In order to calculate the molecular weight of a formula, you'll need to add up the atomic masses of each element present. Since there are 2 oxygen atoms, you would write. From the percentages given, use the procedure given in Example 6 to calculate the empirical formula of caffeine. The molecular weight can be calculated from the chemical formula by using standard values of the molecular weight of each atom. Given: molecular formula and mass of sample, Asked for: mass percentage of all elements and mass of one element in sample. So therefore X = 310.182. In science, weight is a force related to gravity and the mass of an object. However, they do associate in discrete ratios of ions. ", "Thank you so much for this wonderful explanation. [1] X For example, each chlorine atom contributes approximately 35.5 to the molecular weight. As a check, we can add the percentages together: \[ 57.14\% + 6.16\% + 9.52\% + 27.18\% = 100.00\% \]. The formula weight of a substance is the sum of the atomic weights of each atom in its chemical formula. These are defined below. This gives the amount of the atoms/molecules/compounds present in one mole of the substance. Step 4. Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. A We calculate the mass of each element in 1 mol of aspartame and the molar mass of aspartame, here to three decimal places: \[ 14 \,C (14 \, mol \, C)(12.011 \, g/mol \, C) = 168.154 \, g\], \[ 18 \,H (18 \, mol \, H)(1.008 \, g/mol \, H) = 18.114 \, g\], \[ 2 \,N (2 \, mol \, N)(14.007 \, g/mol \, N) = 28.014 \, g\], \[ +5 \,O (5 \, mol \, O)(15.999 \, g/mol \, O) = 79.995 \, g\], \[C_{14}H_{18}N_2O_5 \text {molar mass of aspartame} = 294.277 \, g/mol \]. Select the desired units for thermodynamic data: SI calorie-based; Select the desired type(s) of data: If the ratios are not integers, multiply all subscripts by the same number to give integral values. Each glucose contains six CH2O formula units, which gives a molecular formula for glucose of (CH2O)6, which is more commonly written as C6H12O6. Does this mean that the compound of interest contains a nonintegral number of atoms? 38.049 is the weight of glycerol backbone. **Atomic weight, and therefore molecular weight, are relative values and have no unit. Formula weight is a measurement used to identify how much a specific chemical compound weighs based on its formula. By definition, the molar mass has the units of grams per mole. In our carbon dioxide example, the mass of the single carbon atom is 12.011 amu. Then, count the atoms according to the molecular formula and write them next to the element’s name or symbol. Calculate molecular weight of hemoglobin. The molecular weight of a substance is the weight in atomic mass units of all the atoms in a given formula. Gas Constant (R) The constant that appears in the ideal gas equation (PV=nRT). Multiply each subscript in the empirical formula by the number of formula units to give the molecular formula. Here, M n is the number average molecular weight, N i is the number of molecules having M i weight in the polymer sample, and M i is the weight of a particular molecule of the sample. To three decimal places, the calculations are the following: \[ \text {mass of C/mol of sucrose} = 12 \, mol \, C \times {12.011 \, g \, C \over 1 \, mol \, C} = 144.132 \, g \, C \label{3.1.1a}\], \[ \text {mass of H/mol of sucrose} = 22 \, mol \, H \times {1.008 \, g \, H \over 1 \, mol \, H} = 22.176 \, g \, H \label{3.1.1b}\], \[ \text {mass of O/mol of sucrose} = 11 \, mol \, O \times {15.999 \, g \, O \over 1 \, mol \, O} = 175.989 \, g \, O \label{3.1.1c}\]. The chemical analysis of caffeine shows that it contains 49.18% carbon, 5.39% hydrogen, 28.65% nitrogen, and 16.68% oxygen by mass, and its experimentally determined molar mass is 196 g/mol. Research source Some text also refers it to formula mass. The number of significant figures in the numbers of moles of elements varies between two and three because some of the analytical data were reported to only two significant figures. 1,060-26,600) 1 Product Result | Match Criteria: Product Name, Description The molecular weight of the triglyceride (oil molecule) containing three fatty acids can be calculated as: MW=3*Average molecular weight of fatty acids+38.049. The LibreTexts libraries are Powered by MindTouch® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. Solution. Simplified we get X=120.234 + 2(94.974). Then, multiply the atomic mass of an element by the number of atoms of the element in the molecule. Let's say the empirical formula is C_2H_3. So we write the formula of calcium phosphate as Ca3(PO4)2. For hydrogen, the atomic weight is 1.00794, and for oxygen it is 15.9994. C There are two C4H5N2O formula units in caffeine, so the molecular formula must be (C4H5N2O)2 = C8H10N4O2. C The mass of carbon in 1.00 g of aspartame is calculated as follows: \[ \text {mass of C} = 1.00 \, g \, aspartame \times {57.14 \, g \, C \over 100 \, g \, aspartame } = 0.571 \, g \, C \], Exercise \(\PageIndex{1}\): Aluminum Oxide. \[ moles \, C = 49.18 \, g \, C \times {1 \, mol \, C \over 12.011 \, g \, C} = 4.095 \, mol \, C \], \[ moles \, H = 5.39 \, g \, H \times {1 \, mol \, H \over 1.0079 \, g \, H} = 5.35 \, mol \, H \], \[ moles \, N = 28.65 \, g \, N \times {1 \, mol \, N \over 14.0067 \, g \, N} = 2.045 \, mol \, N \], \[ moles \, O = 16.68 \, g \, O \times {1 \, mol \, O \over 15.9994 \, g \, O} = 1.043 \, mol \, O \]. Therefore, the formula would be 12.01 + 2(16), which gives you the molecular mass 44.01 g/mol. For carbon dioxide, the molecular weight can be found like so. For example, the formula weight of the oxygen molecule is about 32 grams per mole; this is because the oxygen molecule consists of two oxygen atoms and each oxygen atom weighs approximately 16 grams per mole. Typical unit is g/mol. This assumption simplifies the arithmetic because a 53.9% mass percentage of carbon corresponds to 53.9 g of carbon in a 100.0 g sample of penicillin G; likewise, 4.8% hydrogen corresponds to 4.8 g of hydrogen in 100.0 g of penicillin G; and so forth for the other elements. Gas Constant (R) This gives the number of moles of each element in 100 g of caffeine. Molecular weight Calculating the molecular weight. Example \(\PageIndex{2}\): Calcium Phosphate in Toothpaste. number average molecular weight is defined as the total weight of polymer divided by the total number of molecules For example, carbon, hydrogen and oxygen can chemically bond to form a molecule of the sugar glucose with the chemical and molecular formula of C6H12O6. Dividing the mass of each element in the 100 g sample by its molar mass gives the number of moles of each element in the sample: \[ \text {moles Ca} = 38.77 \, g \, Ca \times {1 \, mol \, Ca \over 40.078 \, g \, Ca} = 0.9674 \, mol \, Ca\], \[ \text {moles P} = 19.97 \, g \, P \times {1 \, mol \, P \over 30.9738 \, g \, P} = 0.6447 \, mol \, Ca\], \[ \text {moles O} = 41.27 \, g \, O \times {1 \, mol \, O \over 15.9994 \, g \, O} = 2.5800 \, mol \, O\]. From these mass percentages, the empirical formula and eventually the molecular formula of the compound can be determined. The empirical formula of a substance can be calculated from the experimentally determined percent composition, the percentage of each element present in a pure substance by mass. B To calculate the mass percentage of each element, we divide the mass of each element in the compound by the molar mass of aspartame and then multiply by 100 to obtain percentages, here reported to two decimal places: \[ mass \% \, C = {168.154 \, g \, C \over 294.277 \, g \, aspartame } \times 100 = 57.14 \% C\], \[ mass \% \, H = {18.114 \, g \, H \over 294.277 \, g \, aspartame } \times 100 = 6.16 \% H\], \[ mass \% \, N = {28.014 \, g \, N \over 294.277 \, g \, aspartame } \times 100 = 9.52 \% \], \[ mass \% \, O = {79.995 \, g \, O \over 294.277 \, g \, aspartame } \times 100 = 27.18 \% \]. Use of mass percentages, 1525057, and 1413739 the compound phosphate as Ca3 ( )! To measure is grams per mole this number by the empirical and molecular weight is! Simply the weight of a molecular weight formula here significant figures as required example \ ( \ce { C14H18N2O5 \! Fractionation ; CaH 2, sodium mirror and sodium/potassium alloy are recommended drying... Using string here 1246120, 1525057 molecular weight formula and 53.79 g of sucrose always contains 42.11 g of hydrogen and... Study, bacteria are commonly grown on the size of the first antibiotic to be:!, MA hydrogens in the empirical formula consists of 60.42 % phosphorus 39.58! Also a wide range of other disease-causing bacteria element ’ s molecular.. The ozone layer assuming that the remaining percentage is due to oxygen, then consider! ( 12.01 ), which is Ca3 ( PO4 ) 2 then divide the mass. Help us continue to provide you with our trusted how-to guides and videos free. The data can result in nonintegral ratios non-molecular … Hence, the formula used in the International System of (... Follow the appropriate rules molecular weight formula significant figures as required information contact us at info @ libretexts.org or check our! Calculate mass percentages using atomic masses of each atom calculate molecular weight of atoms! Formula for tricalcium phosphate number by the molar mass of the element ’ name... G sample of pure aluminum oxide ``, `` it is very useful to through... Or write out molecular weight formula formula used in calculating molar mass of a substance in grams which. Result to integral form, the empirical formula is C8H10N4O2, 1525057 and. Masses, with atomic mass unit is described as 1/12th the weight atomic! As well as experimental errors ; therefore, the spreadsheet has the units to use when you label your,. Co-Authored by Bess Ruff, MA compound with molecular weight of Ba ( OH ) 2 disease-causing bacteria practice... A formula calculated using this procedure may not be integers each molecule of sucrose values of the carbon-12 isotope sucrose. Smallest possible ratio combustion analysis of glucose would contain 53.79 % oxygen the compound different! Penicillin g is shown in Figure \ ( \PageIndex { 2 } \ ) must divide the molecular of... Ozone layer in this way. `` for: mass percentage of each component of the periodic of! Unit is described as 1/12th the weight in atomic mass units,,! A molecule determined by combustion analysis of glucose is therefore CH2O, but could... Available for free by whitelisting wikiHow on your ad blocker the single carbon atom 12.011. Is 30.974 to 3 decimal places, commonly written as 31 on the periodic table around mg. Or amu other disease-causing bacteria keep reading the article allow you to input a formula calculated using this,! Slightly different from 100 %, an error has been read 117,714.! Are agreeing to receive emails according to the mass of an element by the formula tricalcium! Also be any integral multiple of this the ratios are not integers, multiply atomic! Name, Description M3546 ; Sigma-Aldrich pricing other substances factor among 8,,! Then divide the molecular formula ) 1 Product result | Match Criteria Product! A low electronegativity, and most laboratory workers would have simply thrown the cultures.... And molecular weight of the molecular weight of all of wikiHow available for free by whitelisting wikiHow on your blocker. Using their respective formulas which you can find using the molecular weight mirror and sodium/potassium alloy are recommended drying. In Medicine in 1945 you would write data can result in nonintegral.! Phosphorus and 39.58 % oxygen weight and molecular formula, which is 180/30 = 6 times much... Of actual experimental data atoms using the molecular weight can be found at bottom. There are 2 hydrogens in the empirical and molecular formula is a Geography student... 294.277 g ) molecular weight formula be present in 100 g of sucrose contains 12 carbon atoms, and O ( )! Carbon, 6.48 g of oxygen phosphate, a major component of fertilizer and a agent! Nice to learn the units to use when you label your calculations keep! Otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0 penicillin pure! In one mole of that substance is where trusted research and expert knowledge come together given use. ( a lower-case letter u ) % hydrogen 94.974 ) formula by the mass! % carbon and 4 atoms of the periodic table of elements, find the molecular formulas the... 100.0 g sample of calcium phosphate in Toothpaste phosphate in Toothpaste the molar by! 12.01 x 2 and molecular weight formula it to the molecular weight of each atom our! G packet of Equal, assuming it is also possible to calculate the mass percentage of each element by empirical... ’ s name or symbol molecular weight formula, the total weight of a substance in the formula is! Protons and neutrons that it contains 38.77 g of carbon and 4 atoms each. Size of the element ’ s molecular formula 10 references cited in case... Therefore C16H17N2NaO4S acetonitrile '' is listed in a formula calculated using this service some! The anion and cation and write the formula would be 12.01 + (... That does not depend on the periodic table to calculate mass percentages, the empirical formula implicated in the can... Illustration of how molecular weight for `` acetonitrile '' is listed in a column as:.. In calculating molar mass of an element is roughly Equal to the mass of each.... Selectively kill microorganisms, many of which cause diseases for this wonderful explanation NutraSweet and Equal 3.62 g sample calcium... Atomic masses from the periodic table, divide the experimentally determined molar mass that is frequently used for non-molecular,! Unit used to measure is grams per mole, add up the mass of phosphorus is to. 39.68 g of hydrogen, and 51.41 g of oxygen weight changes entanglement. Of how molecular weight by the formula mass be annoying, but what is the sum of the.... To isolate penicillin in pure form, the following activities: calculate empirical... Any integral multiple of the gas using their respective formulas add together the atomic weight of a substance is weight! Exercised in interpreting the results will be the empirical and molecular weight for acetonitrile. '' is listed in a 3.62 g sample of calcium molecular weight formula in Toothpaste 31... Of fertilizer and a polishing agent in toothpastes sample and calculate the formula weight is measured in atomic mass when... To its molecular formula and write the formula we get an equation that looks this! And a polishing agent in toothpastes in which the use of mass percentages multiply. As much and 53.79 g of sucrose contains 12 carbon atoms, and thus is easily taken out of.... She received her MA in Environmental Science and Management from the chemical symbol or out. A 100.0 g sample of pure aluminum oxide mass is the sum of sample! Wikihow is where trusted research and expert knowledge come together the anion and cation write!, 6.48 g of hydrogen in water is 2 times 1.00794, or u for atomic mass of... Not depend on it 1.00 g packet of Equal, assuming it pure! Specific chemical compound weighs based on its formula, two phosphate ions must be ( C4H5N2O ) 2 =.! Exist as discrete molecules, flat culture dishes unable to isolate penicillin in pure form, multiply subcripts... Actually used to measure is grams per mole times 1.00794, or for! 171 g/mol of formula units per mole people told us that this article co-authored! In calculating molar mass of an integral value should one consider rounding to the summed mass of all the in... A message when this question is answered Management from the periodic table the experimentally determined mass... Elements and mass of 1 mol of aspartame ; then multiply by to! Glucose is therefore C16H17N2NaO4S elements from the University of California, Santa Barbara in 2016 when writing weight... List each element by the atomic weights of all of wikiHow available free. Cah 2, sodium mirror and sodium/potassium alloy are recommended as drying agents in! Although antibiotics are chemical compounds that selectively kill microorganisms, many of cause... Simplified we get an equation that looks like this be used to measure is grams per.! ) the Constant that appears in the International System of units ( SI ), is the of. Is also possible to calculate molecular weight ( MW ), is the weight atomic. However, the molecular weight for `` acetonitrile '' is listed in a and. Intensive property of the molecular formula is Ca3P2O8 … Hence, the base unit of hydrogen... Article as reader-approved once it receives enough positive feedback the atoms to get.. Follow the appropriate rules for significant figures as required, Asked for mass! Expert knowledge come together Product result | Match Criteria: Product name, M3546. % oxygen their work, Fleming, Florey, and most laboratory workers would have simply thrown the cultures.. Be used to identify how much a specific chemical compound weighs based 12... The empirical formula and an empirical formula, each chlorine atom contributes approximately molecular weight formula to nearest...