pH 计算器 — 计算 pH、pOH & 离子浓度
Enter any pH value, hydrogen ion concentration [H⁺], or pOH to instantly calculate all four related quantities. Uses the formula pH = −log₁₀[H⁺] and the relationship pH + pOH = 14. Results include the solution nature (acidic, neutral, or basic), plus a visual position on the 0–14 pH scale.
pH Calculator
Valid range: 0 to 14
Frequently Asked Questions
什么是pH值？
pH是用来衡量水溶液酸碱性的对数刻度，定义为氢离子浓度[H⁺]的负对数：pH = -log₁₀[H⁺]。pH尺度从0到14：pH < 7为酸性，pH = 7为中性（纯水），pH > 7为碱性（碱性）。由于是对数尺度，pH每差1单位，氢离子浓度相差10倍。
如何从氢离子浓度计算pH？
pH = -log₁₀[H⁺]，其中[H⁺]为氢离子摩尔浓度（mol/L）。例如：[H⁺] = 1×10⁻³ mol/L：pH = -log(10⁻³) = 3（酸性）；[H⁺] = 1×10⁻⁷ mol/L：pH = 7（中性）；[H⁺] = 1×10⁻¹¹ mol/L：pH = 11（碱性）。
pH和pOH有何关系？
在25°C时：pH + pOH = 14（水的离子积常数Kw = 10⁻¹⁴）；pOH = -log[OH⁻]。知道pH即可求pOH：pH 3 → pOH = 11；pH 11 → pOH = 3。[H⁺][OH⁻] = 10⁻¹⁴，因此pH越低（酸性越强），OH⁻浓度越低。
常见物质的pH值是多少？
常见物质pH值：盐酸（浓）0-1；胃酸1.5-3.5；柠檬汁2-3；醋3-4；番茄汁4-4.5；咖啡4.5-5；牛奶6.5-6.8；纯水7.0；血液7.35-7.45；小苏打8.3；海水8.1-8.4；肥皂9-10；家用漂白水10-12；氨水11-12；NaOH（稀溶液）13-14。
如何准确测量pH？
pH测量方法：pH试纸：价格低廉，精度±0.5单位，适合快速粗测；数字pH计：精度0.01单位，需定期用标准缓冲液（pH 4.0、7.0、10.0）校准；光学pH传感器：用于工业和连续监测；比色指示剂：特定pH范围变色，如酚酞（8.2-10变色）、石蕊（4.5-8.3变色）。
为什么血液pH必须保持在7.35-7.45？
血液pH必须严格控制在7.35-7.45（轻微碱性）：pH < 7.35为酸中毒（呼吸性或代谢性）；pH > 7.45为碱中毒。偏离正常范围会影响蛋白质功能、酶活性和氧气输送（pH影响血红蛋白与O₂的结合）。pH < 7.0或> 7.8可危及生命。身体通过缓冲系统（碳酸氢盐、磷酸盐、蛋白质）维持pH恒定。
pH缓冲溶液是什么？
缓冲溶液是能抵抗pH变化的溶液，由弱酸及其共轭碱（或弱碱及其共轭酸）组成。缓冲能力在pH = pKa时最强（Henderson-Hasselbalch方程：pH = pKa + log([A⁻]/[HA])）。常用缓冲体系：醋酸/醋酸钠（pH 3.6-5.6）；磷酸盐（pH 5.8-8.0）；碳酸氢盐（生理缓冲系统）；Tris（生化实验常用，pH 7.0-9.0）。
土壤pH如何影响植物生长？
土壤pH影响营养元素的可利用性：大多数蔬菜和草坪草最适pH 6.0-7.0；蓝莓、杜鹃需pH 4.5-5.5（酸性土）；pH < 5.5时铝、锰溶解度增加，可能有毒；pH > 7.5时铁、锌、锰缺乏（不溶）。调节方法：降低pH加硫磺粉或硫酸铵；升高pH加石灰石（碳酸钙）或熟石灰（氢氧化钙）。
pH Formula
pH is a logarithmic scale that measures the acidity or basicity of an aqueous solution. It is defined as the negative base-10 logarithm of the hydrogen ion concentration [H⁺]. Solutions with pH below 7 are acidic, pH 7 is neutral (pure water at 25 °C), and pH above 7 are basic (alkaline).
How to Calculate pH
pH = −log₁₀[H⁺]
[H⁺] = 10⁻ᵖᴴ
The logarithmic nature means each whole-number change in pH represents a 10× change in [H⁺]. A pH of 3 is 10 times more acidic than pH 4, and 100 times more acidic than pH 5.
pH, pOH, [H⁺], and [OH⁻] Relationships
pH + pOH = 14
pOH = −log₁₀[OH⁻]
[H⁺] × [OH⁻] = 10⁻¹⁴ (Kw at 25 °C)
At 25 °C, the ion product of water (Kw) equals 1 × 10⁻¹⁴ mol²/L². This constant ties together all four quantities — knowing any one of pH, pOH, [H⁺], or [OH⁻] determines all the others.
- pOH = 14 − pH
- [OH⁻] = 10⁻ᵖᴼᴴ = Kw / [H⁺]
pH Scale — Common Substances
The pH scale ranges from 0 (most acidic) to 14 (most basic). Here are approximate pH values for everyday substances.
| Substance | Approx. pH | Nature |
|---|---|---|
| Battery acid (H₂SO₄) | 0 | Strongly acidic |
| Gastric acid (stomach) | 1.5 – 2 | Strongly acidic |
| Lemon juice / vinegar | 2 – 3 | Acidic |
| Orange juice / soda | 3 – 4 | Acidic |
| Black coffee | 5 | Weakly acidic |
| Rainwater / urine | 5.5 – 6.5 | Weakly acidic |
| Pure water (25 °C) | 7 | Neutral |
| Blood / seawater | 7.4 – 8.3 | Weakly basic |
| Baking soda (NaHCO₃) | 8.3 | Weakly basic |
| Ammonia solution | 11 | Basic |
| Bleach (NaOCl) | 12 – 13 | Strongly basic |
| Sodium hydroxide (NaOH) | 14 | Strongly basic |
How to Use This Calculator
- Choose your input mode: pH, [H⁺] Concentration, or pOH.
- Enter the known value in the input field.
- The calculator instantly computes all four related values: pH, pOH, [H⁺], and [OH⁻].
- A color-coded badge shows whether the solution is acidic, neutral, or basic.
- The visual pH scale bar shows your value's position on the 0–14 scale.
Worked Examples
Example 1: Find [H⁺] from pH
Given: pH = 3. Find [H⁺].
[H⁺] = 10⁻³ = 0.001 mol/L
pOH = 14 − 3 = 11; [OH⁻] = 10⁻¹¹ mol/L
Example 2: Find pH from concentration
Given: [H⁺] = 2.5 × 10⁻⁵ mol/L. Find pH.
pH = −log₁₀(2.5 × 10⁻⁵) = 4.60
Example 3: Find pH from pOH
Given: pOH = 4. Find pH.
pH = 14 − 4 = 10 (basic solution)
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