q mass T f Ti Specific heat Our calorimeter is going to be a set of Styrofoam coffee cups. These cups are well known insulators, and they should keep most heat inside themselves. They are not perfect, however, and they will absorb some of the heat from the process, so we need to determine the calorimeter constant. For any process, the first law of thermodynamics must be followed.
E 0 qsystem qsurroundings However, if the calorimeter itself is going to absorb some energy, it must be accounted for as well.
E 0 qsystem qsurroundings qcalorimeter In the first portion of our experiment, a known mass of water with a known temperature will be used to determine how much energy is being absorbed by the calorimeter. Once this is known, the change in enthalpy from the decomposition of hydrogen peroxide can be determined. 2H2O2(aq) 2H2O(l) + O2(g) A solution of hydrogen peroxide will be added to the calorimeter and its temperature will be monitored for a short time. A small amount of iron nitrate will be added to catalyze the reaction and produce a measureable temperature change. This temperature change will be plotted over time. Using this plot, the mass of solution, its specific heat, the calorimeter constant, and the temperature change, we will be able to determine the enthalpy for the reaction.
Procedure Week One – Determination of the calorimeter constant Objective – To measure the amount of energy absorbed by the calorimeter while observing a change in temperature.
1. Using a top loading balance, determine the mass of Styrofoam cup and a stir bar. 2. Place about 100mL of warm deionized water in the cup. Monitor its temperature for 3-4 minutes. Record the temperature every minute. 3. Using a top loading balance, determine the mass of a second Styrofoam cup and a stir bar. 4. Place about 100mL of room temperature water in the cup. Monitor its temperature for 34 minutes. Record the temperature every minute. 5. When the temperature of the warm water is about 20C above the room temperature water, quickly pour it into the room temperature water. Continue monitoring the temperature and recording it every minute. 6. After several minutes, when the temperature is no longer changing quickly, record the mass of the combined water. 7. Repeat this procedure at least one more time.
Week One – Preparation of a standard potassium permanganate solution Objective: To prepare a potassium permanganate solution with a known concentration. This will be used in a second week to standardize a hydrogen peroxide solution.
1. Obtain enough potassium permanganate to make 250.0mL of a 0.02M solution. NOTE: Use the analytical balance for this operation. It is NOT necessary to get exactly the amount you calculated. It is only important to be close to this amount, and to record the amount you took accurately. 2. Dissolve this in a small amount of water before diluting it to a final volume of 250.0mL in a volumetric flask. 3. Transfer this to a clean dry bottle, and store it for use next week.
Week Two – Determination of the Concentration of hydrogen peroxide. Objective: Determine the concentration of hydrogen peroxide and use this result to know how many moles are being decomposed.
1. Pipet 2.00mL of hydrogen peroxide into a small Erlenmeyer flask. Add about 10mL of 4.0M H2SO4 and 50mL of deionized water. 2. Rinse and fill a buret with the potassium permanganate solution that was prepared last week. 3. Start to titrate the solution. It should stay clear until the end point is reached. The endpoint is the lightest permanent pink color that persists. 4. Repeat so that you have three precise trials. 5. Calculate the concentration of the hydrogen peroxide solution. The balanced chemical equation is written below. 2MnO4-(aq) + 5H2O2(aq) + 6H+(aq) 2Mn2+(aq) + 5O2(g) + 8H2O(l)
Week Two – Enthalpy of Decomposition of Hydrogen Peroxide Objective: Use the calorimeter from last week to determine the enthalpy of decomposition of hydrogen peroxide.
1. Add 50.0mL of hydrogen peroxide to the tared Styrofoam cup using a graduated cylinder. 2. Obtain 10.0mL of 0.5M iron(III)nitrate in a graduated cylinder. 3. Start recording the temperature of the hydrogen peroxide solution. At the five minute mark, quickly add the iron nitrate, but do not record the temperature. 4. At the six minute mark start recording temperatures again until you reach the 12 minute mark. 5. Dump out the solution, and repeat if time permits.
Calorimeter Constant Calculations
It is very straightforward to determine the energy that is gained or lost when a known mass of water is heated or cooled. E 0 qsystem qsurroundings qcalorimeter From the data above, you will need to plot the temperature of the room temperature water and extrapolate that line out a bit. That will be its initial temperature (T1). Extrapolate through the points after mixing, and this will be its final temperature (T2). From this the heat gained by the room temperature water can be calculated. qroom mass T2 T1 Cwater
This is repeated for the warm water. Extrapolate the warm water’s temperature through the time when it is mixed. This is will be its initial temperature (T3). Extrapolate through the points after mixing and this will be its final temperature (T2). From this the heat lost by the warm water can be calculated. qwarm mass T3 T2 Cwater
The Calorimeter constant will be the difference between these two. Whatever energy lost by the warm water should have been gained by the room temperature water, except for what was gained by the cup. qroom qwarm qcup T2 T1 Ccup A sample for the plot is below. The vertical line is the time when the two water samples were mixed.
Mixing Curve for Water
42 37
T3
Temp (C)
Room Temp Water 32 27 T1 22 0 2 4 6 Time (min) 8 10 12 T2 Warm Water
Calculations for the Enthalpy of Decomposition of Hydrogen Peroxide
The solution here is mostly water, and it is assumed to have a specific heat of 4.184 J/gC. There are two things that would absorb the energy lost by hydrogen peroxide: the solution, and the cup. qH 2O2 qsolution qcup The ‘q’ of the solution is calculated in a way similar to that of water. The time and temperature information will have to be plotted. The only thing that is different here, is that the temperature of just one thing is being recorded. There will only be two temperatures, T1 and T2. qsolution mass T2 T1 4.184 J
g C
qcup Ccup T2 T1
Here Ccup was determined last week. To determine the H in terms of joules per mole, one will have to divide the energy by the number of moles in the solution. moles M H
2
O2
Volume
H 2O2
Report
Information taken from this lab included the following. Week One Mass of room temperature water Mass of cup(s) and stirring bar(s) Mass of warm water Mass of combined water Initial temperatures for water Post mixing temperatures for water Time Mass of potassium permanganate Volume of potassium permanganate solution Week Two Volume of hydrogen peroxide solution titrated. Volume of potassium permanganate used. Mass of cup and stirring bar. Mass of hydrogen peroxide Mass of mixed peroxide and iron Temperature prior to mixing. Temperature after mixing. Time From this, one will need to calculate:
The concentration of potassium permanganate The concentration of hydrogen peroxide (averaged) The calorimeter constant (averaged) The enthalpy of decomposition of hydrogen peroxide (averaged)
In a 1 – 2 page typed report please give the following:
A brief 2-3 sentence abstract describing the experiment and the final result. Work detailing how quantities were determined. A brief one paragraph discussion dealing with the comparison of the result to the literature value of (-94.6 kJ/mole). What specific sources of error might account for a difference between your result and the literature value.
You May Also Find These Documents Helpful
-
Calculate the molar enthalpy of the NaOH(aq) using the data obtained from this experiment. Show all your work.…
- 700 Words
- 6 Pages
Satisfactory Essays -
4. Use the equation: q = m(SH)ΔT to solve for the amount of heat gained by the…
- 1515 Words
- 7 Pages
Good Essays -
In problem 3 above, the calorimeter has a heat capacity of 8.20 J/goC. If a correction is made to account for heat absorbed by the calorimeter, what is the heat of reaction?…
- 895 Words
- 4 Pages
Powerful Essays -
In this experiment, a device that measures heat, a calorimeter, will be used. For this experiment, a calorimeter will be made with two nested Styrofoam cups, cardboard to cover the top as a lid, a thermometer, as well as about 25mL of water and about 7g of NH4¬NO3. The temperature of the solution will be closely monitored with the thermometer.…
- 377 Words
- 2 Pages
Good Essays -
The primary objective of this lab is to be able to determine the specific heat of a reaction by using a calorimeter. A calorimeter is a device used to determine the specific heat of chemical reaction or a physical change. The specific heat a reactions is used to refer to the amount of heat that is lost or gained when one gram of a particular substance increases or decreases by one degree Celsius. When a chemical reaction occurs in an open container most of the energy gained or lost is in the form of heat. Almost no work is done (i.e. nothing is being moved). Heat flows between the system and surroundings until the two are at the same temperature, when a chemical reaction occurs in which the system absorbs heat, the process is endothermic (it feels cold). When a chemical reaction occurs in which the system produces heat it is exothermic (it feels hot)…
- 2451 Words
- 10 Pages
Good Essays -
Purpose: This lab taught procedures for determining heat of capacity of a calorimeter and measuring enthalpy of change for three reactions. It also enforced methods of analyzing data obtained through experimentation and calculating enthalpy. These procedures are used in the branch of thermodynamics known as thermochemistry which is the study of energy changes that accompany chemical reactions. Concepts from this lab can be used to determine the potential energy of a chemical reaction. Much of the energy people depend on comes from chemical reactions. For example, energy can be obtained by burning fuel, metabolizing of food or discharging a batter.…
- 2424 Words
- 10 Pages
Good Essays -
A coffee cup calorimeter is an apparatus that is used to measure the quantity of thermal energy gained or lost in a chemical reaction. This experiment utilizes this apparatus, which is made from two styrofoam cups with plastic lids and a thermometer, to measure changes in thermal energy of various reactions. When using this type of apparatus, it is assumed that no heat is transferred between the calorimeter and the surroundings, and that no heat is absorbed or released by the cup. This allows for determination of enthalpy change, which will then allow for the calculation of heat absorbed or released.…
- 2683 Words
- 12 Pages
Powerful Essays -
PURPOSE: In this lab we will have the opportunity to measure the energy in a variety of foods, by heating/burning a portion of the food item and catching the heat released into a known mass of water in a calorimeter. We will also identify units of measuring heat such as calories and joules. We will use basic lab equipment provided in our labpaq and we will use several household items as well. We will follow all safety requirements and standard procedures for this lab.…
- 1195 Words
- 5 Pages
Good Essays -
Purpose- To determine the change in enthalpy for four reactions using calorimetry and Hess’s Law…
- 1287 Words
- 6 Pages
Better Essays -
The purpose of the experiment is to determine the enthalpy of neutralization reactions by calorimetry. Calorimetry, is the science of measuring the amount of heat. All calorimetric techniques are therefore based on the measurement of heat that may be generated (exothermic process) or consumed (endothermic process). The device used for measuring the heat changes in this experiment is called calorimeter. A calorimeter is a Styrofoam cup is used as a calorimeter, because it is a container with good insulated walls to prevent heat exchange with the environment.…
- 2522 Words
- 11 Pages
Good Essays -
A calorimeter is an instrument used to measure the change in heat in a reaction. Inside a calorimeter it is filled with water. To find the specific heat of a substance you place the substance inside the water, then measure the change in the temperature of the water and the change in temperature of the substance. The final temperature and amount of heat transferred will always be equal (q of water= q of substance). Then, using basic algebra, you can figure out the specific heat of the…
- 688 Words
- 3 Pages
Good Essays -
The experiment yielded an exothermic reaction. The calculated enthalpy was far less than the theoretical. The cause of this is a lower heat transfer than the theoretical transfer. This can be caused by heat loss from the calorimeter outwards or not letting the reaction to fully take place.…
- 633 Words
- 3 Pages
Better Essays -
This is known as specific heat capacity; it measures the amount of energy needed to raise the temperature of that particular substance by 1 degree Celsius. Specific heat capacity was first discovered in the 18th century by a Scottish scientist by the name of Joseph Black who noticed that different substances of equal masses required distinctive amounts of heat to raise them to similar temperature intervals (Encyclopædia Britannica 2014). The specific heat capacity of water is 4.184 J/g°C. Energy is most commonly measured joules (J) or kilojoules (kJ) during the study of heat transfer between two substances (Tuckerman n.d.); however, there is another measurement for energy which is used to measure the amount of energy in food, and this is referred to as food calories. Food calories are equal to 1000 heat calories and 1 heat calorie is equal to 4.184 joules (Calories in Food – A Factor in Weight Maintenance and Weight Loss n.d.). Consequently, it can be seen that the specific heat of a substance can also be measured in calories. Therefore, the specific heat capacity of water can also be written as 1 cal/g°C. In this lab, the calculations were done using food calories and heat calories in order to determine the caloric content of one marshmallow per…
- 774 Words
- 4 Pages
Good Essays -
While waiting on the water to boil, retrieve a piece of unknown metal to be identified and record its ID letter and its mass. Once the mass of the unknown metal is recorded, put the metal into the boiling water. While waiting on the water and the metal to achieve the same thermal equilibrium, get a coffee cup and measure its mass. Then pour about 50mL of water into a coffee cup, measure the mass of the water and the coffee cup and then determine the mass of the water alone (mass of water and coffee cup – mass of coffee cup). Record the temperature of the boiling water on the hot plate with the metal and then record the temperature of the water in the coffee cup before adding the metal. Use the string attached to the metal to transfer the metal from the hot water bath to the calorimeter. Using a piece of cardboard to cover the top of the calorimeter, record the temperature of the water in the calorimeter. Repeat the experimental procedure three more…
- 1030 Words
- 5 Pages
Better Essays -
Coffee-cup calorimetry occurs inside of a Styrofoam cup. A known volume of water is poured into the cup and a thermometer is placed through the lid and under the surface of the water. When the chemical reaction occurs in the cup, the heat of the reaction is absorbed by the water. The change in water temperature is then used to calculate the amount heat released or absorbed in the reaction. In this experiment, coffee-cup calorimetry is being used to measure the enthalpy of the reaction between H3PO4 and NaOH.…
- 629 Words
- 3 Pages
Good Essays