Calculate The Ph Of A 0.75 M Solution Of Nabr

Use this premium chemistry calculator to determine the ideal pH of sodium bromide solution, understand why the answer is neutral in standard general chemistry, and visualize how pH behaves across concentration changes for a salt made from a strong acid and a strong base.

NaBr pH Calculator

Visualization

7.00 Calculated pH

Neutral Solution character

Na+, Br- Major dissolved ions

Chart uses an ideal model. In advanced physical chemistry, high ionic strength can cause activity effects, so measured pH may deviate slightly from 7.00.

Expert Guide: How to Calculate the pH of a 0.75 m Solution of NaBr

To calculate the pH of a 0.75 m solution of NaBr, the key idea is not the size of the concentration but the acid-base nature of the ions that appear after dissolution. Sodium bromide, written as NaBr, is a salt formed from sodium hydroxide and hydrobromic acid. Sodium hydroxide is a strong base, and hydrobromic acid is a strong acid. When a salt comes from a strong acid and a strong base, neither ion significantly reacts with water in a way that changes hydrogen ion concentration in a typical introductory chemistry treatment. As a result, the solution is considered neutral, so the pH is approximately 7.00 at 25 degrees C.

This often surprises students because the number 0.75 m looks large enough to matter. Concentration matters greatly for many acid-base systems, but for a neutral salt such as sodium bromide, concentration does not create acidity or basicity by itself under the ideal model. The dissolved ions simply separate in water:

NaBr(aq) → Na+(aq) + Br-(aq)

Neither sodium ion nor bromide ion hydrolyzes enough to shift the equilibrium of water in a meaningful way in general chemistry calculations. That is why the standard answer is:

pH of 0.75 m NaBr = 7.00 at 25 degrees C

Why NaBr Is Neutral in Water

To understand the calculation fully, you need to classify each ion:

• Na+ is the conjugate cation of NaOH, a strong base. Conjugate ions of strong bases are negligibly acidic.
• Br- is the conjugate base of HBr, a strong acid. Conjugate bases of strong acids are negligibly basic.
• Because neither ion reacts significantly with water, the solution remains essentially neutral.

In many textbook settings, this logic is enough to finish the problem. You do not need a Ka, Kb, ICE table, or equilibrium calculation. Instead, you identify the salt category correctly and apply acid-base rules.

Step-by-Step Method

1. Identify the dissolved species. NaBr dissociates completely into Na+ and Br-.
2. Ask whether the cation is acidic. Sodium ion comes from the strong base NaOH, so it is not acidic.
3. Ask whether the anion is basic. Bromide comes from the strong acid HBr, so it is not basic.
4. Conclude the solution is neutral. Since neither ion hydrolyzes appreciably, pH is governed by water only.
5. Apply standard neutral pH at 25 degrees C. The ideal answer is 7.00.

What Does 0.75 m Mean?

The symbol m means molality, not molarity. A 0.75 m solution contains 0.75 moles of solute per kilogram of solvent. That is different from molarity, which uses liters of solution. In many acid-base classroom problems involving neutral salts, this distinction does not change the ideal pH conclusion because the issue is ion hydrolysis, not simply concentration. However, in real laboratory work, molality and molarity differ, especially when solution density changes or when precise thermodynamic analysis matters.

So if the question is specifically, “calculate the pH of a 0.75 m solution of NaBr,” the right chemistry move is to recognize that NaBr is a neutral salt. The 0.75 m value tells you the solution is fairly concentrated, but concentration alone does not make NaBr acidic or basic under standard assumptions.

Comparison of Salt Types and Their pH Behavior

Students often do better when NaBr is compared with other salts. The table below shows how salt origin predicts pH behavior.

Salt Example	Parent Acid	Parent Base	Expected Aqueous Behavior	Typical Intro Chemistry pH Trend
NaBr	HBr, strong acid	NaOH, strong base	Neither ion hydrolyzes significantly	Near 7 at 25 degrees C
NH4Cl	HCl, strong acid	NH3, weak base	NH4+ acts as a weak acid	Below 7
CH3COONa	CH3COOH, weak acid	NaOH, strong base	CH3COO- acts as a weak base	Above 7
NH4CH3COO	Weak acid	Weak base	Depends on relative Ka and Kb	Can be below, above, or near 7

The Role of Water Autoionization

In a neutral solution at 25 degrees C, water self-ionizes slightly according to:

2H2O(l) ⇌ H3O+(aq) + OH-(aq)

The ion product of water is:

Kw = 1.0 × 10^-14 at 25 degrees C

In pure water and in an ideal neutral salt solution, the concentrations of hydronium and hydroxide are equal:

[H3O+] = [OH-] = 1.0 × 10^-7 M

Then:

pH = -log(1.0 × 10^-7) = 7.00

This is the numerical basis behind the conclusion that an ideal NaBr solution is neutral.

Real-World Measurements Versus Ideal Classroom Answers

In a more advanced treatment, especially for concentrated electrolyte solutions, chemists discuss activity rather than simple concentration. A 0.75 m sodium bromide solution has notable ionic strength. In practice, pH electrodes can read values slightly above or below 7 even when a solution is chemically “neutral” by the simple strong acid-strong base salt rule. This does not mean the introductory answer is wrong. It means the ideal model and the experimental thermodynamic model are not identical.

For classroom and many exam settings, the accepted answer remains 7.00 unless the instructor explicitly asks you to account for activity coefficients, ionic strength corrections, or non-ideal solution behavior.

Useful Reference Data

The next table summarizes the most relevant chemical facts for solving this problem correctly.

Quantity or Fact	Value or Description	Why It Matters
Salt	Sodium bromide, NaBr	Source compound being analyzed
Cation	Na+	Conjugate of strong base NaOH, so not appreciably acidic
Anion	Br-	Conjugate base of strong acid HBr, so not appreciably basic
Concentration given	0.75 m	Molality, meaning 0.75 mol solute per kg solvent
Neutral pH at 25 degrees C	7.00	Standard ideal answer used in general chemistry
Water ion product, Kw	1.0 × 10^-14	Defines neutral condition at 25 degrees C

Common Mistakes to Avoid

• Confusing molality with molarity. They are different concentration units, though both still lead to a neutral NaBr result in the ideal model.
• Assuming every dissolved salt changes pH. Only salts with ions derived from weak acids or weak bases usually require hydrolysis calculations.
• Thinking bromide is basic because it is an anion. Some anions are basic, but Br- is the conjugate base of a strong acid and is negligibly basic.
• Ignoring temperature. Neutral pH equals 7.00 only at 25 degrees C. At other temperatures, neutrality still means [H3O+] = [OH-], but the numeric pH may shift slightly.
• Overcomplicating the problem. For standard coursework, this is usually a classification problem, not a full equilibrium problem.

How This Problem Might Appear in Homework or Exams

Instructors often test this concept in one of several ways:

1. They may ask directly for the pH of a salt solution such as NaBr.
2. They may ask whether the solution is acidic, basic, or neutral.
3. They may present several salts and ask you to rank them by expected pH.
4. They may try to distract you with a large concentration value such as 0.75 m, 1.0 M, or even 2.0 M.

The winning strategy is always to classify the ions first. Once you see strong acid plus strong base, the answer becomes neutral under the usual assumptions.

Authoritative Chemistry References

For reliable supporting information on acid-base chemistry, solution behavior, and standard reference data, see these authoritative sources:

• NIST Chemistry WebBook
• LibreTexts Chemistry hosted by academic institutions
• U.S. Environmental Protection Agency chemistry resources

Final Answer

If you are solving this in a general chemistry context, the conclusion is straightforward:

The pH of a 0.75 m NaBr solution is 7.00 at 25 degrees C.

The reason is that sodium bromide is a salt of a strong acid and a strong base. Its ions, Na+ and Br-, do not significantly hydrolyze in water, so the solution remains neutral in the ideal model. If you move into advanced analytical or physical chemistry, you may discuss ionic strength and activities, but unless that is requested explicitly, the accepted answer is still neutral.

Educational note: this calculator is designed for standard chemistry instruction. It provides the idealized result used in most classroom settings for a neutral salt such as sodium bromide.