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"; Calorimetry Objectives Lab Report-Specific Heat Of A Metal And Enthalpy (Heat) Of Neutralization Of An Acid-Base Reaction - Chem Homework Help
Calorimetry Objectives Lab Report-Specific Heat of a Metal and Enthalpy (Heat) of Neutralization of an Acid-Base Reaction

word image 1955 Calorimetry

Objectives

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

Introduction word image 1956

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 I kg.m2/s2. Another common unit is the calorie (cal) which is defined as the heat required to raise the temperature of I-g of water by I oc.

1 kg. m2

word image 1957 and 1 cal = 4.184 J

Enthalpy (or heat) of reaction, AH, is the quantitative expression used to express the heat change in chemical reactions that are at constant pressure. AH 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 I-g substance by 1 oc. Specific heat of some common substances are listed in Table 1. Note that either oc or K can be used for the change in temperature, since the difference in a degree is the same for both scales.

Table 1: S ecific Heat Values for Some Common Substances

Substance

Specific

Heat cal/ oc

Specific Heat

Substance

Specific

Heat cal/ oc

Specific Heat

Lead

0.0382

0.160

Iron

0.107

0.450

Tin

0.0502

0.210

Table salt

0.207

0.864

Silver

0.0564

0.236

Aluminum

0.216

0.902

Co

er

0.0944

0.395

Wood

0.406

1.700

Zinc

0.0932

0.390

Water

I .00

4.184

The specific heat of a substance can be calculated by:

Specific heat word image 1958 (1) word image 1959

Or, rearranging for energy,

q (J) = specific heat x mass (g) x AT(O C) (2)

q is the symbol given for heat and AT is the temperature change of the substance, where AT = TJina1 – Tmitial

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 (l) 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,

-qtvf = +qw (3)

Substituting equation (2) into equation (3),

—specific heatM x massM (g) x ATM(OC) = specific heatx massw (g) x ATw(0C) (4)

word image 1960

Rearranging for specific heat of metal gives

specific heat x massw (g) xATw(0C) specific heatM ( O massM (g) x ATM(OC) (5)

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, Afln. The reaction to be studied is:

NaOH(aq) + HCl(aq) NaCl(aq) + H20(1)

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), Afln can be determined.

Heat evolved for the reaction is determined by (l) 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, AT , when the two are mixed:

Heat evolved for the reaction (J) = —specific heat x combined massesacid+base (g) x AT(O C) (6)

The mass (grams) of solution equals the combined masses of the acid and base solutions.

Al-In 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 AHn is calculated as follows:

qreaction

Enthalpy (heat) of neutralization LHn = (7)

# of moles of water produced

CALORIMETRY

Experimental Procedure

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

l . Obtain ajar of “unknown metal” and record the identification code on the Report Sheet. Obtain about I Ocm volume of the metal using a dry 25-mL graduated cylinder. Transfer the metal into a pre-weighed, dry 200-mm test tube, and record the mass of the metal and test tube on the Report Sheet. Determine the mass of the metal by subtraction.

word image 1961 word image 1962 word image 1963 2. 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. word image 1964

word image 1965

Figure 1: Hot water bath setup. (Note — do not allow test tube to rest on bottom of beaker, secure test tube with a clamp.)

word image 1966

Prepare the water for calorimeter and data collection sheet word image 1967

  1. Obtain a calorimeter equipped with stirrer, thermometer and a lid (Figure 2). Measure and record the mass of the word image 1968 calorimeter cup on the Report Sheet. Using the 25-mL measuring cylinder, add —20 mL water to the calorimeter and word image 1969 weigh the calorimeter cup with the water. Determine the mass of water by subtraction and record on the Report Sheet.

word image 1970

  1. Observe the temperature of water in the calorimeter until the temperature remains constant for at least 20 seconds. Record this initial temperature of water on the Report Sheet and Data Table 1 (indicated by -20 sec).

Record the temperature of the metal and transfer the metal to water

  1. After the metal/test tube have been immersed in the boiling water bath for at least 10 minutes, record the temperature of the boiling water (the initial temperature of the metal) on the Report Sheet.

word image 1971 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 I as the guideline for collecting your data.

  1. Remove the test tube from the hot water bath using a mitten and quickly transfer only the metal into the calorimeter through the small hole. Do this quickly but carefully so no metal pieces spill out. Replace the blue lid, swirl the word image 1972 contents gently and start the timer. word image 1973
  2. Record the temperature readings on Data Table 1.
  3. Plot the data — instructions are given in ‘Plot the data Figure 3’ box on next page. word image 1974
  4. Identify Ti(water) (initial temperature ofwater in calorimeter before metal is added), T,nar (Maximum temperature of metal and water mixture) and AT (temperature change of water) clearly on the graph and record these values on the Report Sheet.
  5. Complete the calculations for specific heat of a metal on the Report Sheet.

Complete Trial 2 – Repeats parts A. I 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.

word image 1975word image 1976word image 1977Part 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 MHCI, 25.0-mL0f 1.1 MHN03, 50.0-mL of standardized 1.0 MNaOH

  1. Measure 25.0-mL of 1.1 MHCI in a clean 25.0-mL graduated cylinder. Record the molarity of the acid solution, as indicated on the bottle, on the Report Sheet.
  2. Using a second clean graduated cylinder, transfer 25.0-mL of standardized NaOH solution to the dry calorimeter setup and replace the lid (Figure 2). Record the precise molarity of the NaOH solution, as indicated on the bottle, on the Report Sheet.
  3. Initial temperature of HCI and NaOH can be recorded on the Report Sheet as well as on the Data Table 2 (indicated by 20sec) by reading the temperature from the thermometer (since all solutions are at room temperature)
  4. Carefully but quickly add the acid to the base, replace the lid on the calorimeter and stir gently.
  5. Read and record the temperature every 5 seconds for the first I minute and then every 30 seconds for about 5 minutes on Data Table 2.
  6. Plot the Data instructions are given in ‘Plot the data — Figure 3’ box on next page. word image 1978
  7. Indicate Ti(acidandbase) (average initial temperature of acid and base in calorimeter), (Maximum temperature of word image 1979 mixture) and AT (temperature change of neutralization) clearly on the graph and record these values on the Report Sheet.

Repeat parts B.l through B.7, replacing 1.1 MHCI with 1.1 MI-IN03. Allow the calorimeter to cool to room word image 1980 temperature before starting the trial with HN03.

On the Report Sheet, compare your Ahln values for the two strong acid-strong base reactions. word image 1981

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.

word image 1982

Plot the data (Figure 3)

  1. Use the data collected on Data Table I 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.
  2. Determine from your curve the maximum temperature of the mixture by extrapolation (as shown in Figure 3): (l) insert a best fit linear trend line through the data points on the cooling portion of the curve only; (2) The value of is the temperature at Time = 0 sec, which is simply the y-intercept. An example graph is shown below:
  

Time

Temp Temp All cool

-20

5

10

15

20

25

30

35

40

45 50 55

60

90 120

150

180

210

240

270

300

22.5

24.6

27.1

27.8

28.8

29.1 29.1

29.1 29.1

29 29

29 29

word image 1983

28.8 28.8

28.8 28.8

28.8 28.8

28.6 28.6

28.6 28.6

28.6 28.6

28.5 28.5

28.5 28.5

28.5 28.5

28.5 28.5

28.4 28.4

28.4 28.4

word image 1984 HCI + NaOH – Determination of T(max)

word image 1985

(cooling)

Figure 3: Extrapolation of temperature verses time data for an exothermic reaction

ALORIMETRY

Pre-Laboratory Assignment

DateNamePartner(s)

word image 1986

l. What is the purpose of the insulated wall in a calorimeter?

  1. In Part A of the experiment, what amount of “unknown metal” should be used? How is the precise mass of the “unknown metal” determined?
  2. In Part A of the experiment, why must the “unknown metal” initially be completely dry? How is it kept dry during heating? word image 1987
  3. Determine the specific heat of an unknown metal following a procedure similar to Part A, using the data given: A

35.3g sample of metal was heated in a water bath to 99.50C. When the hot metal was added to a sample of water

(23.2g), the temperature of the water increased from 21.3 0C to a max temperature of 27.50C (obtained from graph).

word image 1988

      1. word image 1989 Mass of metal:
      2. Mass of water: word image 1990

word image 1991

      1. Initial temperature of water in calorimeter (Ti of water):

word image 1992

      1. Initial temperature of metal (boiling water) (Ti of metal):

word image 1993 word image 1994 e. Maximum temperature of metal and water mixture CC): word image 1995

word image 1996

        1. AT of water CC):

Show calculation:

word image 1997

        1. AT of metal CC):

Show calculation:

word image 1998

        1. Heat gained by water (J) using equation 2: Show calculation:

word image 1999

        1. Heat lost by metal (J) using equation 3: Explain:

word image 2000

        1. Specific heat of metal g.oc (rearrange equation 2)

Show calculation:

CALORIMETRY Prelaboratory Assignment

cont.

Date Name Partner(s)

word image 2001

  1. In Part B of the experiment, students are told to obtain 25.0 mL each of the acid and base solutions. They are also told to assume that the density of each solution is equivalent to the density of pure water. Why is this statement necessary?
  2. word image 2002 word image 2003 word image 2004 Two student chemists measured 25.0mL of 1.00 MNaOH in separate calorimeters as in the experimental procedure, Part B. Student I added 25.0mL of 1.10 MHCI in his solution ofNaOH. Student 2 added 22.7mL of I .10 M HCI in his NaOH solution. Each student recorded the temperature change and calculated the enthalpy of neutralization.

Complete the following table to assist in answering the below questions.

NOTE: Limiting reactant needs to be identified to calculate the enthalpy ofneutralization.

Student 1

word image 2005

Moles ofNaOH

word image 2006

Moles of HCI added word image 2007

Limiting reactant

word image 2008

Moles of 1-120 produced word image 2009

Mass of final mixture

word image 2010

Student 2

word image 2011 word image 2012 Moles ofNaOH

word image 2013

Moles of HCI added

word image 2014

Limiting reactant

word image 2015

Moles of 1-120 produced

word image 2016

Mass of final mixture

word image 2017

Explain why and how (higher or lower) the temperature will be different for the two students. Explain the predicted enthalpy of neutralization for the two experiments.

CALORIMETRY

Report Sheet

Date Spring 2020 NamePartner(s)

word image 2018

Part A: Show calculation where indicated for Trial l .

Unknown metal number: N/A

I. Mass of dry 200-mm

Trial 1

Trial 2 word image 2019

2. Mass of dry 200-mm test tube and metal (optional):

word image 2020

word image 2021

  1. Mass of metal:
  2. Mass of calorimeter cup:
  3. Mass of calorimeter cup and water:

61.5936

word image 2022

word image 2023

61.5415

word image 2024

word image 2025

6. Mass of water:

25.0 word image 2026

29.5 word image 2027

7. Initial temperature of cool water in calorimeter (Ti of water):

22.6 word image 2028

23.0 word image 2029

8. Initial temperature of metal (boiling water) (Ti of metal):

99.5

99.4

word image 2030 word image 2031 word image 2032 word image 2033 word image 2034 test tube (optional): word image 2035

Plot the graph using the data collected in Data Table l, then continue with the rest (separate graph for each trial).

    1. Maximum temperature of metal and water mixture from graph, CC):

word image 2036

    1. AT of water CC): word image 2037

Show calculation:

I l . AT of metal CC): word image 2038

Show calculation:

    1. Heat gained by water (J) from equation 2:

word image 2039

Show calculation:

    1. Heat lost by metal (J) from equation 3:

word image 2040

Explain:

    1. word image 2041 Specific heat of metal (rearrange equation 2) word image 2042

Show calculation:

    1. Average specific heat of metal

Most Likely Identity of Metal (see Table 1):

Calorimetry Report Sheet cont.

Name:

 

Part B: word image 2043

Trial with

Trial with

 

HCI + NaOH

HN03 + NaOH

1. Volume of acid (mL)

25.0 ml,

25.0 ml,

3. Volume ofNaOH (mL)

25.0 ml,

25.0 ml,

word image 2044 word image 2045 word image 2046 word image 2047 word image 2048 2. Exact molar concentration of acid 1.1M 1.1 M

word image 2049

  1. Exact molar concentration ofNaOH 1.047 M 1.047 M

word image 2050

  1. Initial temperature of acid and NaOH (Room Temperature) 22.5 oc 22.8 oc

word image 2051

(NOTE: Allow the container to cool to Room Temp before starting trial with HN03)

Plot the graph using the data collected in Data Table 2 and then continue with the rest of data analysis.

  1. Maximum temperature from graph CC) word image 2052

word image 2053

  1. AT of neutralization from graph CC) (show AT on graphs)

word image 2054

9. Mass of final mixture (g) (assume density of water)

50.0 g

50.0 g

  1. word image 2055 Volume of final mixture (mL) 50.0 mL 50.0 mL

word image 2056

  1. Specific heat of mixture
  2. Write the balanced chemical equation for each reaction:

HCI a

+NaOH a

HN03

a

+ NaOH a

  1. Heat evolved for the reaction (J), equation 6:

word image 2057

Show calculation:

  1. Moles ofH+ reacted (mol) word image 2058

word image 2059

Show calculation:

  1. Moles of OH- reacted (mol) word image 2060

Show calculation:

  1. Which is the limiting reactant (H+ or OH-)? word image 2061
  2. Moles of 1-120 formed (mol) based on the limiting reactant word image 2062

Show calculation:

  1. AHn (kJ/m01 HO)

word image 2063

Show calculation:

Compare your two values for Alln. Should AHn be the same or different for the two reactions?

Data Table 1: Record temp at each time interval Data Table 2: Record temp at each time interval

Part A: Specific Heat of Metal

Trial 1

Trial 2

Time

sec

Temp

Time

sec

Time

sec

-20

22.6

-20

23.0

* *Add hot metal time=0sec

* *Add hot metal time=0sec

 

24.3

 

29.6

15

28.9

15

31.0

30

30.3

30

30.9

45

32.0

45

30.7

60

32.0

60

30.5

90

31.9

90

30.5

120

31.8

120

30.3

150

31.6

150

30.0

180

31.6

180

29.9

210

31.5

210

29.8

240

31.5

240

29.7

270

31.4

270

29.7

300

31.2

300

29.6

  

360

29.4

    
    
    
    
    
    
    
    
    

Part B: Enthalpy of Neutralization

HCI + NaOH

HN03 + NaOH

Time (sec)

Temp

Time (sec)

Temp

-20

22.5

-20

22.8

Acid time=()scc

Acid time=0sec

 

24.6

 

27.8

10

27.1

10

28.8

15

27.8

15

29.7

20

28.8

20

29.8

25

29.1

25

29.7

30

29.1

30

29.6

35

29.0

35

29.6

40

29.0

40

 

45

28.8

45

29.4

50

28.8

50

29.3

55

28.8

55

29.2

60

28.6

60

29.1

90

28.6

90

29.1

120

28.5

120

29.1

150

28.5

150

29.0

180

28.5

180

29.0

210

28.5

210

29.0

240

28.5

240

28.9

270

28.4

270

28.9

300

28.4

300

28.8

    
    

*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

CALORIMETRY

Post-lab Questions

Date Name Partner(s)

word image 2064

  1. In Part B, how would the temperature change and experimentally determined heat of neutralization be affected if the concentrations of the acids and the base used in this experiment were doubled? Explain.
  2. In Part B, how would the temperature change and experimentally determined heat of neutralization be affected if the concentrations remained the same but the volume of each acid and base was cut in half? Explain.
  3. a) Write the net ionic equation for the reaction between hydrochloric acid and aqueous sodium hydroxide, then calculate the heat of neutralization (AHn) for the net ionic equation using the standard enthalpies of formation ( AH Of) found in the Appendix of the textbook.

word image 2065 Molecular equation: word image 2066 NaOH(aq) word image 2067

Net ionic equation:

  1. Do the same for the reaction between nitric acid and aqueous sodium hydroxide.

Molecular equation: HN03(aq) + NaOH(aq) word image 2068

Net ionic equation:

  1. Calculate the percent error for your experimental AHnfor each reaction using the following formula. Show method.

experimental value — true value

true value

word image 2069 % error =x 100

% error for HCI + NaOH:

% error for HN03 + NaOH:

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