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Molarity

This section will explain the simplest definition and molarity formula with proper examples. You will learn how this formula is derived and how it can be used differently. After this section, you will find it helpful to understand the definition and formula of molarity. It is a necessary term used in various chapters. Therefore, learning this formula will be mandatory.

Students learned different measurement units, whether mathematics, physics, or chemistry. When it comes to chemistry, there are different units of measurement for other substances - concentration, their volume, etc. - and one such unit widely used in chemistry is the 'mole.'

What is a mole? It is a unit of measurement that is used for a chemical substance, from which the term "molarity" is derived. Molarity, which is also known as the molar concentration of a solution, is a technique for calculating the amount of a substance that a particular chemical solution contains. It is measured by considering two indicators: the number of moles in the solute and the volume of the solution. The volume of the solution is calculated in units of liters. Molarity is symbolized by "M."

Difference between Solute, Solvent, and Solution

Before we continue, let us know the difference between the terms "solute," "solvent," and "solution" to make it easy to understand the concepts that will follow. A solution is defined as a homogeneous mixture containing one or more solutes, meaning that solutes are nothing but materials present in solutions. A solvent is a substance that can easily dissolve a solute. Therefore, what we call a solution is nothing but a solute that dissolves in a solvent to form a solution.

Molarity Definition

Molarity or Molar concentration is known as the number of moles of solute present in a certain amount of solution, i.e., moles per liter of solution.

Molality Definition

Molality is known as the number of moles of solute that can be found in a kilogram of solvent, i.e. moles per kilogram of solvent.

Difference between Molarity and Molality

Although the terms Molarity and Molality may seem somewhat similar because the two words sound almost the same, the contrast between them and their usage is very important for students to understand and know because it makes a huge difference when using them for various calculations. It can be difficult to notice and sometimes escape students' eyes, but there is one important difference between the two terms Molarity and Molality.

Molarity is a calculation of the number of solutes that are present in a liter of solution. As we mentioned earlier, a solution contains both a solute and a solvent. Whereas molality is a calculation of the number of solutes present in a kilogram of the solvent. As we already know, a solvent dissolves a solute.

Mole Fraction Definition

A solution is a mixture of different components. A mole fraction also called a mole fraction, is defined as the amount of one particular component expressed in moles, divided by the total amount of all components present in the solution.

Weight Percentage Definition

Weight percent, which can also be called mass percent, is nothing but the ratio of the mass of the solute to the given mass of the solution multiplied by 100.

Molarity Formula

The equation for finding molarity is the ratio of moles of solute whose molarity is to be calculated to the volume of solvent used to dissolve the given solute.

M = n / V

Where,

M = molality of the solution that is to be calculated

n = number of moles of the solute

V = volume of solution given in terms of litres

Molarity Examples

Q1. A solution is prepared by bubbling 1.56 grams of hydrochloric acid in Water. Given, the volume of the solution is 26.8 mL. Find the molarity of the solution.

Ans. Hdrochloric acid chemical formula= HCl

Water chemical formula= H2O

HCl molecular weight= 35.5 ×1 + 1×1 = 36.5 moles/gram

H2O molecular weight = 1 ×2 + 16 ×1 = 18 moles/gram

Mass of hydrochloric acid = 1.56 g

The number of moles of hydrochloric acid =

nT = mass in grams / molecular weight

nT = 1.56 / 36.5 = 4.27 x 10-2 mole

Now, given volume of the solution = 26.8 mL

Expressing the volume in terms of litres,

volume = 26.8 / 1000 = 2/68 x 10-2 Litre

Now, we calculate the molarity of the solution using the formula given above.

molarity = Number of moles of element / volume of solution in litres

Molarity = 4.27 x 10-2 / 2.68 x 10-2 = 1.59M

Q2. A solution prepared by using 15 g of sodium sulphate. The volume of the solution is 125 ml. Find the molarity of the given solution of sodium sulphate.

Ans. Sodium sulphate molecular formula is Na2SO4.

Water molecular formula is H2O.

The molecular mass of sodium sulphate: M = 23×2+32+16×4 = 142

The number of moles of sodium sulphate in the given question is calculated as,

n = mass in grams / molecular weight = 15 / 142 = 0.106

The volume of the solution is 125 ml.

Expressing the above values in terms of litres,

Volume = 125 / 1000 = 0.125

Now, using the formula above, we calculate the solution's molarity.

molarity = number of moles of solute/volume of solution

Substituting the values, we get,

molarity = 0.106 / 0.125 = 0.85 M

Frequently Asked Question (FAQs)

Q1. What factors affect molarity?

Ans. Molarity is a unit of the concentration that measures the number of moles of a solute per liter of solution. Molarity is affected by temperature because it is totally based on the volume of the solution, and the volume of a substance will be affected by changes in temperature.

Q2. What is the advantage of using molarity?

Ans. The advantage of using molarity is that it's convenient and easy to use because the solute is measured in grams, converted into moles, and then mixed with a volume. Also, the sum of the molar concentrations is the total molar concentration.

Q3. Does molarity depend on temperature?

Ans. Molarity is dependent on temperature, whereas molality is not. With temperature, molarity varies. Molarity is solute moles per liter of solution. Also, as the temperature increases, water expands, so the solution's volume increases.

Q4. What is Molarity in Chemistry?

Ans. Molarity (M) is the total amount of a substance in a certain volume of solution. Molarity is the moles of a solute per liters of a solution. It is also known as the molar concentration of a solution.

Q5. Why is molarity more accurate than molality?

Ans. Molality is a more accurate and precise means of making a concentration because it is unaffected by pressure and temperature changes. It also involves a liquid, that means the concentration also changes. This is because the volume is a liquid and can change with changes in pressure and temperature.

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