Pre-Lab 11B: Specific Heat of a Metal

PurposeIf you have ever walked barefoot on a concrete walkway

or street during the summertime, you have felt its warmth on your feet. In fact, the thermal energy transferred to your feet may send you retreating to the grass or even a swimming pool.

Why is the temperature of the concrete so different compared to the temperature of the soil or the swimming pool?

Even though the sunlight shines on all three surfaces, it is easier to raise the temperature of concrete compared to the water in a swimming pool.

A hot summer day may only raise the temperature in a pool by one or two degrees.

• In this lab many changes have been made, they will be in bold, underlined and in the color green.

• In this experiment, you will use a calorimeter, the specific heat of water, and the law of conservation of energy to determine the specific heat of a sample of steel washers and one gold unknown metal sample.

Key Question

• How can you use specific heat to identify an unknown metal sample?

Background

• Define:– Specific heat– Formula % error– Formula for energy

Drawing

• Draw a calorimeter

Procedure

Do all the experiment on the first metal and then, and only then, move on to the next metal.

Follow this lab absolutely exactly and a quickly as possible: time is critical!!

Section 1:

1) Use four steel washers

2) Make a calorimeter

3) fill calorimeter 3/4 with room temperature water (not tap water)

Mass the water: remember how to find the mass of only the water (tare mass)?

4) Omit

5) -Place a 400 ml beaker w/ 3/4 water on a hot plate, heat to boiling.

-The ring stand, lower 4 washers on the hook into the beaker of boiling water, they do not touch the glass

-Heat washers for 5 minutes.

6) Measure the temperature of the boiling water and record as initial temperature of metal.

7) Measure temp of calorimeter water: record

8) As quickly as possible, remove the hook w/washers from the hot water/shake and slide only washers into the calorimeter, no splashing

close the calorimeter, place thermometer in hole in the top. Slide the thermometer up and down in the calorimeter GENTLY.

9) Once temperature stabilizes, record.

10) Repeat steps 1-9 for only one second metal: gold cube.

-place a large rubber stopper in the beaker which is on the hot plate

-place the gold cube on the rubber stopper

-use tongs to get gold cube out of boiling water, do not use the hook method

Data chart: “mass and temperature data”

replace copper w/ steel

3 columns: eliminate the second unknown

Section 2:

a. Is the temperature change of calorimeter water

c. Use heat equation solve for E of water:

what is the equation?

Ew = Mw Cpw (T2w –T1w)

where do you get the Cp of water?

Section 2:

Name of Substance Specific Heat, J/g °C Aluminum 0.899

Brass 0.380

Copper 0.385

Nickel 0.443

Iron 0.449

Steel 0.470

Water 4.184

Zinc 0.388

d. SHOW YOUR WORK:

This is a key point:

energy released by the metal is equal to the energy absorbed by the water:

Ew = Em

now knowing the value of E for the metal (Em), calculate the specific heat (Cp) of the metal:

Em = Mm Cpm (T2m –T1m) so isolate Cpm: how?

Remember, since the energy is being released by the metal, the Cp value will be negative = loss of heat

f. % error = (calculated – actual) x 100

Because there are two metals record as this:

Lines a through d, use a two column entry system and show your work

e. see front board for known Cp metals

Section 3:

b: use only your data (not the class data)

d: Omit

Post Lab: Lab 11B: Specific Heat of a Metal

PurposeIf you have ever walked barefoot on a concrete walkway or

street during the summertime, you have felt its warmth on your feet. In fact, the thermal energy transferred to your feet may send you retreating to the grass or even a swimming pool.

Why is the temperature of the concrete so different compared to the temperature of the soil or the swimming pool?

Even though the sunlight shines on all three surfaces, it is easier to raise the temperature of concrete compared to the water in a swimming pool.

A hot summer day may only raise the temperature in a pool by one or two degrees.

Key Question

• How can you use specific heat to identity an unknown metal sample?

Background

• Define:– Specific heat– Formula for energy– Formula % error

Knowing the value of E for the metal, calculate the specific heat (Cp) of the metal.

Identify your unknown metal(s) by comparing your calculated value of its specific heat to known specific heat values of common metals provided by your teacher.

Calculate the percent error for your unknown sample(s).

b. Looking at your data, were the experimental values too high or too low? Based on the experimental procedure, give an explanation for your observations.

c. How does the Law of Conservation of Energy allows us to make the calculations needed to determine the specific heat of the mystery metal?

e. Water has a high specific heat. How does the fact that humans are largely made up of water help us regulate our body temperature