Textbook Question
Combustion analysis of a 31.472 mg sample of the widely used flame retardant Decabrom gave 1.444 mg of CO2. Is the molecular formula of Decabrom C12Br10 or C12Br10O?
Ch.3 - Mass Relationships in Chemical Reactions
Chapter 3, Problem 102
Describe the path of a neutral molecule in the mass spectrometer. Why is ionization a necessary first step?
Verified step by step guidance1
Step 1: Understand the purpose of a mass spectrometer, which is to measure the mass-to-charge ratio of ions. This helps in identifying the composition of a sample by analyzing the ions produced from it.
Step 2: Recognize that a neutral molecule cannot be manipulated by electric or magnetic fields, which are essential components of a mass spectrometer. Therefore, ionization is necessary to convert neutral molecules into charged ions.
Step 3: Describe the ionization process, where a neutral molecule is bombarded with high-energy electrons or photons, resulting in the ejection of one or more electrons and the formation of positively charged ions.
Step 4: Explain that once ionized, the charged ions are accelerated by an electric field and then deflected by a magnetic field. The degree of deflection depends on the mass-to-charge ratio of the ions.
Step 5: Conclude that the path of the ionized molecule in the mass spectrometer is determined by its mass-to-charge ratio, allowing for the separation and detection of different ions, which provides information about the molecular structure and composition of the sample.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Mass Spectrometry
Mass spectrometry is an analytical technique used to measure the mass-to-charge ratio of ions. In this process, molecules are ionized, accelerated, and then separated based on their mass. The resulting data provides information about the molecular weight and structure of the compounds present in a sample.
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Atomic Mass
Ionization
Ionization is the process of converting neutral molecules into charged ions, which is essential for mass spectrometry. Since the mass spectrometer operates on the principle of manipulating charged particles, neutral molecules cannot be detected or analyzed. Common ionization methods include electron impact and electrospray ionization, which facilitate the formation of ions from the sample.
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Path of Ions in a Mass Spectrometer
Once ionized, the charged particles are accelerated by an electric field and directed into a mass analyzer. The path of these ions is influenced by their mass and charge, allowing for their separation. After separation, ions are detected, and their abundance is measured, providing a spectrum that reveals the composition of the original sample.
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Related Practice
Textbook Question
The stimulant amphetamine contains only carbon, hydrogen, and nitrogen. Combustion analysis of a 42.92 mg sample of amphetamine gives 37.187 mg of H2O and 125.75 mg of CO2. If the molar mass of amphetamine is less than 160 g/mol, what is its molecular formula?
Textbook Question
Heating elemental cesium and platinum together for two days at 973 K gives a dark red ionic compound that is 57.67% Cs and 42.33% Pt. (a) What is the empirical formula of the compound?
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Textbook Question
The molecular weight of an organic compound was found by mass spectrometry to be 70.042 11. Is the sample C5H10, C4H6O, or C3H6N2? Exact masses of elements are: 1.007 825 (1H); 12.000 00 (12C); 14.003 074 (14N); 15.994 915 (16O).