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Serhud [2]
3 years ago
10

The Half-Life of Pa-234 is 6.75 hours. How much (what fraction) of a sample of this isotope remains after 20.25 hours?

Chemistry
1 answer:
Grace [21]3 years ago
6 0
So in one hour half the amount remains (that's what half life means). In two hours 1/4 (or half of half) would remain and in three hours 1/8 would remain.
So the answer is 1/8
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A solution is prepared by dissolving 27.0 g of urea [(NH2)2CO], in 150.0 g of water. Calculate the boiling point of the solution
andrew11 [14]

<u>Answer:</u> The boiling point of solution is 101.56°C

<u>Explanation:</u>

Elevation in boiling point is defined as the difference in the boiling point of solution and boiling point of pure solution.

The equation used to calculate elevation in boiling point follows:

\Delta T_b=\text{Boiling point of solution}-\text{Boiling point of pure solution}

To calculate the elevation in boiling point, we use the equation:

\Delta T_b=iK_bm

Or,

\text{Boiling point of solution}-\text{Boiling point of pure solution}=i\times K_b\times \frac{m_{solute}\times 1000}{M_{solute}\times W_{solvent}\text{ (in grams)}}

where,

Boiling point of pure water = 100°C

i = Vant hoff factor = 1 (For non-electrolytes)

K_b = molal boiling point elevation constant = 0.52°C/m.g

m_{solute} = Given mass of solute (urea) = 27.0 g

M_{solute} = Molar mass of solute (urea) = 60 g/mol

W_{solvent} = Mass of solvent (water) = 150.0 g

Putting values in above equation, we get:

\text{Boiling point of solution}-100=1\times 0.52^oC/m\times \frac{27\times 1000}{60\times 150}\\\\\text{Boiling point of solution}=101.56^oC

Hence, the boiling point of solution is 101.56°C

5 0
3 years ago
Indicate the number of significant figures in the following measured numbers:
inysia [295]

Answer: a = 2 ; f = 5 ; b = 2 ; g = 2 ; c = 2 ; h = 2 ; d = 4 ; i = 5 ; e = 3 ; j = 7

Explanation: Some rules to follow while calculating sig figs is

1. If a number like 4500 is present, only two sig figs are counted, but none of the zeros are, but if 4500. has a decimal point present, then you should count all the numbers available.

2. If a number like .0005 is present, only count 5 as a sig fig, however if the number is .00050, count the 0 after the 5 in this example (this would then have two sig figs.

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2 years ago
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Andrei [34K]

Answer:

A flower is self-pollinated if pollen is transferred to it from any flower of the same plant and cross-pollinated if the pollen comes from a flower on a different plant.

Explanation:

This is because each flower is capable of fertilizing itself by autogamy. Autogamy means that the male part of a flower sends pollen to the female part of the same flower.

3 0
3 years ago
PLZ HEL I WILL GIVE BRAINLIEST
NemiM [27]

Answer: A material that readily transmits energy is a conductor, while one  that resists energy transfer is called an insulator .

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3 years ago
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