Calculate The Ph Of A 0.0150 M Hno3 Solution

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Use this interactive acid calculator to determine pH, hydrogen ion concentration, pOH, hydroxide ion concentration, and acid strength interpretation for nitric acid solutions. The default setup matches the exact problem: a 0.0150 M HNO3 solution at 25 degrees Celsius.

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How to Calculate the pH of a 0.0150 M HNO3 Solution

To calculate the pH of a 0.0150 M HNO3 solution, the core chemistry idea is that nitric acid is a strong acid. In introductory and most general chemistry settings, strong acids are assumed to dissociate completely in water. That means every mole of HNO3 contributes essentially one mole of hydrogen ions, more precisely hydronium ions in aqueous solution. Because nitric acid is monoprotic, the stoichiometry is one-to-one: one acid molecule gives one hydrogen ion equivalent. Therefore, for a 0.0150 M HNO3 solution, the hydrogen ion concentration is taken as 0.0150 M, and pH is found from the logarithmic definition pH = -log10[H+].

Applying that formula directly gives:

pH = -log10(0.0150) = 1.8239, which rounds to 1.824 when reported to three decimal places.

This result tells you the solution is strongly acidic. A pH well below 7 indicates a high concentration of hydrogen ions relative to neutral water. Because pH is logarithmic, even what looks like a small concentration such as 0.0150 M corresponds to a very acidic environment compared with everyday water samples. This is why nitric acid must be handled with proper laboratory safety procedures, including splash protection, gloves, and ventilation where required.

Why HNO3 Is Treated as a Strong Acid

Nitric acid, HNO3, belongs to the common list of strong acids typically memorized in general chemistry. In dilute aqueous solutions, it dissociates essentially completely:

HNO3(aq) → H+(aq) + NO3-(aq)

Since it dissociates nearly 100%, the initial molarity of HNO3 becomes the equilibrium hydrogen ion concentration for standard classroom calculations. That is the reason this problem is simpler than pH problems involving weak acids such as acetic acid or hydrofluoric acid, where an equilibrium constant is needed.

• HNO3 is a strong acid.
• It is monoprotic, so it donates one proton per molecule.
• Its concentration directly determines [H+].
• No ICE table is needed for this standard calculation.

Step-by-Step Solution

1. Write the known concentration: HNO3 = 0.0150 M
2. Recognize acid behavior: HNO3 is a strong monoprotic acid
3. Set hydrogen ion concentration: [H+] = 0.0150 M
4. Apply the pH formula: pH = -log10[H+]
5. Substitute the value: pH = -log10(0.0150)
6. Calculate: pH = 1.8239
7. Round appropriately: pH ≈ 1.824

If your instructor emphasizes logarithm rules and significant figures, note that the number of decimal places in the pH often reflects the number of significant figures in the concentration. Since 0.0150 has three significant figures, many chemistry courses would report the pH as 1.824.

What About pOH and [OH-]?

Once pH is known, you can also calculate pOH and hydroxide ion concentration. At 25 degrees Celsius, the familiar relationship is:

pH + pOH = 14.00

So for this nitric acid solution:

• pH = 1.824
• pOH = 14.000 – 1.824 = 12.176

Then calculate hydroxide ion concentration with:

[OH-] = 10^(-pOH)

This gives:

[OH-] ≈ 6.67 × 10^-13 M

That very small hydroxide ion concentration is exactly what you would expect for a strongly acidic solution. The hydrogen ion concentration is many orders of magnitude larger than the hydroxide ion concentration.

Comparison Table: Strong Acids and Their pH at Selected Concentrations

The table below shows how pH changes for a strong monoprotic acid when concentration changes. These values are calculated from pH = -log10(C) under the assumption of complete dissociation.

Acid Concentration (M)	Hydrogen Ion Concentration [H+] (M)	Calculated pH	Acidic Interpretation
1.0	1.0	0.000	Extremely acidic
0.100	0.100	1.000	Very strongly acidic
0.0150	0.0150	1.824	Strongly acidic
0.0100	0.0100	2.000	Strongly acidic
0.00100	0.00100	3.000	Acidic
0.000100	0.000100	4.000	Moderately acidic

This comparison highlights a key fact about the pH scale: it is logarithmic, not linear. A tenfold change in hydrogen ion concentration changes pH by exactly one unit. That is why the shift from 0.100 M to 0.0100 M corresponds to pH moving from 1 to 2.

Common Mistakes When Solving This Problem

1. Treating HNO3 as a weak acid

This is the most common error. Nitric acid is not solved with a Ka table in basic pH problems. It is classified as a strong acid, so complete dissociation is assumed.

2. Forgetting it is monoprotic

HNO3 donates one proton per formula unit. If the acid were sulfuric acid, H2SO4, the stoichiometry discussion would be different because there are two ionizable hydrogens, though the second dissociation is not as straightforward in all contexts.

3. Entering the logarithm incorrectly

Remember that pH is the negative logarithm of the hydrogen ion concentration. If you compute log10(0.0150), you get a negative number, and the leading minus sign turns pH into a positive value.

4. Reporting too few or too many digits

For classroom chemistry, 0.0150 M usually supports reporting pH to three decimal places, so 1.824 is a good final answer.

How Strongly Acidic Is pH 1.824?

A pH of 1.824 is far more acidic than ordinary environmental water. For context, pure water at 25 degrees Celsius is pH 7.00. Moving from pH 7.00 to pH 1.824 means the hydrogen ion concentration is dramatically higher. Because every pH unit corresponds to a tenfold change, the difference of 5.176 pH units means the nitric acid solution has approximately 10^5.176 times the hydrogen ion concentration of neutral water. That is roughly 150,000 times greater in terms of [H+].

Reference Substance or Water Type	Typical pH Range	Comparison to 0.0150 M HNO3	Notes
Pure water at 25 degrees C	7.00	Much less acidic	Neutral benchmark used in general chemistry
Typical rain	About 5.0 to 5.6	Far less acidic	Natural rain is mildly acidic due to dissolved gases
Acid rain threshold	Below 5.6	Far less acidic	Frequently cited environmental benchmark
Gastric acid	About 1.5 to 3.5	Comparable range	Highly acidic biological fluid
0.0150 M HNO3	1.824	Reference value	Strong acid, complete dissociation assumed

Deeper Chemistry Context

In a more advanced chemistry course, you may learn that concentrations and activities are not always identical, especially at higher ionic strengths. However, for a general chemistry problem asking you to calculate the pH of a 0.0150 M HNO3 solution, the standard accepted approach is to use concentration directly. At this concentration, the textbook answer is based on complete dissociation and the idealized pH expression.

You may also encounter the distinction between writing H+ and H3O+. Strictly speaking, protons in water are associated with water molecules, so hydronium, H3O+, is the more chemically accurate representation. In most pH formulas, however, chemists use [H+] as a shorthand for the effective hydronium ion concentration.

Formula Summary

• Strong monoprotic acid: [H+] = acid molarity
• pH formula: pH = -log10[H+]
• pOH relationship at 25 degrees C: pOH = 14.00 – pH
• Hydroxide concentration: [OH-] = 10^(-pOH)

Worked Example Using the Exact Problem

Suppose a student is asked, “Calculate the pH of a 0.0150 M HNO3 solution.” The solution process should look like this:

1. HNO3 is a strong acid.
2. Because it is monoprotic, 0.0150 M HNO3 gives 0.0150 M H+.
3. pH = -log10(0.0150).
4. pH = 1.8239.
5. Rounded answer: pH = 1.824.

If the question asks for supporting quantities, you can continue:

• [H+] = 0.0150 M
• pOH = 12.176
• [OH-] = 6.67 × 10^-13 M

When Would the Approach Change?

This direct calculation approach changes under a few circumstances:

• If the acid is weak, you must use Ka and equilibrium methods.
• If the problem involves dilution, first calculate the new molarity using M1V1 = M2V2.
• If the problem is at a temperature where pKw is not 14.00, pOH values shift slightly.
• If the solution is highly concentrated, activity effects may matter in advanced treatments.

Authoritative Chemistry References

For more background on acid-base chemistry, pH definitions, and water chemistry, consult these reliable sources:

• U.S. Environmental Protection Agency: What is Acid Rain?
• LibreTexts Chemistry, widely used in university instruction
• U.S. Geological Survey: pH and Water

Final Answer

The pH of a 0.0150 M HNO3 solution is 1.824 at 25 degrees Celsius, assuming complete dissociation as a strong monoprotic acid.