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Lelu [443]
3 years ago
9

What is the half-life of an isotope that decays to 6.25% of its original activity in 18.9 hours?

Chemistry
1 answer:
inessss [21]3 years ago
8 0
Radioactive material obeys 1st order decay kinetics,
For 1st order reaction, we have 
k = \frac{2.303}{t}Xlog \frac{\text{initial conc.}}{\text{final conc.}}
where, k = rate constant of reaction

Given: Initial conc. 100, Final conc. = 6.25, t = 18.9 hours

∴ k = \frac{2.303}{18.9} X log \frac{100}{6.25} = 0.1467 hours^(-1)

Now, for 1st order reactions: half life = \frac{0.693}{k} =  \frac{0.693}{0.1467} = 4.723 hours.


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In an ion with an unknown charge, the total mass of all the electrons was determined to be 2.19 ✕ 10−26 g, while the total mass
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Answer:

\large \boxed{\text{Fe$^{{2+}}$}}

Explanation:

1. Number of electrons

\text{Number of electrons} = 2.19 \times 10^{-26}\text{ g} \times \dfrac{\text{1 electron}}{9.109 \times 10^{-28}\text{ g}} = \text{24 electrons}

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3. Identify the ion

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A neutral atom of iron would have 26 electrons.

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\text{The symbol for the ion is $\large \boxed{\textbf{Fe$^{\mathbf{2+}}$}}$}

4 0
3 years ago
Which of these atoms are electrically neutral?
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Atoms are electrically neutral because they contain equal quantities of positively charged protons and negatively charged electrons. Electrons and protons have equal but opposite charges, so the result is no net charge. Ions are atoms that have gained or lost electrons.

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2. A sample of iron has the dimensions of 2.0 cm x 3.0 cm x
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2 A(g) + B(g) ---> 2 C(g)Rate = k [A][B]At the beginning of one trial of this reaction, [A] = 3.0 M and [B] = 1.0 M. The obse
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Answer:

Lmol⁻¹s⁻¹

Explanation:

The rate law of the given reaction is:-

Rate=k[A][B]

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Applying in the equation as:-

0.36 M/sec =k × 3.0 M× 1.0 M

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<u>The units of k = Lmol⁻¹s⁻¹</u>

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