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Experiment 37.1

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Experiment 37.1

Determining the standard

enthalpy change of formationof a metal carbonate

Experiment Video

http://localhost/var/www/apps/conversion/tmp/scratch_6/exp37_1e.mpghttp://localhost/var/www/apps/conversion/tmp/scratch_6/exp37_1e.mpghttp://localhost/var/www/apps/conversion/tmp/scratch_6/exp37_1e.mpghttp://localhost/var/www/apps/conversion/tmp/scratch_6/exp37_1e.mpg

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Experiment 37.1

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Objective

To determine the standard enthalpy change of formation of

calcium carbonate.

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Experiment 37.1

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Apparatus and Chemicals

Each group will need:

Safety spectacles Electronic balance

Thermometer (with a reinforced bulb) (10C to

110C)

Beaker (250 cm3) Forceps

Spatula

Expanded polystyrene cup Polystyrene lid with a hole

Weighing bottle (Cont)

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Experiment 37.1

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Apparatus and Chemicals

Measuring cylinder (100 cm3)

Hydrochloric acid (1.0 M, 200 cm3

) Calcium granules (1 g)

Calcium carbonate granules or powder (3 g)

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Experiment 37.1

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Safety precautions

1. Do not touch calcium with bare hands. It may cause

burns.

2. Use calcium granules, but not calcium powder,

otherwise the reaction would be too vigorous.

3. Handle acid with care. In case any acid gets into your

eyes, report to your teacher immediately, and flush your

eyes under running water for at least 3 minutes. If any

acid gets onto your skin, wash the affected area with

plenty of water.

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Experiment 37.1

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Safety precautions

Calcium granules

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Experiment 37.1

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Procedure

A. Reaction of calcium with dilute hydrochloric acid

Determining the standard

enthalpy change of formationof a metal carbonate

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Experiment 37.1

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Procedure

1. (a) Weigh out

approximately 1 g of

calcium granules in a

weighing bottle,M1.

(b) Record the mass in

Table 37.1.

Note

Remember to press theTare button of the

electronic balance to set

the reading to zero

before use.

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Experiment 37.1

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Procedure

2. (a) Using a measuring

cylinder, measure

100 cm3 of 1.0 M

hydrochloric acid

(Figure 37.1a).

Figure 37.1a

measuring

cylinder

100 cm3 of 1.0 M

hydrochloric acid

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Experiment 37.1

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(b) Pour the acid into an expanded polystyrene cup

(Figure 37.1b).

Procedure

Figure 37.1b

measuring cylinder

100 cm3 of 1.0 M

hydrochloric acid

expanded

polystyrene

cup

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Experiment 37.1

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Procedure

(c) Put the cup into a beaker (Figure 37.1c).

(d) Record the temperature of the acid, T1, in Table

37.1.

Figure 37.1c

thermometer

1.0 M hydrochloric acid

beaker

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Experiment 37.1

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Procedure

3. (a) Quickly add the weighed

calcium granules to the

acid.

(b) Quickly cover the cup with

a lid.

CautionDo not touchcalcium with bare

hands. It may cause

burns.

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Experiment 37.1

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Procedure

(c) Insert a thermometer into the solution through the

hole in the lid (Figure 37.2).

1.0 M hydrochloric

acid

Figure 37.2

beaker

lid

thermometer

calcium granules

expanded

polystyrene

cup

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Experiment 37.1

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Procedure

4. (a) Re-weigh the weighing bottle with calcium

granules residue,M2.

(d) Stir the contents gently.

(e) Record the maximum temperature reached by thesolution, T

2, in Table 37.1.

(b) Record the mass in Table 37.1.

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Experiment 37.1

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Total mass of weighing bottle and calcium

granules before addition,M1

(g)

Total mass of weighing bottle and calcium

granules residue after addition,M2

(g)

Mass of calcium granules added for reaction,

M1M2 (g)

Initial temperature of the solution, T1(C)

Final temperature of the solution, T2

(C)

Temperature change, T2T1 (C)

Procedure

Table 37.1

4.05

3.06

0.9926.2

50.7

+24.5

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Experiment 37.1

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Procedure

B. Reaction of calcium carbonate with dilute

hydrochloric acid

Determining the standard

enthalpy change of formation

of a metal carbonate

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Experiment 37.1

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Procedure

5. (a) Weigh out

approximately 3 g of

calcium carbonate in a

weighing bottle,M3.

(b) Record the mass in

Table 37.2.

Note

Remember to press theTare button of the

electronic balance to set

the reading to zero

before use.

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Experiment 37.1

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Procedure

6. (a) Using a measuring

cylinder, measure

100 cm3 of 1.0 M

hydrochloric acid

(Figure 37.3a).

Figure 37.3a

measuring

cylinder

100 cm3 of 1.0 M

hydrochloric acid

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Experiment 37.1

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(b) Pour the acid into an expanded polystyrene cup

(Figure 37.3b).

Procedure

Figure 37.3b

measuring cylinder

1.0 M

hydrochloric acid

expanded

polystyrene

cup

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Experiment 37.1

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Procedure

(c) Put the cup into a beaker (Figure 37.3c).

(d) Record the temperature of the acid, T3, in Table

37.2.

Figure 37.3c

thermometer

1.0 M hydrochloric acidbeaker

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Experiment 37.1

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Procedure

7. (a) Quickly add the weighed calcium carbonate to the

acid.(b) Quickly cover the cup with a lid.

(c) Insert a thermometer into the solution through the

hole in the lid (Figure 37.4).

Figure 37.4beaker

1.0 M hydrochloric acid

lid

thermometer

calcium carbonate

expanded

polystyrene

cup

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Experiment 37.1

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Procedure

8. (a) Re-weigh the weighing bottle with calcium

carbonate residue,M

4.

(d) Stir the contents gently.

(e) Record the maximum temperature reached by thesolution, T

4, in Table 37.2.

(b) Record the mass in Table 37.2.

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Experiment 37.1

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Total mass of weighing bottle and calcium

carbonate before addition,M3

(g)

Total mass of weighing bottle and calcium

carbonate residue after addition,M4

(g)

Mass of calcium carbonate added for

reaction,M3M4 (g)

Initial temperature of the solution, T3

(C)

Final temperature of the solution, T4

(C)

Temperature change, T4T3 (C)

Procedure

Table 37.2

6.07

3.05

3.0226.2

28.5

+2.3

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Experiment 37.1

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Calculations

9. (a) Write a chemical equation (Equation 1) for the

reaction between calcium and dilute hydrochloric

acid.

Ca(s) + 2HCl(aq) CaCl2(aq) + H2(g)

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Experiment 37.1

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(b) Calculate the heat

evolved when

calcium used in partA reacts completely

with dilute

hydrochloric acid.

Calculations

Note

Assume that the specific heat

capacity and density of the

solution are the same as those

of water i.e. 4.2 J g1 K1 and

1.0 g cm3

respectively.

Heat evolved = m cT

=

=

100 cm3 1.0 g cm3 4.2 J g1 K1 24.5 K

10290 J

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Experiment 37.1

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Calculations

(c) Hence, calculate the heat evolved when 1 mole of

calcium reacts completely with dilute hydrochloric

acid.

Number of moles of calcium used =

From the equation, the mole ratio of Ca : HCl

=

= 0.0247 mol

1 : 2

0.99 g

40.1 g mol1

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Experiment 37.1

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Calculations

Number of moles of dilute hydrochloric acid used

Heat evolved when 1 mole of calcium reactscompletely with dilute hydrochloric acid

=

=

is in excess.

=

=

0.1 mol

HCl

=

416599 J mol1

416.6 kJ mol1

10290 J

0.0247 mol

1.0 mol dm3

dm3

1000

100

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Experiment 37.1

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Calculations

10. (a) Write a chemical equation (Equation 2) for the

reaction between calcium carbonate and dilute

hydrochloric acid.

CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2O(l) + CO2(g)

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Experiment 37.1

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Calculations

(b) Calculate the heat

evolved when

calcium carbonateused in part B reacts

completely with

dilute hydrochloric

acid.

Note

Assume that the specific heat

capacity and density of the

solution are the same as those

of water i.e. 4.2 J g1 K1 and

1.0 g cm3

respectively.

Heat evolved = mcT

=

=

100 cm3 1.0 g cm3 4.2 J g1 K1 2.3 K

966 J

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Experiment 37.1

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Calculations

(c) Hence, calculate the heat evolved when 1 mole of

calcium carbonate reacts completely with dilute

hydrochloric acid.

Number of moles of calcium carbonate used

From the equation, the mole ratio of CaCO3 : HCl

=

=

=

0.030 mol

1 : 2

3.02 g

(40.1 + 12.0 + 16.0 3) g mol1

C l l ti

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Experiment 37.1

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Calculations

Number of moles of dilute hydrochloric acid used

Heat evolved when 1 mole of calcium carbonate

reacts completely with dilute hydrochloric acid

=

is in excess.

=

=

=

=

0.1 mol

HCl

32200 J mol1

32.2 kJ mol1

1.0 mol dm3

dm3

1000

100

0.030 mol

966 J

C l l ti

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Experiment 37.1

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Calculations

11. (a) Write an equation (Equation 3) for the formation

of calcium carbonate from its elements.

Ca(s) + C(s) +2

3O2(g) CaCO3(s)

(b) Draw an enthalpy change cycle linking Equations

1, 2 and 3 together. (Hint: Some other equations

are needed to complete the cycle.)

C l l ti

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Experiment 37.1

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Calculations

2HCl(aq)H1

CaCl2(aq) + H2O(l) + C(s) + O2(g)

H3

CaCl2(aq) + H2O(l) + CO2(g)

H4

H2 2HCl(aq)

Hf [CaCO3(s)]

Ca(s) + C(s) + O2(g) CaCO3(s)23

CaCl2(aq) + H2(g) + C(s) + O2(g)2

3

C l l ti

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Experiment 37.1

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(c) Apart from your experimental results in parts A and

B, what other information is needed to calculate the

standard enthalpy change of formation of calciumcarbonate? Look up these necessary data.

Calculations

The following information is needed to be

found for calculating standard enthalpy

change of formation of calcium carbonate:

1. Standard enthalpy change of formation of

water = 285.8 kJ mol1, i.e. H3

2. Standard enthalpy change of formation of

carbon dioxide = 393.5 kJ mol1, i.e. H4

C l l ti

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Experiment 37.1

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12. By using Hesss Law, calculate the standard enthalpy

change of formation of calcium carbonate. (Assuming

that all reactions were carried out under standardconditions.)

Calculations

Hf [CaCO3(s)]

=H1+ H3+ H4 H2= (416.6) + (285.8) + (393.5) (32.2) kJ mol1

= 1063.7 kJ mol1

S

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Experiment 37.1

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Summary

13. The standard enthalpy change of calcium carbonate is

____________ kJ mol1.1063.7

Q ti

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Experiment 37 1 Solution

Question

14. Explain why the method used in this experiment is not

appropriate for metals that are less reactive than

magnesium.

For those metals less reactive than

magnesium, their reaction towards dilute

hydrochloric acid will proceed more slowly. Theerror due to heat loss to the surroundings will

be larger. The heat evolved in the reaction will

thus be underestimated.