CuSO4·5H2O Molar Mass Calculator and Formula

The molar mass calculator for CuSO4·5H2O (copper(II) sulfate pentahydrate) adds the atomic masses of its copper, sulfur, oxygen, and hydrogen atoms. Enter the number of moles to calculate the corresponding mass in grams; the formula also shows the compound’s molar mass.

Formula

The molar mass is the sum of the atomic masses of every atom represented in the chemical formula. For copper(II) sulfate pentahydrate:

CuSO4·5H2O: M = Cu + S + 4O + 5(2H + O)

Using commonly rounded standard atomic masses in grams per mole:

• Copper (Cu): 63.546 g/mol
• Sulfur (S): 32.06 g/mol
• Oxygen (O): 15.999 g/mol
• Hydrogen (H): 1.008 g/mol

Therefore, M = 63.546 + 32.06 + 4(15.999) + 5[2(1.008) + 15.999] = 249.68 g/mol when rounded to two decimal places. In the calculator, M is the molar mass in g/mol, and moles is the amount of CuSO4·5H2O in mol. The mass formula is m = n × M, where m is mass in grams and n is amount in moles. The calculator’s mass output uses 249.68 g/mol, rounded to two decimal places.

Worked Example

With the default amount of 1 mol, the calculation is:

1. Find the formula mass: 63.546 + 32.06 + 4(15.999) + 5[2(1.008) + 15.999] = 249.68 g/mol, rounded to two decimal places.
2. Multiply amount by molar mass: 1 mol × 249.68 g/mol = 249.68 g.

The calculator therefore returns a mass of 249.68 g and a molar mass of 249.68 g/mol. The units cancel in the mass calculation: mol × g/mol = g.

What the Formula Means

CuSO4·5H2O is copper(II) sulfate pentahydrate. The dot indicates that five water molecules are associated with each formula unit of copper(II) sulfate in the crystalline hydrate. It is not a multiplication sign between unrelated compounds, and the five waters must be included when calculating the molar mass of this hydrated form.

Count the atoms in the entire formula: one Cu, one S, four O in the sulfate group, and five water molecules, each with two H and one O. That gives 1 Cu, 1 S, 9 O, and 10 H in total. The four sulfate oxygens and five water oxygens are both included, making nine oxygen atoms altogether.

The formula’s molar mass is an amount-per-mole value, not the mass of one crystal or one formula unit. One mole contains Avogadro’s number of formula units; multiplying the amount in moles by grams per mole gives the sample mass in grams.

When to Use This Calculator

Use the calculator when you know an amount in moles and want its equivalent mass of the pentahydrate. For example, entering 0.50 mol gives 124.84 g using the calculator’s rounded molar mass. It can also help check a conversion from grams to moles by rearranging the same relationship: n = m ÷ M.

For a sample whose mass is already known, divide grams by 249.68 g/mol. A 10.00 g sample corresponds to about 0.04005 mol using the calculator’s value. If your task asks for the number of moles rather than mass, perform that division; the calculator’s input is moles, so it does not directly accept a mass as its input.

Hydrate Versus Anhydrous Copper Sulfate

A frequent source of error is using the molar mass for anhydrous copper(II) sulfate, CuSO4, when the material is CuSO4·5H2O. Anhydrous CuSO4 has a molar mass of about 159.61 g/mol. The pentahydrate is about 249.68 g/mol because it includes five water molecules per formula unit.

Those values answer different questions. Use 249.68 g/mol for the pentahydrate formula as written; use about 159.61 g/mol for anhydrous CuSO4. If a hydrate loses water, its mass and chemical form change. Do not assume that a sample is anhydrous merely because it has been stored or handled; use the identity and condition specified by the material or experiment.

Precision, Units, and Common Errors

• Keep the hydrate water: omitting 5H2O underestimates the molar mass substantially.
• Count oxygen carefully: there are four O atoms in SO4 and five more in the waters, for nine total.
• Match the formula: CuSO4·5H2O is not the same as a different hydrate or anhydrous CuSO4.
• Track units: molar mass is in g/mol; mass is in g. Convert kilograms to grams before using the formula if needed (1 kg = 1,000 g).
• Round only at the end: atomic masses may be listed with slightly different precision in reference tables. The calculator uses 249.68 g/mol, so a result can differ slightly from one computed with more digits.

The number 249.68 g/mol is a practical rounded value based on standard atomic weights. Exact reported values can vary slightly with the atomic-weight table and rounding convention. For routine stoichiometric calculations, use the precision required by the problem or laboratory instructions; do not imply more precision in the final answer than the input data supports.

Frequently Asked Questions

What is the molar mass of CuSO4·5H2O?
The molar mass of copper(II) sulfate pentahydrate is approximately 249.68 g/mol using commonly rounded atomic masses.

How do I calculate the mass from moles?
Multiply the amount in moles by 249.68 g/mol. For example, 0.25 mol × 249.68 g/mol = 62.42 g.

Why is the molar mass higher than CuSO4 alone?
The pentahydrate includes five H2O molecules per formula unit. Their hydrogen and oxygen atoms add about 90.08 g/mol to the mass of anhydrous CuSO4.

How many oxygen atoms are in CuSO4·5H2O?
There are nine: four in the sulfate group and one in each of the five water molecules.

Is CuSO4·5H2O the same as CuSO4?
No. CuSO4·5H2O is the pentahydrate, while CuSO4 without the dot-water notation is anhydrous copper(II) sulfate. Their molar masses are different.

What is the mass of one mole of the pentahydrate?
One mole has a mass of approximately 249.68 g. This is the meaning of its molar mass, expressed as grams per mole.

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in moles | Amount of CuSO4·5H2O | mol | 1 | 0
out mass | Mass of CuSO4·5H2O | g | moles * 249.68 | 2
out molarmass | Molar mass | g/mol | 249.68 | 2