2. Calcium hypochlorite (Ca(OC)2 Fw 142.983 g/mol) is often used as the source o
ID: 528636 • Letter: 2
Question
2. Calcium hypochlorite (Ca(OC)2 Fw 142.983 g/mol) is often used as the source of the hypochlorite ion (OCI, Fw 51.452 g/mol) in solutions used for water treatment. A student must prepare 25.0 mL of 50.0 ppm OCT solution from solid Ca(oct2, which has a purity of 91.5%. What mass of the impure reagent is necessary to prepare the solution, assuming the density of the solution is 1.00 g/mL? 3. A solution containing a weak monoprotic acid that is 4,15% dissociated has a pH of 3.751. Calculate Ka for the acid. 4. A 1.00 L buffer is made containing 50.0 mmol of bromoacetic acid (pKa 2.90 and 75.0 mmol of sodium bromoacetate. What volume of 2.00 M NaoH must be added to increase the pH ofthis buffer to 4.00? 5. How does a photomultiplier tube detect fluorescence from a sample? 6 x and Y are two compounds that absorb infrared radiation. The transmittance of 0.0100 MX and o 0100 M Y were obtained in a 0.00500 cm cell and are listed on the page at the wavenumber maximum absorbance minimum transmittance for each compound, respectively) A mixture of A and B in a 0.00500 cm cell had a transmittance o 34.0 at 2022 i what are the concentrations of X mixture?Explanation / Answer
The photocathode of a photomultiplier converts the energy of incident photons into photoelectrons. The
conversion efficiency (photocathode sensitivity) varies with the incident light wavelength. This relationship
between the photocathode and the incident light wavelength is referred to as the spectral response character-
istics. In general, the spectral response characteristics are expressed in terms of radiant sensitivity and quantum efficiency.
To measure radiant sensitivity and quantum efficiency, a standard phototube or semiconductor detector which is precisely calibrated is used as a secondary standard. At first, the incident radiant flux Lp at thewavelength of interest is measured with the standard phototube or semiconductor detector. Next, the photomultiplier tube to be measured is set in place and the photocurrent Ik is measured. Then the radiant
sensitivity Sk (A/W) of the photomultiplier tube can be calculated from the following equation:
Sk = (A/W) IK
Radiant sensitivity is defined as the photoelectric current generated by the photocathode divided by the
incident radiant flux at a given wavelength, expressed in units of amperes per watts (A/W).
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