MIDTERM PRACTICE - Garlic Bread Review Session [ENDORSED]

[Sydney Takeda 2I]

For question 13A, can someone please explain why the answer is 2.681x10^-26? I got the 2.681, but for some reason I got x10^-23.

Did you remember to convert the mass into kg?

I converted to kg and got the 2.681 part yet still can't manage to get 10^-26 help

[Nawaphan Watanasirisuk 3B]

Can someone explain 1. to me?

Thanks in advance!

[StudentD2B]

Clearly I needed to look at this earlier than I did..

For 11b, would you subtract to n=3 from the n=1 or the n=1 from the n=3

[Sydney Takeda 2I]

Clearly I needed to look at this earlier than I did..

For 11b, would you subtract to n=3 from the n=1 or the n=1 from the n=3

n=1 from n=3! (since the electron is transitioning from the third energy level to the first)

[StudentD2B]

Could someone explain why for 13D (I looked this up on the internet) the atoms have different electron configurations? I know that the electron configurations are:

Neutral SC Atom: 1s2 2s2 2p6 3s2 3p6 3d1 4s2
SC2+ Ion: 1s2 2s2 2p6 3s2 3p6 3d1
Neutral K atom: 1s2 2s2 2p6 3s2 3p6 4s1

But could someone please explain to me why. They both have 19 electrons so they should be isoelectric, but they're not.

[John Kim Lec3Dis3L]

Can someone explain 1. to me?

Thanks in advance!

Step 1: Find the molar masses of CO2 and H2O
Step 2: Calculate the moles of CO2 and H2O by dividing grams by moles
Step 3: Find simplest ratio of two compounds' moles
Step 4: Balance full chemical equation ( _ C?H?O? + _ O2 -> _ CO2 + _ H2O ) using aforementioned ratio values as coefficients
* Note: if ratio coefficients do not balance, try doubling every coefficient

[Daisylookinland]

Can someone please explain 10b to me? I don't understand why they wouldn't all be equal

[Daisylookinland]

Could someone explain why for 13D (I looked this up on the internet) the atoms have different electron configurations? I know that the electron configurations are:

Neutral SC Atom: 1s2 2s2 2p6 3s2 3p6 3d1 4s2
SC2+ Ion: 1s2 2s2 2p6 3s2 3p6 3d1
Neutral K atom: 1s2 2s2 2p6 3s2 3p6 4s1

But could someone please explain to me why. They both have 19 electrons so they should be isoelectric, but they're not.

They are isoelectronic because they have the same number of electrons, but their configurations are different. When writing the electron configurations for an isotope of an atom, write it out how you normally would first: Sc=[Ar]3d^14s^2, and then subtract the electrons from there -- Sc^2- = [Ar]3d^1

Hope that makes sense!

[Daisylookinland]

Could someone explain why for 13D (I looked this up on the internet) the atoms have different electron configurations? I know that the electron configurations are:

Neutral SC Atom: 1s2 2s2 2p6 3s2 3p6 3d1 4s2
SC2+ Ion: 1s2 2s2 2p6 3s2 3p6 3d1
Neutral K atom: 1s2 2s2 2p6 3s2 3p6 4s1

But could someone please explain to me why. They both have 19 electrons so they should be isoelectric, but they're not.

They are isoelectronic because they have the same number of electrons, but their configurations are different. When writing the electron configurations for an isotope of an atom, write it out how you normally would first: Sc=[Ar]3d^14s^2, and then subtract the electrons from there -- Sc^2- = [Ar]3d^1

Hope that makes sense!

[melissa_dis4K]

does anyone know how to solve 8b? i am having trouble with it.

First convert the work function from kJ/mol into J and convert lambda into meters. Then using E(photon)- work function =kinetic energy, we will be solving for E(photon). But first we need to know the kinetic energy to do so use Ek=1/2 Mass* Velocity^2. But notice we don't have velocity yet so we need to solve for velocity by using lambda=h/p, where p=mass* velocity. We know lambda, planks constant, and mass of electron. Solve for velocity. Now you can plug in your velocity and mass of an electron into kinetic energy= 1/2 Mass* Velocity^2. Now we can solve for the E(photon) using E(photon)- work function =kinetic energy. Finally, to find the frequency use E=h*frequency since we know E and we know h we can solve for it. Hope this helps!

[Kaylee Kang 1G]

Thank you so much for the extra practice!!

[Daisylookinland]

Could someone please explain the mathematics behind 13E to me?

[1K Kevin]

Can anyone help explain the process for 11a
Thank You!

[Simran Rai 4E]

Can anyone explain the reasoning for why 6d is true.

6d is true because the answer 10^-11 m is greater 10^-18. If it were less, then wavelength properties wouldn't be measurable.

[Elle_Mendelson_2K]

Will someone explain 10A?

[michellebui_3L]

Does anyone know how to do question 13 a and b? I though I could do 13a but thirteen b said that what she did (which is what I did) was wrong.

She can't divide the speed of light by the wavelength for each potassium ion because you can't use the equation for the speed of light since potassium is an ion.

[michellebui_3L]

Will someone explain 10A?

Atomic radius decreases from left to right, therefore Aluminum would have the bigger radius since it has less protons.

[michellebui_3L]

Can anyone help explain the process for 11a
Thank You!

You can use the equations (-hR)/n^2. Use two of these equations and plug in 1 for n and 3 for the other n. You could also manipulate the equations and subtract the diff so:
((-hR)/(n^2))-((-hR)/n^2)). After, you find the answer, divide it by h to find frequency.

[ElliotPourdavoud 1A]

Thank you so much for this review it really helped me!

[Yvonne Du]

For number 5, I keep getting .127 M after setting the problem up like (.211 M)(.150 L) = M2(.250 L). But in my notes, I believe Lyndon got 1.69 x 10^-2. I was wondering if anyone knows what I am doing wrong. Thanks!

Hi!
Since the problem stated that only 20ml was removed to the 2nd flask, you put 0.02 as your L1 instead of 0.150 L. Now you should get the right answer.

I'm confused as to why .02 L would be the initial volume, if when we calculate the initial molarity (mol/L of KMnO4) in the compound we use .150 L, rather than .020L?

This is because the problem said ONLY 20mL were taken from the 150mL to further produce the mixture. You are taking 20mL to start the second dilution, not using the whole 150mL that you got from the first dilution.

[Yvonne Du]

Will someone explain 10A?

As more electrons and photons are added to the atom from left to right, the force of increasing protons creates a stronger pull that attracts the electrons to get closer to the nucleus. Therefore the atom shrinks for silicon and has a smaller radius than aluminum.

[Sophia Fox 4B]

Will you be posting a similar review sheet for the final?