Question

What are the [H 3

​
O +
]for a solution with pH=5.5 ? Express your answer to one significant figure and include the appropriate units.

Answer 1

The pH of a solution is related to the concentration of hydronium ions (

[

�

3

�

+

]

[H

3

​

O

+

]) by the formula:

pH

=

−

log

⁡

10

(

[

�

3

�

+

]

)

pH=−log

10

​

([H

3

​

O

+

])

Step-by-step explanation:

To find the concentration of hydronium ions (

[

�

3

�

+

]

[H

3

​

O

+

]) for a solution with pH 5.5, we can rearrange the formula:

[

�

3

�

+

]

=

1

0

−

pH

[H

3

​

O

+

]=10

−pH

Substitute the pH value:

[

�

3

�

+

]

=

1

0

−

5.5

[H

3

​

O

+

]=10

−5.5

Calculate this value:

[

�

3

�

+

]

≈

3.16

×

1

0

−

6

 

M

[H

3

​

O

+

]≈3.16×10

−6

M

So, the concentration of hydronium ions for a solution with pH 5.5 is approximately

3.16

×

1

0

−

6

 

M

3.16×10

−6

M (to one significant figure).

Answer 2

The concentration of hydronium ions ([H3O+]) in a solution with a pH of 5.5 is 3 × 10^-6 M, expressed to one significant figure.

Step-by-step explanation:

To find the concentration of hydronium ions ([H3O+]) for a solution with a pH of 5.5, we use the equation pH = -log [H3O+]. Rearranging this equation we get [H3O+] = 10-pH. Substituting the given pH value into this expression, we get [H3O+] = 10-5.5, which equals approximately 3.2 × 10-6 M. However, since the pH was given to two significant figures, the answer should be given to one significant figure, which would be 3 × 10-6 M. Note that significant figures from the pH value determine the accuracy of our final answer.