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2 years ago

If a sample has 25% parent and 75% daughter, how many halflifes have gone by?

Chemistry

1 answer:

Anit [1.1K]2 years ago

6 0

Answer:

Two half lives.

Explanation:

It is known that the decay of isotopes and radioactive material obeys first order kinetics.

Also, it is clear that in first order decay the half-life time is independent of the initial concentration.

That means for a sample 100% to decay to 50 % it will take one half-life, and to decay the remaining 50% to 25% it will take another half-life.

So, for a sample has 25% parent and 75% daughter it will have two half-lives.

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Gennadij [26K]

Actually, Henry's Law is an empirical value. It means that it was not obtained out of raw calculations or correlations. This was gathered from experimental results. Hence, you can search its data. At standard temperature of 25°C (298 K),

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Substituting the values so that T would be in 20°C or 293 K,
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Marat540 [252]

Answer:

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2 years ago

Given the equation Ca + H2O --> Ca(OH)2 + H2 how many grams of calcium will react completely with 10.0 grams of water? *

Yuki888 [10]

Answer: 11.0 g of calcium will react with 10.0 grams of water.

Explanation:

To calculate the moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text {Molar mass}}$

moles of $H_2O$

$\text{Number of moles}=\frac{10.0g}{18g/mol}=0.55moles$

The balanced chemical equation is:

$Ca+2H_2O\rightarrow Ca(OH)_2+H_2$

According to stoichiometry :

2 moles of $H_2O$ require = 1 mole of $Ca$

Thus 0.55 moles of $H_2O$ require= $\frac{1}{2}\times 0.55=0.275moles$ of $Ca$

Mass of $Ca=moles\times {\text {Molar mass}}=0.275moles\times 40g/mol=11g$

Thus 11.0 g of calcium will react with 10.0 grams of water.

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2 years ago

Exercise 2:

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Answer:

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3. 0.2mol

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2 years ago

when 6.25 grams of pure iron are allowed to react with oxygen , a black oxide forms. if the product weighs 8.15 g, what is the e

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We are given with the mass of pure iron that reacts with oxygen to form an oxide which has a given mass as well. the mass of oxygen reacted is 8.15-6.25 g or 1.9 grams. THen we convert the mass of the reactants to moles. Iron is equal to 0.1119 moles and oxygen is equal to 0.1188. We divide each number to the less amount. Hence iron is 1 and oxygen is approx 1. The empirical formula hence is FeO or ferrous oxide or Iron (II) oxide.

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2 years ago