - date accessed- 07/11/16 5. PDF by Beaconsfield School- Rates of reaction Sodium Thiosulfate and Hydrochloric Acid, Date Accessed: 10/11/16...