Chem Homework!

ShivamS · 2013-06-03 02:38:04

Now that we have a science hq section..... My prof. gave me lot's of chem work for since I am going to my high school. Need someone to check them. Thank-you in advance.

1 The atomic masses in the periodic table are not integral numbers. For example, carbon is listed as 12.011 amu (atomic mass unit) instead of 12.000 amu. Why?(we were given a couple of options to select from)

Atomic masses listed in the periodic table are weighted averages of isotopic masses.

2 Screening by core electrons in atoms is _____

more efficient than that by valence electrons

3 According to the Valence Shell Electron Pair Repulsion theory, if there are 5 pairs of electrons in the valence shell of an atom, they will be arranged in a(n) _____ geometry.

trigonal bipyramidal

4 What is the mass in grams of 10.0 million H2O molecules?

2.990 X 10^-16

5 Which of the following is a valid set of quantum numbers?

n=4, l=0, ml=0, ms=-1/2

6 Phenol red has an indicator pH range of 6.8 to 8.4. Its acid color is yellow and basic color is red. In 0.10 M NaOH, this indicator will exhibit what color? red

7 Determine the volume (in liters) occupied by 8.0 g oxygen at STP (MW of O2 = 32 g/mol) 5.6

8 What do you call gases that do not conform to the ideal gas laws? real gases

9 Which of the following terms is used to describe the amount of heat present in a substance?
enthalpy

10 How many grams of phosphoric acid (98 g/mol) are in 175 mL of a 3.5 M solution of phosphoric acid? 60

Last edited by Shivamcoder3013 (2013-06-03 02:43:23)

Agnishom · 2013-06-03 02:42:13

I think 1, 4, 6, 7 & 9 are correct. The others are beyond my knowledge.

What are quantam numbers?

barbie19022002 · 2013-06-03 02:43:16

Es tut mir leid, aber ich denke, ich kann dir nicht helfen, in der Chemie ... wenn Sie ein anderes Thema wäre dann könnte ich Ihnen helfen ..... aber leider leider wieder einmal ... (I'm sorry, but I think I can not help you in chemistry ... if you would have a different theme then I could help you ..... but unfortunately sorry once again ...)

ShivamS · 2013-06-03 02:48:40

Agnishom, you know how in the Bohr model there is only 1 quantum # for the electron configuration? A model called Schrodinger's model let us see the electron distribution in 3d space. That of course needed 3 coordinates which are called quantum numbers. Principal, magnetic and angular. In this case, n=4, l=0, ml=0, ms=-1/2 is right as it is showing an electron in the fourth energy level of orbital s. Also, mind translating that German?

Agnishom · 2013-06-03 02:54:17

Its given in bracket. Check the post again

n is the shell number. Right?

ShivamS · 2013-06-03 02:55:37

n is the number which describes the orbital size

Agnishom · 2013-06-03 04:04:45

Do you have a link to a lesson on tjis?

barbie19022002 · 2013-06-03 23:18:03

Even I got my chemistry homework..I have nearly done everything but I can't solve this two question...

The number of d-electrons in Fe2+ (Z = 26) is not equal to that of? and another one is:

The number of water molecules present in a drop of water (volume 0.0018 ml) at room temperature is?

can anyone help me in solving this two question..

Last edited by barbie19022002 (2013-06-03 23:26:55)

ShivamS · 2013-06-04 00:21:30

The number of d-electrons is not equal to that of p-electrons in CI(Z = 17).
6.023 x 1019 for the second question. Also, tjis?

Last edited by Shivamcoder3013 (2013-06-04 00:21:59)

Bob · 2013-06-04 00:46:56

hi

Which ones from the original post do you still need to be checked?

Oh Just as I posted, you went off-line. Let me explain for when you come back on.

My wife is a really excellent chemistry teacher and probably knows all those answers. But (and other members may not want to read this) she thinks MIF is a waste of time and cannot understand why I keep logging in. She thinks I should be out in the garden doing some jobs for her. But, if I get the short list from you, I can probably ask her to look at them. Especially as I'll have done those jobs by then

Bob

barbie19022002 · 2013-06-04 01:29:57

I thought you were a university student.....I didn't know you are married too..but both the questions are really different please read it nicely.....

ShivamS · 2013-06-04 03:12:41

The ones in the original post. Barbie, he is a teacher.

anonimnystefy · 2013-06-04 03:28:53

Hi Shivamcoder3013

1, 4, 6, 7, 8 and 10 are correct (for 10 I am getting the "exact" answer to be 60.025).

ShivamS · 2013-06-04 11:00:05

2, 3 are wrong? And I rounded the 60. Also, thanks a lot.

Last edited by Shivamcoder3013 (2013-06-04 11:00:23)

anonimnystefy · 2013-06-04 11:21:47

I do not know about the others. 3 seems right, but I am not sure.

barbie19022002 · 2013-06-04 17:26:19

and what about my question can't anyone solve this two....I am having tension..my school is going to re-open very quickly I need to finish it as fast as I can do it..

Agnishom · 2013-06-04 17:52:18

18ml of water consists of 6.022 *10^23 molecules.

So, that consists of around 6.022*10^19 molecules

barbie19022002 · 2013-06-04 18:12:29

how did you do that pls...show me the process too..cause I have to do this in my chem copy..

SteveB · 2013-06-04 19:35:31

I may have joined this discussion too late, but this is my way of doing this question:

The density of water is about 1 g per ml

So 0.0018 ml = 0.0018 g (appox.)

The molar mass of water is: 2x1 + 1x16 = 18 g per mol (approx.)

Then I divided by the molar mass of water to get the number of moles of water:

0.0018 / 18 = 1 x 10^-4 (mol H2O approx.)

Then multiply by Avogadros Constant: 6.022... x 10^23 (atoms or molecules per mol)

1 x 10^-4 x 6.022 x 10^23 = 6.02 x 10^19 (approx.)

Some of the figures I have used are approximate, but since the 0.0018 ml is only
supposed to be approximate I don't think much more accuracy was intended.

Last edited by SteveB (2013-06-04 19:46:20)

barbie19022002 · 2013-06-04 19:57:36

thank you very much...now I understood the process and now i can do it myself..thanks ones again..

Bob · 2013-06-04 22:51:50

hi Shivamcoder3013

It looks like you have a full set of correct answers, well done. (5) is the only one that worries me slightly; not because it is wrong; but because you haven't said what the alternative answers were. But there should only be one correct answer shouldn't there?

I'm way out of my depth here so I don't think I could manage a follow up.

Bob

ShivamS · 2013-06-05 00:19:26

Barbie:

Shivamcoder3013 wrote:

The number of d-electrons is not equal to that of p-electrons in CI(Z = 17).
6.023 x 1019 for the second question. Also, tjis?

Bob, for number 5, we were given 4 options. If you want, I will specify why the others were wrong.

5. n=3, l=2, ml=-3, ms=+1/2 is invalid as -2, -1, 0, 1, 2 are the ml d (l=2).

n=1, l=0, ml=1, ms=+1/2 Also invalid as ml <> 1 if l = 0. That is because if l = 0, it means there is an s-orbital and thus ml = 0.

n=4, l=0, ml=0, ms=-1/2 This is right as it displays electrons in 4th energy level in the s orbital.

All of the above. This is obviously wrong. Also, thanks everyone for checking them.

Last edited by Shivamcoder3013 (2013-06-05 00:19:48)

Math Is Fun Forum

#1 2013-06-03 02:38:04

Chem Homework!

#2 2013-06-03 02:42:13

Re: Chem Homework!

#3 2013-06-03 02:43:16

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#4 2013-06-03 02:48:40

Re: Chem Homework!

#5 2013-06-03 02:54:17

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#8 2013-06-03 23:18:03

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#11 2013-06-04 01:29:57

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#13 2013-06-04 03:28:53

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#16 2013-06-04 17:26:19

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