Experiment Number 9

Specific Heat of a Metal and Relationship to Atomic Weight of an Element

Introduction

Purpose:

The purpose of this activity is designed to familiarize the student with various properties of elements that are used in developing relationships between elements. The student will also become familiar with the set up of chemical apparatus, the use of a balance and the use of chemical reference materials.

Hypothesis

The hypothesis that we will be testing in this experiment is that the specific heat of an element can (1), be used to identify a metallic element, and (2), be used to predict relationships between elements.

Background:

Elements have various properties. In the density lab we looked at two, density and physical appearance. In this laboratory exercise we are going to examine a third, an element's specific heat (also called heat capacity). The specific heat of a substance is defined to be the amount of heat (calories or Joules) it takes to warm 1 gram of substance 1 degree centigrade. The specific heat of water is 1.00 cal/gºC or 4.18 J/gºC. You will have enough data from this experiment to calculate the specific heat of various metals (everybody shares data). Then you will try to determine a simple relationship between specific heat and atomic weight of metal.

Materials & Methods

Materials:

Various metals

Styrofoam cups

Thread

Equipment:

Balance

Beaker, 400 mL

Hot plate

Ring stand

Thermometer

Pipette (25 mL) or graduated cylinder

Pre-Lab Procedure

1. Examine the chart of specific heats for various elements and attempt to determine whether there exists a relationship between atomic number and specific heat.

2. Familiarize yourself with the procedure used below for determining specific heat.

Procedure:

1. Start heating a 400 mL beaker half filled with water. To speed things up use hot water if available.

2. Measure accurately 100 mL of tap water and add to calorimeter (two Styrofoam cups, one inside the other). Record the temperature of the cup as accurately as possible (estimate tenths of a degree).

3. Determine the weight of the metal assigned to you to three significant figures. Check to see that it will rest complete under the water in the calorimeter. If not already done, attach a thread to the piece of metal (long enough so that the thread can be used to place the metal piece in the boiling water bath and remove it).

4. Suspend the metal in the boiling water bath for about 5 min. Record the temperature of the boiling water bath as accurately as possible.

5. Quickly remove the metal from the boiling water bath, blot as quickly as possible on a paper towel and then place the metal in the 100.0 mL of water in the calorimeter.

6. Gently stir the water in the calorimeter with the thermometer while monitoring the temperature of the calorimeter. Record the maximum temperature obtained.

Calculation Method:

The formula for specific heat is as follows:

Heat (J) = Sp. Heat (J/g-ºC) X Mass (g) X ΔT (ºC)

To determine the specific heat of your unknown metal you will first have to determine the joules involved using the specific heat of water and then substitute the determined joules, the mass of the unknown and the temperature change (between 100ºC and final temperature of the water). You then solve for the unknown specific heat. Use the reference materials provided to confirm the identity of the substance.

Results:

Calculate the specific heat of at least three metals. Show your calculations. Compare your experimentally determined specific heat with a list of known specific heats of metals.

Prepare a chart of specific heats of various elements and their atomic number. Attempt to determine a mathematical relation between atomic number and specific heat. Prepare a graph of specific heat versus atomic number.

Questions

1. Why is the metal from the boiling water bath blotted before placing it in the room temperature water?

2. What factors might affect the specific activity determination?

3. A 5.037 g piece of iron heated to 100ºC is placed in a calorimeter that initially contains 27.3 g of water at 21.2°C. If the final temperature is 22.7°C what is the specific heat capacity of the iron?

4. A 25.0347 g piece of nickel is heated to 100°C and placed in a calorimeter that initially contains 125 mL of water at 21.2ºC. What is the final temperature? (you will need to look up the specific heat of nickel.

5. What is the relationship between a metal's specific heat (heat capacity) and its ability to conduct heat or its ability to conduct electricity? What metals would be best suited for cooking utensils and why?