pH question...?

Question

I need help with this question. It is not from an assignment. It is in my book, and it tries to explain how to do it, but I don't understand...

Determine the pH of a solution with a hydrogen concentration of 3.5 x 10^-4

This is what it says.

pH = -log [3.5 x 10^-4]
= -log 3.5 - log 10^-4
= - .54 - (-4)
= - .54 + 4
= 3.46

Where does the .54 come from?

And what Exactly does log mean in this?

Answer 1

all right mate its real simple, don't get lost in the calculation. The book is right. log3.5 on your calculator should give .54. Hense -log3.5 will give -.54. Log is a unit of measurement used to scale an answer to desirably fit a logarithmic curve on a graph. just to clarify pH= -log[H]
hope this helps.

Answer 2

The formula to calculate the pH of a solution is given to you as,
pH = - log ( [H+] )
where [H+] is the molar concentration of the Hydronium ion in solution.

So using this formual a long with the information explicitly stated in the question,
pH = - log (3.5 E-4)
plugging this into a calculator,
pH = 3.46


In you question / book, the author seperated the given concentration into two units for "simplicity" (I would assume), but this is not needed, perhaps he was just trying to save himself some button pushing on a calculator?


.54 is the logorith of 3.5,
-4 is the logorith of 1 E-4.

Your question asking,
"And what Exactly does log mean in this?" has a rather lengthy explanation and pehaps you should consult a mathmatics book for a better explanation than the basic one I will give.

Lets say you want to solve this equation for the value of x,
x^2 = 4
well, you know if you take the square root of both sides you can eliminate the ^2 on the x leaving,
x = 2 (or negative two)

but what if you had this,
2^x = 4
how would you solve that? There is no Xth root to use, so what to do?
You can use logorithms and log rules.
Without going into the details of "why" it works (consult a math book, it really use a useful skill to learn how to use these),
if you take the "log" of both sides you get,
x log (2) = log (4)
then divide by log (2) to solve for x,
x = log (4) / log (2)
x = 2

Note, the log I used here was the "common log" with a base of 10, there are other logoriths which can be used, most noteably, the natural log (using the natural exponent e as the base).

Anyway, there is your ultra brief explanation of how to use logorithms, but you probably got no useful information out of it.

Now, "why", you ask does all this base 10, exponential function stuff have anything to due with the pH of a solution?
It is because the pH is a logorithmic scale....each increase of 1 pH indicates that the H+ concentration is 10 times more concentrated than the one beneath it. A pH of 1 is one thousand times more concentrated (in terms of H+ ions) than a pH of 4.

More on logorithms,
http://www.sosmath.com/algebra/logs/log4/log4.html

Answer 3

it came from -log 3.5

-log 3.5 = -0.54

if your using a calculator, u can directly compute for the ph. just type on your calcu the following

-log(3.5 exp -4)

in the solution from your book, employs the properties of logarithms where if you get the logarithm of a number times a number, it is also the sam as adding the log of the first number to the log of the second number. above, it may appear that the book use subtraction but it is not, -log3.5-log10^-4 is beacause of the negative sign before the log

its like - ( log3.5 + log 10^-4)

Answer 4

Log means if you described the number as 10 to a power, what would that power be.

so log(100) would be 2, because 100 = 10^2
log(3.5) is .54, because 3.5 = 10^.54

Answer 5

From base 10 log of 3.5.

These days you can use a calculator to get log of 3.5e-4 directly. The breakup they use is really antiquated

Answer 6

the .54 is what -log(3.5) equals. and you use log while doing pH's because pH = -log [H+]

where [H+] is the concentration of H+ ions in moles per liter (a mole is a unit of measurement, equal to 6.022 x 1023 atoms).

Answer 7

p7bcfbacd98cfa6ce29d0ad821b14f9 = -log(base 10)[7bcfbacd98cfa6ce29d0ad821b14f97bcfbacd98cfa6ce29d0ad821b14f9] The 'p' comes from 'potenz', German for 'ability' (as in the nth ability of a quantity ... given, i think, that p7bcfbacd98cfa6ce29d0ad821b14f9 is suitable to the 'ability of 10' of the concentration). And the 'H+' from the emblem for hydrogen. p7bcfbacd98cfa6ce29d0ad821b14f9 under 7 is an acidic answer; p7bcfbacd98cfa6ce29d0ad821b14f9 of seven is impartial; and above 7 is undemanding.