Chemistry Lab Notebook | Lab 2: Chemical Equilibrium
Printed Name: Signature: Date:
_______________________ ___________________________ _____________________________
___
Name: Date: Experiment #: 2 Title: Equilibrium
________________ _________________
Purpose: To calculate equilibrium concentrations and the equilibrium constant Kc for the Fe³ ⁺/SCN ⁻ reaction using
spectrophotometry and Beer's Law, and to observe Le Chatelier's principle by imposing stresses on equilibrium systems
and recording how they shift.
Procedure Data / Results / Calculations
Part A: Pre-Lab Dilution Calculations Standard Samples (S1–S6) — [Fe³⁺] is the same for
1. Record the standard solution data table all:
(drops of Fe(NO₃)₃, H₂O, and NaSCN for each [Fe³⁺] = (0.20 M × 20 drops) ÷ 80 drops = 0.050 M
sample S1–S6 and equilibrium mixtures E1–E6; (constant for S1–S6)
total = 80 drops each).
[SCN⁻] initial concentrations (C₁ = 0.002 M):
2. Using the dilution equation C₁V₁ = C₂V₂, S1: 0 drops SCN⁻ → [SCN⁻] = 0 M
calculate the initial [Fe³⁺] and [SCN⁻] for each S2: (0.002 × 2) ÷ 80 = 5.00 × 10⁻⁵ M
sample and equilibrium mixture tube.
S3: (0.002 × 4) ÷ 80 = 1.00 × 10⁻⁴ M
S4: (0.002 × 6) ÷ 80 = 1.50 × 10⁻⁴ M
3. Record all calculated concentrations in your
data table before going to the lab. S5: (0.002 × 8) ÷ 80 = 2.00 × 10⁻⁴ M
S6: (0.002 × 10) ÷ 80 = 2.50 × 10⁻⁴ M
Equilibrium Mixtures (E1–E6) — [Fe³ ⁺] = (0.002 × 40) ÷
80 = 0.001 M (constant)
[SCN⁻] initial: E1 = 0 M | E2 = 1.25×10⁻⁴ M | E3 =
2.50×10⁻⁴ M
E4 = 5.00×10⁻⁴ M | E5 = 7.50×10⁻⁴ M | E6 = 1.00×10⁻³ M
Part B: Spectrophotometry Measurements Absorbance Readings:
1. Blank the Spec-20 spectrophotometer (set to Standards (Fe³⁺ excess → virtually all SCN⁻ converts to
515 nm) using a cuvette of distilled water; press product):
the zero-absorbance button until it reads 0. S1: 0.001 | S2: 0.195 | S3: 0.368
S4: 0.541 | S5: 0.798 | S6: 1.028
2. For each standard sample S1–S6: mix
solution, pour into a cuvette, wipe clean, insert
Equilibrium Mixtures:
into the Spec-20, and record the absorbance
reading. E1: 0.023 | E2: 0.076 | E3: 0.160
E4: 0.305 | E5: 0.508 | E6: 0.591
3. Re-blank the Spec-20, then repeat step 2 for
equilibrium mixtures E1–E6. Record each Calibration Graph (Abs vs. [SCN⁻]):
absorbance. Linear equation: y = 4,066.9x − 0.0199
R² = 0.9941 (excellent linearity — data is valid)
4. Graph absorbance (y-axis) vs. [SCN⁻] (x-axis)
for S1–S6 to obtain a calibration line. Record the
linear equation (y = mx + b) and R² value.
Part C: Equilibrium Concentrations & Kc Reaction: Fe³ ⁺(aq) + SCN ⁻(aq) ⇌ FeSCN² ⁺(aq)
1. Solve the calibration equation for x (= All [Fe³ ⁺ ] ₀ = 1.00×10 ⁻³ M | All [FeSCN² ⁺] ₀ = 0
[FeSCN²⁺]eq) using each equilibrium mixture's Initial Eq. Eq. [Fe³⁺] Eq. [SCN⁻] Kc
absorbance as y: [SCN⁻] [FeSCN²⁺]
x = (Absorbance + 0.0199) ÷ 4,066.9 E2 1.25×10⁻⁴ 2.36×10⁻⁵ 9.76×10⁻⁴ 1.01×10⁻⁴ 238
E3 2.50×10⁻⁴ 4.42×10⁻⁵ 9.56×10⁻⁴ 2.06×10⁻⁴ 225
2. Build an ICE table for each equilibrium E4 5.00×10⁻⁴ 7.99×10⁻⁵ 9.20×10⁻⁴ 4.20×10⁻⁴ 207
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Printed Name: Signature: Date:
_______________________ ___________________________ _____________________________
___
Name: Date: Experiment #: 2 Title: Equilibrium
________________ _________________
Purpose: To calculate equilibrium concentrations and the equilibrium constant Kc for the Fe³ ⁺/SCN ⁻ reaction using
spectrophotometry and Beer's Law, and to observe Le Chatelier's principle by imposing stresses on equilibrium systems
and recording how they shift.
Procedure Data / Results / Calculations
Part A: Pre-Lab Dilution Calculations Standard Samples (S1–S6) — [Fe³⁺] is the same for
1. Record the standard solution data table all:
(drops of Fe(NO₃)₃, H₂O, and NaSCN for each [Fe³⁺] = (0.20 M × 20 drops) ÷ 80 drops = 0.050 M
sample S1–S6 and equilibrium mixtures E1–E6; (constant for S1–S6)
total = 80 drops each).
[SCN⁻] initial concentrations (C₁ = 0.002 M):
2. Using the dilution equation C₁V₁ = C₂V₂, S1: 0 drops SCN⁻ → [SCN⁻] = 0 M
calculate the initial [Fe³⁺] and [SCN⁻] for each S2: (0.002 × 2) ÷ 80 = 5.00 × 10⁻⁵ M
sample and equilibrium mixture tube.
S3: (0.002 × 4) ÷ 80 = 1.00 × 10⁻⁴ M
S4: (0.002 × 6) ÷ 80 = 1.50 × 10⁻⁴ M
3. Record all calculated concentrations in your
data table before going to the lab. S5: (0.002 × 8) ÷ 80 = 2.00 × 10⁻⁴ M
S6: (0.002 × 10) ÷ 80 = 2.50 × 10⁻⁴ M
Equilibrium Mixtures (E1–E6) — [Fe³ ⁺] = (0.002 × 40) ÷
80 = 0.001 M (constant)
[SCN⁻] initial: E1 = 0 M | E2 = 1.25×10⁻⁴ M | E3 =
2.50×10⁻⁴ M
E4 = 5.00×10⁻⁴ M | E5 = 7.50×10⁻⁴ M | E6 = 1.00×10⁻³ M
Part B: Spectrophotometry Measurements Absorbance Readings:
1. Blank the Spec-20 spectrophotometer (set to Standards (Fe³⁺ excess → virtually all SCN⁻ converts to
515 nm) using a cuvette of distilled water; press product):
the zero-absorbance button until it reads 0. S1: 0.001 | S2: 0.195 | S3: 0.368
S4: 0.541 | S5: 0.798 | S6: 1.028
2. For each standard sample S1–S6: mix
solution, pour into a cuvette, wipe clean, insert
Equilibrium Mixtures:
into the Spec-20, and record the absorbance
reading. E1: 0.023 | E2: 0.076 | E3: 0.160
E4: 0.305 | E5: 0.508 | E6: 0.591
3. Re-blank the Spec-20, then repeat step 2 for
equilibrium mixtures E1–E6. Record each Calibration Graph (Abs vs. [SCN⁻]):
absorbance. Linear equation: y = 4,066.9x − 0.0199
R² = 0.9941 (excellent linearity — data is valid)
4. Graph absorbance (y-axis) vs. [SCN⁻] (x-axis)
for S1–S6 to obtain a calibration line. Record the
linear equation (y = mx + b) and R² value.
Part C: Equilibrium Concentrations & Kc Reaction: Fe³ ⁺(aq) + SCN ⁻(aq) ⇌ FeSCN² ⁺(aq)
1. Solve the calibration equation for x (= All [Fe³ ⁺ ] ₀ = 1.00×10 ⁻³ M | All [FeSCN² ⁺] ₀ = 0
[FeSCN²⁺]eq) using each equilibrium mixture's Initial Eq. Eq. [Fe³⁺] Eq. [SCN⁻] Kc
absorbance as y: [SCN⁻] [FeSCN²⁺]
x = (Absorbance + 0.0199) ÷ 4,066.9 E2 1.25×10⁻⁴ 2.36×10⁻⁵ 9.76×10⁻⁴ 1.01×10⁻⁴ 238
E3 2.50×10⁻⁴ 4.42×10⁻⁵ 9.56×10⁻⁴ 2.06×10⁻⁴ 225
2. Build an ICE table for each equilibrium E4 5.00×10⁻⁴ 7.99×10⁻⁵ 9.20×10⁻⁴ 4.20×10⁻⁴ 207
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