need help figuring out new equation (2)

[tburgmag]

i have the equation:
pH = -log[H+]

H+ being hydrogen ion concentration of a solution in moles per liter

i was given H+ concentration of 1.26x10^(-8) i came up with a pH of approx 7.9. did i calculate this correctly?

2nd question and main question.
how do i change the equation to find the H+ when the pH is known.
all i can figure is to divide both sides by -log making the equation

pH/-log = H+
however this doesnt make sense. a number needs to be punched in calculator after -log????
any help is appreciated. i need to solve for pH 4.2 and 8.7. Thanks.

 

[Deleted member 4993]

i have the equation:
pH = -log[H+]

H+ being hydrogen ion concentration of a solution in moles per liter

i was given H+ concentration of 1.26x10^(-8) i came up with a pH of approx 7.9. did i calculate this correctly? <<< Correct

2nd question and main question.
how do i change the equation to find the H+ when the pH is known.
all i can figure is to divide both sides by -log making the equation

pH/-log = H+ <<< This is a "text" operation - not a mathematical operation

however this doesnt make sense. a number needs to be punched in calculator after -log????

\(\displaystyle -log(x) \, = \, log(\frac{1}{x})\)

any help is appreciated. i need to solve for pH 4.2 and 8.7. Thanks.

 

[tburgmag]

i still dont get it.
Does X = the pH??

-log(4.2) = -0.623
log(1/4.2) = -0.623

is 0.623 the hydro ion count

making pH of 8.7
-log(8.7) = -0.9395

this doesnt seem right. What am i missing??

 

[mmm4444bot]

Instead of using the symbolism pH and H+ as mathematical notation in my equations, I'm using the following assignments.

p = the pH value

H = the ion concentration (in moles/liter)

p = -log(H)

To solve this equation for H in terms of p, multiply both sides by -1 and then write the inverse relationship.

-p = log(H)

The inverse is exponeniation.

10^(-p) = H

If you're not familiar with this switch, perhaps you haven't seen a formal definition of logarithms.

When some positive base (b) is raised to an exponent (x), we get a power (P).

P = b^x

This equation expresses the power of b in terms of the exponent x.

To express the exponent in terms of the power, we define the base_b logarithm as follows.

x = log_b(P)

In other words, logs are exponents!!

In particular, the symbol log_b(P) is the exponent to which b must be raised in order for the resulting power to equal P.

pH values are defined using base 10 logarithms ("common logs").

Here's the logarithm definition using the common base b = 10.

P = 10^x

x = log(P)

Note: When the base is 10, many people don't write the logarithm as log_10(N); they simply write log(N). In other words, when we see a log expressed without indicating the base, we assume the base is 10.

If I wrote anything that you do not understand, please reply with specific questions.

Cheers,

~ Mark