Lab Report: Determination of Copper in Bronze

Purpose:

The purpose of this experiment is to calculate the amount of copper in bronze using the calorimetric method and to observe the formation of complex ions and redox reactions.

Procedure:

Part A: Preparation of Bronze Sample

Stage 1: Weighing the Bronze Sample

1. Weigh a bronze sample with a precision balance and record the weight as 0.1287 grams.

Stage 2: Reaction with Nitric Acid

2. In a clean glass container, add 2.00 ml of concentrated nitric acid (HNO₃) to the bronze sample. Observe the formation of a light blue color solution and brown color fumes.

Stage 3: Dilution

3. Dilute the solution with 30 ml of RO water. Observe the change in color from light blue to sky blue, with the formation of white fumes.

Part B: Preparation of Standard Copper Solution

Stage 4: Standard Copper Solution Preparation

4. Prepare a standard copper solution with a known concentration of 1000.02 mg/L (1.00002 mg/ml) and a wavelength of 620 nm.

Stage 5: Measurement of Transmittance

5. Measure the percent transmittance (%T) of the standard copper solution at various volumes.

Record the values in Table 4.

Observations:

Part A: Preparation of Bronze Sample

Sample #BRS 81

Substances	Quantities
Bronze (weight)	0.1287g
HNO3 added (volume)	2.00 ml

Table 2: Qualitative Measurements

Reactions	Observations
HNO3 + CuSn	Light blue color solution and brown color fumes were produced.
Dilution of copper nitrate	Solution turned to sky blue color from light blue. White color fumes were formed.

Part B: Preparation of Standard Copper Solution

Table 3: Qualitative Measurements

Substances	Quantities
Concentration of copper	1000.02 mg/L = 1.00002 mg/ml
Wavelength	620 nm

Table 4: Observation of Percent Transmittance and Volume of Cu⁺²

Standard of Solution #	Volume of Cu+2 (ml)	Volume of NH4(OH)3	Total Volume (ml)	% Transmittance
Blank	-	5.00	25.00	100
1	0.50	5.00	25.00	95.3
2	1.00	5.00	25.00	91.6
3	1.50	5.00	25.00	88.1
4	2.00	5.00	25.00	82.8
5	2.50	5.00	25.00	82.1
6	3.00	5.00	25.00	78.8
Unknown	3.50	5.00	25.00	80.7

Calculation:

Standard copper solution concentration = C₁ = 1.00002 mg/ml

Standard solution concentration #1 = C₂ = (?)

Standard copper solution Volume = V₁ = 0.50 ml

Copper solution Total Volume = V₂ = 25.00 ml

C₂ = C₁ * V₁ / V₂ = 1.00002 mg/ml * 0.50 ml / 25.00 ml = 0.02 mg/ml

Table 5: Concentration of Standard Solutions

Standard Solutions #	Volume of Copper (ml)	Concentration of Standard Solution (mg/ml)	Total Volume (ml)
1	0.5	0.02	25
2	1	0.04	25
3	1.5	0.06	25
4	2	0.08	25
5	2.5	0.10	25
6	3	0.12	25

For sample solution 1:

%T = 95.3 %

T = %T / 100 = 95.3 / 100 = 0.953

A = -log(T) = -log(0.953) = 0.0209

Table 6: Absorbance of Standard Solutions

Standard Solutions #	% Transmittance (T)	Absorbance
1	95.3	0.0209
2	91.6	0.0381
3	88.1	0.0550
4	82.8	0.0820
5	82.1	0.0857
6	78.8	0.1035
Unknown	80.7	0.0931

Graph 1: %Transmittance vs. Concentration of Copper (mg/ml)

This graph shows the relationship between the percent transmittance (%T) and the concentration of copper (mg/ml) for the unknown copper solution. The equation for the linear regression line is as follows:

Mass % of copper in bronze:

%T of unknown copper solution = 80.7

From graph;

Y = -166.14x + 98.08

80.7 = -166.14x + 98.08

166.14x = 98.08 – 80.7

166.14x = 17.38

x = 17.38 / 166.14

x = concentration of unknown = 0.1046 mg/ml

Copper solution volume added to unknown = V₁ = 2.00 ml

Concentration of copper solution in 25 ml volumetric flask = C₂ = (?)

Total volume of copper solution = V₂ = 25

C₂ = C₁ * V₁ / V₂ = 0.1046 mg/ml * 2.0 ml / 25.00 ml = 0.008368 mg/ml

For total mass of bronze:

Mass of bronze = 0.1287 g = 128.7 mg

128.7 mg bronze is present in 100 ml;

x mg bronze is present in 1 ml.

x = 128.7 / 100 = 1.28 mg/ml bronze

Mass % of copper = mass of copper / total mass of bronze * 100% = 0.008368 mg/ml / 1.28 mg/ml * 100% = 0.65%

Graph of Absorbance vs. Concentration

This graph illustrates the relationship between the absorbance and the concentration of copper (mg/ml) for the unknown copper solution. The equation for the linear regression line is as follows:

Y = 0.8326x + 0.0059

Absorbance for unknown sample = 0.9774

0.8326x = 0.0931 + 0.0059

x = concentration of copper in bronze sample = 0.1047 mg/ml

Amount of bronze = 1.28 mg/ml

Copper quantity in bronze sample = 0.1047 mg/ml

For mass % of copper in bronze:

mass % of copper = amount of copper / amount of bronze * 100% = 0.1047 / 1.28 * 100% = 8.18%

Discussion:

In issue 4, a graph is plotted between normal solution concentration (mg/ml) %T Vs. %T on the X-axis. While in issue 5, a graph is plotted between absorbance Vs. concentration, with absorbance on the X-axis. The quantity of copper in bronze is 0.65% from the %T graph, while the quantity of copper in bronze is 8.18% from the absorbance graph. The calculated mass percentage of copper is compared to determine the accuracy of the results.

According to the Beer-Lambert Law, the equation that relates concentration is:

Absorbance, A = ε * l * c

Where,

ε = absorbance coefficient

l = cell path length

c = concentration of sample

For calorimetry evaluation, dilute solutions are the most precise. The calorimeter can sense the color quantity and color intensity of the sample solution in calorimetry assessment. Diluted solutions are essential to obtain accurate results, as concentrated solutions can distort the graphs and lead to inaccuracies in calculations.

Errors:

Errors in this experiment can occur if sand particles are present on the cuvette, as they can interfere with the measurement. Additionally, incomplete reactions or full responses can lead to inaccurate results, as unreacted ions in the solution can affect the percentage transmittance and absorbance values.

Conclusion:

In conclusion, this experiment successfully determined the amount of copper in bronze through a calorimetric method. The absorbance was plotted against concentration, and the mass percentage of copper in bronze was calculated from the absorbance graph. The results were compared to ensure accuracy in the determination of copper content in bronze, which was found to be 8.18%.