Calculate the Weight of NaH2PO4
A professional tool for chemistry and laboratory preparation involving Sodium Dihydrogen Phosphate.
Anhydrous (NaH2PO4) – 119.98 g/mol
Monohydrate (NaH2PO4 · H2O) – 137.99 g/mol
Dihydrate (NaH2PO4 · 2H2O) – 156.01 g/mol
Select the specific form of the chemical reagent you are using.
Molarity & Volume (Prepare Solution)
Fixed Number of Moles
Choose how you want to derive the required mass.
Unit: M (mol/L)
Please enter a valid positive number.
mL
L
Amount of solution to prepare.
Please enter a valid positive number.
Unit: mol
Please enter a valid positive number.
Required Weight of NaH2PO4
0.00
g
Molar Mass Used:
119.98 g/mol
Total Moles Required:
0.000 mol
Formula Weight (mg):
0.00 mg
Mass (g) = Molarity (mol/L) × Volume (L) × Molar Mass (g/mol)
Composition Breakdown
Figure 1: Mass contribution by element in the selected NaH2PO4 form.
Stoichiometry Reference Table
| Hydration Form | Molar Mass (g/mol) | Mass for 1 mol (g) |
|---|---|---|
| Anhydrous (NaH2PO4) | 119.98 | 119.98 |
| Monohydrate (· H2O) | 137.99 | 137.99 |
| Dihydrate (· 2H2O) | 156.01 | 156.01 |
What is NaH2PO4 (Sodium Dihydrogen Phosphate)?
Sodium Dihydrogen Phosphate (NaH2PO4), also known as monosodium phosphate (MSP), is an inorganic compound of sodium with a dihydrogen phosphate anion. It is one of several sodium phosphates widely used in industrial applications, food processing, and academic laboratories. When you need to calculate the weight of NaH2PO4, you are typically preparing a buffer solution, often in conjunction with disodium phosphate (Na2HPO4).
This chemical typically exists in three primary forms depending on the water content in its crystal lattice: anhydrous (no water), monohydrate (one water molecule), and dihydrate (two water molecules). Correctly identifying the form on your reagent bottle is critical because the presence of water molecules significantly alters the molecular weight, affecting the mass required to achieve a specific molarity.
This calculator is designed for lab technicians, students, and researchers who need precise mass calculations for preparing phosphate buffers or standard solutions.
NaH2PO4 Weight Formula and Mathematical Explanation
To accurately calculate the weight of NaH2PO4, we use the fundamental principles of stoichiometry. The core relationship connects mass, molar mass, and the amount of substance (moles).
The general formula is:
Mass (g) = Moles (mol) × Molar Mass (g/mol)
If you are preparing a solution from a target molarity and volume, the formula expands to:
Mass (g) = Molarity (mol/L) × Volume (L) × Molar Mass (g/mol)
Variables Breakdown
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| Mass (m) | Physical weight to measure | Grams (g) | 0.1g – 1000g |
| Molarity (M) | Concentration of solution | Moles/Liter (M) | 0.01M – 2.0M |
| Volume (V) | Total liquid amount | Liters (L) | 0.1L – 5L |
| MW (Molar Mass) | Weight of 1 mole of substance | g/mol | 119.98 – 156.01 |
Table 2: Key variables used in the NaH2PO4 mass calculation.
Practical Examples (Real-World Use Cases)
Example 1: Preparing a 0.5M Phosphate Buffer Stock
A researcher needs to prepare 500 mL of a 0.5 M solution using Anhydrous NaH2PO4.
Inputs:
- Concentration: 0.5 mol/L
- Volume: 0.5 L (500 mL)
- Molar Mass (Anhydrous): 119.98 g/mol
Mass = 0.5 × 0.5 × 119.98 = 29.995 grams.
Interpretation: The researcher must weigh roughly 30g of the powder and dissolve it in water to reach a final volume of 500 mL.
Example 2: Using the Monohydrate Form
A student finds a bottle labeled "Sodium Dihydrogen Phosphate Monohydrate" and needs 2 moles for a reaction.
Inputs:
- Target Amount: 2 moles
- Form: Monohydrate (NaH2PO4 · H2O)
- Molar Mass: 137.99 g/mol
Mass = 2 × 137.99 = 275.98 grams.
Interpretation: Because the monohydrate contains water, the mass required is higher than if the anhydrous form were used (which would have been approx 240g).
How to Use This NaH2PO4 Calculator
- Select Hydration State: Check your reagent bottle. Is it Anhydrous, Monohydrate, or Dihydrate? Select the matching option to ensure the correct molar mass is used.
- Choose Calculation Basis: If you are making a liquid solution, choose "Molarity & Volume". If you just need a specific chemical amount for a reaction, choose "Fixed Number of Moles".
- Enter Values: Input your desired concentration (M) and volume (mL/L), or the number of moles.
- Read Results: The primary result is the weight in grams you need to measure on your balance.
Key Factors That Affect NaH2PO4 Results
- Hydration State: This is the most critical factor. Using the anhydrous mass for a monohydrate chemical will result in a solution that is too dilute.
- Purity of Reagent: Commercial chemicals are rarely 100% pure. If your reagent is 98% pure, you may need to divide the calculated mass by 0.98 to get the actual weighing amount.
- Temperature: While mass doesn't change with temperature, the volume of water does. Prepare solutions at the temperature they will be used (usually room temperature, 20-25°C).
- Hygroscopic Nature: Anhydrous NaH2PO4 is hygroscopic (absorbs moisture from air). If left open, it gains weight, potentially skewing measurements.
- Buffer pH Adjustment: Simply dissolving NaH2PO4 gives an acidic pH (around 4.5). To achieve a neutral pH (7.4), you usually mix it with Na2HPO4 or add NaOH. This calculator only gives the mass of the starting salt.
- Solubility Limits: Ensure your target molarity does not exceed the solubility limit of the salt in water (approx 6-7 M at room temp), otherwise it will not dissolve completely.
Frequently Asked Questions (FAQ)
Q: What is the molecular weight of NaH2PO4?
A: The anhydrous form is approx 119.98 g/mol. The monohydrate is 137.99 g/mol, and the dihydrate is 156.01 g/mol.
Q: Can I substitute Monohydrate for Anhydrous?
A: Yes, but you must adjust the weight. Multiply the anhydrous weight by (137.99 / 119.98) to get the equivalent monohydrate weight.
Q: What is NaH2PO4 used for?
A: It is primarily used as a buffering agent, a leavening agent in baking, and a phosphate source in fertilizers.
Q: Why is my solution cloudy?
A: This might indicate contaminants in the water or that you have exceeded the solubility limit. Always use deionized water.
Q: How does this differ from Na2HPO4?
A: NaH2PO4 is monosodium (one Na, acidic). Na2HPO4 is disodium (two Na, basic). They are often combined to make neutral phosphate buffers.
Q: Does temperature affect the weighing process?
A: Balances can drift with temperature changes, but physically the mass of the salt is constant. Volume measurements for molarity are temperature-dependent.
Q: How accurate is this calculator?
A: It uses standard atomic weights. For ultra-precision analytical chemistry, ensure you use the exact atomic weights specified by your governing body (e.g., IUPAC).
Q: Is NaH2PO4 toxic?
A: It is generally considered safe (GRAS) for food use but can be an irritant in pure powder form. Always wear PPE in the lab.
Related Tools and Internal Resources
- Molarity Calculator – General tool for calculating molarity for any compound.
- Phosphate Buffer Calculator – Calculate mixing ratios for specific pH levels.
- Molecular Weight Search – Find the molar mass of other common lab chemicals.
- Laboratory Solution Preparation Guide – Best practices for dissolving salts and adjusting pH.
- Na2HPO4 Weight Calculator – Calculate mass for the disodium phosphate counterpart.
- Serial Dilution Calculator – Plan your dilution series accurately.