Elements, Ions, and Isotopes

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AP Chemistry › Elements, Ions, and Isotopes

Questions 1 - 10

Am-242 undergoes beta-decay at a half-life of 16 hours. If a chemist starts with a sample of of Am-242 and allows it to undergo beta-decay, how much of the original sample remains after 4 days?

Explanation

With each half-life, the amount of Am-242 is halved. 4 days is 96 hours, which is 6 half-lives. For half-life questions use the formula:

$\left(\frac {1}{2}\right)^{n}=proportion;of;original;sample;remaining$

Where is the number of half lives.

$\left(\frac {1}{2}\right)^{6}=0.015625$

$0.015625 \cdot 512g=8g$

Thus of Am-242 is left after 4 days.

Am-242 undergoes beta-decay at a half-life of 16 hours. If a chemist starts with a sample of of Am-242 and allows it to undergo beta-decay, how much of the original sample remains after 4 days?

Explanation

With each half-life, the amount of Am-242 is halved. 4 days is 96 hours, which is 6 half-lives. For half-life questions use the formula:

$\left(\frac {1}{2}\right)^{n}=proportion;of;original;sample;remaining$

Where is the number of half lives.

$\left(\frac {1}{2}\right)^{6}=0.015625$

$0.015625 \cdot 512g=8g$

Thus of Am-242 is left after 4 days.

What kind of radiation has no charge or mass?

alpha

beta

gamma

delta

Explanation

This is the definition of gamma radiation.

What kind of radiation has no charge or mass?

alpha

beta

gamma

delta

Explanation

This is the definition of gamma radiation.

The isotope $_{40}^{19}\textrm{K}$ of potassium is used to date geological materials. One of the decay reactions this isotope undergoes is:

$_{19}^{40}\textrm{K} \rightarrow; _{20}^{40}\textrm{Ca} + X$

In order for the nuclear reaction to be balanced can be:

either an electro or β radiation

an electron

a proton

β radiation

Explanation

A beam of electrons is known also as β radiation. An electron has atomic number of and zero mass number. Hence, the reaction can be written:

$_{19}^{40}\textrm{K} \rightarrow; _{20}^{40}\textrm{Ca} ; +; _{-1}^{0}\textrm{X}$

Where $_{-1}^{0}\textrm{X}$ can be either, an electron or β radiation. The mass number is balanced because and the atomic number is balanced because $19=20+\left ( -1\right )$ . This kind of nuclear reactions are called beta decay reactions.

The isotope $_{40}^{19}\textrm{K}$ of potassium is used to date geological materials. One of the decay reactions this isotope undergoes is:

$_{19}^{40}\textrm{K} \rightarrow; _{20}^{40}\textrm{Ca} + X$

In order for the nuclear reaction to be balanced can be:

either an electro or β radiation

an electron

a proton

β radiation

Explanation

A beam of electrons is known also as β radiation. An electron has atomic number of and zero mass number. Hence, the reaction can be written:

$_{19}^{40}\textrm{K} \rightarrow; _{20}^{40}\textrm{Ca} ; +; _{-1}^{0}\textrm{X}$

As atomic radius decreases, the force of attraction between the nucleus of the atom and its electrons .

increases

decreases

stays the same

cannot be determined

Explanation

As the atomic radius decreases, electrons are drawn closer to the nucleus. Since the electromagnetic force between the positively charged nucleus and negatively charged electrons is a function of distance, the force of attraction, or effective nuclear charge, exerted on each electron will be greater.

As atomic radius decreases, the force of attraction between the nucleus of the atom and its electrons .

increases

decreases

stays the same

cannot be determined

Explanation

An electron falling to a lower energy level gives off a blue glow (λ=475nm). How much energy is emitted?

3.14x10-40J

4.184 x 10-19 J

4.184 x 10-17 J

3.14x10-37J

Energy is not emitted

Explanation

E=hf, or E=hc/λ

h is Planck's constant with a value of 6.62606957 × 10-34 m2 kg / s. Converting 475nm to m gives 4.75x10-7m. c is the speed of light with 3x108m/s. Putting these variables into the second equation you get 4.174x10-19J

An electron falling to a lower energy level gives off a blue glow (λ=475nm). How much energy is emitted?

3.14x10-40J

4.184 x 10-19 J

4.184 x 10-17 J

3.14x10-37J

Energy is not emitted