answer.
Ask question
Login Signup
Ask question
All categories
  • English
  • Mathematics
  • Social Studies
  • Business
  • History
  • Health
  • Geography
  • Biology
  • Physics
  • Chemistry
  • Computers and Technology
  • Arts
  • World Languages
  • Spanish
  • French
  • German
  • Advanced Placement (AP)
  • SAT
  • Medicine
  • Law
  • Engineering
Reil [10]
2 years ago
13

Cesium-137, a component of radioactive waste, has a half-life of 30.2 yr. If a sample of waste has an initial activity of 15.0 C

i due to cesium-137, how long will it take for the activity due to cesium-137 to drop to 0.250 Ci?
Chemistry
1 answer:
saw5 [17]2 years ago
4 0

Answer:

It takes 178.4 years to drop the activity from 15.0 Ci to 0.25 Ci

Explanation:

Step 1: Data given

Half-life time = 30.2 years

Initial activity = 15.0 Ci

Final activity = 0.250 Ci

Step 2: Calculate the time needed

N / No = e^(-0.693 * t / T1/2)

⇒ with N = The activity after dropped = 0.250 Ci

⇒ with N0 = the initial activity = 15.0

⇒ with t= the time (in years) needed to drop the activity from 15.0 to 0.250

⇒ with t1/2 = the half- life time is 30.2 years  

0.250 / 15.0 = e^(-0.693 * t / 30.2)

ln(0.250/15.0) = (-0.693 * t / 30.2)

-4.09 * 30.2 = -0.693t

-123.65 = -0.693t

t= 178.4 years

It takes 178.4 years to drop the activity from 15.0 Ci to 0.25 Ci

You might be interested in
400 mL of hydrogen are collected over water at 18 C and a total pressure of 740 mm of mercury. (Vapor pressure of H2O at 18 C=15
MrRa [10]

Answer:

a)15.5 mmHg is the partial pressure of water vapor.

b) 724.5 mmHg is the partial pressure of hydrogen gas.

Explanation:

Total pressure of gases = T = P = 740 mmHg

Vapor pressure of the water = p_1=15.5 mmHg

Partial pressure of the hydrogen gas = p_2=?

Partial pressure of the water = p_1=15.5 mmHg

15.5 mmHg is the partial pressure of water vapor.

Using Dalton's law of partial pressure:

P=p_1+p_2

740 mmHg=15.5 mmHg+p_2

p_2=740 mmHg-15.5mmHg =724.5 mmHg

724.5 mmHg is the partial pressure of hydrogen gas.

6 0
2 years ago
A sample of 508.4 grams of copper completely reacted with oxygen to form 572.4 grams of a copper oxide product. how many grams o
Svet_ta [14]

According to law of conservation of mass, mass can neither be destroyed nor created in a chemical reaction. Thus, sum of masses of reactants must be equal to sum of masses of products in a reaction.

The chemical reaction is as follows:

2Cu+O_{2}\rightarrow 2CuO

Here, sum of masses of Cu and oxygen gas should be equal to CuO formed.

2m_{Cu}+m_{O_{2}}=2m_{CuO}

Thus, mass of oxygen will be:

m_{O_{2}}=2(572.4-508.4)g=128 g

This can be further proved as follows:

The balanced chemical reaction is as follows:

2Cu+O_{2}\rightarrow 2CuO

Here, 2 moles of Cu completely reacts with 1 mole of O_{2} to give 2 moles of CuO.

Thus, 1 mole of Cu reacts with 0.5 moles of O_{2} .

The mass of Cu is 508.4 and molar mass is 63.546 g/mol, number of moles can be calculated as follows:

n=\frac{m}{M}=\frac{508.4 g}{63.546 g/mol}=8 mol

Thus, number of moles of  O_{2} reacting will be:

n_{O_{2}}=8\times 0.5 mol=4 mol

Molar mass of oxygen molecule is 32 g/mol thus, mass can be calculated as follows:

m=n×M=4 mol×32 g/mol=128 g/mol

This satisfies the law of conservation of mass.


7 0
2 years ago
Analyze the importance of chemistry in our society using the branches of chemistry as examples
ICE Princess25 [194]

Answer:

Explanation: Well each branch has its own little job especially when it comes to society. First we have the Organic Chemistry Branch It includes the study of all the possible compounds which have carbon in them. Then we have the Inorganic Chemistry Branch, the inorganic compounds find their use in medicine, food, agriculture and also technology. Next we have the  Biochemistry Branch it deals with chemistry happening inside the living bodies of animals and plants. This subject is huge and plays an important role in medicine, agriculture, poultry, fisheries, etc. And finally we have the Physical Chemistry Branch it deals with the physical properties of chemicals or substances. It includes topics like gaseous laws (Dalton law), thermal conduction in liquids, gases, solids. The conductivity of electrolytes (used in batteries) liquids etc. It also deals with processes like sublimation, melting point, boiling point, the crystal structure of compounds, etc.

6 0
2 years ago
penicillin. an important antibiotic (antibacterial agent), was discovered accidentally by the scottish bacteriologist alexander
dmitriy555 [2]

Answer:

mass percent of carbon       = 57.78 %

mass percent of hydrogen   = 6.40 %

mass percent of nitrogen    = 8.96 %

mass percent of oxygen    = 20.49 %

mass percent of sulfur     =  10.24 %

Explanation:

Given data

Molecular formula = C₁₄H₂₀N₂O₄S

molecular mass (total mass) = 312.39 g/mol

Percentage of carbon = ?

Percentage of hydrogen = ?

Percentage of oxygen = ?

Percentage of nitrogen = ?

Percentage of sulfur = ?

Solution

1st we find out number of moles of each element from the molecular formula

  Number of moles of carbon  = 14 mol

  Number of moles of hydrogen   = 20 mol

  Number of moles of nitrogen   = 2 mol

  Number of moles of oxygen  = 4 mol

  Number of moles of sulfur   = 1 mol

Now we find out the mass of each element

as we know that

     <em>mass = number of moles × molecular mass</em>

 mass of carbon  = 14 mol × 12 g/mol

 mass of carbon  = 168 g

 mass of hydrogen   = 20 mol × 1 g/mol

 mass of hydrogen   = 20 g

 mass of nitrogen   = 2 mol × 14 g/mol

 mass of nitrogen   = 28 g

 mass of oxygen  = 4 mol × 16 g/mol

 mass of oxygen  = 64 g

 mass of sulfur   = 1 mol × 32 g/mol

 mass of sulfur   =  32 g

now we find out the mass percent of each element

<em>         mass percent = ( mass ÷ total mass ) × 100</em>

 mass percent of carbon  = ( 168 g ÷ 312.39 g/mol ) × 100

 mass percent of carbon  = 57.78 %

 mass percent of hydrogen   = ( 20 g ÷ 312.39 g/mol ) × 100

 mass percent of hydrogen   = 6.40 %

 mass percent of nitrogen   = ( 28 g ÷ 312.39 g/mol ) × 100

 mass percent of nitrogen   = 8.96 %

 mass of oxygen  =( 64 g ÷ 312.39 g/mol ) × 100

 mass percent of oxygen  = 20.49 %

 mass percent of sulfur   = ( 32 g ÷ 312.39 g/mol ) × 100

 mass percent of sulfur   =  10.24 %

7 0
2 years ago
You want to determine ΔH o for the reaction Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g) To do so, you first determine the heat capacity
Assoli18 [71]

Answer:

(A) The heat capacity of the calorimeter is therefore = −2.1428KJ÷13.5°C

= −0.1587KJ/°C

 

(B) ΔHo for the reaction Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g) = –15.42KJ

Explanation:

Solution

 

Calculate the heat actually evolved.

                 q = mcΔt

 

Finding the mass of the reactants in grams we have.

 

Use density. (50 mL + 50 mL ) = 100 mL of solution.

 

100 mL X 1.04g/mL     = 104 grams of solution. (mass = Volume X Density)

                       

 

Find the temperature change.

 

       Δt =tfinal - tinitial = 30.4°C – 16.9°C = 13.5°C

 

    q = mcΔt

       = 104grams × 3.93J/g°C  × 13.5°C = 5.51772×103J

                                         

 

       = 5.51772 × 103 J

 

This is the heat lost in the reaction between HCl and NaOH, therefore q = -5.52 × 103 J.

 

this is an exothermic heat producing reaction.

 To calculate the total heat of the reaction or heat per mole we have

  

50.0 mL of HCl X 2.00 mol HCl /(1000 mL HCl ) = 0.100 mol HCl

                            

 

The same quantity of base, 0.100 mole NaOH, was used.

The energy per unit mole is given by

  

i.e. molar enthalpy = J/mol = -5.52 × 103J / 0.100 mol

            = -5.52 × 104 J/mol

            = -55177.2 J/mol

            = -55.177 kJ/mol

 

Therefore, the enthalpy change for the neutralization of HCl and NaOH, that is the enthalpy, heat, of reaction is ΔH = -55.177 kJ/mol

Heat absorbed by the calorimeter = −57.32kJ − 55.177 kJ = −2.1428KJ

The heat capacity of the calorimeter is therefore = −2.1428KJ÷13.5°C

= −0.1587KJ/°C

 

(B) For the ZnCl we have

 

Calculate the heat actually evolved.

                            q = mcΔt

 

Finding the mass of the reactants in grams we have.

 

Use density.  100 mL of solution of HCl

 

100 mL X 1.015g/mL        = 101.5 grams of solution. (mass = Volume X Density)

                       

 

Find the temperature change.

 

       Δt =tfinal - tinitial = 20.5°C – 16.8°C = 3.7 °C

 

    q = mcΔt

       = 101.5grams × 3.95J/g°C  × 3.7°C = 1483.422×103J

                                         

 

       = -1483.422×103J

 

This is the heat lost in the reaction between HCl and NaOH, therefore q = -1.483 × 103 J.

 

this is an exothermic heat producing reaction.

 To calculate the total heat of the reaction or heat per mole we have

  

100.0 mL of HCl X 1.00 mol HCl /(1000 mL HCl ) = 0.100 mol HCl

                            

 

 

The energy per unit mole is given by

  

i.e. molar enthalpy = J/mol = -1.483 × 103J / 0.100 mol

                                         = -1.483 × 104 J/mol

                                         = -14834.22 J/mol

                                         = -14.834 kJ/mol

 

Therefore, the enthalpy change for the neutralization of HCl and NaOH, that is the enthalpy, heat, of reaction is ΔH = -14.834 kJ/mol

ΔHo for the reaction Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)

= -14.834 kJ –(0.1587KJ/°C×3.7°C) = -15.42KJ

ΔHo for the reaction Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g) = –15.42KJ

5 0
2 years ago
Other questions:
  • A compound is 80.0% carbon and 20.0% hydrogen by mass. assume you have a 100.-g sample of this compound. how many grams of each
    11·1 answer
  • A sample of ch4o with a mass of 32.0 g contains ________ molecules of ch4o.
    7·1 answer
  • Write the symbol for the monatomic ion that has a charge of 1– and the condensed electron configuration [ne]3s23p6.
    5·2 answers
  • The seven most abundant ions in seawater make up more than 99% by mass of the dissolved compounds. Here are their abundances in
    5·1 answer
  • The refractive index, n of a polymer was determined as a function of temperature. The results are given in the table. Determine
    7·1 answer
  • A car uses 12.5 L of gasoline to travel a distance of 275 km. Convert this into units of miles per gallon (mi/gal).
    14·1 answer
  • A phosphorus atom with 4 bonds has a charge of ___.
    6·1 answer
  • If 28.0% of a sample of gallium-66 decays in 4.46 hours, what is the half-life of this isotope (in hours)?
    10·1 answer
  • What is the IUPAC name of the following compound?
    13·1 answer
  • gypsum is insoluble in water. you are asked to purify a sample of gypsum that is contaminated with a soluble salt.
    6·1 answer
Add answer
Login
Not registered? Fast signup
Signup
Login Signup
Ask question!