| Scientists have defined unified atomic mass in terms of what isotope? | Carbon-12 |
| Unified atomic mass | one twelfth of the mass of a carbon-12 |
| Relative atomic mass | ratio of the average mass of the atoms of an element to the unified atomic mass units |
| Values of the relative atomic mass in the Periodic Table are determined by what... | Determined by using the weighted average mass of the atoms of a particular elements |
| What term do we use for the mass of a particular isotope of an element which has the Avogadros number of atoms (6.02 x 10^23) | Relative isotopic mass |
| How do we find the relative molecular mass | By adding up the relative atomic masses of all the atoms present in one molecule |
| For silicon dioxide the formula is SiO2. This is also known as its? | Formula units |
| What term do we use compounds containing ions | Relative formula mass |
| Compounds can form crystals which have water as part of their structure. What is this water called? | Water of crystallisation |
| A compound containing water of crystallisation is called? | Hydrated compounds |
| A compound which does not contain water of crystallisation is called? | Anhydrous compounds |
| What is the main use of mass Spectrometry? | Main use of mass spectrometry is in the identification of organic compounds. |
| What is fingerprinting? | Other form of spectroscopy, a substance can be identified by matching its spectrum against the spectra of known substances stored in a database. |
| The peak at highest mass-to-change ratio is caused by the ....ion? | Molecular ion |
| How is a molecular ion formed? | A molecular ion is formed when 1 electron is removed from a molecule to form an ion with a single positive charge. |
| Fragmentation of a compound in a mass spectrometer causes what? | Fragmentations of a compound in a mass spectrometer causes certain bonds to break |
| The breaking of single bonds such as C-C , C-O or C-N is the most common cause of what? | Fragmentation |
| What does the formula of a compound show us? | Formula of a compound shows us the number of atoms of each element present in one formula unit or one molecule of the compound |
| Explain Avogadro constant | Number of particles equivalent to the relative atomic mass or relative molecular mass of a substance in grams. |
| What is the numerical value for Avogadro constant | 6.02 x 10^23 |
| Define term mole, in terms of Avogardros constant. | A mole is the amount of substance which contains 6.02 x 10^23 specified particles |
| What is meant by the stoichiometry of the equation? | Ratio of moles of the reactants and products |
| What do we use in order to find the mass of products formed in a chemical reaction? (3) | - Mass of reactants
- Molar mass of reactants
- balanced equations |
| The reactant which has number of moles in excess is called | Excess reagent |
| The reactant which is not in excess is called | limilting reagent |
| What must you remember in calculating which reactant is limiting? (2) | - work out number of moles of reactant
- take into account ratio of the reactants shown in
equation (the stoichiometry) |
| Use the formula of a compound and relative atomic masses to calculate percentage by mass of a particular element in a compound. | %by mass =
Atomic mass x number of moles of particular elements in a compound
-------------------------------------------------------------
Molar mass of compounds |
| In many chemical reactions, especially organic reactions, not all reactants are changed to products you want, why? (3) | - other reactions going on at same time
- reactants or products are lost in atmosphere
- Reaction does not go to completion |
| What is the formula when calculating percentage yield? | actual yield
--------------------------------------------- x100
predicted yield (theoretical yield ) |
| What is actual yield | moles of product obtained by experiment |
| What is predicted yield? | moles or mass of product obtained by calculation if no side products are formed and all of a specific reactants is converted to specific products |
| What is the empirical formula of a compound? | Simplest whole number ratio of elements present in one molecule or formula unit of compound |
| In order to deduce the molecular formula we need to know what (2)? | - relative formula mass of the compound
- empirical formula |
