When you have a sample of material and you want to know what it is made of one t
ID: 1454799 • Letter: W
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When you have a sample of material and you want to know what it is made of one tool you can use is a mass spectrometer. A mass spectrometer is able to determine the masses of the atoms in a sample which is a first step towards determining its composition.
As shown in Figure 1(c), the sample is ionized and the ions are accelerated to make a beam. This is passed through a “velocity filter” which ensures that only ions of a particular speed enter the spectrometer. Inside the spectrometer there is a magnetic field which curves the paths of the ions. Ions of different masses and charges follow different paths. For any given strength of the B-field only ions of a particular charge/mass ratio will reach the detector. So by varying the strength of the magnetic field and watching how many ions arrive at the detector we can determine what kinds of atoms are in the sample.
(a) The figure showing the mass spectrometer has four particle paths labeled with 1 through 4. Are the charges of these particles positive or negative? Explain.
(b) Suppose that all of the ions entering the spectrometer are “singly ionized”, which just means that they have all lost or gained a single electron. Explain what the difference must be between the particles following paths 2, 3 and 4.
(c) For ions to reach the detector they must travel in a semi-circle of radius 7.000 cm (i.e. the detector is 14 cm from the point where the ion beam enters the spectrometer). The ions entering the mass spectrometer are all moving at 1.500 × 105 m/s. It is found that when the B-field in the spectrometer is set to 0.5115 T there is a strong signal from some type of ion from the sample reaching the detector. What is the mass of these ions? Use this mass to identify what type of atom from the sample is being detected.
out of page only ions going at a particular speed enter the. spectrometer atoms from sample are onized and accelerated to make a beam ons withh different masses and charges follow different paths inside the spectrometer 4 ons on a particular path arrive at the detector Schematic diagram showing operation of a mass spectrometerExplanation / Answer
a) Charges 2,3,4 are positive. 1 is negative. The force is given by q(vxB). Assuming along x-axis and B along y-axis, postive charges will be deflected along z axis and negative along -z-axis.
b) Assuming charge and initial velocity to be same, the masses are different.
r = mv/qB
c) Mass, m = rqB/V
7cm, q=1.5x10^-19C, B=.5115T, V=1.5x10^5m/s
m=3.82x10^-26Kg
It can be Sodium.
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