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• CBSE Class 11 Chemistry Notes

# Stoichiometry and Stoichiometric Calculations

Jeremias Richter, a German chemist, was the first to create or discover the word Stoichiometry. The quantitative analysis of the reactants and products involved in a chemical reaction is known as chemical stoichiometry. The name “stoichiometry” comes from the Greek words “stoikhein” (element) and “metron” (measure). We will study what it implies and discuss the various components of this topic further below.

### What Is Stoichiometry?

The calculation of products and reactants in a chemical reaction is known as stoichiometry.  It is a key concept in chemistry that allows us to compute reactant and product amounts using balanced chemical equations. The balanced equation’s ratios are used in this case. In general, all reactions are influenced by one fundamental factor which is the amount of substance present.

Stoichiometry is the measurement of the products and reactants in any chemical reaction. The term “stoichiometry” is derived from two Greek words: “stoichion,” which refers to element determination, and “metry,” which refers to measurement.

Moreover, stoichiometry is founded on the law of conservation of mass, which states that the total mass of reactants equals the total mass of products, proving that product and reactant numbers are frequently stated as a positive integer ratio. This illustrates that if you know the number of specific products, calculating the product amount is simple. The computation of other reactants is also possible if the quantity of one reactant is known and the resultant quantity can be calculated via an experiment.

Stoichiometry is a measurement of the quantitative relationship between the products and reactants of a chemical process expressed in mass or volume ratios. Stoichiometry is a fundamental mathematical principle that describes the rule of conservation of mass, which states that matter cannot be generated or destroyed, but can only be transformed from one condition to another. A balanced stoichiometry is required for a chemical reaction to occur and progress to completion. In a chemical reaction, the quantity of each chemical element on the product side should be equal to the corresponding element quantity on the reactant side. Stoichiometry assists in determining the amount of substance required or present. The following are characteristics that can be measured:

• The mass of reactants and products
• Molecular mass
• A chemical equation, states the reactant side.
• Chemical equations

### What is the Stoichiometric Coefficient?

The number of molecules involved in a process is known as the stoichiometric coefficient or stoichiometric number. When you look at a balanced reaction, you’ll see that both sides of the equation have the same amount of elements. The number in front of atoms, molecules, or ions is known as the stoichiometric coefficient. Fractions and whole numbers can both be used as stoichiometric coefficients. The coefficients essentially assist us in determining the mole ratio between reactants and products.

Both sides of the equation have the same amount of components in a balanced reaction. The stoichiometric coefficient is the number written in front of atoms, ions, and molecules in a chemical reaction to balance the number of each element on both the reactant and product sides of the equation. While fractions can be used as stoichiometric coefficients, whole numbers are more commonly utilized and preferred. Since they establish the mole ratio between reactants and products, these stoichiometric coefficients are useful. The Stoichiometric coefficient is the number of molecules of a reactant that participate in a reaction.

Consider the following equation:

aA + bB ⇌ cC + dD

The Stoichiometric coefficients of the A, B, C, and D, respectively, are a, b, c, and d in this equation.

### Stoichiometry in Chemical Analysis

Chemists frequently utilize stoichiometric calculations, which follow a quantitative analysis approach, to quantify the amounts of chemicals present in a sample. There are two primary forms of analysis. We’ll go over them in more detail later.

• Gravimetric Calculation-In analytical chemistry, gravimetric analysis refers to the quantitative determination of analyte based on the mass of the solid. The gravimetric analysis produces the most precise results of any other analytical method since a substance’s weight can be measured with more precision than other fundamental quantities.

The following are several types of gravimetric analysis.

• Precipitation gravimetry – It entails isolating an ion in solution by a precipitation reaction, filtering, washing the precipitate to remove impurities, and finally weighing and measuring the precipitate’s mass by difference.
• Volatilization gravimetry – The process of separating components of a mixture by heating or chemically decomposing the sample is known as volatilization gravimetry.
• Electrogravimetry – It comprises the electrochemical reduction of metal ions at the cathode as well as the deposition of ions on the cathode at the same time. The mass of analyte initially present in the sample is determined by weighing the cathode before and after electrolysis, and the weight difference corresponds to the mass of analyte initially present in the sample.
• Volumetric Analysis- Volumetric analysis is the process of quantifying a substance in terms of volume. In volumetric analysis, a known volume (V1) of a material whose concentration (N1) is known reacts with an unknown volume (V2) of a solution of a substance whose concentration (N2) must be predicted. At the end of the response, the volume, V1, is recorded. The following equation is used to compute the N2 concentration.

N2 x V2 = N1 x V1

Volumetric analysis terms include:

• Titration – Titration is the process of determining the volume of solution required to thoroughly react with the volume of another solution.
• Indicator – Indicators are chemicals that change color as the reaction progresses.
• Titrant – A titrant is a solution with a known strength.
• Titrate – The solution whose concentration is to be estimated is referred to as titrate.

### Stoichiometric Calculations

It’s essential to solve stoichiometric problems. It necessitates an understanding and use of the mole idea, as well as the balancing of chemical equations and the careful conversion of units. Chemical equation-based difficulties can be categorized as.

• Mole to mole relationships- In these problems, the moles of one of the reactants or products are computed if the moles of the other reactants and products are given.
• Mass-Volume relationship- The mass or volume of one of the reactants or products is estimated using the mass or volume of other substances in these problems.
• Mass-mass relationship- The mass of one of the reactants or products must be computed if the mass of the other reactants or products is given in these problems.
• Volume-volume relationship- The volume of one of the reactants or products is given in these problems, while the volume of the other must be estimated.

### Sample Questions

Question 1: Calculate how much sodium hydroxide will be needed to make 500mL of a 0.10 M solution.

The molar mass of NaOH = 40g

Volume of NaOH= 500ml = 0.5 L

Molarity = 0.10M

Molarity = moles / volume in litres

So, weight of NaOH = molar mass of NaOH x volume  x molarity

= 0.10 x 40 x 0.5

= 2 g

Question 2: What are Stoichiometric Calculations, and how do they work?

Stoichiometric calculations entail a number of steps, including solving a balancing equation, determining the moles of chemicals produced in a reaction, and converting units to moles and vice versa using various conversion factors.

Question 3: To make 3 M 400 ml HCl, how much 11M HCl should be diluted with water?

Given that, M1 = 11M, and M2 = 3M

Also, V1 = ? , anx V2= 400ml

Now, M1 x V1 = M2 x V2

V1 = (3×400) / 11

= 109 ml

Question 4: What is the Application of Stoichiometry in Real Life?

Stoichiometry is used in the manufacturing of soaps, gasoline, tires, deodorants, fertilizers, and other products.

Question 5: By reacting nitrogen with hydrogen, how many moles of nitrogen are required to make 8.2 moles of ammonia?

The balanced chemical equation is,

N2    +     3H2       →       2NH3

2 mole of NH3 are produced from = 1 mole of N2

8.2 mole of NH3 are produced from = (1/2) x 8.2

= 4.1 mol of N2

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