# Typical training tasks on Instrumental methods of analysis to prepare for the boundary control module 2.

15) Ca 2+ content was determined in the cheese extract by flame photometry. The analysis was performed by the addition method. The strength of the photocurrent during photometry of the analyzed sample ( x ) is equal to 17.0 μA. When adding the standard Ca 2+ solution to the same sample volume, the following data were obtained:

 x+s ext. , μg / cm 3 x+ 10.0 x+ 20.0 x+ 30.0 I , µA 35.0 52.0 70.0

Find the content of Ca 2+ in the cheese extract (µg/cm 3 ).

a) 10.0; b) 5.0; c) 3.0.

Decision:

Building a graph The point of intersection of the straight line with the abscissa axis corresponds to the content of the analyte in the analyzed solution.

Typical training tasks on Instrumental methods of analysis to prepare for the boundary control module 2.

16) The excitation potential of the resonant level of the potassium atom is 1.6 eV. Calculate the wavelength (nm) of the resonance line in the atomic spectrum of potassium.

a) 500; b) 775; c) 650.

Decision: ∆E=h . = h . c/ λ

h=4.135 . 10 -15 EV/S

c = 3 . 10 8 m/s = 3 . 10 17 nm/s

λ = h . c/ ΔE = 4.135 . 10 -15 . 3 . 10 17 / 1.6 = 775 nm

Typical training tasks on Instrumental methods of analysis to prepare for the boundary control module 2.

17) When photometry of standard aqueous solutions of Na + salt on a flame photometer, the following data were obtained:

 s (Na + ), μg / cm 3 10 20 I , µA 30.5 50.5

When analyzing an aqueous sample, the photocurrent strength was 45.0 μA. Find the content of Na + in the water sample (µg/cm 3 ).

a) 8.5; b) 17; c) 0.17.

Decision:

Building a graph C x u003d 17 μg / cm 3

Typical training tasks on Instrumental methods of analysis to prepare for the boundary control module 2.

18) When determining protein in barley, the optical density of the analyzed sample is 0.44 ( l = 2.0 cm). The optical density of a standard solution containing 0.50 mg/cm 3 of protein is 0.60 ( l = 3.0 cm). Calculate the protein content of barley (mg/cm3).

a) 1.1; b) 5.5; c) 0.55.

Decision:

We determine ε x for the standard solution.

A = ε x . c . l

ε x u003d 0.60 / 3 . 0.50 = 0.4

Knowing ε x , we determine C x

A x = ε x C x l x

C x u003d 0.44 / 2 . 0.4 u003d 0.55 mg / cm 3

Typical training tasks on Instrumental methods of analysis to prepare for the boundary control module 2.

19) The optical density of the water extract from the meat after the biuret reaction is 0.40. Find the light transmission of the analyzed extract (%).

a) 80.0; b) 39.8; c) 50.0.

Decision:

A u003d – lg TT u003d 10 A u003d 10 -0.40 u003d 10 1 . 10 0.60 = 0.398 percent 39.8%

Typical training tasks on Instrumental methods of analysis to prepare for the boundary control module 2.

23) Fe 3+ ions contained in apple juice reducers to Fe 2+ . During coulometric titration of the analyzed sample with electrogenerated Sn 2+ ions at a constant current strength of 5.0 mA in an HCl solution, the electrolysis ended in 85 s. Calculate the mass (mg) of Fe 3+ in apple juice.

a) 0.25; b) 0.12; c) 0.17.

Decision:

m= jtM /nF = 5 . 10 -3 . 85 . 55.85/1 . 96500 = 0.25 mg

Fe 3+ + e Fe 2+

Typical training tasks on Instrumental methods of analysis to prepare for the boundary control module 2.

24) To build a calibration graph, we obtained voltammograms of standard Pb 2+ solutions and measured the wave height:

 c (Pb 2+ ) . 10 6 , g / cm 3 0.5 1 1.5 2 h , mm 4 8 12 16

To determine Pb 2+ in waste water, 50.00 ml of water were taken and the wave height was measured, it was 11.0 mm. Calculate the molar concentration of Pb 2+ in wastewater.

a) 6.73 . 10 -6 ; b) 6.73 . 10 -5 ; c) 3.4 . 10 -6 .

Answer: 6.73 . 10 -6 mol/l

Decision:

We build a graduated graph Determine the unknown concentration

With Pb 2+ = 1.4 . 10 -6 g/ml

n( Pb 2+ ) = 1.4 . 10 -6 / 208 u003d 6.73 . 10 -9 mol

1 mn u003d 10 -3

Therefore, C ( Pb 2+ ) = 6.73 . 10 -9 / 10 -3 u003d 6.73 . 10 -6 mol/l