# Quantitative Aspects Continued

## Quantitative aspects of chemical change continued

The next set of lesson builds on the last topics. Topics covered next are:

• ### 1 mole of gas occupies $$\text{22.4}$$ $$\text{dm^{3}}$$ and expansion to any number of moles of gas

Earlier, we learnt about the molar volume of gases. This concept is refreshed here and then expanded on to cover any number of moles of gases. This is a very important result that is used in stoichiometric calculations to go from volume of a gas to number of moles and from there via the balanced equation to the desired quantity of one of the products or reactants in that reaction.

• ### Interpretation of chemical equations

You should be able to understand that chemical equations can be interpreted in words or in symbols (as seen in another lesson) or in terms of the quantities of the substances involved in the reaction. This second interpretation is a valuable skill for stoichiometric calculations.

• ### Calculation of molar concentration of solutions and expanding this to titration calculations

Earlier, you learnt about calculating concentration, in the next set of lessons, concentration calculations are expanded to cover titrations.

• ### Limiting reagents

Earlier, you saw how to use the balanced chemical equation to move from products to reactants and vice versa. This is now expanded on to include information about both reactants where you have to determine which reactant is limiting and which is in excess before calculating the amount of product formed.

• ### Percent yield

Here, we introduce percent yield. Care must be taken here to ensure that you do not mix up theoretical yield and percent yield. The percent yield can only be determined from experiment, while the theoretical yield comes from stoichiometric calculations.

• ### Empirical and molecular formula

This is revision from earlier lessons. You are reminded how to calculate the empirical and molecular formula of a substance and are reminded about percent composition.

• ### Percent purity

The concept of percent purity is the last concept that is covered. This looks at how pure a sample of a compound is. Note that percent composition deals with how much of a particular element is in a substance while percent purity deals with how much of a compound is in a sample or how pure your final product in a reaction is.

• ### Calculations involving gases, liquids and solids

At the end of this tutorial, we bring together all the concepts that we have learnt. We introduce the idea that the balanced chemical equation can be used to calculate any quantity of a substance from any of the other products or reactions in that reaction. This is particularly important as reactions do not occur in just one state but occur in multiple states and being able to move freely between, for example, calculating moles of a gas to calculating mass of a substance, is an important skill.

Wherever we look in real life we see the importance of mixing things in precise quantities. Cooking and baking, the medicines you take when sick, the products that you buy, all of these rely on the ingredients being mixed in specific amounts. And even the amount of product formed relies on how much of each ingredient is used. In the next set of lessons, we will look at some of these quantities and how they can be calculated.

Earlier, we learnt about writing chemical equations and about the information that can be obtained from a balanced chemical equation. In the next set of lessons, we are going to explore these concepts further and learn more about gases, solutions and reactions. We will explore the concept of theoretical yield in greater detail and learn about limiting reagents. We will begin by taking a closer look at gases and solutions and work out how to solve problems relating to them.