Calculate the OH and pH of 2.250 g of LiOH
Use this premium lithium hydroxide calculator to determine moles, hydroxide concentration, pOH, and pH for a LiOH solution. Enter the mass and final solution volume, then generate a chart and a step by step chemistry breakdown instantly.
LiOH pH Calculator
Enter your values and click Calculate OH and pH to see the full solution.
What this calculator solves
- Converts LiOH mass into moles using its molar mass.
- Calculates hydroxide concentration from the final solution volume.
- Finds pOH using the base 10 logarithm.
- Determines pH at 25 C using pH = 14 – pOH.
- Shows a chart to help visualize the chemical results.
Molar mass of LiOH = 6.94 + 16.00 + 1.008 = 23.948 g/mol
moles LiOH = mass / 23.948
[OH–] = moles / volume in liters
pOH = -log10[OH–]
pH = 14.00 – pOH
How to calculate the OH and pH of 2.250 g of LiOH
Calculating the hydroxide concentration and pH of a lithium hydroxide solution is a standard strong base problem in general chemistry. The key idea is that lithium hydroxide, written as LiOH, dissociates essentially completely in water under ordinary introductory chemistry conditions. That means every mole of LiOH yields one mole of hydroxide ions, OH–. Once you know how many moles of LiOH are present and what volume the solution occupies, you can determine the hydroxide molarity, then calculate pOH and finally pH.
If a problem only states 2.250 g of LiOH, you still need the final solution volume to calculate concentration and pH. In many textbook examples, the unstated or implied assumption is that the mass is dissolved and the total volume is brought to 1.000 L. This calculator uses that exact default, but also lets you enter any volume you want. That makes it useful for laboratory prep, homework checking, and solution analysis.
Step 1: Write the dissociation equation
Lithium hydroxide is a strong base, so its dissociation in water is written as:
LiOH(aq) → Li+(aq) + OH–(aq)
This tells you the mole ratio between LiOH and OH– is 1:1. If you have 0.0500 mol of LiOH, you get 0.0500 mol of hydroxide ions.
Step 2: Calculate the molar mass of LiOH
To convert grams to moles, use the atomic masses of lithium, oxygen, and hydrogen. A common general chemistry value is:
- Lithium = 6.94 g/mol
- Oxygen = 16.00 g/mol
- Hydrogen = 1.008 g/mol
So the molar mass of LiOH is:
23.948 g/mol = 6.94 + 16.00 + 1.008
Step 3: Convert 2.250 g LiOH into moles
Use the mole formula:
moles = mass / molar mass
Substitute the known values:
moles LiOH = 2.250 g / 23.948 g/mol = 0.09395 mol
Because LiOH produces hydroxide in a 1:1 ratio, the moles of OH– are also:
moles OH– = 0.09395 mol
Step 4: Find the hydroxide concentration
Concentration is moles per liter:
[OH–] = moles / volume
If the final solution volume is 1.000 L, then:
[OH–] = 0.09395 mol / 1.000 L = 0.09395 M
This is the hydroxide molarity. If your volume is smaller than 1 liter, the concentration will be higher. If your volume is larger, the concentration will be lower. That is why volume matters so much in pH calculations.
Step 5: Calculate pOH
The pOH is defined as:
pOH = -log10[OH–]
Substitute the hydroxide concentration:
pOH = -log10(0.09395) ≈ 1.03
A lower pOH means a more basic solution. Since 0.09395 M is a relatively strong hydroxide concentration, the pOH is close to 1.
Step 6: Convert pOH into pH
At 25 C, the standard relationship is:
pH + pOH = 14.00
Therefore:
pH = 14.00 – 1.03 = 12.97
So, for the default case of dissolving 2.250 g of LiOH in enough water to make 1.000 L of solution, the answer is:
- [OH–] = 0.09395 M
- pOH = 1.03
- pH = 12.97
Why LiOH is treated as a strong base
Introductory acid base chemistry classifies alkali metal hydroxides like LiOH, NaOH, and KOH as strong bases because they dissociate almost completely in water. This simplifies the problem significantly. For weak bases, you would need an equilibrium constant, such as Kb, and an ICE table. For lithium hydroxide, you generally do not need equilibrium algebra for basic pH exercises in dilute to moderate solution ranges. The stoichiometric conversion from LiOH to OH– is enough.
| Quantity | Formula Used | Value for 2.250 g LiOH in 1.000 L | Unit |
|---|---|---|---|
| Molar mass of LiOH | 6.94 + 16.00 + 1.008 | 23.948 | g/mol |
| Moles of LiOH | 2.250 / 23.948 | 0.09395 | mol |
| Moles of OH– | 1:1 ratio with LiOH | 0.09395 | mol |
| Hydroxide concentration | 0.09395 / 1.000 | 0.09395 | M |
| pOH | -log(0.09395) | 1.027 | unitless |
| pH | 14.00 – 1.027 | 12.973 | unitless |
How solution volume changes the answer
A common mistake is to compute moles correctly but skip the volume step. The same 2.250 g sample of LiOH will produce very different pH values depending on dilution. Here are several realistic examples using the same amount of LiOH but different final volumes. This table shows why concentration, not just mass, determines pH.
| Mass LiOH | Final Volume | [OH–] | pOH | pH at 25 C |
|---|---|---|---|---|
| 2.250 g | 0.100 L | 0.9395 M | 0.027 | 13.973 |
| 2.250 g | 0.250 L | 0.3758 M | 0.425 | 13.575 |
| 2.250 g | 0.500 L | 0.1879 M | 0.726 | 13.274 |
| 2.250 g | 1.000 L | 0.09395 M | 1.027 | 12.973 |
| 2.250 g | 2.000 L | 0.04697 M | 1.328 | 12.672 |
Real chemistry context for lithium hydroxide
Lithium hydroxide is a strong inorganic base that appears in analytical chemistry, battery materials work, industrial processing, and carbon dioxide scrubbing discussions. In water, its hydroxide ion controls the basicity of the solution. Because pH is logarithmic, even modest changes in concentration can shift pH noticeably. In concentrated basic solutions, pH values can approach 14 under the idealized 25 C classroom convention.
From a practical standpoint, LiOH is corrosive and should be handled with proper protective equipment. In laboratory conditions, students often calculate pH before preparing the solution so they know how strongly basic it will be. This can inform glove choice, spill procedures, waste handling, and dilution planning.
Common mistakes students make
- Using mass directly as concentration. Grams are not molarity. You must first convert to moles, then divide by liters.
- Forgetting the volume. pH cannot be determined from mass alone unless the final volume is known or assumed.
- Using the wrong molar mass. Always verify the formula and the atomic masses used.
- Confusing pH and pOH. For bases, calculate hydroxide concentration first, then pOH, then pH.
- Ignoring the 1:1 dissociation ratio. One mole of LiOH gives one mole of OH–.
Authority sources for deeper study
If you want to verify the chemistry framework behind pH, hydroxide concentration, and atomic mass data, consult these authoritative educational and government resources:
- LibreTexts Chemistry educational resource
- NIST atomic weights and relative atomic masses
- U.S. EPA overview of acidic and basic substances
- University of Wisconsin chemistry resources
Worked example summary
Let us summarize the full solution one more time in a clean sequence. Start with 2.250 g LiOH. Divide by the molar mass, 23.948 g/mol, to get 0.09395 mol LiOH. Because LiOH is a strong base with a 1:1 ion ratio, you also have 0.09395 mol OH–. If the total solution volume is 1.000 L, then [OH–] = 0.09395 M. Taking the negative log gives pOH = 1.027. Finally, subtract from 14.00 to get pH = 12.973.
That means the solution is strongly basic, as expected for a dissolved alkali metal hydroxide. If your homework or lab prompt uses a different volume, simply replace the 1.000 L term with the actual final volume. The calculator above automates that step and updates the chart in real time.
Final answer for the default setup
For 2.250 g of LiOH dissolved to make 1.000 L of solution at 25 C:
- Moles of LiOH = 0.09395 mol
- [OH–] = 0.09395 M
- pOH = 1.03
- pH = 12.97