Question

Atomic emission spectroscopy and the method of standard addition are used to determine the Na* concentration and its uncertainty in an unknown sample. Increasing amounts of a 1.75 μg/mL standard Na+ solution are added to a series of volumetric flasks containing 10.00 mL of the unknown solution. The volumetric flasks are then diluted to a final volume of 200.0 mL. Atomic emission spectroscopy is then used to measure the emission intensity of each solution

unknown volume (mL) standard volume (mL) final volume (mL) emission intensity
15.00 0.00 200.0 328.0
15.00 5.00 200.0 471.0
15.00 10.00 200.0 619.0
15.00 15.00 200.0 784.0
15.00 20.00 200.0 925.0


Based on the data in the table above, determine the original concentration of Na* as well as its uncertainty in the unknown sample.

Answer 1

To determine the original concentration of Na* in the unknown sample, use the method of standard addition and plot the emission intensities against the added standard volume. Interpolate the original concentration from the plot. The uncertainty in the concentration can be estimated using statistical analysis methods.

Step-by-step explanation:

To determine the original concentration of Na* in the unknown sample, we can use the method of standard addition. This method involves adding known amounts of a standard solution to the unknown solution and measuring the emission intensity using atomic emission spectroscopy. By plotting the emission intensities as a function of the added standard volume, we can determine the concentration of Na* in the unknown sample.

In this case, we added increasing amounts of a 1.75 μg/mL standard Na+ solution to volumetric flasks containing 10.00 mL of the unknown solution. The volumetric flasks were then diluted to a final volume of 200.0 mL. The emission intensities were measured for each solution.

Using the data from the table, we can plot the emission intensities against the added standard volume. From the plot, we can determine the emission intensity for the unknown solution. By comparing this intensity to the intensities of the standard solutions, we can interpolate the original concentration of Na* in the unknown sample.

Regarding the uncertainty in the concentration, it can be estimated using statistical analysis methods such as error propagation or confidence intervals. These methods take into account the uncertainties in the measurement of the emission intensities and the added standard volumes.