Materials Included In Kit

Additional Materials Required

Safety Precautions

Onion’s fusible alloy contains bismuth, lead and tin. Lead is extremely toxic by inhalation and ingestion as a dust or fume; it is a possible carcinogen as a dust or fume. Bismuth is slightly toxic by inhalation and ingestion and is flammable in the finely divided form. However, in the form of Onion’s fusible alloy, these hazards are greatly reduced. Do not ingest the alloy or heat the alloy unless it is submerged in water. Take precautions to avoid burns when heating the metals in the boiling water. Use tongs, and allow the boiling water to cool before pouring it down the drain to prevent steam burns. Wear chemical splash goggles, chemical resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information. 

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Save all materials for future labs.

Lab Hints

• Provide the metal specimen set of 4 and the steel sample from the specific heat set as the unknowns. Place each sample on a piece of paper, labeled wih the sample’s item number. The rest of the specific heat set (copper, aluminum, tin and zinc) have their identities engraved on the bottom, so they will not work for this purpose.
• Provide each student group with one of the copper, brass, steel (2), Onion’s fusible alloy and aluminum samples.
• Measurured water in calorimeter should be between 60–100 g.
• The specific heat metals set shows the identity of the metals engraved on the bottom of each. Given time, you can have students confirm the known. Steel from this set is a good metal to use as an unknown because it is an alloy of carbon and iron and only has Fe (iron) engraved at the bottom and not carbon.
• Onion’s fusible alloy contains approximately 50% bismuth, 30% lead and 20% tin. While pure bismuth metal melts at 271 °C, pure lead melts at 328 °C, and pure tin melts at 232 °C, Onion’s fusible alloy melts at only 92 °C (197° F)—that is 8 °C (15° F) below the boiling point of water. Students will not be able to collect the specific heat of Onion’s fusible alloy because it will melt.
• Students use the 25-mL graduated cylinder for density measurements.

Teacher Tips

• This laboratory activity was specifically written, per teacher request, to be completed in one 50-minute class period. It is important to allow time between the Prelab Homework Assignment and the Lab Activity.

Further Extensions

Alignment to the Curriculum Framework for AP^® Chemistry

Enduring Understandings and Essential Knowledge
The type of bonding in the solid state can be deduced from the properties of the solid state. (2D)
2D2: Metallic solids are good conductors of heat and electricity, have a wide range of melting points, and are shiny, malleable, ductile, and readily alloyed.

Chemical reactions can be classified by considering what the reactants are, what the products are, or how they change from one into the other. Classes of chemical reactions include synthesis, decomposition, acid−base, and oxidation−reduction reactions. (3B)
3B3: In oxidation−reduction (redox) reactions, there is a net transfer of electrons. The species that loses electrons is oxidized, and the species that gains electrons is reduced.

Energy is neither created nor destroyed, but only transformed from one form to another. (5B)
5B2: When two systems are in contact with each other and are otherwise isolated, the energy that comes out of one system is equal to the energy that goes into the other system. The combined energy of the two systems remains fixed. Energy transfer can occur though either heat exchange or work.
5B3: Chemical systems undergo three main processes that change their energy: heating/cooling, phase transitions, and chemical reactions.
5B4: Calorimetry is an experimental technique that is used to measure the change in energy of a chemical system.

Learning Objectives
2.25 The student is able to compare the properties of metal alloys with their constituent elements to determine if an alloy has formed, identify the type of alloy formed, and explain the differences in properties using particulate level reasoning.
2.26 Students can use the electron sea model of metallic bonding to predict or make claims about the macroscopic properties of metals or alloys.
5.4 The student is able to use conservation of energy to relate the magnitudes of the energy changes occurring in two or more interacting systems, including identification of the systems, the type (heat versus work), or the direction of energy flow.
5.5 The student is able to use conservation of energy to relate the magnitudes of the energy changes when two nonreacting substances are mixed or brought into contact with one another.
5.6 The student is able to use calculations or estimations to relate energy changes associated with heating/cooling a substance to the heat capacity, relate energy changes associated with a phase transition to the enthalpy of fusion/vaporization, relate energy changes associated with a chemical reaction to the enthalpy of the reaction, and relate energy changes to PΔV work.
5.7 The student is able to design and/or interpret the results of an experiment in which calorimetry is used to determine the change in enthalpy of a chemical process (heating/cooling, phase transition, or chemical reaction) at constant pressure.

Science Practices
1.4 The student can use representations and models to analyze situations or solve problems qualitatively and quantitatively.
4.2 The student can design a plan for collecting data to answer a particular scientific question.
4.3 The student can collect data to answer a particular scientific question.
5.1 The student can analyze data to identify patterns or relationships.
5.2 The student can refine observations and measurements based on data analysis.
5.3 The student can evaluate the evidence provided by data sets in relation to a particular scientific question.
6.2 The student can construct explanations of phenomena based on evidence produced through scientific practices.
6.4 The student can make claims and predictions about natural phenomena based on scientific theories and models.
7.1 The student can connect phenomena and models across spatial and temporal scales.

Answers to Prelab Questions

1. A student prepares for the AP^® Chemistry exam by studying thermodynamics in lab. Before performing calorimetry experiments, she determines the specific gravity of four metal cylinders (see Figure 2). Review the procedures in a and b, and answer the questions/statements in italics
   {12383_Answers_Figure_2}
   1. Density by Measurement Procedure:
      • Record the mass of each cylinder to the nearest 0.1 g.
      • Carefully measure the dimensions (diameter and length) of the metal cylinders to the nearest millimeter (0.1 cm).
      • How will the student calculate the volume of the cylinder?

        The volume of the cylinder may be calculated using V = πr²L, where r is the radius and L is the length of the cylinder.

      • Determine how to calculate density of each cylinder.

        The density of each cylinder may be calculated using the equation Density = Mass/Volume with units of g/cm³.

   2. Density by Displacement Procedure:
      • Record the mass of each cylinder to the nearest 0.1 g.
      • Fill a 50- or 100-mL plastic graduated cylinder about half way with water. Record the volume of water in milliliters.
      • Carefully place the metal cylinder into the graduated cylinder. It works best to tip the graduated cylinder and slide the metal cylinder in along the side.
      • Record the new volume of water in the cylinder.
      • Determine how the student calculates the volume of the metal sample.

        The volume of the metal sample can be calculated using this equation:
        V_metal = V_metal + water – V_water.

      • Determine how to calculate the density of each cylinder.

        The density of each cylinder may be calculated using the equation Density = Mass/Volume with units of g/cm³.

2. The student determined that if the density of a metal is known, its atomic radius can be mathematically determined. Review the following calculations, and answer the questions/statements in italics.

   Determination of Aluminum Metal Radii:

   • Density of aluminum from Question 1 = 2.70 g/cm³.
   • Calculate the mass of one aluminum atom.

     The molar mass of aluminum is 26.9815 g/mol.
     26.9815/6.022 x 10²³ = 4.48 x 10^–23 g.

   • Aluminum has a face-centered unit cell, shown in Figure 3. Refer to your AP Chemistry textbook for more information on metallic unit cells.
     {12383_Answers_Figure_3}
   • Face-centered unit cells have 4 atoms in the unit cell. Use the mass of the aluminum atom to calculate the mass of the unit cell.

     4.48 x 10^–23 g x 4 = 1.79 x 10^–22 g.

   • Determine the size of the unit cell by (mass of the unit cell/density of aluminum), with units of cm³.

     1.79 x 10^–22 g/2.70 g/cm^–3 = 6.64 x 10^–23 cm³

   • Convert the size of the unit cell to units of cm to determine the length of the cell.
     {12383_Answers_Equation_6}
   • Use the Pythagorean Theorem (A² + B² = C²) to determine the length of the hypotenuse.
     {12383_Answers_Figure_4}
     {12383_Answers_Equation_7}
   • Look at Figure 4. How many radii are there? Calculate the radius of each aluminum atom. Convert the value from cm to pm.

     There are 4 radii. Therefore, 5.73 x 10^–8 cm/4 = 1.43 x 10^–8 cm
     1.43 x 10^–8 cm x (1 x 10¹⁰ pm/1 cm) = 143 pm

3. Specific gravity is a comparison (or ratio) of the mass of a substance to the mass of an equal volume of water. What is the relationship between specific gravity and density? 

   Specific gravity is a similar term to density. Specific gravity is a comparison (or ratio) of the mass of a substance to the mass of an equal volume of water. Since the density of pure water is 1.00 g/cm³ at 20 °C, the specific gravity is equivalent to density. Specific gravity, however, is unitless.

4. Look at the student’s calorimetry setup. Label the experiment equipment.
   {12383_Answers_Figure_5}
5. The student wrote her own procedure to confirm the specific heat values of the metal samples in the following table. Answer questions in parts a–c.
   {12383_Answers_Table_1}
   1. Calorimetry Procedure:
      • Weigh a specific heat metal sample on a balance to the nearest 0.1 g.
      • Place the metal sample in a boiling water bath for approximately 5–10 minutes. Why is this step necessary?

        Placing the metal sample in boiling water is necessary because the metal must be hot in order to measure heat transfer in the calorimeter.

      • Fill a coffee cup calorimeter with a measured quantity of room temperature or slightly chilled water. Measure and record the temperature of the water in the calorimeter in °C.
      • Using tongs, lift up the heated metal sample from the boiling water bath and carefully place it into the water in the calorimeter.
      • Stir the water in the calorimeter with a stirring rod, slowly and constantly. Use a thermometer to measure and record the highest temperature that the water reaches. Does the heat gained by the water equal the heat lost by the sample?

        Yes, the heat gained by the water equals the heat lost by the sample.

   2. Calculate the heat gained by the water in the tin calorimetry experiment from the table. The metal was heated to 100 °C in a calorimeter containing 60 g of water at 18 °C, and the temperature of the water increased to 22 °C.

      q (gained by water) = (60 g) x (1.00 cal/g∙°C) x (4 °C) = 240 calories

   3. Calculate the heat lost by the same metal sample.

      (60 g) x (1.00 cal/g∙°C) x (4 °C) = –[(58.00) x (c) x (–78 °C)]&
      c = 0.053 cal/g∙°C (0.222 J/g °C)

6. Work with your partner to determine the identity of your metal sample—there are 6 unknown metal samples to choose from and 5 known metal samples to observe. Write a procedure prior to arriving to lab to be approved by the instructor. As a class, reason through the data and determine the identity of the metal samples. Data tables with known density and specific heat values will be provided.

   Each student group determines the density and specific heat of each metal sample. They should also make overall physical observations on their sample. As a class, compare the chart given below to determine the identity of each metal. The Onion’s fusible alloy is the only metal that is not in cylindrical form and it is a fusible alloy. Fusible alloys are low melting point alloys. They usually contain bismuth, lead, tin, cadmium or indium and have a melting point in the range of 51–260 °C. Onion’s fusible alloy contains approximately 50% bismuth, 30% lead and 20% tin. While pure bismuth metal melts at 271 °C, pure lead melts at 328 °C, and pure tin melts at 232 °C, Onion’s fusible alloy melts at only 92 °C (197° F)—that is 8 °C (15° F) below the boiling point of water. Students will not be able to collect the specific heat of Onion’s fusible alloy because it will melt.

   {12383_Answers_Table_2}

References

AP^® Chemistry Guided-Inquiry Experiments: Applying the Science Practices; The College Board: New York, NY, 2013.

Introduction

This advanced activity is all about metals! Determine the identity of a metal cylinder and strengthen concepts from Big Ideas 2 and 5 for exam day. As a cooperative class activity, work in student group stations and conduct tests and observations to determine the metal at each station. The Prelab Homework Assignment completed prior to wet lab day solidifies the concepts and experiment setup needed to successfully complete the lab.

Concepts

• Heat capacity
• Enthalpy
• Calorimetry
• Alloys

Background

Metals contain a type of bonding called metallic bonding in which unique physical properties arise—malleability, high melting point, ductility and the ability to conduct heat and electricity. Depending on the metal’s identity, these properties vary, and some are more practical for commercial applications. In fact, pure metals are excellent starting base metals to create alloys, which often have vastly improved properties that render them useful. An alloy is a mixture of two or more metals (or a metal and a nonmetal fused together, often molten) dissolved in each other, so they differ from pure metals by containing more than one type of atom. The properties of an alloy are often very different than the properties of its components. There are two types of alloys (see Figure 1): interstitial—different, smaller metal or non-metal atoms are added between the spaces of the existing metal atoms, and substitutional—different metal or non-metal atoms replace the existing metal atoms and are of similar size.

Calorimetry and specific gravity are experimental methods available to determine the identity of metal samples—pure and alloyed. Transfer of heat or heat flow always occurs in one direction—from a region of higher temperature to a region of lower temperature—until some final temperature is reached. The transfer of heat energy can be detected by measuring the resulting temperature change, ΔT, calculated by subtracting the initial temperature from the final temperature. The measure of heat capacity, or the quantity of heat needed to raise the temperature of one gram of a substance by one degree Celsius at constant pressure, is termed specific heat and is represented by the symbol c. The SI units for specific heat are given in J/g∙°C, and the non-SI units are cal/g∙°C (Note: 1 calorie = 4.184 Joules). The amount of heat delivered by a material (q) is equal to the mass of the material delivering the heat (m) multiplied by the specific heat of the material (c) multiplied by the temperature change associated with delivering the heat (ΔT). The equation can be written as follows: To make accurate measurements of heat transfer and to prevent heat loss to the surroundings, an insulating device called a calorimeter is used. A calorimeter measures heat flow. The heat given off by a material is absorbed by the calorimeter and its contents (often water or other materials with known heat capacities). The heat gained by the water in the calorimeter (or gained by the calorimeter itself if dry) must be equal in magnitude (and opposite in sign) to the heat lost by the sample. Since then Equation 5 may be used to calculate the specific heat of an unknown metal sample.

Prelab Questions

Complete the Prelab Homework Assignment set (Student PDF) before lab day. This dry portion of this experiment solidifies the thermodynamics concepts needed for lab day. Determine the identities of the metal samples on lab day. Consult your instructor for appropriate disposal procedures.

Safety Precautions

Onion’s fusible alloy contains bismuth, lead and tin. Lead is extremely toxic by inhalation and ingestion as a dust or fume; it is a possible carcinogen as a dust or fume. Bismuth is slightly toxic by inhalation and ingestion and is flammable in the finely divided form. However, in the form of Onion’s fusible alloy, these hazards are greatly reduced. Do not ingest the alloy or heat the alloy unless it is submerged in water. Take precautions to avoid burns when heating the metals in the boiling water. Use tongs and allow the boiling water to cool before pouring it down the drain to prevent steam burns. Wear chemical splash goggles, chemical resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information. 

Student Worksheet PDF

12383_Student1.pdf