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The molar mass of NaOH, its properties and uses

Sodium hydroxide (NaOH) is also referred to as caustic soda or lye is an inorganic compound. Its chemical formula is made of metal ion sodium which is attracted to a non metal ion hydroxide (OH-). This is due to the fact that sodium hydroxide is an ionic compound. It is a solid that is white in color and it is also an alkali salt and a highly caustic metallic base that is available in pellets, granules and flakes. Sodium hydroxide can also be a solution in a number of several concentrations. It forms around fifty percent weight of a saturated solution in water. Sodium hydroxide is a white crystal at room temperature with a melting point of 318 ̊C (604.4 ̊F) and boiling point 1388 ̊C (2530.4 ̊F). Its density is 2.13 g/cm3. Sodium hydroxide is a strong base, and it easy to absorbs CO2 and H2O when exposed. It is used in unclogging drains and in processing food. It is also used in processes to make products like soap textile and plastic. At times, it can be replaced with potassium hydroxide which is also a strong base and it gives the same results. The chemical properties of sodium peroxide are:

  • When neutralized with acids or dissolved in water it liberates heat, which is capable of igniting combustible materials. It is also very soluble in alcohol and glycerin and is highly corrosive and has an acidity of 13.
  • Reaction with acids: NaOH reacts with protic acids to give out water and salts. For example, when it reacts with hydrochloric acid, it forms sodium chloride.
  • Reaction with acid oxides: NaOH reacts with the acidic oxides like sulfur dioxide. Reactions like these are used to scrub the harmful acidic gases that are produced when coal is burnt. This prevents their release into the atmosphere.
  • Reaction with oxides and amphoteric metals: Aqueous sodium hydroxide solution when reacted with glass at ambient temperature, it forms silicates.
  • Precipitant: NaOH is used to precipitate transition metal hydroxides.

The molecules that form NaOH are often measured in experiments and it is very important for these measurements to be accurate. With careful calculation, you can determine the number of moles needed in a sodium hydroxide reaction. And after knowing the number of moles the molar mass of NaOH concept can be used to calculate the number of grams that sodium hydroxide needs. The molar mass of sodium hydroxide is the sum of the total mass of all atoms that make up the mold of its molecule.

How to calculate the molar mass of sodium hydroxide

In chemistry, 6.022 x 1023 is very important. It is known as Avogadro's number and has the symbol N. It was named after Amedeo Avogadro, a chemist from Italy who in 1811 made contributions that were recognized later in 1860 after he had died. His contributions helped a lot with the measurement of atomic weights. Avogadro's number has a mol¯1unit associated with it which means 6.022 x 1023 mol¯1. The superscripted ‘minus one’ implies that the unit mol is in the denominator. There is an understood numerator of one, as in 1/mol but it varies based on the entity involved. If you are referring to an element, you can write atoms/mol. If you are referring to a compound, you will write molecules per mol and whatever is found in the numerator depends on the entity either atom, molecule, ion or an electron used in the problem. Consequently, the units’ names in the numerator are not used and instead, a one is used. From the Avogadro's number role in chemistry, the counting of atoms or molecules is very difficult since they are very small. However, atoms or molecules can be counted by weighing large amounts of them on a balance. When you weigh one mole of sodium hydroxide on a balance, it is called the molar mass of NaOH and has the unit g/mol (grams per mole). This idea is very important because it is used all the time in all substances. The molar mass of NaOH is the weight in grams of one mole and one mole has 6.022 x 1023 entities. Therefore, the molar mass of NaOH is the mass in grams of 6.022 x 1023 entities. To get molar mass of NaOH all you need to do is find its molecular weight and stick the unit "g/mol" after that number.

Molecular weight is the quantity calculated by multiplying an element’s atomic weight by the number of atoms in the formula and then adding all the products together. Molecular weight can be used to determine the molar mass of NaOH and reagents in a chemical reaction. The molar mass of NaOH or any other substance affects the conversion and that is why before calculating, it is important to know the substance. With a chemical formula of a compound and the elements periodic table, you can add the atomic weights and find the molar mass of NaOH and other substances easily.

In order to find the molar mass of NaOH, you will begin with the units per mole. In calculating a chemical compound’s molecular weight, you will see how many grams are there in one mole of the substance. In simple terms, the molecular weight is the weight in atomic mass units of all atoms in the given formula. The molar mass of NaOH is the mass of one mole of NaOH and to calculate it you add up the product of the relative atomic mass and the atoms of all elements which include sodium hydroxide as shown in its formula NaOH.

Examples of sodium hydroxide molar mass calculations

The sodium hydroxide compound is made up of three elements which are sodium, hydrogen and oxygen. The first step in calculating the molar mass of NaOH is finding the atomic masses of sodium, hydrogen and oxygen in the periodic table. The second step is to count the number of atoms that sodium, hydrogen and oxygen have from the sodium hydroxide formula (NaOH). And since there are no subscripts in the formula, it means that each of the three elements has one atom. The third step in getting the molar mass of NaOH is adding the masses of sodium, oxygen and hydrogen. Molecular weight of NaOH is equal to 22.98977 + 15.9994 + 1.00794. The molar mass of NaOH is 39.99711 g/mol. To get the percentage composition of each element; Sodium (Na) has one atom in NaOH. The atomic mass of sodium is 22.989770 and its mass percentage in sodium hydroxide will be 22.989770 divided by 39.99711 and the result is multiplied by 100%. The mass percentage will be 57.479%. The number of hydrogen atoms in sodium hydroxide is one. The atomic mass of hydrogen is 1.00794 and the mass percent of hydrogen in NaOH will be (1.00794/39.99711)*100%. The mass percentage will be equal to 2.520%. Oxygen also has one atom in sodium hydroxide. The atomic mass of oxygen is 15.9994 and its mass percent in sodium hydroxide is (15.9994/39.99711), which is equal to 40.001%.

If you are required to determine the molar mass of NaOH used in forming 500ml of a 0.1M solution of sodium hydroxide, you will take one mole of NaOH solution and dissolve it in 40(molar mass of NaOH) grams of NaOH in 500ml of water. You will then convert the 500 ml to liters by dividing 500 by 1000. You will find that for 0.5 liters of 0.1M solution you need 0.1M of solute. 0.1M of the solute x 40 (molar mass of NaOH) = 4 grams of sodium hydroxide. By dissolving 4 grams of sodium hydroxide in 0.5 liters of water, you will make a solution of 0.1M solution.

The molar mass of NaOH can be used in converting between the mass of NaOH and the number of molecules in NaOH. For example, you can be asked to find the number of moles in 90 grams of NaOH. And since molar mass of NaOH is 40 grams per mole, you will divide the 90 grams of NaOH by the molar mass of NaOH to get the moles of sodium hydroxide. This is similar to multiplying the reciprocal of the molar mass of NaOH. And if the equation is arranged well, the mass units in grams will cancel out and you will be left with the moles as a unit. The final answer will be 2.25 moles of NaOH in 90 grams of NaOH.

In determining the mass and molar mass concentration of a sodium hydroxide solution that has 12 grams of sodium hydroxide in 600ml of solution, you begin by determining the mass of sodium hydroxide required to make 500 cm3 (0.500 dm3) of a 0.500 mol dm-3(0.5M) solution. And since the molar mass of NaOH is 40, molarity is equal to moles / volume, so moles needed = molarity x volume in dm3. 500 cm3 = 500/1000 = 0.50 dm3 and mol NaOH needed = 0.500 x 0.500 = 0.250 mol NaOH. Therefore, mass is equal to mol x formula mass = 0.25 x 40 = 10g NaOH. Another example of using the molar mass of NaOH is in the calculation of the mass of sodium sulfate gotten when 20 grams of sodium hydroxide are reacted with sulfuric acid. (Ar of H = 1, Ar of O = 16, Ar of Na = 23, Ar of S = 32). The molar mass of NaOH is 40 and the molar mass of Na2SO4 = 23 + 23 + 32 + 16 + 16 + 16 + 16 = 142. The molar mass of NaOH is 40 g/mol and molar mass of Na2SO4 is 142 g/mol and so the number of moles of NaOH is equal to mass ÷ molar mass = 20 ÷ 40 = 0.5 mol. From the equation, 2 mol of sodium hydroxide reacts with 1 mol of Na2SO4, so 0.5 mol of sodium hydroxide will react with 0.25 mol of Na2SO4. The mass of Na2SO4 = moles × molar mass = 0.25 × 142 = 35.5 g.

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