Chapter 1 · Introduction

Answers · Sharp, Principles of Stable Isotope Geochemistry, 1st ed. (2007) · ← Problems

Answer 1

  1. Phosphorus has only one isotope.
  2. Although it sometimes takes more work to track down the early papers, the information is often as valuable. It is also scientifically “correct” to credit the author who was the first to address a problem.
  3. Certainly, there are a great deal of applications of stable isotopes to biomedicine. Stable isotopes are a marvelous tracer for reactions, metabolic pathways, etc. The applications are endless.

Answer 2

Start with the equation E = ½mv², where E represents energy, m denotes mass, and v designates velocity. For two isotopologues, E is the same, so the velocity of one isotopologue relative to another is given by m1v1² = m2v2². The masses of 12C16O16O and 13C16O16O are 44 and 45, respectively, so that

v44 = (45/44)½·v45 = 1.0113·v45reconstructed

The velocity of 12C16O16O is greater than that of 13C16O16O. Therefore, the probability of the lighter isotopologue being involved in photosynthesis in marine plants is higher, so that the δ13C value of marine plants should favor the light isotope of carbon.

[Worked grid (constructed). Click a cell to see its formula in the editing bar; Reset restores the worked state.]

Answer 3

The relative mass difference between Si isotopes is vastly higher than between Se isotopes. Therefore, Si isotopes should fractionate much more strongly than Se isotopes.

[Worked grid (constructed). Δm/mean m is 0.0351 for Si vs 0.0253 for Se.]

Answer 4

  1. Salts are less soluble in D2O because bonds to D are less polar than bonds to H.
  2. Because the molecule is heavier, its translational velocities are slower and the vapor pressure is lower. Also, the D–O bond is stronger than the H–O bond, and the polymeric bonding will also be slightly stronger.

Answer 5

  1. Fluorine is monoisotopic. Its mass in amu is determined relative to that of 12C and can be determined as accurately as techniques allow. In contrast, sulfur has multiple isotopes, and their relative abundance varies in nature, so different sulfur samples have different atomic weights, depending upon the abundance of the different isotopes.
  2. The atomic weight of an element is given by AW = Σi xi·MWi. With 10B = 10.0129 amu (19.9%) and 11B = 11.0093 amu (80.1%), AW = 0.199 × 10.0129 + 0.801 × 11.0093 = 10.81. check vs print [The printed abundance digits are garbled in the extraction; the printed result reads 10.812.]
  3. 12C16O16O = 43.9898, 13C17O16O = 45.9974, 13C18O18O = 49.0017. reconstructed [The printed answer line is garbled in the extraction; values computed from the isotope masses of Table 1.4.]

[Worked grids (constructed), matching the worksheets in the problem set.]

Transcribed from Z. Sharp, Principles of Stable Isotope Geochemistry, 1st ed. (Pearson Prentice Hall, 2007), end-of-chapter problem set (published source). Reference-scale names are written VSMOW, VPDB and VCDT where the original used SMOW, PDB and CDT, with the original numerical constants unchanged; historical usages (e.g. Craig's definition of SMOW) are kept as printed.

The source PDF's text layer scrambles mathematics, so equations and some values were reconstructed during transcription. Bracketed notes and anything tagged reconstructed or check vs print are editorial (constructed), not part of the original, and the warn-tagged items should be verified against the print copy.