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AleksandrR [38]
3 years ago
7

An electron in a hydrogen atom relaxes to the n=4 level, emitting light of 74 THz.

Chemistry
1 answer:
Solnce55 [7]3 years ago
6 0
Delta E = Ef - Ei
E = energy , h = plank constant  , v = frequency
h= 6.626 * 10 ^-34 j*s  ,  T = 10 ^ 12  , v = 74 * 10 ^12 Hz  ,  Hz = s^-1 

E = ( 6.626 * 10^ -34 j*s) ( 74 * 10 ^ 12 s^ -1 )  =   4.90 * 10 ^ -20 J
Delta E  = Ef  -  Ei
-4.90 * 10 ^ -20 J =  -2.18 * 10 ^ -18J ( 1/4 ^2 - 1/x ^2)
0.0225 = 0.0625 -  ( 1/x ^ 2)
0.225 - 0.0625 =  - 1/ x ^ 2 

- 0.0400 = - 1/x ^2    =   -1 / - 0.0400    =   x^2
25   =  x^2 
     x = 5 




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Pachacha [2.7K]
<span>The student should follow following steps to make 1 L of </span>2.0 M CaCl₂.<span>
<span>
1. First he should calculate the number of moles of 2.0 M CaCl</span></span>₂ in 1 L solution.<span>

</span>Molarity of the solution = 2.0 M<span>
Volume of solution which should be prepared = 1 L

Molarity = number of moles / volume of the solution

Hence, number of moles in 1 L = 2 mol

2. Find out the mass of dry CaCl</span>₂ in 2 moles.<span>

moles = mass / molar mass

Moles of CaCl₂ = 2 mol</span><span>
Molar mass of CaCl₂ = </span><span>110.98 g/mol

Hence, mass of CaCl</span>₂ = 2 mol x <span>110.98 g/mol
                                     = 221.96 g

3. Weigh the mass accurately 

4. Then take a cleaned and dry1 L volumetric flask and place a funnel top of it. Then carefully add the salt into the volumetric flask and finally wash the funnel and watch glass with de-ionized water. That water also should be added into the volumetric flask.

5. Then add some de-ionized water into the volumetric flask and swirl well until all salt are dissolved.

<span>6. Then top up to mark of the volumetric flask carefully. 
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4 0
2 years ago
A student is worried about determining if a chemical is radioactive. Which
Mamont248 [21]

Answer:

Hazards Identification

Explanation:

A safety data sheet, SDS, is an informational document provided by the manufacturer or importer of a hazardous chemical detailing the chemical, physical, health, and environmental health hazards associated with the chemical as well as safety precautions in handling the chemical.

Some of the sections in the SDS include:

Product Information: It identifies the chemical as well as its recommended uses. The contact information of the manufacturer is also provided.

Fire fighting methods: It gives measures and guidelines necessary for fighting a fire caused by the chemical.

Physical and chemical properties: states the physical and chemical properties of the chemical substance such as:  appearance, odor, pH, melting/freezing point, boiling point and boiling range, flammability, etc.

Hazards identification: states the hazards of the chemical and the necessary warnings regarding the hazards. Some of the information provided include: hazard classification of the chemical (for example flammable liquid, oxidizing gases,explosives, etc), signal word, hazard statement (for example radioactive), pictograms, precautionary statements, etc.

<em>From the above information provided, the student should refer to the hazards identification section.</em>

8 0
3 years ago
What takes up space?<br> O A. Light<br> O B. Matter<br> O C. Sound<br> O D. Energy
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Answer:

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Explanation:

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6 0
3 years ago
Read 2 more answers
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Ede4ka [16]

Answer:

\Delta _fH_{C_3H_8}=-102.7kJ/mol

Explanation:

Hello,

In this case, we can consider that the given heat of combustion is indeed the heat of reaction since it corresponds to the combustion of propane, which is computed by using the heat formation of all the involved species as shown below:

\Delta _cH=3*\Delta _fH_{CO_2}+4*\Delta _fH_{H_2O}-\Delta _fH_{C_3H_8}-5*\Delta _fH_{O_2}

Thus, since the heat of formation of gaseous carbon dioxide is -393.5 kJ/mol, water -241.8 kJ/mol and oxygen 0 kJ/mol, the heat of formation of propane is:

\Delta _fH_{C_3H_8}=3*\Delta _fH_{CO_2}+4*\Delta _fH_{H_2O}-5*\Delta _fH_{O_2}-\Delta _cH\\\\\Delta _fH_{C_3H_8}=3*(-393.5)+4*(-241.8)-5*0-(-2045)\\\\\Delta _fH_{C_3H_8}=-102.7kJ/mol

Best regards.

8 0
3 years ago
Organisms can either be made of one cell or made of more than one cell
Alika [10]

Answer:

The statement is true.

Explanation:

Organisms can be unicellular (made up of one cell) or multicellular (consisting of more than one cell).

I hope this helps in any way :)

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