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3 years ago

The half-life of Radium-226 is 1590 years. If a sample contains 100 mg, how many mg will remain after 4000 years?

1 answer:

4 0

We can calculate the amount left after 4000 years by using the half-life equation. It is expressed as:

A = Ao e^-kt

where A is the amount left at t years, Ao is the initial concentration, and k is a constant.

From the half-life data, we can calculate for k.

1/2(Ao) = Ao e^-k(1590)
k = 4.36 x 10^-4

A = 100 e^-<span> 4.36 x 10^-4(4000)
</span>A = 17.48 mg

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3 years ago

One difference between mixtures and pure substances is that A) mixtures can be physically separated. B) mixtures are made of one

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john dalton's original atomic theory contained the following key ideas. which part(s) of these ideas was/were incorrect?

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John Dalton's original atomic theory contained the following key ideas and the incorrect one is that elements are made of tiny indivisible particles called atoms and is denoted as option A.

This is defined as the smallest unit of matter which forms a chemical element and Dalton proposed that it was indivisible which was later proved wrong.

It was later discovered that atom is made up of sub atomic particles such as proton, electron and neutron. This was therefore the reason why option A was chosen as the most appropriate choice.

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The options include:

A. elements are made of tiny indivisible particles called atoms

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C. Atoms can join together in whole number ratios to form compounds.

D. The atoms of each element are unique

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1 year ago

A student wants to dissolve the maximum amount of CaF2 (Ksp = 3.2 x 10^−11) to make 1 L of aqueous solution.

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Letter C on the model titration curve corresponds to the point where pH equals the numerical value of pKa for HPr

<h3>What is a titration curve?</h3>

A titration curve is a graph of the pH of a solution against increasing volumes of an acid or a base that is added to the solution.

The pH of a solution is the negative logarithm to base ten of the hydrogen ion concentration and is a measure of the acidity or alkalinity of the solution.

The pKa is the acid dissociation constant of an acid solution.

In a titration of a strong acid and strong base, the pH at equivalence point is equal to the pKa of the acid.

The equivalence point is the point when equal moles of acids and base has reacted.

In the given titration curve, pH = pKa at point C.

In conclusion, for a titration curve of strong acid and base, at equivalence point, pH is equal to pKa of acid.

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