what reacts most violently with cold water?

[PopeJoja]

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k, mg, fe, or zn

it's potassium, but why exactly. They just say it's because it's an alkali metal. should I just assume that group will combust more readily, or am I missing something?

thanks

 

[90210]

k, mg, fe, or zn

it's potassium, but why exactly. They just say it's because it's an alkali metal. should I just assume that group will combust more readily, or am I missing something?

thanks

Did they provide a table of standard reduction half reactions or standard oxidation half reactions? You could probably figure out that way.

For standard reduction half reactions = most negative = weakest oxidizing agent (most easily oxidized)

For standard oxidation half reactions = most positive = strongest reducing agent (most easily oxidized)

Aside from that, I'm not sure I'd be able to figure this one out. Unless the metals they were referring to were cations. In that case, the more positive charge = more acidic. The more acidic, the less likely they'd get protonated (ie. react with water). Just a wild guess.

 

[NurWollen]

Did they provide a table of standard reduction half reactions or standard oxidation half reactions? You could probably figure out that way.

For standard reduction half reactions = most negative = weakest oxidizing agent (most easily oxidized)

For standard oxidation half reactions = most positive = strongest reducing agent (most easily oxidized)

Aside from that, I'm not sure I'd be able to figure this one out. Unless the metals they were referring to were cations. In that case, the more positive charge = more acidic. The more acidic, the less likely they'd get protonated (ie. react with water). Just a wild guess.

Potassium seems like the obvious answer, since it's the only one I've never been allowed to handle.

 

[90210]

Actually I do recall reading somewhere that all group I and group II metals are considered to be some of the strongest reducing agents (because they all readily lose an electron or two to react an octet). Generally, they are even more reactive as you go down the column because the electron cloud increases and the valence electron is held less tightly.

Group 1 metals react with:
Water to form Hydroxides (aq) + H2 (g)
Oxygen Gas to form Metal Oxides(s)
Hydrogen Gas to form Metal Hydrides(s)
Nitrogen Gas to form Metal Amides(s)
Bromine Liquid to form Metal Bromide(l)

Group 2 metals are also very good reducing agents (easily oxidized) for the same reason discussed above -- they all readily lose two electrons to become a +2 caction with a filled octet. They are not as reactive as group 1 metals however.

Group 2 metals react with:
Water to form Hydroxides (aq) + H2(g)
Oxygen Gas to form Metal Oxides(s)
Hydrogen Gas to form Metal Hydrides(s)
Nitrogen Gas to form Metal Amides(s)
Bromine Liquid to form Metal Bromide(l)

Since my book mentioned it, it's probably worthwhile to remember these facts. Personally though, I would remember they react with the first 3 reactions (Water, Oxygen, and Hydrogen) and just recall that they are all strong reducing agents.

Hope this helps.

 

[90210]

Potassium seems like the obvious answer, since it's the only one I've never been allowed to handle.

Ha, well you're using outside experience, which is good. Unfortunately, I slacked off in lab since we were primarily quizzed and graded on our lab reports. But anyways, I think it's difficult to gauge the relative reactivity of group 1 and 2 metals vs. transition metals unless you were specifically told they are generally more reactive reducing agents. I looked it up and saw my book mentioned that though.

 

[blue0rchid]

Book (both BR and EK) said alkali metals are stronger reducing agents than alkaline earth metals, because they only need to lose one valence electron.
Also their reactivity increases as going down the periodic table.
K has one 3rd shell valence electron -> lose it easier than two 2nd shell valance electrons.

 

[banner18]

Ha, well you're using outside experience, which is good. Unfortunately, I slacked off in lab since we were primarily quizzed and graded on our lab reports. But anyways, I think it's difficult to gauge the relative reactivity of group 1 and 2 metals vs. transition metals unless you were specifically told they are generally more reactive reducing agents. I looked it up and saw my book mentioned that though.

Transition metals are not as reactive as you might expect, the presence of D orbitals makes it less reactive than those in the group I and II. This is a general knowledge mcat question that will be asked but probs in a more subtle way in a passage. You dont need the half-reactions to figure it out.

 

[MT Headed]

I remember studying something like this in the "periodic trends" portion of general chemistry. The reactivity of metals definitely increased going down and to the left on the periodic table.

In class we figured that the most reactive, non-radioactive metal must be Cesium, and we jokingly renamed him Sleazium - because he would stick that 6s1 electron in just about anything!

 

[PopeJoja]

Potassium seems like the obvious answer, since it's the only one I've never been allowed to handle.

haha. just wait until you enter the medical field. you will def handle it then.

Actually I do recall reading somewhere that all group I and group II metals are considered to be some of the strongest reducing agents (because they all readily lose an electron or two to react an octet). Generally, they are even more reactive as you go down the column because the electron cloud increases and the valence electron is held less tightly.

Group 1 metals react with:
Water to form Hydroxides (aq) + H2 (g)
Oxygen Gas to form Metal Oxides(s)
Hydrogen Gas to form Metal Hydrides(s)
Nitrogen Gas to form Metal Amides(s)
Bromine Liquid to form Metal Bromide(l)

Group 2 metals are also very good reducing agents (easily oxidized) for the same reason discussed above -- they all readily lose two electrons to become a +2 caction with a filled octet. They are not as reactive as group 1 metals however.

Group 2 metals react with:
Water to form Hydroxides (aq) + H2(g)
Oxygen Gas to form Metal Oxides(s)
Hydrogen Gas to form Metal Hydrides(s)
Nitrogen Gas to form Metal Amides(s)
Bromine Liquid to form Metal Bromide(l)

Since my book mentioned it, it's probably worthwhile to remember these facts. Personally though, I would remember they react with the first 3 reactions (Water, Oxygen, and Hydrogen) and just recall that they are all strong reducing agents.

Hope this helps.

this is great. thanks!

I remember studying something like this in the "periodic trends" portion of general chemistry. The reactivity of metals definitely increased going down and to the left on the periodic table.

In class we figured that the most reactive, non-radioactive metal must be Cesium, and we jokingly renamed him Sleazium - because he would stick that 6s1 electron in just about anything!

this is too funny.

 

[movax]

Yep, Group I is hilariously reactive with water. Look at some videos of Francium + H2O on YouTube if there are any, I remember seeing one where a single drop of Fr was added to a petri dish full of water, and the resulting explosion destroyed the dish.

Group I is more than happy to lose an electron so its configuration will match that of the preceding noble gas.