Home-based Learning 2011

HCI C1 H2 Chemistry

Home-Based Learning 2014

4

C1 H2 Chemistry

Home-based Learning 2014

Name:

CT Group: 14S

Aims

1.To be familiar with calorimetry in relation to the determination of the enthalpy change of combustion of ethanol.

2.To encourage planning and independent learning.

Instructions

1. Access the Labskills module on Moodle:

(Main page My Courses Chemistry 2014/2015 Practicals and Planning

LabSkills Measuring enthalpy change Enthalpy of combustion)

Familiarize yourself with calorimetric experiments for the calculation of DHc under laboratory conditions.

2. Complete the task below by typing your answers (please underline).

3. Submit the print-out of your completed HBL exercise to your tutor by Tue 27 May 2014

Task

You will consider two different methods that can be used to determine the enthalpy change of combustion, DHc, under laboratory conditions, for ethanol, using the apparatus and information below.

CH3CH2OH(l) + 3 O2(g) 2 CO2(g) + 3 H2O(l)DHc, ethanol

thermometer

shield

lid

copper can

water

spirit lamp that contains ethanol

The two methods have different independent and dependent variables as tabulated below.

Method 1

Method 2

Independent variable

Fixed mass of alcohol burnt

Fixed temperature rise

Dependent variable

Temperature rise

Mass of alcohol burnt

An incomplete procedure for Method 1 is given below. The procedure lacks some details such as the apparatus to be used, the precision of the apparatus and omits some instructions for measurement and recording of raw data. Fill these details in.

Method 1

1. Transfer 100.0 cm3 of water into a dry copper can using measuring cylinder.

2. Using the electronic balance, weigh approximately 10 g of ethanol in the spirit lamp. Leave the spirit lamp on the mass balance. Record the mass of the spirit lamp, lid and ethanol(m1).

3. Place the tripod over the electronic mass balance. Ensure that it is not resting on the mass pan.

Place the copper can containing water on the tripod.

4. Adjust the height of the spirit lamp by placing a wooden block under the spirit lamp so that the flame of the lamp when lit is close to the copper can. Record (m2).

5. Record the initial temperature (T1) of the water using a thermometer.

6. Light the spirit lamp. Stir the water gently using the thermometer during heating.

7. When the mass reading on the electronic balance has fallen by 0.5 g, extinguish the flame.

8. Record the highest temperature (T2) read on the thermometer after the flame has been extinguished.

9. Reweigh the final mass of the spirit lamp (m3). State two controlled variables in the experiment:

Volume of the water in the copper can and the concentration of ethanol burnt

Write a complete procedure for Method 2, including the details which were omitted in the procedure for Method 1.

Method 2 (based on variables stated in the table on pg 2)

Evaluation

Discuss one significant source of error common for both methods and one source of error that is unique and most pertinent for each of the methods used above.

In your discussion,

state the error

deduce its impact on the value of DHc obtained

suggest one modification which would minimize the error.

Common error for both Method 1 and Method 2

Error pertinent to Method 1

Error pertinent to Method 2

Submit the print-out of your HBL exercise to your Chemistry tutor by Tue 27 May 2014.