Form 6 Chemistry Practical - 迦密聖道中學 Carmel ：表6化学实践迦密聖道中學卡梅尔

Form 6 Chemistry Practical - 迦密聖道中學 Carmel ： 表 关于同志近三年现实表现材料材料类招标技术评分表图表与交易pdf视力表打印pdf用图表说话 pdf 6化学实践迦密聖道中學卡梅尔 Carmel Holy Word Secondary School (AL Chemistry) Form 6 Chemistry Practical Experiment 4: The Enthalpy Change of Neutralization HARMFULCORROSIVEIntroduction Neutralization is the reaction between an acid and a base, and is an exothermic reaction. The -1standard enthalpy change of neutralization between a strong acid and a strong base is –57.3 kJmol. The temperature rise due to the heat given out can be used to find the end-point of titration. In this experiment, TWO methods are used to find the end-point of titration, which is then used to : (i) find the molarity of a sodium hydroxide solution, and (ii) the enthalpy change of neutralization. Different combinations of acid and alkali are used and compared. Preparation by students Two sheets of graph paper Apparatus Polystyrene foam cup with lid, thermometer (-10? to 110?), beaker, pipette, pipette filler, burette, measuring cylinder, filter funnel Chemicals Hydrochloric acid, nitric acid, ethanoic acid, sodium hydroxide solution, potassium hydroxide solution, aqueous ammonia (refer to the labels on their bottles for accurate molarities) Safety Precaution Nitric acid is irritant. Sodium hydroxide and potassium hydroxide are corrosive. Wash with running water when contacted with skin. Procedure Each group of students is assigned with ONE combination of acid and alkali as in the table below. Group Class Number Acid Alkali 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1/3 Carmel Holy Word Secondary School (AL Chemistry) Method 1 1. Weigh the empty clean polystyrene cup. 32. Measure 35cm of the acid with a measuring cylinder and put it in the polystyrene cup. 3 3. Add 5 cmof the alkali into the polystyrene cup. Stir well and measure the highest temperature reached as quickly as possible. 4. Repeat steps 2 to 3 with other volumes of acid and alkali as shown in the table below. 5. Record the results in a table. 1 2 3 4 5 6 7 3Volume of acid / cm 35 30 25 20 15 10 5 3Volume of alkali / cm 5 10 15 20 25 30 35 Method 2 36. Transfer 25.0cm of the alkali solution into a polystyrene cup which is placed in a beaker. 37. Fill a burette with the acid solution to a mark between 0 and 10cm. 8. Record the temperature of the alkali solution. 39. Add 2.0cm of the acid into the polystyrene cup, stir the mixture and record the temperature. 310. Add another 2.0cm to the mixture and measure the temperature again. 3 3 11. Repeat adding 2.0cmat time and record the temperature until 40.0cmof the acid has been added. 12. Record the results in a table. Data Treatment Method 1 1. Plot the temperature change against the volume of alkali solution added on a graph paper. From the graph, find the end-point of neutralization. 2. Calculate the molarity of the alkali. 3. Calculate the enthalpy change of neutralization. Method 2 4. Plot the temperature of solution against the volume of acid solution added. 5. Draw 2 best fitted straight lines through the points and extend them until they meet. 6. Find the end-point of neutralization from the graph. 7. Calculate the molarity of the alkali solution. 8. Calculate the enthalpy change of neutralization. 2/3 Carmel Holy Word Secondary School (AL Chemistry) Question 1. What are the assumptions made in the calculations in steps 3 and 8? 2. Explain which method is more suitable to find (a) the end-point of neutralization? (b) The enthalpy change of neutralization? 3. Collect the result of the enthalpy change of neutralization from method 1 of ALL other groups and tabulate them in the following form. -1?H / kJmol Group Acid Alkali neut 1 HCl NaOH 2 HCl KOH 4. What do you notice about the relationship between the enthalpy change of neutralization and the strength of acid and the alkali? Relevant Data -1 -1Specific heat capacity of water = 4.2 kJ kgK -1 -1 Specific heat capacity of polystyrene cup = 1.3 kJ kgK -3Density of water = 1.0 g cm 3/3