H 1 Hydrogen 1.00794 | Periodic Table | He 2 Helium 4.002602 | |||||||||||||||

Li 3 Lithium 6.941 | Be 4 Beryllium 9.012182 | of the Elements | B 5 Boron 10.811 | C 6 Carbon 12.0107 | N 7 Nitrogen 14.0067 | O 8 Oxygen 15.9994 | F 9 Fluorine 18.9984032 | Ne 10 Neon 20.1797 | |||||||||

Na 11 Sodium 22.98976... | Mg 12 Magnesium 24.305 | mouse/touch for more information | Al 13 Aluminum 26.9815386 | Si 14 Silicon 28.0855 | P 15 Phosphorus 30.973762 | S 16 Sulfur 32.065 | Cl 17 Chlorine 35.453 | Ar 18 Argon 39.948 | |||||||||

K 19 Potassium 39.948 | Ca 20 Calcium 40.078 | Sc 21 Scandium 44.955912 | Ti 22 Titanium 47.867 | V 23 Vanadium 50.9415 | Cr 24 Chromium 51.9961 | Mn 25 Manganese 54.938045 | Fe 26 Iron 55.845 | Co 27 Cobalt 58.933195 | Ni 28 Nickel 58.6934 | Cu 29 Copper 63.546 | Zn 30 Zinc 65.38 | Ga 31 Gallium 69.723 | Ge 32 Germanium 72.63 | As 33 Arsenic 74.9216 | Se 34 Selenium 78.96 | Br 35 Bromine 79.904 | Kr 36 Krypton 83.798 |

Rb 37 Rubidium 85.4678 | Sr 38 Strontium 87.62 | Y 39 Yttrium 88.90585 | Zr 40 Zirconium 91.224 | Nb 41 Niobium 92.90628 | Mo 42 Molybdenum 95.96 | Tc 43 Technetium (98) | Ru 44 Ruthenium 101.07 | Rh 45 Rhodium 102.9055 | Pd 46 Palladium 106.42 | Ag 47 Silver 107.8682 | Cd 48 Cadmium 112.411 | In 49 Indium 114.818 | Sn 50 Tin 118.71 | Sb 51 Antimony 121.76 | Te 52 Tellurium 127.6 | I 53 Iodine 126.90447 | Xe 54 Xenon 131.293 |

Cs 55 Caesium 132.9054 | Ba 56 Barium 132.9054 | Hf 72 Hafnium 178.49 | Ta 73 Tantalum 180.94788 | W 74 Tungsten 183.84 | Re 75 Rhenium 186.207 | Os 76 Osmium 190.23 | Ir 77 Iridium 192.217 | Pt 78 Platinum 195.084 | Au 79 Gold 196.966569 | Hg 80 Mercury 200.59 | Ti 81 Thallium 204.3833 | Pb 82 Lead 207.2 | Bi 83 Bismuth 208.9804 | Po 84 Polonium (209) | At 85 Astatine (210) | Rn 86 Radon (222) | |

Fr 87 Francium (223) | Ra 88 Radium (226) | Rf 104 Rutherfordium (267) | Db 105 Dubnium (268) | Sg 106 Seaborgium (271) | Bh 107 Bohrium (272) | Hs 108 Hassium (270) | Mt 109 Meitnerium (276) | Ds 110 Darmstadium (281) | Rg 111 Roentgenium (280) | Cn 112 Copernicium (285) | Uut 113 Unutrium (284) | Uuq 114 Flerovium (289) | UuP 115 Ununpentium (288) | Lv 116 Livermorium (293) | Uus 117 Ununseptium (294) | Uuo 118 Ununoctium (294) | |

La 57 Lanthanum 138.90547 | Ce 58 Cerium 140.116 | Pr 59 Praseodymium 140.90765 | Nd 60 Neodymium 144.242 | Pm 61 Promethium (145) | Sm 62 Samarium 150.36 | Eu 63 Europium 151.964 | Gd 64 Gadolinium 157.25 | Tb 65 Terbium 158.92535 | Dy 66 Dysprosium 162.5 | Ho 67 Holmium 164.93032 | Er 68 Erbium 167.259 | Tm 69 Thulium 168.93421 | Yb 70 Ytterbium 173.054 | Lu 71 Lutetium 174.9668 | |||

Ac 89 Actinium (227) | Th 90 Thorium 232.03806 | Pa 91 Protactinium 231.0588 | U 92 Uranium 238.02891 | Np 93 Neptunium (237) | Pu 94 Plutonium (244) | Am 95 Americium (243) | Cm 96 Curium (247) | Bk 97 Berkelium (247) | Cf 98 Californium (251) | Es 99 Einstenium (252) | Fm 100 Fermium (257) | Md 101 Mendelevium (258) | No 102 Nobelium (259) | Lr 103 Lawrencium (262) |

Whether you're doing an experiment or taking an exam, at some point in chemistry class you'll need to calculate molarity. Molarity is the measure of how concentrated a solution is by stating how many moles of a solute are in each liter of the solution. To calculate molarity, you only need the molarity formula and a few pieces of information.

## Understanding the Formula

To calculate molarity, you need to do a basic division problem. Since molarity is the moles of a solute per liter of solution, the formula is the number of moles of solute divided by the number of liters of solution. To better recall this formula, keep in mind that molarity can also be written as "mol/L" or "moles per liter."

## Figuring out Moles

While grasping the formula for molarity is straightforward, you may get a bit confused about figuring out how many moles of a solute you have. Remember, a solute is the substance dissolved in a solution. To calculate how many moles of a solute you have, you need to know how many grams of solute were used, the chemical formula of the solute and the atomic weights of the elements that make up the solute. Atomic weights can be found on the periodic table of the elements. Once you have this information, you can calculate how many moles of solute you have by adding up the individual elements' atomic weights, then dividing the grams of solute by the atomic weight of the solute.

## Sciencing Video Vault

## Measuring the Solution

The final key piece of information you need to calculate molarity is the number of liters of solution you have. Because molarity is moles of solute in one liter of solution, you need to convert the amount of solution you have into liters. For example, if on an exam or in the lab, you are given the amount of solution in milliliters, you'll need to divide that amount by 1,000 to change it into liters for the molarity formula.

## Putting it Together

The following example shows how to put everything together to calculate molarity if you have 20 grams of NaOH dissolved into 500 milliliters of water. First, you'll convert the 500 milliliters to liters -- 500 divided by 1,000 -- giving you 0.500 liters of solution. Then, you'll take the solute apart to determine its atomic weight. Since sodium's atomic weight is 23 grams, oxygen's is 16 grams and hydrogen's is 1 gram, one mole of NaOH is 40 grams. With 20 grams of NaOH, this means you have 0.5 moles of the solute: 20 divided by 40. Now that you have the number of moles and have converted your solution to liters, you can figure out that the molarity of the solution -- 0.5 moles divided by 0.5 liters -- is 1 mole per liter.

## Going Further

Using the molarity formula and a bit of algebra, you can determine other numbers based on information you're given about a solution. If you know molarity and how many liters you have, you can calculate how many moles of solute are in the solution or how many grams of the solute were used. Likewise, given molarity and the amount of solute used or the number of moles, you can figure out how many liters of solution you have.