Question

what is the expected absorbance of a standard solution made by dissolving 0.0070 mol of nicl2 * 6h20 in water to make 100 ml of solution?

Answer 1

This value is typically found in scientific literature or determined experimentally. Once you have
`\( \varepsilon \)`, you can plug it into the formula to get the absorbance.

To calculate the expected absorbance of a standard solution made by dissolving
`\( \text{NiCl}_2 \cdot 6\text{H}_2\text{O} \)` in water, we need to use the Beer-Lambert Law. This law states that absorbance (A) is directly proportional to the concentration (c) of the solution and the path length (l) of the cuvette, and it is expressed as:

`\[ A = \varepsilon \cdot c \cdot l \]`

Where:

-
`\( A \)` is the absorbance,

-
`\( \varepsilon \)` is the molar absorptivity (or extinction coefficient) of the substance,

-
`\( c \)` is the concentration of the solution in moles per liter (M),

-
`\( l \)` is the path length of the cuvette in centimeters (usually 1 cm in standard cuvettes).

The concentration \( c \) of the solution can be calculated as follows:

`\[ c = \frac{\text{number of moles of solute}}{\text{volume of solution in liters}} \]`

Given:

- Number of moles of
`\( \text{NiCl}_2 \cdot 6\text{H}_2\text{O} \) = 0.0070` moles,

- Volume of solution = 100 mL = 0.100 L.

We can calculate the concentration. However, to calculate the absorbance, we also need the value of
`\( \varepsilon \),` which is specific to
`\( \text{NiCl}_2 \cdot 6\text{H}_2\text{O} \)` and depends on the wavelength of light used. This value is usually determined experimentally and should be provided in your lab manual or scientific literature.

Let's first calculate the concentration, and then I'll explain how to proceed with the absorbance calculation.

The concentration of the
`\( \text{NiCl}_2 \cdot 6\text{H}_2\text{O} \)` solution is approximately 0.070 M (moles per liter).

To calculate the absorbance (A) using the Beer-Lambert Law, you will need the molar absorptivity
`(\( \varepsilon \))` of
`\( \text{NiCl}_2 \cdot 6\text{H}_2\text{O} \)` at the specific wavelength of light you are using for the measurement. The path length (l) of the cuvette is typically 1 cm in standard setups.

The formula for absorbance would be:

`\[ A = \varepsilon \cdot 0.070 \cdot 1 \]`

Answer 2

The absorbance of the solution is approximately 0.45.

To get the absorbance of this solution, the concentration first needs to be calculated.

To calculate the concentration of the solution, you can use the concentration formula (c):

`\[c = \frac{\text{moles of solute}}{\text{volume of solution}}\]`

Given that you have 0.0070 mol of
`\(NiCl_2 \cdot 6H_2O\)` dissolved in 100 mL of solution, you need to convert the volume to liters by dividing by 1000 (since 1 L = 1000 mL).

`\[c = \frac{0.0070 \, \text{mol}}{100 \, \text{mL} * (1)/(1000) \, \text{L/mL}}\]`

`\[ c = \frac{0.0070 \, \text{mol}}{0.1 \, \text{L}} \]`

`\[ c = 0.07 \, \text{mol/L} \]`

So, the concentration of the standard solution is
`\(0.07 \, \text{mol/L}\)`.

Tracing the equivalent absorbance of
`\(0.07 \, \text{mol/L}\)` concentration of the solution on the graph, you will see that the value lies between 0.4 and 0.5. In other words, the absorbance of the solution is approximately 0.45.