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The Quantitative Relationship Involving Concentrations of Reactants and Products at Equilibrium

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Experiment 19b

The Quantitative Relationship Involving Concentrations of Reactants and Products at Equilibrium

Nicole LeBlanc                                                                                                                  Block A

Miss Tomlinson                                                                                           March 13th, 2018

Objectives:

  1. to prepare various dilutions of Fe3+ ion and to react them with SCN-
  2. to measure the concentration of FeSCN2+ ion produced by means of a spectrophotometer
  3. to use a spectrophotometer to discover a constant mathematical relationship among the concentrations of reactants and products at equilibrium

Materials:

Apparatus                                                              Reagents

5 test-tubes (18mm x 150mm)                                        0.200M Fe (NO3)3 (acidified)

1 graduated cylinder (25 mL)                                        0.0020m KSCN

1 graduated cylinder (10mL)

3 beakers

test-tube rack

5 spectrophotometer tubes

spectrophotometer

lab apron

safety goggles

Procedure:

Refer to pages 198-200 in Heath Chemistry Laboratory Experiments Canadian Edition.

Diagram:

n/a

Data and observations

Table 1

Test tube number

Initial [Fe3+]

Initial [SCN-]

Absorbance

1(a)

0.1M

0.0010M

1.11

2(b)

0.04M

0.0010M

1.0

3(c)

0.0160M

0.0010M

0.96

4(d)

0.0064M

0.0010M

0.751

5(e)

0.002560M

0.0010M

0.462

Calculations

1. Initial amounts for [Fe3+] and [SCN-] were calculated for each test tube.

Initial [Fe3+] in test tube A:

Initial [Fe3+] =  [pic 1]

          = 0.200M [pic 2]

          =0.100M

In all other test tubes:

Initial [Fe3+] = [pic 3]

Ex. Initial [Fe3+] test tube B:

 Initial [Fe3+] = (0.200M) [pic 4]

Initial [SCN-] = [KSCN]  [pic 5]

                   = (0.0020M) [pic 6]

                       SCN-[pic 7]

Test tube B

Test tube C

Test tube D

Test tube E

Ratio of constancy

Equilibrium[pic 8]

9.0x10-4

8.6x10-4

6.8x10-4

4.2x10-4

n/a

Equilibrium [Fe3+]

3.9x10-2

1.5x10-2

5.7x10-3

2.1x10-3

n/a

Equilibrium [SCN-]

1.0x10-4

1.4x10-4

3.2x10-4

5.8x10-4

n/a

4a

3.6x10-1

9.7x10-2

1.2x10-2

1.5x10-3

2.3x102

4b

2.3x102

4.2x10-2

3.6x102

3.3x102

1.8

4c

3.5x10-9

1.8x10-9

1.2x10-9

5.2x10-10

2.8

4d

3.4x101

1.8x101

9.0

6.6

6.6

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