SSCE VCE Chemistry Measuring Solubility and Concentration: Sodium is an essential element i

Question

Sodium is an essential element in our diets. However, the amount of sodium present in some foods is often much higher than levels recommended for health. A sauce was analysed using atomic absorption spectroscopy to determine the sodium content.

A 25.00 mL sample of the sauce was diluted to 1.00 L with deionised water.

Four aqueous samples of known NaCl concentration were also prepared as standard solutions. The absorbances of the four standard solutions and the diluted sauce solution were measured. The results are given in the table below.

| concentration of Na^+(aq) in mg L^-1 | absorbance |
|----------------------------------------|------------|
| 100 mg L^-1                           | 0.051      |
| 200 mg L^-1                           | 0.100      |
| 300 mg L^-1                           | 0.149      |
| 400 mg L^-1                           | 0.199      |
| diluted sauce                         | 0.185      |

a. Use the above data for the Na^+(aq) standards to plot a calibration line on the graph below.

b. Use your calibration graph to determine the sodium ion concentration in the diluted sample of the sauce and in the original sauce. Enter your answers in the table below.

| concentration of Na^+(aq) in diluted solution of sauce in mg L^-1 | concentration of Na^+(aq) in original (undiluted) sauce in mg L^-1 |
|----------------------------------------------------------------------|----------------------------------------------------------------------|

c. i. What important assumption must you make in order to calculate the NaCl content of the sauce from the Na^+ concentration?

ii. Calculate the concentration of NaCl in the original (undiluted) sauce in g L^-1.

iii. The maximum recommended daily NaCl intake for a healthy adult is 2.5 g. What percentage of a maximum daily recommended intake would be consumed by a person who eats 10 mL of the original (undiluted) sauce?

d. Why is it that atomic absorption spectroscopy will measure only the sodium ion concentration in your sample and not the concentration of some other substance or substances as well?

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

Worked Solution & Example Answer:Sodium is an essential element in our diets - VCE - SSCE Chemistry - Question 1 - 2003 - Paper 1

a. Use the above data for the Na^+(aq) standards to plot a calibration line on the graph below.

b. Use your calibration graph to determine the sodium ion concentration in the diluted sample of the sauce and in the original sauce.

i. What important assumption must you make in order to calculate the NaCl content of the sauce from the Na^+ concentration?

ii. Calculate the concentration of NaCl in the original (undiluted) sauce in g L^-1.

iii. The maximum recommended daily NaCl intake for a healthy adult is 2.5 g. What percentage of a maximum daily recommended intake would be consumed by a person who eats 10 mL of the original (undiluted) sauce?

d. Why is it that atomic absorption spectroscopy will measure only the sodium ion concentration in your sample and not the concentration of some other substance or substances as well?

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