Topscore Test 2 General Chemistry

[Meas]

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Topscore Test 2 General Chemistry:

I am having some problems calculating oxidation states and I am not sure if the oxidation states that I calculated for each element is correct in the following questions:

48)Sn(NO3)2
Sn: +2
N: +2
O: -2

--The overall oxidation state of this molecule adds up to zero. I assumed that NO3 has a negative charge, but using the oxidation states that I predicted from above, NO3 will have an overall charge of 4 [3(-2) from O & +2 from N].

52) Al2(SO4)3
Al: +3
S: +6
O: -2

I also have some problems with calculations:

61) If you have a solution of 1L of H2O and 234 g of NaCl, what is the osmotic pressure at STP (R=0.1L*atm/mol*K)

A: 218.4atm

--I used MRT X i = 234g X (mol/58g) X 1/1L X (0.1L atm/mol K) X 300K X 2(this is the # of ions that dissociated) = 238atm

68)What volume of HCL was added if 20mL of 1M NaOH is titrated with 1M HCl to produce a pH=2?

--With a pH of 2, there should be excess H+ but all the OH- should have reacted with H+. 0.02L X 1M = 50mol of OH-. So, 50mol of OH- should react with 50mol of H+ and a pH of 2 will have a H+ concentration of 10^-2. But I still don’t know the volume of HCl. Any ideas? I feel like I am going in circles for this question.

Any responses will be highly appreciated!

 

[suhshi]

Topscore Test 2 General Chemistry:

I am having some problems calculating oxidation states and I am not sure if the oxidation states that I calculated for each element is correct in the following questions:

48)Sn(NO3)2
Sn: +2
N: +2
O: -2

--The overall oxidation state of this molecule adds up to zero. I assumed that NO3 has a negative charge, but using the oxidation states that I predicted from above, NO3 will have an overall charge of 4 [3(-2) from O & +2 from N].

52) Al2(SO4)3
Al: +3
S: +6
O: -2

I also have some problems with calculations:

61) If you have a solution of 1L of H2O and 234 g of NaCl, what is the osmotic pressure at STP (R=0.1L*atm/mol*K)

A: 218.4atm

--I used MRT X i = 234g X (mol/58g) X 1/1L X (0.1L atm/mol K) X 300K X 2(this is the # of ions that dissociated) = 238atm

68)What volume of HCL was added if 20mL of 1M NaOH is titrated with 1M HCl to produce a pH=2?

--With a pH of 2, there should be excess H+ but all the OH- should have reacted with H+. 0.02L X 1M = 50mol of OH-. So, 50mol of OH- should react with 50mol of H+ and a pH of 2 will have a H+ concentration of 10^-2. But I still don’t know the volume of HCl. Any ideas? I feel like I am going in circles for this question.

Any responses will be highly appreciated!

for Nitrogen i think the oxidation state is 5+
NO3- : O is -2 and thus to make it equal to -1, N must be +5

the state of Al will always be 3+
so thats right

for the osmotic pressure question, i used 273 K

and for the last

(x)(1 M HCl)= (.01)(40 +x)

x=.4

you need 20 mL HCl to neutralize and extra .4 to bring to ph =2

 

[Meas]

Hey suhshi, thanks for your help! For the osmotic pressure, using 273K, i have an answer of 220 which I guessed it's close to the answer 218.

For the last question, I see that you used the formula c1v1 = c2v2, but I am not sure where you got the 40ml from.

Thanks & looking forward to your reply!

for Nitrogen i think the oxidation state is 5+
NO3- : O is -2 and thus to make it equal to -1, N must be +5

the state of Al will always be 3+
so thats right

for the osmotic pressure question, i used 273 K

and for the last

(x)(1 M HCl)= (.01)(40 +x)

x=.4

you need 20 mL HCl to neutralize and extra .4 to bring to ph =2

 

[Meas]

I just realized that I had a question about this before! For this equation, (x)(1 M HCl)= (.01)(40 +x)

-the right side is the final concentration & volume of the mixture of acid & base

I always thought that c1v1 = c2v2 is for neutralization such that the resulting solution has a pH of 7. Please correct me if I am wrong.

Also, what happens when you mix, say, a 30mL of 0.5M HF with 40mL of 0.8M NaOH. How would you figure out the final concentration of the mixture?

Thanks!