Questions tagged [isotope]

This tag should only be applied where the effects are specifically related to variance in mass number with the same atomic number (existence of isotopes). Examples include: radioactivity and other nuclear properties, kinetic effects, specific relevance to spectroscopy (e.g., NMR, IR), isotope separation, isotopic analysis.

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36 views

What is the maximum molar mass of an O2 molecule? [closed]

Given that naturally occurring oxygen contains: $$ \begin{array}{rl} 99.76~\% & \ce{^{16}O} \\ 0.20~\% & \ce{^{18}O} \\ 0.04~\% & \ce{^{17}O} \\ \end{array} $$ what is the maximum molar ...
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If all molecules have basically the same KE at a given temperature, why do lighter isotopes evaporate more readily?

One of the proxies used for paleoclimate is the ratio of oxygen-18 to oxygen-16 in ice cores and in sedimentary rocks. The idea is that water molecules with oxygen-18 generally evaporate less readily ...
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34 views

How do isotopes with different nuclear spins behave at temperatures near 0 Kelvin? [closed]

Suppose I had two isotopes of the same element, one with a spin of zero and another with a spin of 3/2. If I somehow put those isotopes at temperatures near 0K, how would those two isotopes behave ...
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66 views

Can the enrichment of Uranium be done via manipulating the boiling/melting point difference between differing isotopes of the same element?

I have a Physics question for which I could not find the answer on the Internet, so I would like to see if y'all know the answer to it. I have found that heavy water will have a different boiling ...
3
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2answers
289 views

Long-lived, non-lethal radioisotope for fiction [closed]

I'm writing something where the characters are looking for someone among a large set of people. They don't know who this person is and they don't know what they're looking for, so their best bet is to ...
3
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1answer
63 views

What is the heaviest possible water using oxygen and hydrogen isotopes, and what might it's physical properties be? [closed]

After a cursory internet search, it appears to me that Hydrogen-3 (a part of Tritiated Water) is the heaviest stable* hydrogen isotope. Oxygen-21 is the heaviest isotope of Oxygen with a half-life of ...
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2answers
88 views

Biological activity of the isotopes of the same element

I have a question regarding biological activity of different isotopes of the same elements, notably $\ce{^206Pb}$ and $\ce{^208Pb}$. Lead is known to be toxic, such that it can replace calcium from ...
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1answer
56 views

What does radioactive decay look like?

Some element isotopes have half-lives that are as short as a couple minutes to an hour. Does that mean you can watch it (or catch it on video) turn into 2 different elements? What would something like ...
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22 views

Normalising Kinetic Isotope Effect Per Deuterium Atom

I've synthesised a protic and deuterated version of a specific molecule where there are two deuterium atoms in the latter. I then go about and measure the kinetic isotope effect (KIE) for a reaction ...
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2answers
67 views

How do we know the natural abundance of isotopes on Earth?

Without knowing the Average Atomic Mass or the percent abundance, how do we know that Protium is the most prevalent hydrogen isotope? What methods did scientists use to come to this conclusion? How ...
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22 views

isotopic composition database for carbon isotopes

I am seeking an isotopic composition database for carbon isotopes, since I would like to make a figure showing the different isotopic compositions of different materials. The best woudl be if the ...
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2answers
55 views

Probability of forming dihydrogen with molecular weight 3 [closed]

During a lecture, my professor told us that the probability $P$ to form a hydrogen molecule $\ce{H2}$ with mass number 3 could be calculated out of the abundances, $\gamma$, of the isotopes of this ...
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203 views

Who figured out that different isotopes have different numbers of neutrons?

I reasearched about the history of the discovery of neutrons and couldn't find who found out that isotopes are a change in the number of neutrons. Can you please tell me who it was that made this ...
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1answer
68 views

Why burn methane to CO2 for isotopic analyis?

I am wondering why mathane is burned to CO$_2$ for isotopic analysis, e.g with a mass spec? I have looked into several text books, they all describe how to do it but not why. Is it because of a ...
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1answer
91 views

The unit of relative atomic mass [closed]

The mass of Carbon-12 atom is 12.0000000 a.m.u. For relative isotopic mass, e.g. Mg-24 atom is 24 compare with the c-12 as standard. However, why is it unitless? Shouldn't it be 24 a.m.u.?
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How much D2O is in Vienna Standard Mean Ocean Water?

I'm curious how much $\ce{D2O}$ (heavy water) is in Vienna Standard Mean Ocean Water. I am interested in $\ce{D2O}$ molecules and not $\ce{HDO}$/$\ce{D+}$/ $\ce{DH2O+}$/$\ce{D2HO+}$/$\ce{D3O+}$ or any ...
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1answer
144 views

Behavior of Natural Abundance and Mass Spec Ratios

The presence of sulfur in a mass spec is 96% and 4%. I believe this to be because the natural occurrence of sulfur isotopes are within these proportions. However, chlorine behaves in a 66%/33% ratio ...
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1answer
103 views

An expression for equilibrium constant of isotope reaction

Consider the isotope exchange reaction: $$\ce{C ^{16}O + 1/2 ^{18}O {}^{18}O <=> C^{18}O + 1/2 ^{16}O^{16}O}$$ The equilibrium constant for the reaction is: $$K=\frac{\prod (a_i)^{n_i}_{products}...
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63 views

Why isn't carbon-14 included in CIAAW list of isotopic abundances? [closed]

According to Wikipedia, standard atomic weight is based on the published isotopic abundances of CIAAW: The standard atomic weight $(A_\mathrm{r},$ standard) of a chemical element is the weighted ...
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175 views

Do isotopes have the same ionization energy? [duplicate]

When learning about isotopes and IE in High School this question have come to my mind recently. I have asked the teacher, she told me that she read articles about it however could not come to a ...
4
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1answer
172 views

Stronger ESI signal for deuterated substances

I observe a constant phenomenon in my ESI measurements, which indicates that deuterated substances give a stronger signal than the same substance in non-deuterated form. Unfortunately I can't make any ...
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1answer
97 views

Why do isotopes have different chemical reaction rates? [duplicate]

Isotopes of a given element differ in the rates at which they undergo chemical reaction. Why is this so? The only explanation I could think of is that the gravitational force on the electrons ...
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1answer
46 views

Is enthalpy affected by isotopes?

Enthalpy is a sum of $U$ and $PV$, and I thought that for different isotopes, internal energy values may differ. Is it true? There are three stable isotopes of $\textrm{Mg}$, mass number 24, 25, and ...
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1answer
69 views

Type of structural isomerism

What is the type of structural isomerism in which isotopes move around? Examples $\ce{CH2D-NH2}$ and $\ce{CH3-NHD}$ $\ce{CH2D-NH-CH3}$ and $\ce{CH3-ND-CH3}$ $\ce{CH2D-NH-CH2CH3}$ and $\ce{CH3-NH-CHD-...
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875 views

What is the relationship between entropy and heat capacity?

The molar heat capacity of hydrogen gas and deuterium gas are nearly the same, $\pu{28.8 J K-1 mol-1}$ and $\pu{29.2 J K-1 mol-1}$, respectively, but the absolute entropy of deuterium ($\pu{145.0 J K-...
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26 views

Do radioisotopes emitted particles influence their chemistry? [duplicate]

Supposedly, a isotopes have the same chemistry, i.e. how they bond to other atoms. Is this true for radioisotopes? I can imagine a nucleus emitting particles that interact with existing bonds in its ...
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87 views
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45 views

Ionization and bond energy of isotope [closed]

Is there a database with the direct values, or the ingredients to calculate them, for ionization and bond energies of isotopes (i.e. $^{17}O_2$). If I understand it right, ionization energy can be ...
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1answer
15 views

Effect of pH on sulphur isotope variation on a landscape

I recently ran a forest regression model, this model showed me that increasing soil pH increases sulphur isotope variation across the landscape. I am not how this is possible and if it makes sense
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131 views

Finding Symmetry number of a molecule [closed]

An isotopic variant of the molecule SF$_6$ is S$^{19}$F$_4^{18}$F$_2$, with the two $^{18}$F nuclei oriented axially, so that the $^{18}$F-S-$^{18}$F angle is 180°and the four $^{19}$F nuclei form a ...
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2answers
325 views

Do isotopic groups cause optical activity?

I understood the simplified reason for optical activity of a compound based on the difference in the angular velocities of counter-rotating circularly polarized light. The difference is due to the ...
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2answers
175 views

Kinetics of converting a water + heavy water mixture to HDO

Imagine an initial 50%-50% mixture of normal ($\rm H_2 \rm O$) and heavy water ($\rm D_2 \rm O$). I think, simply mixing them, the result will exponentially converge to an equilibric state, where ...
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1answer
735 views

Characteristics of Isotopes [closed]

I'm currently applying information theory to physics, and have begun considering the nature of isotopes, and in particular, how much information is contributed to the properties of an element by its ...
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51 views

Classic/killer/easy application for the deuterium kinetic isotope effect?

I'm a physicist. While visiting someone's o-chem class I learned about the existence of the deuterium kinetic isotope effect. This seems like an extremely sweet example of zero-point energy, and I ...
2
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1answer
65 views

Does the distillation of alcohol cause the fractioning of isotopes and carbon-12 enrichment?

In water, distillation causes fractioning of the $\ce{^{18}O}/\ce{^{16}O}$ oxygen isotopes (Wikipedia). Does something similar happen to the $\ce{^{13}C}/\ce{^{12}C}$ and possibly $\ce{^{14}C}$ ...
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18 views

What is mass-independent isotope separation/fractionation?

How can any separation/fractionation of isotopes be mass-independent, if the only difference between two isotopes is mass? The only clue(s) on Wikipedia mention molecular symmetry, 'forbidden' spin-...
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29 views

Why do foraminifera use less magnesium in their shells when the water is cold?

When scientists study ancient seabed cores, they say they can judge the temperature of the water in the past by analyzing the magnesium to calcium ratio in foraminifera shells (both in the form of ...
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3answers
723 views

Why are isotopes an issue in reading mass spectra?

It is my understanding that the isotope distribution for carbon and hydrogen, for example, are skewed heavily toward one species, i.e., one isotope accounts for ~99% of the abundance of the element in ...
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3answers
148 views

Strontium-89 vs strontium-90

Why is radioactive strontium-89 is considered medically useful for bones (along with other benefits) whereas strontium-90 (also being radioactive) is harmful for human body? How does the addition of ...
2
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1answer
342 views

What makes an isotope stable? [closed]

I have heard many times that when there is the “right balance” of protons and neutrons the atom will be stable, and therefore it will decay to achieve this stability. But what about this supposed ...
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1answer
122 views

Removing PTFE marks on glass bottles after using magnetic stir bars

I am using magnetic stir bars to agitate solutions for 4 weeks at a time. I have noticed at the bottom of the glass bottles that white marks have accumulated where the stir bar spins. Even with ...
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3answers
6k views

Confused by notation of atomic number Z and mass number A on periodic table of elements

I'm totally confused by the different conventions and when to use what. In the Periodic Table I see $$\ce{^{6}_{12}C}$$ However, in books when talking about isotopes I see $$\ce{^{12}_{6}C}$$ I ...
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0answers
33 views

Isotope labeled experiment analysis

I'm analyzing a dataset generated with LC-MS from cells that were fed $\ce{^13C}$-Glucose. There are 3 groups in total each with a different media conditions. My goal is to identify differences ...
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1answer
90 views

Number of stable molecules of artificial molecule XY4 [closed]

Suppose element X has $5$ stable isotopes, and element Y has $6$ stable isotopes. Find the number of natural molecules, knowing that an X has a charge of $+4$ and Y has a charge of $-1$. What I tried ...
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130 views

How to define the reduced mass for estimating Kinetic Isotope Effects

I am trying to think about radical reactions using zero-point energies (from the harmonic oscillator model). I have read that substitution of a bond with isotopes can alter the rate of a reaction. ...
4
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1answer
110 views

Must a sample of a deuterated compound be isotopically pure for kinetic isotope experiments?

I'm trying to do a project on the primary kinetic isotope effect on the dehydroxylation of $\alpha-FeOOH$, goethite. The goethite consists of edge-sharing double octahedra of 3 oxyanions and 3 ...
3
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3answers
89 views

Isotopes of Elements

When we talk about the substance $\ce{H2O}$ with a molar mass of $\pu{18.0 g/mol}$, what hydrogen and oxygen isotopes are present in the $\ce{H2O}$ molecules? In other words, what isotopes do the ...
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4answers
3k views

Is an isobar the same as an isotope?

I am a little bit confused about what an isobar is. Its online definition is that it's an element with the same number of neutrons but a different number of protons from an element $\ce{X}$. To me, ...
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2answers
3k views

Francium has isotopes so how can its atomic mass be a whole number?

Why do francium, radon, radium, and actinium have whole numbers for average atomic mass even though they have isotopes? But then elements like beryllium, fluorine, and sodium are listed as having no ...
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1answer
64 views

Can I expect 18O-hydroxide when adding slight amount of NaOH-16O to 18O-water?

In adding $\ce{^{16}O}$-sodium hydroxide to $\ce{^{18}O}$-water to get a $0.25\pu M$ solution, is the hydroxide in form of $\ce{^{16}O}$-hydroxide or $\ce{^{18}O}$-hydroxide? is there an oxygen ...