Chemistry, asked by Pickatchu7764, 11 months ago

Can you identify the following as weak acid, strong acid, weak base, strong base, or neutral? How do you determine this?

Answers

Answered by tannoypathak
0

Simply from the

K

a

, or the

pKa

. Or, the

K

b

, or the

pKb

, if comparing by dissociation in water.

The higher the

K

a

or lower the

pKa

, the stronger the acid.

The lower the

K

a

or higher the

pKa

, the weaker the acid.

Converting from

K

a

to

K

b

,

K

b

=

10

14

K

a

.

Converting from

pKa

to

pKb

,

pKb

=

14

pKa

.

Weaker acids have stronger conjugate bases and vice versa, so there's no need to think about it much more than that.

These are all relative to water, so clearly, pure water is considered neutral.

KOH

, an alkali metal hydroxide, easily dissociates to release

OH

into solution, which classifies it as a strong base. No need to check

pKa

here.

HCl

, a binary acid, easily dissociates to release

H

+

into solution, with

pKa

7

. Strong acid.

CH

3

COOH

is a carboxylic acid, whose

pKa

is about

5

(actually, this one is

4.74

). Often called acetic acid. Considered to be a weak acid, but still dissociates its proton significantly.

H

2

SO

4

has a

pKa

1

of

3

so it dissociates very easily. Strong acid.

H

2

CO

3

has a

pKa

1

of about

6.4

. Considered to be a weak acid, but still dissociates its first proton significantly.

H

3

PO

4

has a

pKa

1

of about

2.16

. Considered to be a relatively weak acid, but still dissociates its first proton significantly.

H

2

O

has a

pKa

of about

15

. Obviously neutral, since it cannot be a solute in its own solution and alter its own pH.

H

3

O

+

has a

pKa

of about

1.7

, so it's a strong acid.

HCN

has a

pKa

of about

9.2

. Considered to be a weak acid, but still dissociates its first proton significantly.

NH

4

OH

forms like this:

NH

3

(

a

q

)

+

H

2

O

(

l

)

NH

+

4

(

a

q

)

+

OH

(

a

q

)

K

b

=

[

NH

+

4

]

[

OH

]

[

NH

3

]

=

1.8

×

10

5

pKa

9.25

.

Thus,

NH

4

OH

dissociates significantly to form

NH

3

in solution, and most consider it a strong acid, even though its

pKa

is so close to that of

HCN

.

Lastly, make sure you know that acidity and basicity is all relative. You MUST compare the

p

K

a

s. Strong acids are only considered strong because they dissociate significantly in water.

If water had a lower

pKa

, these strong acids would be weaker. Similarly, if you dissolved

HCl

in

H

2

SO

4

,

HCl

would be considered a weak acid

I hope it will help you

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