Ch 12.1 Help

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Ch 12.1 Help

Post  Daisy on Thu Nov 13, 2008 3:01 am

Question 1
1) A temperature is quoted as 60.16 oF. What is it in oC (see sheet 3)?

Answer: 15.644444444444442
How to solve:
Tc = (5/9)*(Tf-32)
Tc = temperature in degrees Celsius
Tf = temperature in degrees Fahrenheit

Question 2
2) A temperature difference is quoted as 22.27 oC. What is the temperature difference quoted in oK (see sheet 3) ? Indicate with a positive (negative) sign whether the relation between DT in oC and oK is (not) the same for DT in oC and oF.

Answer: -22.27
How to solve:
Change in temperature will be the same in degrees Kelvin.

Question 3
3) A substance with a density of 0.5031 g/cm3 occupies a volume of 2.905 cm3. What is the number of Atomic Mass Units (see sheet 6) ? Indicate with a negative (positive) sign whether the chemical composition of the substance has (does not have) to be known.

Answer: 8.80425e+23
How to solve:

Question 4
4) What is the mass of 2.828 moles of H2O in kg (see sheet 6,8') ? Indicate with a negative (positive) sign whether the mass of the same number of hydrogen moles and oxygen moles is (not) the same.

Answer: 0.050903999
How to solve:
Mass of H2O in 1 mole = 18g = .018kg
Set up a proportion then solve for the mass
(mass of substance/moles of substance) = (molecular mass of substance/one mole)
(mass/2.828 moles) = (.018kg/1 mole)
mass of 2.828 moles = 0.050903999

Daisy
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ques 3

Post  Kathleen on Thu Nov 13, 2008 1:57 pm

So for three, I just used the numbers from the given question above and I get an answer pretty close to the one provided, but I don't even know if this is the way the notes say how to do it because I didn't look at them, i just used chemistry knowledge.

So i think you'd have to find the mass first

D= m/v , so D*v = mass
You should get a mass of about 1.4615
Then you do 1.4615 grams x (6.02214e23) = 8.801e23
The third decimal place is off so I'm not sure exactly what to do but maybe someone else can work off of this to find the right way?

And my guess is that it would be positive since I didn't even know the composition while attempting this. Any input?

Kathleen
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question 3

Post  guest145 on Mon Nov 17, 2008 5:39 pm

for this question u=m/(1.66e-27 kg).
so find mass in kg, which is m=(rho*Volume)/1000

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Q3

Post  meg on Mon Nov 17, 2008 9:10 pm

i dont understand what you mean..

meg
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Q3

Post  meg on Mon Nov 17, 2008 9:17 pm

...and does anyone know how we are supposed to enter that answer on MapleTA for the quiz. Im not sure if im getting it wrong because im not entering in my ans right...thank

meg
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Re: Ch 12.1 Help

Post  Kathleen on Mon Nov 17, 2008 10:40 pm

Yeah I'm not getting question 3 right either. I've tried it in #.###e+# format, and #.###e# format

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Question 3

Post  Kathleen on Mon Nov 17, 2008 10:44 pm

Okay, so Question 3...

Do the formula that is provided above - Density x Volume/1000 = X
Then do X/(1.66e-27) = your answer
I don't know why it is 1.66e-27, maybe guest145 could explain where they got that?

And you have to actually put your whole answer in...so this was my question:
A substance with a density of 1.1953 g/cm3 occupies a volume of 4.184 cm3. What is the number of Atomic Mass Units

1.1953x4.1484/1000 = .0050011352
.0050011352/ (1.66e-27) = 3.012732048e24

The answer I actually put into Maple TA that was graded as correct was: 3012732048000000000000000 , which means you have to put all the numbers from your calculator plus any additional zeroes to add up to 24 places after the decimal point

Kathleen
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question 3

Post  guest145 on Mon Nov 17, 2008 10:56 pm

well, of course i can explain. The answer is indeed in slide 6, in which 1 u=1.66 e-27kg, and we all know that u is the atomic mass unit!

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Re: Ch 12.1 Help

Post  k on Tue Nov 18, 2008 1:32 am

lol thank you, I figured that but I haven't actually printed out or even looked at the slides for these quizzes yet

k
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Q3

Post  meg on Tue Nov 18, 2008 5:21 pm

Ok i finally got it now...thanks for ur help!!

meg
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Re: Ch 12.1 Help

Post  Question on Tue Nov 18, 2008 6:46 pm

can anyone who got question 3 correct post what you did because i have tried using the equation posted and cant get the right answer. thanks

Question
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#3

Post  super mo on Wed Nov 19, 2008 1:59 am

as an old chem lab Prof once said,"Think about your units."
you are multiplying g/cm^3 and cm^3. cm^3 cancel out, you are only left with grams. Grams must be converted then to kg by multiplying by 0.001 or (as posted above) divide by 1000. Entering your answer by moving the decimals and having all of those zero's is accepted by MapleTA, so count carefully before your enter your answer!

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#3

Post  guest 23 on Wed Nov 19, 2008 4:03 am

if u = 1.66*10^-27kg and we know the mass, why wouldnt we do (1.66*10^-27)*(mass in kg)
Above it says mass/(1.66*10^-27)

guest 23
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Correct Syntax for Question 3

Post  Baloneyf on Wed Nov 19, 2008 2:41 pm

Use capital " E "

Ex. Answer = 3.02348E24

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