Stoichiometric relationships are an essential part of the IB Chemistry curriculum, and mastering these concepts is crucial to your success in the subject. In this blog, we'll explore stoichiometry in detail and provide tips and practice problems to help you improve your understanding.

Stoichiometry involves calculating the amounts of reactants and products in a chemical reaction, based on the balanced chemical equation. The IB Chemistry syllabus includes a range of stoichiometry topics, including mole calculations, limiting reagents, and theoretical yield.

Here are some tips to help you master stoichiometric relationships in IB Chemistry:

Practice, practice, practice: Stoichiometry involves a lot of calculations and conversions, so the more you practice, the more confident you'll become. Start with simple problems and work your way up to more complex ones.

Understand the concept of the mole: The mole is a fundamental unit of measurement in chemistry, and understanding how to use it is essential for stoichiometry. Make sure you understand the relationship between moles, mass, and number of particles.

Keep your units consistent: In stoichiometry, it's important to keep your units consistent throughout the problem. Make sure you're using the correct units for mass, volume, and concentration.

Use dimensional analysis: Dimensional analysis is a powerful tool for solving stoichiometry problems. It involves converting between units using conversion factors, which are ratios that relate two different units.

Know your formulas: Make sure you're familiar with the formulas for calculating moles, mass, and concentration. These formulas will be essential for solving stoichiometry problems.

To help you practice your stoichiometry skills, here are some example problems:

Q1. How many grams of sodium chloride can be produced from 25.0 grams of sodium and 35.5 grams of chlorine gas, according to the following balanced equation?

2 Na (s) + Cl2 (g) → 2 NaCl (s)

Solution:

To answer this question, you can start by using the balanced chemical equation to determine the mole ratio between the reactants and the product. For every 2 moles of sodium (Na) used, one mole of sodium chloride (NaCl) is produced. Similarly, for every one mole of chlorine gas (Cl2) used, one mole of sodium chloride is produced.

First, let's calculate the number of moles of each reactant:

Moles of Na: 25.0 g / 22.99 g/mol = 1.09 mol

Moles of Cl2: 35.5 g / 70.90 g/mol = 0.50 mol

Based on the balanced equation, the limiting reactant is Cl2 since it produces the lesser amount of product. Therefore, we will use the mole ratio based on the amount of Cl2 used to determine the amount of NaCl produced.

Moles of NaCl: 0.50 mol Cl2 x (2 mol NaCl / 1 mol Cl2) = 1.00 mol NaCl

Finally, we can calculate the mass of NaCl produced using the molar mass of NaCl:

Mass of NaCl: 1.00 mol NaCl x 58.44 g/mol = 58.44 g

Therefore, 25.0 grams of sodium and 35.5 grams of chlorine gas can produce 58.44 grams of sodium chloride according to the given balanced equation.

Q2. If 10.0 grams of aluminum are reacted with excess hydrochloric acid, what is the theoretical yield of aluminum chloride, according to the following balanced equation?

2 Al (s) + 6 HCl (aq) → 2 AlCl3 (aq) + 3 H2 (g)

Solution:

To determine the theoretical yield of aluminum chloride produced when 10.0 grams of aluminum are reacted with excess hydrochloric acid, we need to use stoichiometry and the balanced chemical equation provided.

Here are the steps:

1. Convert the given mass of aluminum to moles using its molar mass (27.0 g/mol):

Moles of Al = 10.0 g / 27.0 g/mol = 0.370 moles Al

2. Using the balanced chemical equation, we can see that 2 moles of Al react with 6 moles of HCl to produce 2 moles of AlCl3:

2 Al + 6 HCl → 2 AlCl3 + 3 H2

Therefore, the mole ratio of AlCl3 to Al is 2:2 or 1:1.

3. Calculate the moles of AlCl3 that can be produced based on the moles of Al:

Moles of AlCl3 = 0.370 moles Al

4. Finally, calculate the mass of AlCl3 produced using its molar mass (133.34 g/mol):

Mass of AlCl3 = Moles of AlCl3 × Molar mass of AlCl3 = 0.370 moles AlCl3 × 133.34 g/mol = 49.34 g AlCl3

Therefore, the theoretical yield of aluminum chloride that can be produced when 10.0 grams of aluminum are reacted with excess hydrochloric acid is 49.34 grams of AlCl3. It's important to note that the actual yield of the reaction may be different due to factors such as incomplete reaction or impurities in the reactants.

Q3. If 25.0 mL of 0.100 M hydrochloric acid is reacted with 25.0 mL of 0.100 M sodium hydroxide, what is the concentration of the resulting sodium chloride solution?

HCl (aq) + NaOH (aq) → NaCl (aq) + H2O (l)

Solution:

To determine the concentration of the resulting sodium chloride solution when 25.0 mL of 0.100 M hydrochloric acid is reacted with 25.0 mL of 0.100 M sodium hydroxide, we need to use stoichiometry and the balanced chemical equation provided.

Here are the steps:

1. Determine the number of moles of hydrochloric acid and sodium hydroxide used:

Moles of HCl = 0.100 M × 0.0250 L = 0.00250 moles HCl Moles of NaOH = 0.100 M × 0.0250 L = 0.00250 moles NaOH

2. Using the balanced chemical equation, we can see that 1 mole of HCl reacts with 1 mole of NaOH to produce 1
mole of NaCl:

HCl + NaOH → NaCl + H2O

Therefore, the mole ratio of NaCl to HCl (or NaOH) is 1:1.

3. Calculate the moles of NaCl produced based on the moles of HCl (or NaOH):

Moles of NaCl = 0.00250 moles HCl (or NaOH)

4. Determine the total volume of the resulting solution:
Total volume = 25.0 mL + 25.0 mL = 50.0 mL = 0.0500 L

5. Finally, calculate the concentration of the resulting sodium chloride solution in terms of molarity (M):

Concentration of NaCl = Moles of NaCl / Total volume = 0.00250 moles / 0.0500 L = 0.0500 M

Therefore, the concentration of the resulting sodium chloride solution when 25.0 mL of 0.100 M hydrochloric

acid is reacted with 25.0 mL of 0.100 M sodium hydroxide is 0.0500 M.

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