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2 years ago

The half life of a certain radioactive element is 1,250 years what percent of the atoms remain after 7500 years

2 answers:

7 0

Each half-life results in ~50% (1/2) of the original element remaining.

7500/1250 = 6 half-lives, so 100(1/2)^6
= 100(0.015625)
= 1.5625% of the original element would remain

True [87]2 years ago

6 0

<h2>Answer:</h2>

The amount of element after 7500 years will be 1.607% of initial amount.

<h3>Explanation:</h3>

The half life of certain elements shows the time after which half of the amount of the element will disintegrate.

Half life of given atom = 1250 years.

The amount of element after 7500 years:

Total number of half life during this period = 7500/1250 = 6.

The amount of element after 1 half life = 50%

After 2nd half life = 25%

After 3rd half life = 12.5%

After 4 half life = 6.25%

After 5 half life = 3.125

After 6 half life = 1.607%

So the amount of element after 7500 years will be 1.607% of initial amount.

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A 600.0 mL sample of 0.20 MHF is titrated with 0.10 MNaOH. Determine the pH of the solution after the addition of 600.0 mL of Na

Leona [35]

Answer: pH=12.69

Explanation:

${\text{Moles of HF}=Molarity\times {\text{Volume of solution in liters}}$

${\text{Moles of HF}=0.20M\times 0.6L=0.12 moles$

$HF\rightarrow H^++F^-$

Initial 0.12 0 0

Eqm 0.12-x x x

$K_a=\frac{[H^+][F^-]}{[HF]}$

$3.5\times 10^{-4}=\frac{x^2}{0.12-x}$

(neglecting small value of x in comparison to 0.12)

$x=4.2\times 10^{-5}$

Moles of $H^+=4.2\times 10^{-5}$

$NaOH\rightarrow Na^++OH^-$

${\text{Molesof NaOH}}=Molarity\times {\text{Volume of solution in liters}}$

${\text{Moles of NaOH}}=0.10M\times 0.6L=0.06 moles$

0.06 moles of NaOH will give 0.06 moles of $[OH^-]$

Now $4.2\times 10^{-5}$ moles of $OH^-$ will be neutralized by $4.2\times 10^{-5}$ moles of $H^+$ and $(0.06-4.2\times 10^{-5})=0.059$ moles of $OH^-$ will be left.

Molarity of $OH^-=\frac{0.059moles}{1.2L}=0.049M$

$pOH=-\log[OH^-]=-\log[0.049]=1.31$

pH = 14 - pOH= 14 - 1.31 = 12.69

5 0

2 years ago

The interior of a refrigerator has a volume of 0.600 m3. the temperature inside the refrigerator in 282 k, and the pressure is 1

Dafna11 [192]

In this instance we can use the ideal gas law equation to find the number of moles of gas inside the refrigerator
PV = nRT
where
P - pressure - 101 000 Pa
V - volume - 0.600 m³
n - number of moles
R - universal gas constant - 8.314 J/mol.K
T - temperature - 282 K
substituting these values in the equation
101 000 Pa x 0.600 m³ = n x 8.314 J/mol.K x 282 K
n = 25.8 mol
there are 25.8 mol of the gas
to find the mass of gas
mass of gas = number of moles x molar mass of gas
mass = 25.8 mol x 29 g/mol = 748.2 g
mass of gas present is 748.2 g

6 0

2 years ago

What name is used to describe the H-N-H group?

mamaluj [8]

Answer:

an amine group

Explanation:

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5 0

2 years ago

A 63.5 g sample of an unidentified metal absorbs 355 ) of heat when its temperature changes

insens350 [35]

0.208 is the specific heat capacity of the metal.

Explanation:

Given:

mass (m) = 63.5 grams 0R 0.0635 kg

Heat absorbed (q) = 355 Joules

Δ T (change in temperature) = 4.56 degrees or 273.15+4.56 = 268.59 K

cp (specific heat capacity) = ?

the formula used for heat absorbed and to calculate specific heat capacity of a substance will be calculated by using the equation:

q = mc Δ T

c = $\frac{q}{mΔ T}$

c = $\frac{355}{63.5X 268.59}$

= 0.208 J/gm K

specific heat capacity of 0.208 J/gm K

The specific heat capacity is defined as the heat required to raise the temperature of a substance which is 1 gram. The temperature is in Kelvin and energy required is in joules.

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2 years ago

We know from the relative amounts of 16O and 18O that global temperatures and global climate have changed over time. Why is it i

Andru [333]

Answer:

In order to take steps by humans for controlling the change in climate.

Explanation:

It is important that scientist find out the change which occurs in the climate with the passage of time by performing experiments and also repeat the experiments in order to verify their findings. Due to these experiments, scientists also find out the reasons behind of climate change which enable us to take steps in preventing the change that occurs in the environment. it is also important for scientists to be able to explain how they know that climate has changed over time in order to explain that he is not assuming or making predictions, he has to provide evidence for his statement which is only be possible through experiments.

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2 years ago