Mol Wt Of Sucrose

So You Need The Molecular Weight Of Sucrose

It is 342.30 grams per mole. That is the number you want most of the time, assuming you are using standard atomic weights from the periodic table. C12H22O11 breaks down to roughly 144.1 for carbon, 22.2 for hydrogen, and 176.0 for oxygen. Add them up and you get approximately 342.30 g/mol. Simple arithmetic. The tricky part is usually not the math. I used to calculate this by hand in early lab days before we had decent software. You write out the formula, look up each element's atomic weight, multiply by the subscript, and sum. That is still the method you should understand because spreadsheets and online calculators will happily give you the wrong number if you feed them bad input. Here is a scenario that cost me about three hours once. I was preparing a standard curve for HPLC analysis and needed sucrose solutions at specific molarities. I pulled a molecular weight value from an old SDS that listed 342.3, but it was rounded to one decimal. When I calculated the mass needed for a 50 mM solution in 250 mL, the difference seemed negligible until I ran the samples and the peak areas were off by nearly two percent across the board. The calibration line looked fine visually but the residuals told a different story. I recalculated using the full precision value of 342.2965 g/mol and everything aligned.

The takeaway is that rounding early compounds. If you are doing anything where precision matters above around four significant figures, keep all decimal places through the entire calculation and only round the final result. Another thing people miss is that sucrose can pick up water from the air. It is somewhat hygroscopic. If you are weighing out analytical grade sucrose that has been sitting in a jar for a while, the actual amount of pure sucrose in your weigh is slightly less than what the balance reads. A desiccator does help. Pre-drying at 60 degrees Celsius for a couple of hours before use was the workaround I settled on for work that needed tight tolerance, though honestly for most routine prep work leaving it in a properly sealed container is sufficient.

When The Number Changes Depending On What You Are Doing

The 342.30 figure assumes you are working with anhydrous sucrose. There are other forms to consider. In food science and beverage manufacturing, you might encounter invert sugar, which is a 1:1 mixture of glucose and fructose produced by hydrolyzing sucrose with acid or the enzyme invertase. The molecular weight of each monosaccharide is about 180.16 g/mol, so invert sugar is roughly half the molar mass per gram compared to intact sucrose. If a recipe or protocol calls for sucrose but you substitute invert sugar without adjusting for that difference, you will be off significantly. There is also sucrose octaacetate and other derivatized forms used in specialized applications. Their molecular weights are completely different and you should never assume they are interchangeable in molar calculations. For routine laboratory work, standard biochemical protocols, or formulation chemistry, the anhydrous value of 342.2965 g/mol is what you should use. Different sources may show slight variations depending on which atomic weight tables they reference. IUPAC publishes periodic updates and the differences are usually in the fourth or fifth decimal place, so unless you are working at the sub-millimole level, any value between 342.29 and 342.30 will serve you fine.

If you need a practical reference, the PubChem entry for sucrose lists 342.3 g/mol and the Sigma Aldrich product data sheet for analytical grade sucrose gives 342.30 g/mol. Those are reliable enough for everyday use. Just make sure the product specification matches your needs and check whether the material certificate notes any water content or lot-specific adjustments.