# 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