Sodium is an essential element in our diets - VCE - SSCE Chemistry - Question 1 - 2003 - Paper 1

From the calibration graph, find the absorbance of the diluted sauce (0.185). Locate this value on the y-axis and draw a horizontal line to intersect the calibration curve. From the point of intersection, drop a vertical line down to the x-axis, reading off the corresponding concentration. Then, multiply this value by the dilution factor (40) to get the concentration in the original sauce.

It is assumed that all the sodium in the sauce comes from NaCl, meaning that no other sources of sodium are present that could affect the concentration.

To find the concentration of NaCl, convert the Na⁺ concentration to grams using the molar mass of NaCl (58.44 g/mol). The sodium concentration can be converted as follows:

$n(Na) = \frac{concentration(Na^+)}{1 L} \times ext{molar mass of Na} = 1.49 \times 10^{-3} g$

Then use the relation:

$m(NaCl) = n(Na) \times \frac{58.44 g/mol}{22.99 g/mol}$

Calculate the amount of NaCl in 10 mL:

$mass(NaCl) = \text{concentration} \times volume = 0.038 g$

Compute the percentage:

$percentage = \left( \frac{0.038 g}{2.5 g} \right) \times 100 = 1.52\%$

Atomic absorption spectroscopy is selective for specific elements based on their distinct absorption wavelengths. Therefore, it will measure sodium alone, while other substances in the sample do not interfere with this measurement.