Chemistry, 13.07.2019 22:20, highschoolboy

The fraction of a radioactive isotope remaining at time t is (1/2)^t/t1/2 where t1/2 is the half-life. if the half-life of carbon−14 is 5,730 yr, what fraction of carbon−14 in a piece of charcoal remains after
(a) 14.0 yr?
(b) 1.900 × 10^4 yr? × 10 (enter your answer in scientific notation.)
(c) 1. × 10^5 yr? × 10 (enter your answer in scientific notation.)

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answered: terry94

a) $1.065\times 10^{-8}$ fraction of carbon−14 in a piece of charcoal remains after 14.0 years.

b) $0.000\times 10^{-3}$ fraction of carbon−14 in a piece of charcoal remains after $1.900\times 10^4 years$

c) $0.0000\times 10^{-4}$ fraction of carbon−14 in a piece of charcoal remains after $1.0000\times 10^5 years$ .

Explanation:

The fraction of a radioactive isotope remaining at time t is given by:

$[A]=\frac{(\frac{1}{2})^t}{t_{\frac{1}{2}}}$

Taking log both sides:

$\log [A]=t\log[\frac{1}{2}]-\log [t_{\frac{1}{2}}]$

[A] = fraction at given time t

$t_{\frac{1}{2}}$ = half life of the carbon−14 =5,730 years

a)When , t = 14 years

$\log [A]=t\log[\frac{1}{2}]-\log [t_{\frac{1}{2}}]$

$\log [A]= 14 years\times (-3010)-\log [5,730 years]$

$[A]=1.065\times 10^{-8}$

b)When , t = $1.900\times 10^4 years$

$\log [A]=t\log[\frac{1}{2}]-\log [t_{\frac{1}{2}}]$

$\log [A]= 1.900\times 10^4 years\times (-3010)-\log [5,730 years]$

$[A]=0.000\times 10^{-3} [/tex$

c)When , t = $1.0000\times 10^5 years$

$\log [A]=t\log[\frac{1}{2}]-\log [t_{\frac{1}{2}}]$

$\log [A]= 1.0000\times 10^5 years\times (-3010)-\log [5,730 years]$

$[A]=0.0000\times 10^{-4}$

answered: Guest

explanation:

the largest database of organic compounds lists about 10 million substances, which include compounds originating from living organisms and those synthesized by chemists. the number of potential organic compounds has been estimated at 1060—an astronomically high number. the existence of so many organic molecules is a consequence of the ability of carbon atoms to form up to four strong bonds to other carbon atoms, resulting in chains and rings of many different sizes, shapes, and complexities. the simplest organic compounds contain only the elements carbon and hydrogen, and are called hydrocarbons. even though they are composed of only two types of atoms, there is a wide variety of hydrocarbons because they may consist of varying lengths of chains, branched chains, and rings of carbon atoms, or combinations of these structures. in addition, hydrocarbons may differ in the types of carbon-carbon bonds present in their molecules. many hydrocarbons are found in plants, animals, and their fossils; other hydrocarbons have been prepared in the laboratory. we use hydrocarbons every day, mainly as fuels, such as natural gas, acetylene, propane, butane, and the principal components of gasoline, diesel fuel, and heating oil. the familiar plastics polyethylene, polypropylene, and polystyrene are also hydrocarbons. we can distinguish several types of hydrocarbons by differences in the bonding between carbon atoms. this leads to differences in geometries and in the hybridization of the carbon orbitals.

answered: Guest

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.

chemical decomposition is opposite of chemical synthesis.