Answer:
Explanation:
Since the student fills up the buret with NaOH without rinsing it with small amount of NaOH , the water that is remaining stuck with the walls of the buret will dilute the solution of NaOH and it will result in lowering the morality of the solution . The molar concentration of the NaOH will no longer remain the same . It will lead to wrong calculation and hence wrong result.
The washing of burette in titration with NaOH solution results in the maintaining the concentration of the NaOH in the solution and allows the correct calculation of the molarity.
What is titration?The titration has been the reaction of the acid with the base resulted in the formation of salt and water and had the neutralization reaction.
The molarity of the base has been used in the analysis of the acid concentration on the neutralization reaction.
The skipping of the step of washing with NaOH resulted in the altering in the concentration of the NaOH with the stuck water on the walls of the burette, and thereby resulted in wrong calculation.
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The system is originally at equilibrium with [butane] = 1.0 M and [isobutane] = 2.5 M.If 0.50 mol/L of isobutane is suddenly added and the system shifts to a new equilibrium position, what is the equilibrium concentration of butane?
Answer:
1.14 M
Explanation:
Let's consider the following reaction.
butane ⇄ isobutane
We can use the concentrations at equilibrium to calculate the equilibrium constant.
Kc = [isobutane] / [butane]
Kc = 2.5 / 1.0
Kc = 2.5
If we add 0.50 M of isobutane, we get [isobutane] = 2.5 + 0.50 = 3.0 M.
This will be an initial concentration in an ICE chart.
butane ⇄ isobutane
I 1.0 3.0
C +x -x
E 1.0+x 3.0-x
The equilibrium constant is:
Kc = 2.5 = [isobutane] / [butane]
2.5 = (3.0-x) / (1.0+x)
2.5 + 2.5x = 3.0-x
x = 0.14
The equilibrium concentration of butane is:
[butane] = 1.0+x = 1.14 M
3. A certain Chemical Industry company has a quality control job opening. The job is open for any major with basic knowledge of chemistry. You decided to apply. In the interview the HR personnel gives you a sealed folder from a certain lot to test your laboratory experience, as well as your quantitative and volumetric analysis skills. The chemical contained in the sample is benzoic acid (C-H602) and it is known to be a monoprotic acid. In order to get the job, you need to determine if the sample's purity is acceptable based on their standards. Inside the folder you found a vial with a solid sample labeled BA-I, a periodic table, and the following data: 1.250 g of the sample required 20.15 mL of 0.500 M concentration of NaOH to reach the end point. The lot can be denied if the purity is below 99.5 % purity.
1) What is the purity in the sample?
2) Is it the purity acceptable?
3) Would you repeat the titration experiment?
Answer:
1) 97.6%
2) No the purity is not acceptable because the standard is 99.5% purity.
3) Yes I will repeat the titration experiment to confirm my result.
Explanation:
Equation of the reaction;
C7H6O2(aq) + NaOH(aq) ---------> C7H5ONa(aq) + H2O(aq)
From the information provided;
Number of moles of NaOH reacted = concentration × volume = 20.15/1000 × 0.500 = 0.01 moles
From the reaction equation;
1 mole of C7H6O2 reacts with 1 mole of NaOH
Hence 0.01 moles of C7H6O2 will react with 0.01 moles of NaOH
Mass of C7H6O2 reacted = number of moles of C7H6O2 × molar mass of C7H6O2
Molar mass of C7H6O2 = 122.12 g/mol
Mass of C7H6O2 reacted = 0.01 moles × 122.12 g/mol = 1.22 g
Percentage by mass of pure C7H6O2 in the impure sample = 1.22/1.250 × 100 = 97.6 %
Nicotinic acid, HC6H4NO2, is a B vitamin. It is also a weak acid with Ka = 1.4 × 10-5. Calculate [H+] and the pH of a 0.041 M solution of HC6H4NO2.
Answer:
[H+] = 7.576x10⁻⁴M
pH = 3.12
Explanation:
Based on the equilibrium of the nicotinic acid in water:
HC6H4NO2(aq) + H2O(l) ⇄ C6H4NO2-(aq) + H3O+(aq)
Ka = [C6H4NO2-] [H3O+] / [HC6H4NO2]
As both C6H4NO2-(aq) and H3O+(aq) comes from the same equilibrium, we can approximate their concentration as X and replace:
Ka = [C6H4NO2-] [H3O+] / [HC6H4NO2]
1.4x10⁻⁵ = [X] [X] / [0.041M]
5.47x10⁻⁷ = X²
7.576x10⁻⁴M = X = [H+]And as pH is defined as -log [H⁺]
pH = 3.12Describe three factors that could limit the growth of the prairie dog population
Answer:
Changes in environment, food source changes and disease?
Explanation:
I dont know what the answer choices are
Answer:
changes in the environment
Explanation:
like digging big holes.
Hope this helps!
What do scientists call all of the compounds that contain carbon and are found in living things?
organic
inorganic
acidic
nonacidic
Answer:
Organic
Explanation:
Edge student
Measurements show that unknown compound X has the following composition: element mass % carbon 41.0% hydrogen 4.58% oxygen 54.6% Write the empirical chemical formula of X.
Answer:
CHO
Explanation:
Carbon = 41%, Hydrogen = 4.58%, oxygen = 54.6%
Step 1:
Divide through by their respective relative atomic masses
41/ 12, 4.58/1, 54.6/16
3.41 4.58 3.41
Step 2:
Divide by the lowest ratio:
3.41/3.41, 4.58/3.41, 3.41/3.41
1, 1, 1
Hence the empirical formula is CHO
Answer:
The empirical formula of X is C3H4O3.
Explanation:
Quickly please! Which is a group of tissues that work together to carry out a common function?
cell
organ
organelle
organ system
Answer:
organ system
Explanation:
Answer:
B) organ
Explanation:
if u trust urself do it
Study these images.
4 photos of clouds. 1: Sky covered with large, flat layers of blue, grey clouds. 2: A tall, fluffy cloud shaped like an anvil. 3: Round, puffy clouds in a blue sky. 4: Thin, wispy clouds high in the sky.
Which image shows a cumulonimbus cloud?
1
2
3
Answer:
3
Explanation:
I wish you the best, its three or 2
Answer:
2
Explanation:
Edge 2021
Observing a phenomenon in the lab includes which of the following?
Throwing away irrelevant items
Sorting through and disposing of police reports
Collecting evidence
Identifying unique features of evidence
Answer:
D
Explanation:
Identifying unique features of evidence
A laboratory is a place where scientific investigations and experiments are conducted. Observing a phenomenon in the lab includes identifying unique features of evidence. Thus, option D is correct.
What is observation?
An observation is said to be the deduction that is seen or heard and is due to the actions of the process or event that are gained from the information from a conducted experiment.
It is an important factor in an experiment and research and is used in the lab to falsify or prove the hypothesis. It is made based on the experimental setup and involves various steps.
The observations are used to draw conclusions and inferences based on the detailed identification of the characteristics of the evidence. The evidence supports the observation.
Therefore, option D. the features of evidence are the correct option.
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The Adálie penguins feed on krill that live on the underside of ice sheets. Which of the following would help Adálie penguins survive during the melting of Antarctic sea ice?
The correct answer is Migrating farther into the sea
Explanation:
The Adálie penguins rely on ice sheets to obtain food as the krill they feed on is only found underside of the ice. This implies as the Antarctic sea ice melts Adálie penguins need to look for new places to find krill as if there are no ice sheets there are no krill for these penguins. Due to this, it is likely these penguins are forced to migrate or move farther into the sea to survive because it is likely in these zones there are ice sheets and therefore places where they can find krill. Despite this, this process might lead to a significant decline in the population of penguins due to the competence for food and the process of migration itself. Thus, the one that would help Adáline penguins to survive during the melting of Antarctic sea ice is migrating farther into the sea.
Have a nice day! :)
The Adálie penguins feed on krill that live on the underside of ice sheets. Adálie penguins survive during the melting of Antarctic sea ice help migrating farther into the sea. Therefore, option A is correct.
What is migration ?The term migration is defined as the movement of either people or animals from one area to another.
The Adálie penguins rely on ice sheets for food because the krill they eat is only found on the underside of the ice. As a result, it is likely that these penguins are forced to migrate or move further into the sea to survive.
Regardless, this process may result in a significant decline in penguin population due to food competence and the migration process itself.Thus, the one that will assist Adáline penguins in surviving during the melting of Antarctic sea ice is migrating deeper into the sea.
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Your question is incomplete,most probably your question was
The Adálie penguins feed on krill that live on the underside of ice sheets. Which of the following would help Adálie penguins survive during the melting of Antarctic sea ice? Migrating farther into the sea Breeding during summer months Growing strong toe nails to grip ice Spending more time raising their young
The pressure caused by a sample of gas is 2.25 atm. 1 atm is
equal to 1.01 kPa. What is the pressure in Newton per square
centimeter?
Answer:
[tex]0.326\frac{N}{cm^2}[/tex]
Explanation:
Hello.
In this case, considering that 1 atm equals 1.01 kPa, we can compute the pressure in kPa first as shown below:
[tex]2.25atm*\frac{1.01kPa}{1atm} =3.26kPa[/tex]
Now, we convert kPa to Pa, considering 1 kPa equals 1000 Pa:
[tex]3.26kPa*\frac{1000Pa}{1kPa}=3260Pa[/tex]
Now, since Pa is equal to N/m², and 1 m equals 100 cm, the pressure in newton per square centimeter turns out:
[tex]3260\frac{N}{m^2}*(\frac{1m}{100cm})^2 \\\\0.326\frac{N}{cm^2}[/tex]
Best regards.
what is the first step in the scientific inquiry process
Answer:
make an observation that describes a problem
Explanation:
Answer:
The first step in the Scientific Method is to make objective observations.
Explanation:
....-
1. Assume this experiment (after the extractions are complete) left you with 4 pure products (aspirin, acetaminophen and caffeine, and the binder). Your lab mate distracted you after you had labeled the binder and now you can’t remember which of the remaining 3 products is which. What would be a simple test that you can perform in the laboratory to distinguish between the 3 remaining solids isolated from your experiments?
Answer:
Explanation:
Out of aspirin, acetaminophen and caffeine, aspirin is an acid because it is acetyl saliciylic acid . Hence it can be tested with litmus paper .
acetaminophen contains phenolic functional group , hence it is a weak acid . It can be tested with any test with which phenol test are done, like with neutral solution of ferric chloride .
caffeine is weak basic substance . It can also be tested with the help of testing a basic substance .
The atom is neutral because
(10 Points)
O protons
neutrons
O
electrons =neutrons
protons -electrons
O nucleus = electron
Y
Answer:
the answer is B
Explanation:
When an atom has an equal number of electrons and protons, it has an equal number of negative electric charges
4. Horizontal rows of the Periodic Table are called:
a, Clusters
Groups
b. Families
d) Periods
What happen when a piece of sodium is exposed in air?
Answer:
I literally got this from google.
Explanation:
In ordinary air, sodium metal reacts to form a sodium hydroxide film, which can rapidly absorb carbon dioxide from the air, forming sodium bicarbonate. ... In a comparatively dry atmosphere, sodium burns quietly, giving off a dense white caustic smoke, which can cause choking and coughing.
Happy almost Halloween! :)
The solubility of limestone, CaCO3, at 25˚C is 0.00067 g/100 mL. Write the chemical equation for the solubility equilibrium of this sparingly soluble salt in water. Then compute the molar solubility and the solubility product constant Ksp for CaCO3 at 25˚C.
Answer:
4.5 × 10⁻⁹
Explanation:
Step 1: Write the reaction for the solution of CaCO₃
CaCO₃(s) ⇄ Ca²⁺(aq) + CO₃²⁻(aq)
Step 2: Convert the solubility of CaCO₃ from g/L to mol/L
We will use the following conversion factors:
The molar mass of CaCO₃ is 100.09 g/mol.1 L= 1000 mL.There are 0.00067 g of CaCO₃ per 100 mL of solution.[tex]\frac{0.00067 gCaCO_3}{100mLSol} \times \frac{1molCaCO_3}{100.09gCaCO_3} \times \frac{1000mLSol}{1LSol} = 6.7 \times 10^{-5} M[/tex]
Step 3: Calculate the solubility product constant (Ksp)
To relate Ksp and the molar solubility (S), we need to make an ICE chart.
CaCO₃(s) ⇄ Ca²⁺(aq) + CO₃²⁻(aq)
I 0 0
C +S +S
E S S
The solubility product constant is:
Ksp = [Ca²⁺].[CO₃²⁻] = S² = (6.7 × 10⁻⁵)² = 4.5 × 10⁻⁹
The potential energy of a roller coaster is 50 joules. The kinetic energy of the same coaster is 50 joules. What is the mechanical energy of the coaster? O joules 50 joules 100 joules
Answer:
100 joules
Explanation:
The mechanical energy (M.E) of an object describes the objects ability to do work. The mechanical energy encompasses the object's energy due to its position (potential energy) and its energy due to motion (kinetic energy).
Therefore,
M.E = K.E + P.E
According to this question, potential energy (P.E) of the roller coaster is 50J and the kinetic energy (K.E) is also 50J. Hence, the mechanical energy (M.E) is
M.E = 50J + 50J
M.E = 100J
If the P.E and K.E of a roller coaster is 50 Joules respectively, the mechanical energy of the roller coaster is 100 Joules.
Given the following data:
Potential energy of roller coaster = 50 Joules.Kinetic energy of roller coaster = 50 Joules.To find the mechanical energy of the roller coaster:
The mechanical energy of a physical object or body is the total sum of the potential energy (P.E) and kinetic energy (K.E) possessed by an object.
Mathematically, mechanical energy is given by the formula;
Substituting the given parameters into the formula, we have;
[tex]M.E = 50 + 50[/tex]
Mechanical energy (M.E) = 100 Joules.
Therefore, the mechanical energy of the roller coaster is 100 Joules.
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Question 1 of 10
What is technology?
A. An understanding of something new.
B. The steps that engineers go through to create a product.
C. Something created using science for use by society.
D. A method that is used to solve problems,
SUBMIT
Answer:
C.
Explanation:
You can use the series of elimination for this. First, you look at A. Technology is not an understanding of something new, so we cross that out. Second, you look at B. Technology isn't a series of steps, so we can mark that one off. Third, you look at C. Technology is something created using science for use by society, so we can keep that in mind. Lastly, we check D. Technology doesn't match up to the definition, so we can cross that one out. The answer that would make the most sense would be D.
What should be the temperature of the solvent before adding it to the sample to be recrystallized?
Answer:
Near the boiling point of the solvent
Explanation:
The process of recrystallization is hinged on the fact that the amount of solute that can be dissolved by a solvent increases with temperature. The process involves creation of a solution by dissolving a solute in a solvent at or near its boiling point. At the boiling point of the solvent, the solute has a greater solubility in the solvent; not much volume of the hot solvent is required to dissolve the solute.
Before the solution is later cooled, you can now filter out insoluble impurities from the hot solvent. The quantity of the original solute drops appreciably because impurities have been removed. At this lower temperature, the solution becomes saturated and the solute can no longer be held in solution hence it forms pure crystals of solute, which can be recovered.
Recrystallization must be carried out using the proper solvent. The solute must be relatively insoluble in the solvent at room temperature but more soluble in the solvent at elevated temperature.
Bromine is found above iodine in Group 17 of the periodic table. If an ion formed by bromine has a charge of 1-, what is the charge on an ion
formed by iodine?
A. -7
B. -2
C. -1
D. +1
Answer:
Explanation:
Iodine is the most flexible of the atoms in Group 17 of the periodic table. It can have more than 1 charge, especially when combined with oxygen. The answer that you are expected to give, I think is C. Iodine's dominant charge is - 1
(a) Write a briefexperimental procedure for the chromic acid test.Include all observations such ascolor change, precipitation, etc.(5 points)(b) What functional groups can be distinguished by this test?(2points)(c) What is the reason for the color change if you get a positive chromic acid test?(3points)(d) Sketch a reaction mechanism for a positive chromic acid test with the above given molecules.(10points) g
Answer:
See explanation
Explanation:
a) -About 1-2 drops of the unknown is dissolved in approximately 1 mL of analytical grade acetone standard solution. The test solution is added and shaken thoroughly. If a positive test is not immediately observed, the set should be allowed to stand for 1-2 minutes. A positive result means the appearance of a green color.
b) The functional groups that can be distinguished by the test are alcohols and aldehydes.
Aldehydes give a positive test to chromic acid but ketones do not.
Primary and secondary alcohols give a positive test to chromic acid but tertiary alcohols do not.
c) Chromic Acid Test involves Cr in the +6 oxidation state. A positive test implies the reduction of orange Cr^6+ to green chromium Cr^3+.
d) The compounds were not shown but this image attached from lumen learning summarizes the reaction mechanism of chromic acid test.
2 2 6 2 6 2 10 3
1s 2s 2p 3s 3p 4s 3d 4p
=
Answer:
ARSENIC
Explanation:
It has an atomic number of 33
Into which two smaller groups are plants divided.
(a)vascular and nonvascular
(b)seed and seedless
(c)monocots and dicots
(d)seeds and spores
giving 17 points please help
A solution is made by mixing of 42.g water and 77.g of acetic acid HCH3CO2. Calculate the mole fraction of water in this solution.
Moles of [tex]H_2O[/tex] ,
[tex]n_{H_2O}=\dfrac{42}{2\times 1 + 16}=\dfrac{42}{18}\\\\n_{H_2O}=2.33\ moles[/tex]
Moles of acetic acid [tex]HCH_3CO_2[/tex] ,
[tex]n_{A.A}=\dfrac{77}{1 + 12 + 3 + 12 + 16\times 2}=\dfrac{77}{60}\\\\n_{A.A}=1.28\ moles[/tex]
Mole fraction of water :
[tex]M.F_{H_2O}=\dfrac{n_{H_2O}}{n_{H_2O}+n_{A.A}}\\\\M.F_{H_2O}=\dfrac{2.33}{2.33+1.28}\\\\M.F_{H_2O}=0.645[/tex]
Therefore, mole fraction of water in this solution is 0.645 .
Hence, this is the required solution.
The half life of oxygen is 2 minutes. What fraction of a sample of 0.15 will remain after 5 half lives?
Answer:
3.13%.
Explanation:
The following data were obtained from the question:
Original amount (N₀) = 0.15
Half life (t½) = 2 mins
Number of half-life (n) = 5
Fraction of sample remaining =.?
Next, we shall determine the amount remaining (N) after 5 half-life. This can be obtained as follow:
Amount remaining (N) = 1/2ⁿ × original amount (N₀)
NOTE: n is the number of half-life.
N = 1/2ⁿ × N₀
N = 1/2⁵ × 0.15
N = 1/32 × 0.15
N = 0.15/32
N = 4.69×10¯³
Therefore, 4.69×10¯³ is remaining after 5 half-life.
Finally, we shall the fraction of the sample remaining after 5 half-life as follow:
Original amount (N₀) = 0.15
Amount remaining (N) = 4.69×10¯³
Fraction remaining = N/N₀ × 100
Fraction remaining = 4.69×10¯³/0.15 × 100
Fraction remaining = 3.13%
Writing key words in the margin is part of which note-taking procedure?
Select one:
a. record
b. review
c. reduce
d. recite
Your task is to create a buffered solution. You are provided with 0.10 M solutions of formic acid and sodium formate. Formic acid has a pKa of 3.75. 2. Create approximately 20 mL of buffer solution with a pH of 4.25.
Answer:
15.2mL of the 0.10M sodium formate solution and 4.8mL of the 0.10M formic acid solution.
Explanation:
To find the pH of a buffer based on the concentration of the acid and conjugate base we must use Henderson-Hasselbalch equation:
pH = pKa + log [A⁻] / [HA]
Where [A⁻] could be taken as moles of the sodium formate and [HA] moles of the formic acid
4.25 = 3.75 + log [A⁻] / [HA]
0.5 = log [A⁻] / [HA]
3.162 = [A⁻] / [HA] (1)
As both solutions are 0.10M and you want to create 20mL of the buffer, the moles are:
0.10M * 20x10⁻³L =
2x10⁻³moles = [A⁻] + [HA] (2)
Replacing (2) in (1):
3.162 = 2x10⁻³moles - [HA] / [HA]
3.162 [HA] = 2x10⁻³moles - [HA]
4.162[HA] = 2x10⁻³moles
[HA] = 4.805x10⁻⁴ moles
[A⁻] = 2x10⁻³moles - 4.805x10⁻⁴ moles = 1.5195x10⁻³moles
That means, to create the buffer you must add:
[A⁻] = 1.5195x10⁻³moles * (1L / 0.10mol) = 0.0152L =
15.2mL of the 0.10M sodium formate solution[HA] = 4.805x10⁻⁴ moles * (1L / 0.10mol) = 0.0048L =
4.8mL of the 0.10M formic acid solutionA student measured the masses of four different-sized blocks. The student determined that each block had a mass of 50 grams.
(There is a small block, a little bit bigger block, a big block and the biggles block)
Which block has the least density?
Answer:..
Explanation:
Use the Rydberg Equation to calculate the energy in Joules of the transition between n = 7 and n = 3 for the hydrogen atom. Find the frequency in Hz of this transition if the wavelength is 1000nm.
Answer:
The energy of each transition is approximately [tex]1.98\times 10^{-19}\; \rm J[/tex].
The frequency of photons released in such transitions is approximately [tex]3.00\times 10^{14}\; \rm Hz[/tex].
Explanation:
The Rydberg Equation gives the wavelength (in vacuum) of photons released when the electron of a hydrogen atom transitions from one main energy level to a lower one.
Let [tex]\lambda_\text{vac}[/tex] denote the wavelength of the photon released when measured in vacuum.Let [tex]R_\text{H}[/tex] denote the Rydberg constant for hydrogen. [tex]R_\text{H} \approx 1.09678 \times 10^{7}\; \rm m^{-1}[/tex].Let [tex]n_1[/tex] and [tex]n_2[/tex] denote the principal quantum number of the initial and final main energy level of that electron. (Both [tex]n_1\![/tex] and [tex]n_2\![/tex] should be positive integers; [tex]n_1 > n_2[/tex].)The Rydberg Equation gives the following relation:
[tex]\displaystyle \frac{1}{\lambda_\text{vac}} = R_\text{H} \cdot \left(\frac{1}{{n_2}^2}} -\frac{1}{{n_1}^2}\right)[/tex].
Rearrange to obtain and expression for [tex]\lambda_\text{vac}[/tex]:
[tex]\displaystyle \lambda_\text{vac} = \frac{1}{\displaystyle R_\text{H}\cdot \left(\frac{1}{{n_2}^2} - \frac{1}{{n_1}^2}\right)}[/tex].
In this question, [tex]n_1 = 7[/tex] while [tex]n_2 = 3[/tex]. Therefore:
[tex]\begin{aligned} \lambda_\text{vac} &= \frac{1}{\displaystyle R_\text{H}\cdot \left(\frac{1}{{n_2}^2} - \frac{1}{{n_1}^2}\right)} \\ &\approx \frac{1}{\displaystyle 1.09678 \times 10^{7}\; \rm m^{-1} \cdot \left(\frac{1}{3^2} - \frac{1}{7^2}\right)} \approx 1.0 \times 10^{-6}\; \rm m \end{aligned}[/tex].
Note, that [tex]1.0\times 10^{-6}\; \rm m[/tex] is equivalent to [tex]1000\; \rm nm[/tex]. That is: [tex]1.0\times 10^{-6}\; \rm m = 1000\; \rm nm[/tex].
Look up the speed of light in vacuum: [tex]c \approx 3.00\times 10^{8}\; \rm m \cdot s^{-1}[/tex]. Calculate the frequency of this photon:
[tex]\begin{aligned} f &= \frac{c}{\lambda_\text{vac}} \\ &\approx \frac{3.00\times 10^{8}\; \rm m\cdot s^{-1}}{1.0\times 10^{-6}\; \rm m} \approx 3.00 \times 10^{14}\; \rm Hz\end{aligned}[/tex].
Let [tex]h[/tex] represent Planck constant. The energy of a photon of wavelength [tex]f[/tex] would be [tex]E = h \cdot f[/tex].
Look up the Planck constant: [tex]h \approx 6.62607 \times 10^{-34}\; \rm J \cdot s[/tex]. With a frequency of [tex]3.00\times 10^{14}\; \rm Hz[/tex] ([tex]1\; \rm Hz = 1\; \rm s^{-1}[/tex],) the energy of each photon released in this transition would be:
[tex]\begin{aligned}E &= h \cdot f \\ &\approx 6.62607 \times 10^{-34}\; \rm J\cdot s^{-1} \times 3.00 \times 10^{14}\; \rm s^{-1} \\ &\approx 1.98 \times 10^{-19}\; \rm J\end{aligned}[/tex].
The energy of the transition between n = 7 and n = 3 is 1.96 × 10^-19 J while the frequency is 3 × 10^14 Hz.
Using the Rydberg Equation for energy;
ΔE = -RH(1/n^2final - 1/n^2initial)
Given that;
nfinal = 3
ninitial = 7
RH = 2.18 × 10^-18 J
ΔE = - 2.18 × 10^-18(1/3^2 - 1/7^2)
ΔE = - 2.18 × 10^-18(0.11 - 0.02)
ΔE = - 1.96 × 10^-19 J
For the second part;
Since the wavelength is 1000nm, we have;
λ = 1000nm
c = 3 × 10^8 m/s
f = ?
c = λf
f = c/λ
f = 3 × 10^8 m/s/1000 × 10^-9 m
f = 3 × 10^8 m/s/ 1 × 10^-6 m
f = 3 × 10^14 Hz
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