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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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How many moles of MgO can be made from 5 moles of Mg?<br> 2Mg + O2 -&gt; 2MgO
kkurt [141]

Answer:

Explanation:

The expected product is MgO, so the 1-to-1 mole ratio Mg to O in the product is all that is required.

3 0
2 years ago
B. If the initial pressure of gas inside the balloon was 1.65 atm, what is the new pressure?
Orlov [11]

Question 1 :

V1/T1 = V2/T2

3.0L/273K = V2/373K

To get the value of Z, cross multiply

3.0L x 373K = 273K x V2

1119 = 273V2

Divide both sides by 273

1119/273 = 273V2/273

4.10L = V2

The new volume is 4.10 liters

Question 2 :

P1/T1 = P2 /T2

P1 = 880 kPA= 880 *10^3 Pa

T1 = 250 K

T2 = 303 K

P2 =?

Substituting for P2

P2 = P1 T2/ T1

P2 = 880 kPa * 303 / 250

P2 = 266,640 kPa/ 250

P2 = 1066.56 kPa.

The new pressure of the gas is 1066.56 kPa

Question 3 :

Given that:

Volume of gas V = 4.80L

(since 1 liter = 1dm3

4.80L = 4.80dm3)

Temperature T = 62°C

Convert Celsius to Kelvin

(62°C + 273 = 335K)

Pressure P = 2.9 atm

Number of moles of gas N = ?

Apply ideal gas equation

pV = nRT

2.9atm x 4.8dm3 = n x (0.0082 atm dm3 K-1 mol-1 x 335K)

13.92 atm dm3 = nx 2.747 atm dm3 mol-1

n = 13.92/2.747

n = 5.08 moles

There are 5.08 moles of gas contained in the sample

Question 4 :

Volume of gas V = 3.47L

(since 1 liter = 1dm3

3.47L = 3.47dm3)

Temperature T = 85.0°C

Convert Celsius to Kelvin

(85.0°C + 273 = 358K)

Pressure P = ?

Number of moles of gas N = 0.100 mole

Apply ideal gas equation

pV = nRT

p x 3.47dm3 = 0.10 x (0.0082 atm dm3 K-1 mol-1 x 358K)

p x 3.47dm3 = 0.29 atm dm3

p = (0.29 atm dm3 / 3.47 dm3)

p = 0.085 atm

If 1 atm = 760 mm Hg

0.085atm = 0.085 x 760

= 64.6 mm Hg

The pressure of the gas is 64.6 mm hg

8 0
2 years ago
You have to make 500 mL of a 1.50 M BaCl2. You have 2.0 M barium chloride solution available. Determine how to make the needed d
Inga [223]

Answer:

You need 375 mL of BaCl2 solution.

Explanation:

M1V1=M2V2

Dilution formula. Substitute known values and solve for V1.

M1 = 2.0 M

M2 = 1.50 M

V2 = 500 mL

(2.0 M)(V1) = (1.50 M)(500 mL)

V1 = (1.50 M)(500 mL) / (2.0 M)

V1 = 375 mL

7 0
2 years ago
A 250 cm^3 solution containing 1,46 g of sodium chloride is added to an excess of silver nitrate solution. The reaction is given
faust18 [17]

Answer:

The mass of the precipitate  that AgCl is 3.5803 g.

Explanation:

a) To calculate the molarity of solution, we use the equation:

\text{Molarity of the solution}=\frac{\text{Mass of solute}\times 1000}{\text{Molar mass of solute}\times \text{Volume of solution (in mL)}}

We are given:

Mass of solute (NaCl) = 1.46 g

Molar mass of sulfuric acid = 58.5 g/mol

Volume of solution = 250 cm^3 =250 mL

1 cm^3= 1 ml

Putting values in above equation, we get:

\text{Molarity of solution}=\frac{1.46g\times 1000}{58.5g/mol\times 250}\\\\\text{Molarity of solution}=0.09982 M

0.09982 M is the concentration of the sodium chloride solution.

b) NaCl (aq)+AgNO_3 (aq)\rightarrow AgCI(s)+NaNO_3(aq)

Moles of NaCl = \frac{1.46 g}{58.5 g/mol}=0.02495 mol

according to reaction 1 mol of NaCl gives 1 mol of AgCl.

Then 0.02495 moles of NaCl will give:

\frac{1}{1}\times 0.02495 mol=0.02495 mol of AgCl

Mass of 0.02495 moles of AgCl:

0.02495 mol\times 143.5 g/mol=3.5803 g

The mass of the precipitate  that AgCl is 3.5803 g.

3 0
3 years ago
Which of these illustration shows isotopes of the elements boron b
Delvig [45]
The isotopes are elements with the same number of protons but different number of neutrons.

Boron atomic number is 5. That is the number of protons.

The natural occurring isotopes of boron contain 5 or 6 neutrons. Other, non stable isotopes, contain from 1 to 16 neutrons.
5 0
3 years ago
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