Last few MCAT questions

[CanadianPre-Med]

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1. Necessary to know that 1 Cal = 4184 J?

2. In electrophoresis, positively-charged amino acids travel towards the cathode. Is this because the electrode is positively charged allowing the positively charged amino acids to reach their respective pIs (i.e. is the cathode positive)?

 

[CanMed]

I think the cathode is negatively charged. That is why positively charged amino acids are attracted to it.

 

[CanadianPre-Med]

Yeah, you're right. Normally the cathode wants the cations, but it's the reverse here. Thanks.

 

[OrGoMan]

Yeah, you're right. Normally the cathode wants the cations, but it's the reverse here. Thanks.

Wait, what? Normally the cathode wants the anions, because its positive. In this case, since cathode is negative, it wants the Cations cuz their positive.

 

[HailToTheThielf]

cathode=negative=cations
anode=positive=anions

 

[Khanal007]

This is the way I remember it (I dunno if I'm just gonna add confusion):

There seem to be 3 different "things" that use anodes and cathodes: electrophoresis, galvanic cell, and electrolytic cell. I remember it by telling myself that out of the three, only in the galvanic cell, is the cathode positive, in the other two its the opposite.

 

[totalcommand]

With a galvanic cell, - and + are assigned based on the flow of electrons. Because the flow of electrons is to the cathode (where reduction occurs), the cathode is + and the anode is -.

In an electrolytic cell (like electrophoresis), - and + are assigned based on the flow of cations in the solution. Because cations will flow toward the cathode in order to be reduced (i.e. Ag+ + e- --> Ag @ cathode), the cathode is assigned - and the anode is assigned +.