To perform simple calorimetry experiments.
To use calorimetry results to calculate the specific heat of an unknown metal.
To determine the enthalpy of neutralization for a strong acid-strong base reaction
Any chemical or physical change involves a transfer of heat (energy), where heat may exit the system (exothermic) or be absorbed by the system (endothermic). The amount of heat that flows into or out of the system is determined with a technique called calorimetry (heat measurement). A calorimeter is a laboratory apparatus that is composed of an insulated container, a thermometer, a mass of water, and the system to be studied, and is used to measure the quantity and direction of heat flow accompanying the chemical or physical change.
Heat is measured in the energy units, Joules (J), defined as 1 kg.m2/s2. Another common unit is the calorie (cal) which is defined as the heat required to raise the temperature of 1-g of water by 1°C.
Enthalpy (or heat) of reaction, DH, is the quantitative expression used to express the heat change in chemical reactions that are at constant pressure. DH values are negative for exothermic reactions and positive for endothermic reactions and are often expressed as J/mol or kJ/mol.
The specific heat of any substance can be determined in a calorimeter. The specific heat is an intensive physical property of a substance (independent of sample size) and is the quantity of heat necessary to raise the temperature of 1-g substance by 1°C. Specific heat of some common substances are listed in Table 1. Note that either °C or K can be used for the change in temperature, since the difference in a degree is the same for both scales.
Table 1: Specific Heat Values for Some Common Substances
|Substance||Specific Heat (cal/g °C)||Specific Heat (J/g °C)||Substance||Specific Heat (cal/g °C)||Specific Heat (J/g °C)|
The specific heat of a substance can be calculated by:
Or, rearranging for energy,
q is the symbol given for heat and ΔT is the temperature change of the substance, where ΔT = Tfinal – Tinitial
Part A: Specific Heat of a Metal
When two objects at different temperatures come into contact, heat flows from the hotter to the colder object until the two objects reach the same temperature (Tf). In part A, the specific heat of a metal that does not react with water is determined by (1) heating a measured mass of metal, M, to a known (higher) temperature; (2) which is then placed into a measured amount of water at a known (lower) temperature; and (3) the final equilibrium temperature of the system after the two are combined is measured.
The heat lost by the hot metal (indicated by negative sign – exothermic) is equal to the heat gained by the cooler water (indicated by positive sign – endothermic) which is expressed by,
Substituting equation (2) into equation (3),
Rearranging for specific heat of metal gives
These equations assume no heat loss to the calorimeter when the metal and water are combined.
Part B: Enthalpy (Heat) of Neutralization of an Acid-Base Reaction
The transfer of heat that results from an acid/base neutralization reaction carried out at constant pressure is called the enthalpy of neutralization, ΔHn. The reaction to be studied is:
NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
As with any chemical reaction, the extent of the reaction is dependent on the amount of limiting reactant present. Given the moles of limiting reactant used in this reaction and the measured heat of the reaction (q), ΔHn can be determined.
Heat evolved for the reaction is determined by (1) assuming the density and the specific heat for the acid and base solutions are equal to that of water, and (2) measuring the change in temperature, ΔT , when the two are mixed:
The mass (grams) of solution equals the combined masses of the acid and base solutions.
DHn will be reported in units of kilojoules per mole (kJ/mol) of water produced. Thus, the amount of water that can be produced given the amounts of each reactant must be calculated, and ΔHn is calculated as follows:
Part A: Determination of the Specific Heat of a Metal
Materials: Calorimeter equipped with aluminum cup, stirrer, thermometer and lid, 25-mL graduated cylinder, 200-mm test tube, unknown metal, hot plate, 400-mL beaker, second thermometer for boiling water bath.
Prepare a boiling water bath in a 400-mL beaker as shown in Figure 1.
Prepare the metal
|Figure 2: Calorimeter setup|
|Figure 1: Hot water bath setup. (Note – do not allow test tube to rest on bottom of beaker, secure test tube with a clamp.)|
Place the 200-mm test tube with the dry metal in the water bath, making sure that the water level is well above the metal in the test tube (Figure 1). Heat the water to boiling and maintain the temperature for 10 minutes so the temperature of the metal will reach thermal equilibrium with the boiling water. Prepare the calorimeter while the water is heating.
Prepare the water for calorimeter and data collection sheet
Record the temperature of the metal and transfer the metal to water
NOTE: Have a timer ready for the next step and start the timing as soon as the metal is added to the cool water. Use the time intervals found in Data Table 1 as the guideline for collecting your data.
Complete Trial 2 – Repeats parts A.1 through A.10 for the same dry metal sample. Allow the calorimeter to cool to room temperature before starting the second trial.
DISPOSAL AND CLEANUP
Dry the metal using a paper towel and place in the appropriately labeled “drying” beaker – do not place wet metal back in original container and do not mix dissimilar metals. Rinse and dry all calorimeter components thoroughly using a paper towel, and return to original storage.
Part B: Enthalpy (Heat) of Neutralization of an Acid-Base Reaction
Materials: Calorimeter equipped with plastic cup, stirrer, thermometer and lid, second thermometer, two 25-mL graduated cylinder, 25.0-mL of 1.1 M HCl, 25.0-mLof 1.1 M HNO3, 50.0-mL of standardized 1.0 M NaOH
Repeat parts B.1 through B.7, replacing 1.1 M HCl with 1.1 M HNO3. Allow the calorimeter to cool to room temperature before starting the trial with HNO3.
On the Report Sheet, compare your DHn values for the two strong acid-strong base reactions.
DISPOSAL AND CLEANUP
Dispose of all solutions in the sink with plenty of running tap water. Rinse and dry all calorimeter components thoroughly using a paper towel, and return to original storage.
|Plot the data (Figure 3) Use the data collected on Data Table 1 for Part A and Data Table 2 for Part B to plot the graph using graph paper or by using appropriate software. Plot the temperature (y-axis) as a function of time in seconds (x-axis). If a graph paper is used, make sure to use the entire graph paper. Determine from your curve the maximum temperature of the mixture by extrapolation (as shown in Figure 3): (1) insert a best fit linear trend line through the data points on the cooling portion of the curve only; (2) The value of “Tmax” is the temperature at Time = 0 sec, which is simply the y-intercept. An example graph is shown below: Figure 3: Extrapolation of temperature verses time data for an exothermic reaction|
Date ____Fall 2020____ Name ___________________________ Partner(s) __ ____________________
Part A: Show calculation where indicated for Trial 1.
Unknown metal number: ___N/A____ Trial 1 Trial 2
Plot the graph using the data collected in Data Table 1, then continue with the rest (separate graph for each trial).
Most Likely Identity of Metal (see Table 1):
Calorimetry Report Sheet cont. Name: _______________ _______
Part B: Trial with Trial with
HCl + NaOH HNO3 + NaOH
(NOTE: Allow the container to cool to Room Temp before starting trial with HNO3)
Plot the graph using the data collected in Data Table 2 and then continue with the rest of data analysis.
|HCl (aq) + NaOH (aq) à||HNO3 (aq) + NaOH (aq) à|
Compare your two values for DHn. Should DHn be the same or different for the two reactions?
Data Table 1: Record temp at each time interval
|Part A: Specific Heat of Metal|
|Trial 1||Trial 2|
|Time (sec)||Temp||Time (sec)||Time (sec)|
|**Add hot metal time=0sec||**Add hot metal time=0sec|
Data Table 2: Record temp at each time interval
|Part B: Enthalpy of Neutralization|
|HCl + NaOH||HNO3 + NaOH|
|Time (sec)||Temp||Time (sec)||Temp|
|**Add Acid time=0sec||**Add Acid time=0sec|
This data is in the included Excel files.
*Temperature of cool water at -20 seconds can be used as temperature just before the addition of metal in Part A when plotting graph. The same concept applies for Part B.
** Time = 0 sec is when the metal (or acid) is added – this temperature is determined from the graph and not by using the thermometer. Start timing as soon as the metal is added to cold water in Part A (or acid is added to base in Part B), and measure the temperature of the mixture within 5 seconds of adding metal (acid).
***add time to the row if more data is needed
Date _____________ Name ________________________________ Partner(s) _______________________
Molecular equation: HCl(aq) + NaOH(aq) à
Net ionic equation:
Molecular equation: HNO3(aq) + NaOH(aq) à
Net ionic equation:
% error for HCl + NaOH:
% error for HNO3 + NaOH:
Try it now!
How it works?
Follow these simple steps to get your paper done
Place your order
Fill in the order form and provide all details of your assignment.
Proceed with the payment
Choose the payment system that suits you most.
Receive the final file
Once your paper is ready, we will email it to you.
No need to work on your paper at night. Sleep tight, we will cover your back. We offer all kinds of writing services.
No matter what kind of academic paper you need and how urgent you need it, you are welcome to choose your academic level and the type of your paper at an affordable price. We take care of all your paper needs and give a 24/7 customer care support system.
Admission Essays & Business Writing Help
An admission essay is an essay or other written statement by a candidate, often a potential student enrolling in a college, university, or graduate school. You can be rest assurred that through our service we will write the best admission essay for you.
Our academic writers and editors make the necessary changes to your paper so that it is polished. We also format your document by correctly quoting the sources and creating reference lists in the formats APA, Harvard, MLA, Chicago / Turabian.
If you think your paper could be improved, you can request a review. In this case, your paper will be checked by the writer or assigned to an editor. You can use this option as many times as you see fit. This is free because we want you to be completely satisfied with the service offered.