jhk43

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i found this exam pretty hard.

Q1. Why is CO3(-2) strongly basic in water? ph=11+. shouldnt it be mildly basic, since its the conjugate base of a very weak acid?

Q2. Lets say you neutralize 99.9% of a pH 1 acid solution. what pH are u left with? 0,3,6,7?
 

premyo2002

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I haven't reviewed Acid/Base chemistry, but I thought that if a an acid is weak, this means it wants to hold on to protons (H), So the conjugate base, would want to hold on to protons. This means weak acid--->stronger base, weak base----> stronger acid


As for your second question, it should be about a little less than 7 if you neutralize most of it with a weak base, if you use a string base it would be 7. They are basically asking, "what's the equivalence point"
 

rugbyboy

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1) Conjugate base of a weak acid is a very strong base. Also true vice versa HCl very strong acid , Cl- very weak base.

2) 3
 

jhk43

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Q1. Why is CO3(-2) strongly basic in water? ph=11+. shouldnt it be mildly basic, since its the conjugate base of a very weak acid?

HCO3- <--> H+ CO3(-2)

HCO3- is a mildly weak acid. CO3(-2) should be a mildly weak base.

HCl is a strong acid. conjugate base is a VERY weak base (negligible).
 
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ASDIC

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pH 1 means... [H+] = 1 x 10 ^-1

so 0.1 % of [H+] remains which equals ((0.1/100) x 1 x 10^-1)

= 1 x 10^-4 ==> pH ~ 4

4 is close to 3.

on the mcat...they will not give exact answer in the choices. So, Kaplan advises that one should just make an approximation.
 

Cerberus

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Originally posted by jhk43
Q1. Why is CO3(-2) strongly basic in water? ph=11+. shouldnt it be mildly basic, since its the conjugate base of a very weak acid?

HCO3- <--> H+ CO3(-2)

HCO3- is a mildly weak acid. CO3(-2) should be a mildly weak base.

HCl is a strong acid. conjugate base is a VERY weak base (negligible).

CO3(-2) <-> HCO3- +H3O+<->H2CO3 +H2O <-> H2O+CO2

:)
 
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