mass-to-charge ratio

Examples of mass-to-charge ratio in the following topics:

• Mass Spectrometry to Measure Mass

  • Mass spectrometry is a powerful characterization method that identifies elements, isotopes, and compounds based on mass-to-charge ratios.
  • Mass spectrometers separate compounds based on a property known as the mass-to-charge ratio: the mass of the atom divided by its charge.
  • Mass analyzers separate the ions according to their mass-to-charge ratios.
  • Depending on the applied voltage, only ions of a certain mass-to-charge ratio will pass through the analyzer.
  • They are separated according to their mass-to-charge ratios.

• Characteristics of Mass Spectra

  • A mass spectrum will usually be presented as a vertical bar graph, in which each bar represents an ion having a specific mass-to-charge ratio (m/z) and the length of the bar indicates the relative abundance of the ion.
  • Most of the ions formed in a mass spectrometer have a single charge, so the m/z value is equivalent to mass itself.
  • The highest-mass ion in a spectrum is normally considered to be the molecular ion, and lower-mass ions are fragments from the molecular ion, assuming the sample is a single pure compound.
  • Even though these compounds are very similar in size, it is a simple matter to identify them from their individual mass spectra.
  • Both distributions are observed, but the larger ethyl cation (m/z=29) is the most abundant, possibly because its size affords greater charge dispersal.

• Mass-to-Mass Conversions

  • It is not possible to directly convert from the mass of one element to the mass of another.
  • Because there is no direct way to compare the mass of butane to the mass of oxygen, the mass of butane must be converted to moles of butane:
  • Taking coefficients from the reaction equation (13 O2 and 2 C4H10), the molar ratio of O2 to C4H10 is 13:2.
  • But by converting the butane mass to moles (0.929 moles) and using the molar ratio (13 moles oxygen : 2 moles butane), one can find the molar amount of oxygen (6.05 moles) that reacts with 54.0 grams of butane.
  • A chart detailing the steps that need to be taken to convert from the mass of substance A to the mass of substance B.

• Mass-to-Mole Conversions

  • Mass-to-mole conversions can be facilitated by employing the molar mass as a conversion ratio.
  • The relative atomic mass is a ratio between the average mass of an element and 1/12 of the mass of an atom of carbon-12.
  • The molar mass value can be used as a conversion factor to facilitate mass-to-mole and mole-to-mass conversions.
  • The compound's molar mass is necessary when converting from grams to moles.
  • After the molar mass is determined, dimensional analysis can be used to convert from grams to moles.

• Overview of Atomic Structure

  • Although similar in mass, protons are positively charged, while neutrons have no charge.
  • Therefore, the number of neutrons in an atom contributes significantly to its mass, but not to its charge.
  • Therefore, they do not contribute much to an element's overall atomic mass.
  • Electrons contribute greatly to the atom's charge, as each electron has a negative charge equal to the positive charge of a proton.
  • Compare the behavior of electrons to that of other charged particles to discover properties of electrons such as charge and mass.

• Fusion Reactors

  • Fusion between the nuclei is opposed by the repulsive positive electrical charge common to all nuclei because they contain protons.
  • The difference in mass is released as energy according to Albert Einstein's mass-energy equivalence formula, E = mc2.
  • The temperatures required to provide the nuclei with enough energy to overcome their repulsion is a function of the total charge.
  • The large mass ratio of the hydrogen isotopes makes their separation easy compared to the difficult uranium enrichment process.
  • This is because the rest of mass of helium and a neutron combined is less than the rest mass of deuterium and tritium combined, providing energy according to E=mc2.

• The Law of Definite Composition

  • The law of definite composition states that chemical compounds are composed of a fixed ratio of elements as determined by mass.
  • It stated that chemical compounds are formed of constant and defined ratios of elements, as determined by mass.
  • Therefore, by mass, carbon dioxide can be described by the fixed ratio of 12 (mass of carbon):32 (mass of oxygen), or simplified as 3:8.
  • Dalton's law of multiple proportions expanded on the law of definite composition to postulate that, in situations in which elements can combine to form multiple combinations, the ratio of the elements in those compounds can be expressed as small whole numbers.
  • The law of definite composition has applications to both molecular compounds with a fixed composition and ionic compounds as they require certain ratios to achieve electrical neutrality.

• The Law of Multiple Proportions

  • The law of multiple proportions states that elements combine in small whole number ratios to form compounds.
  • The law, which was based on Dalton's observations of the reactions of atmospheric gases, states that when elements form compounds, the proportions of the elements in those chemical compounds can be expressed in small whole number ratios.
  • In CO2, the ratio of the amount of oxygen compared to the amount of carbon is a fixed ratio of 1:2, a ratio of simple whole numbers.
  • In CO, the ratio is 1:1.
  • Dalton's law of multiple proportions is part of the basis for modern atomic theory, along with Joseph Proust's law of definite composition (which states that compounds are formed by defined mass ratios of reacting elements) and the law of conservation of mass that was proposed by Antoine Lavoisier.

• Molar Ratios

  • Molar ratios, or conversion factors, identify the number of moles of each reactant needed to form a certain number of moles of each product.
  • Because the law of conservation of mass dictates that the quantity of each element must remain unchanged over the course of a chemical reaction, each side of a balanced chemical equation must have the same quantity of each particular element.
  • The coefficients in a balanced equation can be used as molar ratios, which can act as conversion factors to relate the reactants to the products.
  • The molar ratios identify how many moles of product are formed from a certain amount of reactant, as well as the number of moles of a reactant needed to completely react with a certain amount of another reactant.
  • From this reaction equation, it is possible to deduce the following molar ratios:

• Study of Photosynthesis

  • Mass spectrometry has been used to study the ratio of carbon isotopes in various plants to understand the mechanisms of photosynthesis.
  • Mass spectrometry has been used to study the ratio of isotopes in various plants to understand the mechanisms of photosynthesis.
  • For example, in laboratory experiments, labeling the atmosphere with oxygen-18 allows us to measure the oxygen uptake by the photorespiration pathway.
  • Grasses in temperate environments, such as barley, rice, and wheat, follow a C3 photosynthetic pathway that yields distinctive isotopic ratios.
  • Grasses in hot, arid environments, specifically maize, but also millet, sorghum, sugar cane, and crabgrass, follow a C4 photosynthetic pathway that produces higher ratios of 13C to 12C.