Answer:
e) 400 mg of a radioactive substance with a half-life of 8 hours after decaying for 8 hours
a) 800 mg of a radioactive substance with a half-life of 2 years after decaying for 4 years.
Explanation:
a) 800 mg of a radioactive substance with a half-life of 2 years after decaying for 4 years.
Number of half lives passed = Time elapsed/ half life
Number of half lives passed = 4 year/2 year
Number of half lives passed = 2
at time zero = 800 mg
At first half life = 800 mg/2 = 400 mg
At 2nd half life = 400 mg/2 = 200 mg
b) 1,000 mg of a radioactive substance with a half-life of 5 years after decaying for 20 years
Number of half lives passed = Time elapsed/ half life
Number of half lives passed = 20 year/ 5 year
Number of half lives passed = 4
at time zero = 1000 mg
At first half life = 1000 mg/2 = 500 mg
At 2nd half life = 500 mg/2 = 250 mg
At 3rd half life = 250 mg/2 = 125 mg
At 4th half life = 125 mg/2 = 62.5 mg
c) 300 mg of a radioactive substance with a half-life of 1 year after decaying for 1 year
Number of half lives passed = Time elapsed/ half life
Number of half lives passed = 1 year/ 1 year
Number of half lives passed = 1
at time zero = 300 mg
At first half life = 300 mg/2 = 150 mg
d) 600 mg of a radioactive substance with a half-life of 6 hours after decaying for 18 hours
Number of half lives passed = Time elapsed/ half life
Number of half lives passed = 18 hours / 6 hours
Number of half lives passed = 3
at time zero = 600 mg
At first half life = 600 mg/2 = 300mg
At 2nd half life = 300 mg/2 = 150 mg
At 3rd half life = 150 mg/2 = 75 mg
e) 400 mg of a radioactive substance with a half-life of 8 hours after decaying for 8 hours
Number of half lives passed = Time elapsed/ half life
Number of half lives passed = 8 hours / 8 hours
Number of half lives passed = 1
at time zero = 400 mg
At first half life = 400 mg/2 = 200 mg
A student wants to examine a substance without altering its composition. Which of the following describes a property of the substance that the student should examine?
Toxicity, because it can be observed by altering the state of the substance
Boiling point, because it can be observed by altering the state of the substance
Toxicity, because it can be observed by replacing the atoms of the substance with new atoms
Boiling point, because it can be observed by replacing the atoms of the substance with new atoms
Answer: Boiling point, because it can be observed by altering the state of the substance
Explanation:
Physical property is defined as the property of a substance which becomes evident during physical change in which there is alteration in shape, size etc. No new substance gets formed during physical change. Example: Melting point
Chemical property is defined as the property of a substance which becomes evident during chemical change in which a change in chemical composition takes place. A new substance is formed in these reactions. Example: Reactivity with other substances
Thus Boiling point is a propertywhich can be examined without altering the composition, because it can be observed by altering the state of the substance
what is the noble gas configuration for zirconium?
A. [Xe] 5s2 4d1
B. [Xe] 4d1
C. [Kr] 4d1
D. [Kr] 5s2 4d1
Answer:
[Kr] 4d² 5s²
Explanation:
Which of the following conditions favor the SN1 mechanism as opposed to the SN2 mechanism?
I. tertiary alkyl halide
II. primary alkyl halide
III. polar solvent
a. only I
b. only Il
c. I and Ill
d. Il and Ill
Answer:
c. I and Ill
Explanation:
SN1 mechanism is a unimolecular nucleophillic substitution reaction mechanism. "Unimolecular" implies that only one molecule is involved in the rate determining step and that is the alkyl halide. The rate determining step of SN1 reaction is the formation of a carbocation which subsequently reacts with a nucleophile in the fast step.
SN1 reactions occur mostly with tertiary alkyl halides due to sterric reasons. SN2 mechanism involves a crowded transition state because it is a concerted reaction mechanism. This is not possible in a tertiary alkyl halide due to the presence of bulky groups around the tertiary carbon atom hence tertiary alkyl halides do not undergo nucleophilic reaction by SN2 mechanism.
Secondly, polar solvents aid in the ionization of the alkyl halide thus assisting in the formation of the carbocation which participates in the second step of the reaction.
if you are using a formula where you need the change in temperature, explain why it is not important whether your temperatures are both in Kelvin or Celsius?
Answer:
This is because, Kelvins and Celcius degrees both agree at fixed points i.e; the lower fixed point and upper
Oxygen is a __________ and nitrogen is a __________. metalloid, metalloid nonmetal, metal nonmetal, nonmetal nonmetal, metalloid metal, metalloid
Answer:
"nonmetal, nonmetal"
Explanation:
Oxygen is a non metal and Nitrogen is a non metal. It is 8th element of the periodic table. It is located in period 2 and group 16.
Nitrogen lies at the group 15 of the periodic table. Its atomic no is 7. Its valency is 2.
Hence, the correct option is (c) "nonmetal, nonmetal".
What is the shorthand electron configuration for CI?
Answer:
Since the 3s if now full we'll move to the 3p where we'll place the remaining five electrons. Therefore the Chlorine electron configuration will be 1s22s22p63s23p5. The configuration notation provides an easy way for scientists to write and communicate how electrons are arranged around the nucleus of an atom.
PLEASE HELP QUICK!
Your organ systems do not function
independently. Consider the following
scenarios, and explain how different
organ systems are working together.
a) You step on hot pavement in the
summer and quickly pull your foot
back.
(b) after running up the stairs you
breathe a little harder.
(c) A friend has a cold, and three days
later you have a cold too.
Answer:A
Explanation:
Your muscular system is at work
You have 5.00 L of 6.0 M KNO3. What volume does the solution need to be diluted to
for the concentration to be 0.1 M? Can anyone help me? ASAP
Acids are substances that surround us in our everyday life. The uses of acids range from providing essential nutrients for our bodies to dissolving metals. Some acids are safe to handle with our bare hands or even use in food preparation. Other acids will severely burn human skin. Why these substances can all be acids and yet have such different properties?
Answer: Strong and Weak Acids
Explanation:
Acids, also known as electrolytes, are compounds that break down into cations (positively charged ions) and anions when dissolved in water (negatively charged ions). Solid Electrolytes (Acids) fully ionize,
Whereas weak electrolytes (acids) only partly ionize.
g calculate the quantity of energy produced per gram of uranium 235 for the neutron induced Fusion of uranium
Answer:
Energy released by 1 g of U-235 = 7.603 * 10¹⁰ J
Explanation:
Uranium-235, U-235 undergoes neutron-induced fission to give the following products:
1 neutron + ²³⁵U --> ¹⁴¹Ba + ⁹²Kr + 3 neutrons
Masses of reactants and products:
neutron = 1.009 amu, uranium-235 = 235.044 amu, Ba-141 = 140.910 amu, Kr-92 = 91.910 amu
mass defect = mass of reactants - mass of products
mass defect = (235.044 + 1.009) - (140.910 + 91.910 + 3 * 1.009)
mass defect = 236.053 - 235.847 = 0.206 amu
1 amu = 1.6 * 10⁻²⁷ kg
Using E = mc²
E = 0.206 * 1.6* 10⁻²⁷ kg * (3 * 10⁸ m/s)² = 2.966 * 10⁻¹¹ J
therefore, 1 atom of U-235 releases 2.966 * 10⁻¹¹ J of energy
energy released by 1 g of U-235 can be calculated as follows:
1 mole or 253 g of U-235 contains 6.02 * 10³ atoms
1 g of U-235 will contain 6.02 * 10³/235 = 2.563 * 10²¹ atoms
Energy released by 1 g of U-235 = 2.563 * 10²¹ * 2.966 * 10⁻¹¹ J = 7.603 * 10¹⁰ J
According the equation: 2H,O+ electricity → 2H2 + O2
A) An electrolytic cell, because it absorbs energy.
B) A voltaic cell, because it releases energy. C) A voltaic cell, because it absorbs
energy.
D) An electrolytic cell, because it releases energy.
E) All of them
Answer:
A) An electrolytic cell, because it absorbs energy.
Explanation:
The major difference between an electrolytic cell and a voltaic cell is that, in an electrolytic cell, there must be input of energy from outside (a cell) to drive the non spontaneous reaction while in a voltaic cell, the reaction proceeds on its own and releases energy which could be harnessed to do work.
Hence, considering the equation; 2H2O+ electricity → 2H2 + O2 , energy is supplied as electricity in order for the process to take place. This is an example of an electrolytic cell.
Silver nitride is formed when a silver cation that has a 1+ charge combines with a nitrogen anion that has a 3- charge. Write the formula for the compound silver nitride.
For the following reaction,use the identity of the alkyl halide and nucleophile to determine which substitution mechanism occurs.Then determine which solvent affords the faster reaction.
A) SN1,H2O
B) SN1,DMF
C) SN2,H2O
D) SN2,DMF
Answer:
a) SN1/H2O
b) SN1/CH3OH
c)SN2/DMF
d)SN2/HMPA
Explanation:
The reactions are shown in the image attached.
Let me restate the basic facts about SN1 and SN2 reaction mechanisms. SN1 reaction occurs by unimolecular mechanism and involves a carbocation, a poor nucleophile and a polar protic solvent.
An SN2 reaction is a bimolecular synchronous reaction that passes through a single transition state. It requires a good nucleophile and a polar aprotic solvent.
For reaction a and b, we observe that the alkyl halide is tertiary hence the reaction occurs by SN1 mechanism in the presence of a polar protic solvent.
Reactions c and d involves primary and secondary alkyl halides respectively and good nucleophiles. The best solvents to be used are polar aprotic solvents and the reaction follows SN2 mechanism.
Perform the following calculations and report each answer with the correct number of significant figures.
628 × 342 b. 5.45 – 2.3 c. 28.0/13.483
d. 14.98 + 27,340 + 84.7593
Answer:
a)215000
b) 3.2
c) 2.08
d) 27439.74
Explanation:
Significant figures:
When we add or subtract the values the number of significant figures after decimal in result must be equal to the given measurement having less number of decimal places.
b) 5.45 -2.3
3.2
d) 14.98 + 27,340 + 84.7593
27439.74
When we multiply or divide the values the number of significant figures must be equal to the less number of significant figures in given value.
a) 628 × 342
214776
we will round off this value into 3 significant figures.
215000
c) 28.0/13.483
2.08
How many grams of sucrose must be dissolved in 250 ml to prepare the 0.15 mol / L solution?
Answer:
How could you prepare 250 mL of 0.20M NaCl using only a solution of 1.0M NaCl and water? To prepare a 250 mL 0.20 M NaCl solution, I would place 50 mL of the 1.0 stock solution to a 250 mL volumetric flask and then add 200 mL of water. A bottle of the antiseptic hydrogen peroxide (H2O2) is labeled 3.0% (v/v).
How many joules of heat are given off when 5.00g of water cool from 348.0K to 298.0K?
Answer:
Q = -1045 J
Explanation:
Given data:
Mass of water = 5.00 g
Initial temperature = 348.0 K
Final temperature = 298.0 K
Heat given off = ?
Solution:
Specific heat capacity:
It is the amount of heat required to raise the temperature of one gram of substance by one degree.
Specific heat capacity of water is 4.18 J/g.K
Formula:
Q = m.c. ΔT
Q = amount of heat absorbed or released
m = mass of given substance
c = specific heat capacity of substance
ΔT = change in temperature
ΔT = 298.0 K - 348.0 K
ΔT = - 50 K
Q = 5.0 g ×4.18 J/g.K× - 50 K
Q = -1045 J
1.If you could look at the deep ocean floor, which is the best description of what you would see?
A. flat, silt-covered, lifeless regions
B. high mountains and deep valleys
C. ocean ridges with active volcanoes
D. coral reefs with many varieties of life
2.The section of a continent that lies just off the shoreline and extends beneath the ocean is called the continental ______.
A. plain
B. shelf
C. basin
D. ridge
please help <3
Answer:
Q1 D
Explanation:
Q2 C
How many Joules are required to raise the temperature of 4.66 g of CCl4 from 20.9◦C to 76.8◦C?
The specific heat capacity of CCl4 is 0.856 J/g◦C.
Heat required to raise temperature : 224.02 J
Further explanationGiven
mass CCl4 = 4.66 g
Δt= 76.8 - 20.9 =55.9 °C
c = The specific heat capacity of CCl4 = 0.856 J/g◦C.
Required
Heat /energy required
Solution
Heat can be formulated
Q=m.c.Δt
[tex]\tt Q=4.66\times 0.86\times 55.9\\\\Q=224.02~J[/tex]
What is the formula for hexaboron tetrabromide
Answer:
The formula for the compound isB6Br7
What would humans need to live on another planet?
Answer:
In its astrobiology roadmap, NASA has defined the principal habitability criteria as "extended regions of liquid water, conditions favorable for the assembly of complex organic molecules, and energy sources to sustain metabolism". In August 2018, researchers reported that water worlds could support life.
Which of the following salts will be less soluble in 0.10 M NaCl than it is in pure water?
PbF2
CaCO3
All of the options are less soluble in 0.10 M NaCl than in pure water.
PbCl2
The less soluble salt : PbCl₂
Further explanationGiven
0.1 M NaCl
Required
The less soluble salt
Solution
If we see from the answer option, the salt that is more difficult to dissolve in NaCl is PbCl₂ because it has the same ion (Cl)
When PbCl₂ is dissolved in water, ionization will occur
PbCl₂ ⇒ Pb²⁺+ 2Cl⁻
So, when dissolved in NaCl, NaCl itself will be ionized
NaCl ⇒ Na⁺ + Cl⁻
Based on the principle of equilibrium, the addition of an ion (one of the ions is enlarged), the reaction will shift towards the ion that was not added. In addition to this Cl ion, the reaction will shift to the left so that the solubility of PbCl₂ will decrease (the reaction to the right decreases)
Deuterium is the isotope of hydrogen of mass number 2, with a proton and a neutron in its nucleus. The chemistry of deuterium is nearly identical to the chemistry of hydrogen, except that C−D bond is slightly (5.0KJ/mole) stonger than the C−H bond. Reaction rates tend to be slower if a C−D bond as opposed to a C−H bond is broken in a rate limiting step. This effect on the rate is called a kinetic isotope effect.
a. True
b. False
Answer:
True
Explanation:
We know that the zero-point-energy of a C-D system is quite lower than the zero point energy of the C-H bond so the C-D bond is stronger.
Kinetic isotope effect refers to the change in the rate of reaction owing to a change of one of the atoms of the reactants by replacing it with one of its isotopes.
Since we know that the C-D bond is stronger than the C-H bond, when we replace hydrogen with deuterium in a reaction's rate determining step we experience a little lag in the rate of reaction. This is referred to as the kinetic isotope effect in physical organic chemistry.
Which of the following alkyl halides will react fastest with CH3OH in an SN1 mechanism?
A) I B) II C) III D) IV
Answer:
IV
Explanation:
The complete question is shown in the image attached.
Let us call to mind the fact that the SN1 mechanism involves the formation of carbocation in the rate determining step. The order of stability of cabocations is; tertiary > secondary > primary > methyl.
Hence, a tertiary alkyl halide is more likely to undergo nucleophilic substitution reaction by SN1 mechanism since it forms a more stable cabocation in the rate determining step.
Structure IV is a tertiary alkyl halide, hence it is more likely to undergo nucleophilic substitution reaction by SN1 mechanism.
Strontium-90, a radioactive isotope with applications in medicine, has a half-life of approximately 30 years. Out of a 100-gram sample, approximately how much remains after 170 years? 2 grams 8 grams 17 grams 81 grams
There are 2 grams remain
Further explanationGiven
t1/2 = 30 years
t = 170 years
No = 100 g
Required
Remaining sample
Solution
General formulas used in decay:
[tex]\large{\boxed{\bold{N_t=N_0(\dfrac{1}{2})^{t/t\frac{1}{2} }}}[/tex]
Input the value :
[tex]\tt Nt=100.\dfrac{1}{2}^{170/30}\\\\Nt=1.969\approx 2~grams[/tex]
18.2 mL of a 0.156 M solution of lead(II) nitrate are added to 26.2 mL of a 0.274 M solution of potassium iodide.
What is the mass of the Pbl2 precipitate formed in the reaction Pb(NO3)2 (aq) + 2 KI (aq) - Pbl2 (s) + 2 KNO3? The molar mass of Pbly is 461.0 g/mol.
Provide your answer in units of grams, with the correct number of significant digits. Enter your answer as a number only; do not include units.
The mass of the Pbl2 : 1308.87
Further explanationGiven
18.2 mL of a 0.156 M Pb(NO3)2
26.2 mL of a 0.274 M KI
Reaction
Pb(NO3)2 (aq) + 2 KI (aq) - Pbl2 (s) + 2 KNO3
Required
the mass of the Pbl2
Solution
mol Pb(NO3)2 = 18.2 x 0.156 = 2.8392 mlmol
mol KI = 26.2 x 0.274 =7.1788 mol
Limiting reactant Pb(NO3)2(smaller ratio of mol : reaction coeffiecient)
mol Pbl2 based on limiting reactant (Pb(NO3)2)
From equation, mol ratio of Pb(NO3)2 : Pbl2 = 1 : 1, so mol Pbl2=mol Pb(NO3)2=2.8392
Mass Pb(NO3)2 :
[tex]\tt mass=mol\times MW\\\\mass=2.8392\times 461\\\\mass=1308.87~grams[/tex]
What mass of carbon monoxide gas (CO) would occupy a volume of 4.30 L at STP? Explain how you got the answer.
Answer:
5.38 g of CO.
Explanation:
From the question given above, the following data were obtained:
Volume of CO = 4.3 L
Mass of CO =?
Next, we shall determine the number of mole of CO that occupied 4.3 L at STP. This can be obtained as follow:
Recall = 1 mole of any gas occupy 22.4 L at STP.
1 mole of CO occupied 22.4 L at STP.
Therefore, Xmol of CO will occupy 4.3 L at STP i.e
Xmol of CO = 4.3 / 22.4
Xmol of CO = 0.192 mole.
Thus, 0.192 mole of CO occupy 4.3 L at STP.
Finally, we shall determine the mass of CO as follow:
Mole of CO = 0.192 mole.
Molar mass of CO = 12 + 16 = 28 g/mol
Mass of CO =?
Mole = mass /Molar mass
0.192 = mass of CO / 28
Cross multiply
Mass of CO = 0.192 × 28
Mass of CO = 5.38 g.
Therefore, 5.38 g of CO occupied 4.3 L at STP.
Uncontrolled energy:
A. Produces order
B.causes destruction
C. Can make things
D. Can do useful work
Answer:
B
Explanation:
uncontrolled energy damage the body
Answer: causes destruction
Explanation:
The _____ time it takes to completely _____ food, the _____ the food will deteriorate.
less -- unfreeze -- more
more -- hydrate -- less
less -- freeze -- less
The answer is C.less -- freeze -- less
To be considered a source of water pollution, the source must include a chemical.
Please select the best answer from the choices provided
ОТ
OF
Answer:
it is true because i just took the test and i did research on it
Explanation:
i study this and because i did research
Answer:
trueeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
Explanation: eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
The difference between a solid
and a gas is that
A. solids can change their volume but gases
cannot.
B. solids can take the shape of its container, and
gases cannot.
C. solids have high energy levels and gases have
low energy levels.
D. solids have low energy levels and gases have
high energy levels.