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arlik [135]
3 years ago
15

An unknown radioactive substance has a half-life of 3.20hours . If 46.2g of the substance is currently present, what mass A0 was

present 8.00 hours ago?Express your answer with the appropriate units.
Americium-241 is used in some smoke detectors. It is an alpha emitter with a half-life of 432 years. How long will it take in years for 34.0% of an Am-241 sample to decay?

Express your answer with the appropriate units.

A fossil was analyzed and determined to have a carbon-14 level that is 80% that of living organisms. The half-life of C-14 is 5730 years. How old is the fossil?

Express your answer with the appropriate units.
Chemistry
1 answer:
iogann1982 [59]3 years ago
7 0

Answer:

a) a0 was 46.2 grams

b) It will take 259 years

c) The fossil is 1845 years old

Explanation:

<em>An unknown radioactive substance has a half-life of 3.20hours . If 46.2g of the substance is currently present, what mass A0 was present 8.00 hours ago?</em>

A = A0 * (1/2)^(t/h)

⇒ with A = the final amount = 46.2 grams

⇒ A0 = the original amount

⇒ t = time = 8 hours

⇒ h = half-life time = 3.2 hours

46.2 = Ao*(1/2)^(8/3.2)

Ao = 261.35 grams

<em>Americium-241 is used in some smoke detectors. It is an alpha emitter with a half-life of 432 years. How long will it take in years for 34.0% of an Am-241 sample to decay?</em>  

t = (ln(0.66))-0.693) * 432 = 259 years

It will take 259 years

<em>A fossil was analyzed and determined to have a carbon-14 level that is 80% that of living organisms. The half-life of C-14 is 5730 years. How old is the fossil?</em>

<em />

t = (ln(0.80))-0.693) * 5730 = 1845

The fossil is 1845 years old

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hoa [83]

Answer:

i)The carbon particles are formed when the gas is not completely burnt(True)

ii)A solid or liquid must be change to gaseous state in order to make flame(TRUE)

iii)A non- luminous Bunsen flame produces has three visible regions(FALSE)

iv)The luminous Bunsen flame produces less soot than the non- luminous flame(FALSE)

v)A yellow Bunsen flame is obtained when the air holes are opened(FALSE)

vi)The luminous Bunsen flame is hotter than a non- luminous Bunsen flame(FALSE)

vii)Bunsen burner uses kerosene as a source of heat(FALSE)

Explanation:

i)When the incomplete combustion ,then CO(carbon monoxide) and C(carbon) are produced. <u>The unburnt carbon get deposited as</u><u> Soot</u>.

In complete combustion CO2(carbon dioxide) is produced.

ii)Fire, is the mixture of hot gases.Flame are result of chemical reaction between oxygen and fuel(e.g butane ,wood).Flame contain,carbon dioxide , heat ,light,steam.

iii)There are total three regions of flame in which the outer most region is the non-luminous .The non-luminous part is <u>blue(one visible region</u>) and does not emit-light.

iv) Luminous Bunsen flame produces more soot than the non- luminous flame because luminous flame contain more unburnt particles as compare to non-luminous.

luminous part has less oxygen available for complete combustion of fuel

v)When the air hole is open it means excess oxygen is supplied to the fuel.

In this case clean and luminous flame is produced.When air hole is close yellow flame is produced.

vi)Non-luminous part of flame is more hot because of complete combustion due to proper availability  of oxygen. Sometime the particle of non-luminous flame get ionize also.

vii).The bunsen burner uses Natural gas(methane) or LPG(propane and butane)as sources of heat because these are easily burnt not kerosene.

4 0
3 years ago
Dmitri mendeleev contribution to the periodic table.
Pepsi [2]

In 1871, a Russian Chemist, Dimitri Mendeleev, gave a useful scheme for classification of elements. He presented the first regular periodic table in which elements of similar chemical properties were arranged in eight vertical columns called groups. The horizontal rows of table were called periods. He arranged elements in ascending order of their  atomic masses and found that elements having similar chemical properties appeared at regular intervals. This observation was called Periodic Law.

8 0
2 years ago
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enot [183]

Answer:

C

Explanation:

A gas is a state of matter that has no fixed shape and no fixed volume gases have lower density than other states of matter such as solids and liquids.

7 0
3 years ago
Which of the following is an oxidation-reduction reaction? Fe2O3 3CO Right arrow. 2Fe 3CO2 CuSO4 2NaOH Right arrow. Cu(OH)2 Na2S
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The reaction, Fe2O3 + 3CO------> 2Fe + 3CO2 is an oxidation-reduction reaction.

An oxidation-reduction reaction is a reaction in which there is a change in oxidation number from left to right in the reaction. This is because, a specie is oxidized and another specie is reduced.

In the reaction;  Fe2O3 + 3CO------> 2Fe + 3CO2, we can see that the oxidation number of iron decreased from +3 on the left hand side to zero on the right hand side. The oxidation number of carbon was increased from + 2 to +4.

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6 0
2 years ago
If 200.4g of water is mixed with 101.42g of salt the mass of the final solution would be reported as
d1i1m1o1n [39]

Answer:

301.8 g

Explanation:

We prepare a solution with 200.4 g of water (solvent) and 101.42 g of salt (solute). The mass of the solution is equal to the sum of the mass of the solvent and the mass of the solute.

m(solution) = m(solute) + m(solvent)

m(solution) = 200.4 g + 101.42 g

m(solution) = 301.8 g (we round-off to one decimal according to the significant figures rules)

8 0
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