Chemical Formulae, Equations, Calculations Flashcards
How do you write a balanced chemical equation?
When balancing equations, there needs to be the same number of atoms of each element on either side of the equation:
Work across the equation from left to right, checking one element after another
If there is a group of atoms (such as nitrate group, NO3–), which has not changed from one side to the other, then count the whole groups, rather than counting the individual atoms.
How do you calculate relative formula masses from relative atomic masses?
Calculated from the mass number and relative abundances of all the isotopes of a particular element.
What is a mole?
The mass of substance containing the same number of fundamental units as there are atoms in exactly 12.000 g of 12C. Mole is the unit representing the amount of atoms, ions, or molecules.
One Mole is the amount of a substance that contains 6 x 1023 particles (Atoms, Molecules or Formulae) of the substance (6 x 1023 is known as the Avogadro Number).
What is the mole triangle?
Mass
Moles
Relative Formula mass
What are reacting masses?
Reacting Masses: Chemical equations can be used to calculate the moles or masses of Reactants and Products
Use information from the question to find the mole of a substance / reactant
Identify the ratio of the substance and reactants and find the moles of others
Apply mole calculations to find answer.
What is percentage yield?
Percentage Yield: Calculation of the percentage of yield obtained from the theoretical yield. In practice, some product will be lost during the process when purifying the product by filtration or evaporation or when transferring a liquid or when heating.
What is the equation for percentage yield?
Percentage Yield = ( Yield Obtained / Theoretical Yield ) x 100
How do you find the formulae of a metal oxide, experiment?
Method:
Measure mass of crucible with lid
Add sample of metal into crucible and measure mass with lid (calculate the mass of metal by subtracting the mass of empty crucible)
Strong heat the crucible over a Bunsen burner for several minutes
Lift the lid frequently to allow sufficient air into the crucible for the metal to fully oxidise without letting magnesium oxide escape
Continue heating until the mass of crucible remains constant (maximum mass), indicating that the reaction is complete
Measure the mass of crucible and contents (calculate the mass of metal oxide by subtracting the mass of empty crucible).
How do you work the empirical formula?
Mass of Metal: Subtract mass of crucible from metal and mass of empty crucible
Mass of Oxygen: Subtract mass of metal used from the mass of magnesium oxide
Step 1 – Divide each of the two masses by the relative atomic masses of elements
Step 2 – Simplify the ratio
How do you find the formula of crystals, experiment?
Measure mass of evaporating dish
Add a known mass of hydrated salt
Heat over a bunsen burner, gently stirring, until the blue salt turns completely white, indicating that all the water has been lost
Record the mass of the evaporating dish and contents.
Then use the empirical formula to measure the amount both substances.
Working out the empirical formula for crystals?
Mass of White Anhydrous Salt: Measure Mass of White Anhydrous Salt Remaining
Mass of Water: Subtract Mass of White Anhydrous Salt Remaining from the Mass of Known Hydrated Salt
STEP 1 – Divide Each of the Two Masses by the Relative Atomic Masses of Elements
STEP 2 – Simplify the Ratio of Water to Anhydrous Salt
How to determine the formula of a Metal Oxide by combustion?
Measure mass of crucible with lid
Add sample of metal into crucible and measure mass with lid (calculate the mass of metal by subtracting the mass of empty crucible)
Strong heat the crucible over a bunsen burner for several minutes
Lift the lid frequently to allow sufficient air into the crucible for the metal to fully oxidise without letting Magnesium Oxide escape
Continue heating until the mass of crucible remains constant (maximum mass), indicating that the reaction is complete
Measure the mass of crucible and contents (calculate the mass of metal oxide by by subtracting the mass of empty crucible)
Working out Empirical Formula / Formulae:
Mass of Metal: Subtract Mass of Crucible from Metal and Mass of Empty Crucible
Mass of Oxygen: Subtract Mass of Metal used from the Mass of Magnesium Oxide
Step 1 – Divide Each of the Two Masses by the Relative Atomic Masses of Elements
Step 2 – Simplify the Ratio
How to determine the formula of a Metal Oxide by reduction?
Method:
Measure mass of metal oxide
Place metal oxide into a horizontal boiling tube held by a clamp and heat using bunsen burner
Heat until metal oxide completely changes colour, meaning that all the Oxygen has been reduced
Measure mass of the remaining metal powder
Working out Empirical Formula / Formulae:
Mass of Metal: Measure Mass of the Remaining Metal Powder
Mass of Oxygen: Subtract Mass of the Remaining Metal Powder from the Mass of Metal Oxide
Step 1 – Divide Each of the Two Masses by the Relative Atomic Masses of Elements
Step 2 – Simplify the Ratio
What is an empirical formula?
Empirical Formula: Gives the simplest whole number ratio of atoms of each element in the compound
Calculated from knowledge of the ratio of masses of each element in the compound
What is a molecular formula?
Molecular Formula: Gives the exact numbers of atoms of each element present in the formula of the compound
Divide the relative formula mass of the molecular formula by the relative formula mass of the empirical formula
Multiply this to each number of elements
