gchem qs

[113zami]

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1) how many ml of H2O must be added to 65 ml of 5.5M solution of NaOH in order to prepare a 1.2M NaOH?
a) 235
b) 232.9
c)215

ansr is a but I keep getting b, what am i doing wrong?

2) in the balanced equation which of the following is the best oxidizing agent:

8Al(s)+3NO3(-)(aq)+5 OH(-)(aq)+18H2O(l)--->8Al(OH)4(-)(aq)+3NH3(g)

a)NO3(-)
b)Al(OH)4(-)
c)NH3(g)

ansr is a, but I just want to make sure that i have the correct reasoning cuz both a and b are oxidizing agents, but a transfers 3 electrons where as b transfers 2 electrons is that why a is a better oxidizing agent than b?

3) identify the reducing agent in the following rxn:

AgNO3(aq) + CuNO3(aq)---> Ag(s) +Cu(NO3)2(aq)

a) Cu
b)NO3

don't have the correct ansr for this one, but how do you determine the oxidation state for Cu and N ? because Cu has oxidation numbers +1 or +2 and N oxidation numbers can range from -3 to +5 so how do you know which numbers to pick?

thanks for the help

 

[MattH25]

1) how many ml of H2O must be added to 65 ml of 5.5M solution of NaOH in order to prepare a 1.2M NaOH?
a) 235
b) 232.9
c)215

ansr is a but I keep getting b, what am i doing wrong?

2) in the balanced equation which of the following is the best oxidizing agent:

8Al(s)+3NO3(-)(aq)+5 OH(-)(aq)+18H2O(l)--->8Al(OH)4(-)(aq)+3NH3(g)

a)NO3(-)
b)Al(OH)4(-)
c)NH3(g)

ansr is a, but I just want to make sure that i have the correct reasoning cuz both a and b are oxidizing agents, but a transfers 3 electrons where as b transfers 2 electrons is that why a is a better oxidizing agent than b?

3) identify the reducing agent in the following rxn:

AgNO3(aq) + CuNO3(aq)---> Ag(s) +Cu(NO3)2(aq)

a) Cu
b)NO3

don't have the correct ansr for this one, but how do you determine the oxidation state for Cu and N ? because Cu has oxidation numbers +1 or +2 and N oxidation numbers can range from -3 to +5 so how do you know which numbers to pick?

thanks for the help

#1 it looks like they are rounding off for sig figs. Since there are only 2 sig figs for least certain when you multiply 65ml by 5.5M and then divide by 1.2ml answer should be 300 instead of ~297.9

#2 I'll have to take a look at, been a while since I looked at redox reactions.

#3 Since it's aqueous I would assume the oxidation number would be the same as the charge on the ion. So CuNO3 would have Cu at +1 and nitrate at -1 (Nitrogen in nitrate would be +5 and the total oxygen would be -6 giving an overall charge of -1). Cu would be the reducing agent since it is oxidized up to a +2 charge as a product.

 

[113zami]

thanks, make sense
can anyone tackle the 2nd question plz, I mean i know that in order to find the relative strengths of oxidizing and reducing agents you have to look at the oxidation and reduction potentials but how can you tell for a question like this, when they're not given?

 

[USU24]

2) in the balanced equation which of the following is the best oxidizing agent:

8Al(s)+3NO3(-)(aq)+5 OH(-)(aq)+18H2O(l)--->8Al(OH)4(-)(aq)+3NH3(g)

a)NO3(-)
b)Al(OH)4(-)
c)NH3(g)

ansr is a, but I just want to make sure that i have the correct reasoning cuz both a and b are oxidizing agents, but a transfers 3 electrons where as b transfers 2 electrons is that why a is a better oxidizing agent than b?

Yes. That is why. The more electrons it can transfer = the better an oxidizing agent.