1:29 calculate reacting masses using experimental data and chemical equations

1:29 calculate reacting masses using experimental data and chemical equations

Example: When calcium carbonate (CaCO3) is heated calcium oxide is produced. You can use reacting mass calculations to calculate the mass of calcium oxide produced when heating 25 g of calcium carbonate.

     CaCO3     –>         CaO      +      CO2

Step 1: Calculate the amount, in moles, of 25 g of calcium carbonate (CaCO3)

    \[M_r(CaCO_3)=(1 \times 40) + (1\times12) + (3 \times 16) \]

    \[M_r(CaCO_3)= 100\]

    \[Amount = \frac{mass(g)}{M_r} \]

    \[Amount = \frac{25}{100} \]

    \[Amount = 0.25 mol \]

Step 2: Deduce the amount, in moles, of CaO produced from 0.25 mol of CaCO3.

This step involves using the ratio of CaCO3 to CaO from the chemical equation.

     CaCO3     –>         CaO      +      CO2

From the equation you can see that the ratio of CaCO3 to CaO is 1:1.

Therefore if you have 0.25 mol of CaCO3 this will produced 0.25 mol of CaO.

Step 3: Calculate the mass of 0.25 mol of CaO.

    \[M_r(CaO)=(1 \times 40) + (1 \times 16) \]

    \[M_r(CaO)= 56\]

    \[Mass(CaO)=amount \times M_r \]

    \[Mass(CaO)= 0.25 \times 56\]

    \[Mass(CaO)= 14g\]

 

A simple format for laying out this method can be used.

Example: What mass of ammonia (NH3) is formed when 7 g of nitrogen (N2) is combined with hydrogen (H2).

     

 

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Section 1: Principles of chemistry

      a) States of matter

      b) Atoms

      c) Atomic structure

     d) Relative formula masses and molar volumes of gases

     e) Chemical formulae and chemical equations

     f) Ionic compounds

     g) Covalent substances

     h) Metallic crystals

     i) Electrolysis

 Section 2: Chemistry of the elements

     a) The Periodic Table

     b) Group 1 elements: lithium, sodium and potassium

     c) Group 7 elements: chlorine, bromine and iodine

     d) Oxygen and oxides

     e) Hydrogen and water

     f) Reactivity series

     g) Tests for ions and gases

Section 3: Organic chemistry

     a) Introduction

     b) Alkanes

     c) Alkenes

     d) Ethanol

Section 4: Physical chemistry

     a) Acids, alkalis and salts

     b) Energetics

     c) Rates of reaction

     d) Equilibria

Section 5: Chemistry in industry

     a) Extraction and uses of metals

     b) Crude oil

     c) Synthetic polymers

     d) The industrial manufacture of chemicals