| The sum of the relative atomic masses of all the atoms in a chemical formula. | Relative Formula Mass (Mr) |
| What is the relative atomic mass (Ar) of an element? | The relative atomic mass (Ar) of an element is its average atomic mass, which is the same as its mass number and is shown in the periodic table. |
| The weighted average of the atomic masses of the isotopes of an element, taking into account their relative abundances. | Average Atomic Mass |
| How can the relative formula mass (Mr) of a compound be calculated? | The relative formula mass (Mr) of a compound can be found by adding up the relative atomic masses of all the atoms in its molecular formula. |
| A formula that indicates the types and numbers of atoms in a molecule of a compound. | Molecular Formula |
| What is the molecular formula of CO2? | The molecular formula of CO2 indicates that it contains 1 carbon atom and 2 oxygen atoms. |
| A colorless gas with a molecular formula of CO2, consisting of one carbon atom bonded to two oxygen atoms. | Carbon Dioxide (CO2) |
| How is the relative formula mass (Mr) of CO2 calculated? | The Mr of CO2 = 12 (for carbon) + (16 × 2) (for oxygen) = 44. |
| Why is the relative atomic mass of oxygen multiplied by 2 in the calculation of the Mr of CO2? | The Ar of oxygen has to be multiplied by 2 because there are 2 oxygen atoms in the CO2 molecule. |
| The simplest whole number ratio of elements in a compound. | Empirical Formula |
| What is the empirical formula? | The empirical formula is the simplest whole number ratio of elements in a compound. |
| The formula showing the actual number of each type of atom in a molecule. | Molecular Formula |
| What does the molecular formula of a compound show? | The molecular formula shows the number of each atom in the molecule. |
| A hydrocarbon with the molecular formula C4H10. | Butane |
| What is the molecular formula of butane? | Butane has the molecular formula C4H10. |
| A hydrocarbon with the molecular formula C5H10. | Pentene |
| What is the molecular formula of pentene? | Pentene has the molecular formula C5H10. |
| A hydrocarbon with the empirical formula C2H5. | Butane |
| What is the empirical formula of butane? | Butane has the empirical formula C2H5. (the simplest ratio of carbon to hydrogen is 2 : 5) |
| A hydrocarbon with the empirical formula CH2. | Pentene |
| What is the empirical formula of pentene? | Pentene has the empirical formula CH2. (the simplest ratio of carbon to hydrogen is 1 : 2) |
| A formula that specifies the actual number of atoms of each element in a molecule. | Molecular Formula |
| How can you determine a molecule's molecular formula using its empirical formula and relative formula mass? | By knowing the empirical formula and relative formula mass, you can work out the molecular formula. |
| A formula that shows the simplest whole-number ratio of atoms of each element in a compound. | Empirical Formula |
| What is the difference between a molecular formula and an empirical formula? | The molecular formula specifies the actual number of atoms of each element in a molecule, while the empirical formula shows the simplest whole-number ratio of atoms. |
| The sum of the relative atomic masses of the atoms in a formula unit of a compound. | Relative Formula Mass (Mr) |
| What information do you need to determine a molecule's molecular formula? | You need the molecule's empirical formula and relative formula mass. |
| What is an example of determining a molecule's molecular formula using its empirical formula and Mr? | For example, a molecule has an empirical formula of CH2 and an Mr of 56. |
| What is the relative formula mass of the empirical formula CH2? | The relative formula mass is 14 (12 + (2 × 1) = 14). |
| The quantitative relation between two amounts showing the number of times one value contains or is contained within the other. | Ratio |
| What does dividing the relative formula mass of the molecule by the relative formula mass of the empirical formula indicate? | It indicates how many times bigger the molecular formula is compared to the empirical formula. |
| If the Mr of the empirical formula CH2 is 14, and the molecules' Mr is 56, how many times bigger is the molecular formula compared to the empirical formula? | In this case it's 4 times bigger (56/14 = 4). |
| The process of combining two or more numbers to find a product. | Multiplication |
| How can you determine the molecular formula using the calculated value and the empirical formula? | By multiplying the empirical formula by the calculated value to obtain the molecular formula. |
| A formula showing the simplest whole-number ratio of atoms in a compound. | Empirical Formula |
| How can the empirical formula of a simple compound be determined using reacting masses? | The empirical formula of a simple compound can be determined using reacting masses. |
| The masses of substances that react together in a chemical reaction. | Reacting Masses |
| In the given example, what substance reacted with a mass of 160 g? | Calcium (Ca). |
| In the given example, what substance reacted with a mass of 64 g? | Oxygen (O2). |
| A unit of measurement used in chemistry to express amounts of a substance. | Moles (mol) |
| How can the moles of each reactant be calculated using their masses and Mr? | Use the equation moles = mass/Mr to calculate the moles of each reactant. |
| The quantitative relation between two amounts, often expressed as a fraction or proportion. | Ratio |
| What does the ratio of 4 moles of calcium to 2 moles of oxygen imply? | It implies the ratio of calcium to oxygen in the formula is 4:2, which simplifies to 2:1. |
| What is the empirical formula of the compound determined from the given reacting masses? | The empirical formula is CaO. |
| Lab experiments can help to calculate the empirical formula of a simple compound, for example, magnesium oxide. | Lab Experiments |
| First weigh a crucible and its lid and record the mass (this is Mass 1). | Crucible Weighing - Step 1 |
| Place a piece of magnesium ribbon into the crucible, put the lid on, and weigh it again (this is Mass 2). | Magnesium Placement - Step 2 |
| Place the crucible in a clay triangle above a Bunsen burner for heating. | Heating Setup - Step 3 |
| Heat the magnesium for a few minutes, lifting the lid with tongs every 20 seconds to allow oxygen in. | Heating Procedure - Step 4 |
| Allow the crucible to cool, then reweigh the crucible, lid, and the magnesium oxide produced in the crucible (this is Mass 3). | Cooling and Re-Weighing - Step 5 |
| Subtract Mass 2 from Mass 1 to determine the mass of the magnesium. | Magnesium Mass Calculation - Step 6 |
| Subtract Mass 3 from Mass 2 to calculate the mass of oxygen that reacted with the magnesium. | Oxygen Mass Calculation - Step 7 |
| From the reacting masses of magnesium and oxygen, calculate the empirical formula of magnesium oxide (MgO). | Empirical Formula Determination - Step 8 |
