Calculate The Ph Of 8.5X 10 3 M Hbr

Use this premium calculator to solve the pH of hydrobromic acid from scientific notation. HBr is a strong acid, so it dissociates essentially completely in water. For 8.5 x 10^-3 M HBr, the hydrogen ion concentration is treated as equal to the acid concentration, which makes the pH calculation direct and reliable for standard general chemistry work.

How to calculate the pH of 8.5 x 10^-3 M HBr

To calculate the pH of 8.5 x 10^-3 M HBr, start by identifying the acid type. Hydrobromic acid, written as HBr, is a strong acid. In introductory and most intermediate chemistry settings, strong acids are assumed to dissociate completely in water. That means one mole of HBr releases one mole of hydrogen ions, often represented as H+ or more precisely as hydronium in water. Because of that full dissociation, the hydrogen ion concentration is essentially the same as the original molar concentration of the acid.

For this problem, the concentration is 8.5 x 10^-3 M. That means:

[H⁺] = 8.5 x 10^-3 M

Once you know the hydrogen ion concentration, use the pH formula:

pH = -log₁₀[H⁺]

Substituting the concentration:

pH = -log₁₀(8.5 x 10^-3)

Evaluating the logarithm gives a pH of about 2.07. This tells you the solution is definitely acidic, because any pH below 7 is acidic under the usual 25 C convention. A pH near 2 indicates a fairly strong acidic environment compared with ordinary drinking water, which generally sits much closer to neutral.

Why HBr is treated as a complete dissociator

HBr belongs to the common list of strong acids taught in general chemistry. These acids ionize so extensively in water that their undissociated amount is negligible for many calculations. This is why you do not need an ICE table or an equilibrium expression for a standard textbook problem involving a moderate concentration of HBr. Instead, the concentration of the acid directly gives the concentration of hydrogen ions.

• HBr is a strong acid.
• It dissociates nearly 100 percent in water.
• Each HBr formula unit contributes one hydrogen ion.
• Therefore, [H+] equals the formal acid concentration.

Step by step calculation

1. Write the concentration in scientific notation: 8.5 x 10^-3 M.
2. Recognize that HBr is a strong monoprotic acid.
3. Set [H+] equal to 8.5 x 10^-3 M.
4. Apply the definition of pH: pH = -log10[H+].
5. Compute: pH = -log10(8.5 x 10^-3).
6. Round appropriately: pH = 2.07.

Breaking down the logarithm in a useful way

Many students find logarithms easier when they separate the number into its coefficient and exponent. Here is the same calculation using log rules:

log(8.5 x 10^-3) = log(8.5) + log(10^-3)

Since log(10^-3) = -3 and log(8.5) ≈ 0.929, then:

log(8.5 x 10^-3) ≈ 0.929 – 3 = -2.071

Now apply the negative sign in the pH formula:

pH = -(-2.071) = 2.071

Rounded to two decimal places, the pH is 2.07.

Comparison table: pH values for several strong acid concentrations

Strong acid concentration, M	Hydrogen ion concentration, M	Calculated pH	Interpretation
1.0 x 10^-1	1.0 x 10^-1	1.00	Very strongly acidic
1.0 x 10^-2	1.0 x 10^-2	2.00	Strongly acidic
8.5 x 10^-3	8.5 x 10^-3	2.07	Strongly acidic, slightly less acidic than 0.010 M
1.0 x 10^-3	1.0 x 10^-3	3.00	Acidic, but 10 times less concentrated in H+
1.0 x 10^-4	1.0 x 10^-4	4.00	Moderately acidic

What the answer means chemically

A pH of 2.07 means the solution contains a relatively high concentration of hydrogen ions compared with neutral water. Because the pH scale is logarithmic, each decrease of one pH unit corresponds to a tenfold increase in hydrogen ion concentration. So a solution at pH 2 is about 10 times more acidic than a solution at pH 3, and about 100 times more acidic than a solution at pH 4, assuming the comparison is made using hydrogen ion concentration.

In practical chemistry, this matters because reaction rates, corrosion behavior, solubility, enzyme activity, and material compatibility can all depend strongly on pH. Hydrobromic acid solutions are commonly handled only with proper laboratory controls because they are corrosive and can cause burns. Even though this calculator focuses on the mathematical side, the chemistry behind the number is tied directly to safety and reactivity.

Common mistakes when solving this problem

• Forgetting the negative exponent. The concentration is 8.5 x 10^-3, not 8.5 x 10^3.
• Ignoring that HBr is strong. You do not use a weak acid equilibrium setup here.
• Dropping the negative sign in the pH formula. pH is -log10[H+], not just log10[H+].
• Rounding too early. Keep extra digits until the end, then round the final pH.
• Confusing pH with pOH. This problem asks for pH directly from hydrogen ion concentration.

Comparison table: pH context from environmental sources

Government science sources commonly describe natural waters as occupying a much narrower pH range than laboratory acid solutions. The table below places the calculated HBr result into broader context using widely cited pH benchmarks.

Sample or benchmark	Typical pH range	Source type	How it compares with pH 2.07
Pure water at 25 C	7.0	Standard chemistry reference	The HBr solution is far more acidic
Most natural surface waters	About 6.5 to 8.5	EPA and USGS educational guidance	The HBr solution is several pH units lower and much more acidic
Acid rain, often cited	Below 5.6	Environmental chemistry education	pH 2.07 is far more acidic than typical acid rain
0.010 M strong acid solution	2.00	General chemistry calculation	Very close to the HBr result of 2.07

Why significant figures matter

In pH calculations, the number of decimal places in the pH usually reflects the number of significant figures in the concentration. The concentration 8.5 x 10^-3 has two significant figures, so the pH is generally reported with two digits after the decimal: 2.07. This reporting style helps maintain consistency between measured quantities and calculated quantities. If your instructor uses a different significant figure convention, follow the course rule, but in most cases 2.07 is the accepted final value.

Quick method for similar problems

If you see any strong monoprotic acid such as HCl, HBr, HI, or HNO3, and the concentration is given directly, the method is usually the same:

1. Assume complete dissociation.
2. Set [H+] equal to the acid molarity.
3. Use pH = -log10[H+].

This shortcut works because each mole of a monoprotic strong acid supplies one mole of hydrogen ions. Be more careful with polyprotic acids or very dilute solutions, where simplifying assumptions may need adjustment. For the present problem, however, the straightforward strong acid method is the correct one.

Trusted references and authority links

For readers who want to validate the chemistry or review the meaning of pH in scientific and environmental contexts, these authoritative sources are helpful:

• U.S. Environmental Protection Agency, What is pH?
• U.S. Geological Survey, pH and Water
• University of Washington Chemistry Department

Final answer

The pH of 8.5 x 10^-3 M HBr is:

pH = 2.07

That answer follows directly from the fact that HBr is a strong acid and dissociates essentially completely in water. Therefore, the hydrogen ion concentration equals the acid concentration, and the negative base 10 logarithm of that value gives the pH.