Pag 3 - enthalpy determination

Question 1

Describe the method for the determination of the enthalpy change of neutralisation

Answer 1

• measure 25cm3 of HCL uing a 25cm3 measuring cylinder and add it to a polyterence cup
• place the cup in 250cm glass beaker
• contruct a suitable table to record the temperature of the acid at minute intervals for up to 10 minute
• measure 25cm3 of ofium hydroxide into 25cm3 meauring cylinder
• start the timer and record the intial temperature of the HCl in the cup
• continure to record the temperature each minture for three mintures
• at the fourth minute add the sodium hydroxide to the cup
• do not record the temperature
• at the 5 minute continue recording the temperature up until 10 minute stir the solution in the cup each time the temperature is recorded

Question 2

How do you carry out the calculations for determining the enthalpy change of neutralisation

Answer 2

• plot a graph of temperature against time
• draw a line of best fit through the points before the additions of sodium hydroxide and draw a second line of best fit through the poits after addition of odium and extrapolate both of these line to four minute
• use the graph to determine the temperature change at the fourth minute
• calculate the energy aborbed by the solution uing q=mct
• calculate amount of HCL used
• calculate the enthalpy change of neutralisation

Question 3

What are the errors that can occur for determining the enthalpy change of neutralisation and how do you overcome this

Answer 3

• heat transfer to and from surrounding
• inaccuracy in temperature measurement -electronic thermometer can be used

Question 4

What are the safety risks for determining the enthalpy change of neutralisation

Answer 4

• sodium hydroxide - cause severe skin burn and eye damage
• Hydrochloric acid - caue severe skin burns and eye damage