amount of substance Flashcards
What is relative atomic mass [A_r]?
The average mass of an atom of an element, taking into account its naturally occurring isotopes, relative to 1/12 the relative atomic mass of an atom of carbon-12.
It takes into account the percentage abundances of the isotopes.
How is relative atomic mass [A_r] calculated?
A_r = (isotope mass number x % abundance) + (isotope mass number x % abundance) … Sum of % isotope abundance.
Usually not a whole number.
What is relative molecular mass [M_r]?
Average mass of a molecule in relation to 1/12 the relative atomic mass of a carbon-12 atom.
How is relative molecular mass [M_r] calculated?
M_r = sum of A_r in the formula for the molecule.
What is relative formula mass [M_r] used for?
Used for ionic compounds because they don’t exist as molecules.
What is the Avogadro constant?
The number of particles in one mole, specifically 6.022 x 10^23.
What does one mole of a substance represent?
It contains the same number of atoms as the relative atomic mass of any element in grams.
Fill in the blank: The concentration of a solution is how many moles are dissolved per _____ dm^3.
1
What is the unit for concentration in solutions?
mol dm^-3.
How do you convert cm^3 to dm^3?
Divide by 1000.
What is the equation for calculating moles in solutions?
Moles = conc x vol/1000.
What is the ideal gas equation?
pV = nRT.
What does ‘p’ stand for in the ideal gas equation?
Pressure (Pa).
What does ‘V’ stand for in the ideal gas equation?
Volume (m^3).
What is the ideal gas constant (R)?
8.31 JK^-1 mol^-1.
How do you convert Celsius to Kelvin?
Add 273.
What is the empirical formula?
The simplest whole number ratio of atoms of each element in a compound.
How do you determine the empirical formula from experimental data?
Find masses or % from the experiment, work out moles of each element, divide by the smallest number of moles, convert to a whole number ratio.
What is the molecular formula?
The actual number of atoms of each element in a molecule/compound.
How do you calculate the molecular formula from the empirical formula?
Relative molecular mass (M_r) / Relative mass of empirical formula.
What is a balanced equation?
Same number of atoms on both sides of the equation.
What is an ionic equation?
An equation that ignores anything other than aqueous reactants and products, simplifying by considering ions present.
What are spectator ions?
Ions that do not take part in the overall reaction.
How do you determine limiting reagents?
Work out moles of both reactants, compare mole ratios.
What is the method for calculating the mass of product?
Write out balanced equation, fill in known masses, work out moles, use mole ratio, multiply by M_r of product.
What does percentage yield indicate?
How efficient the process was and how much was lost during the reaction.
What are some reasons for actual yield being less than theoretical yield?
- Incomplete reactions
- Practical losses
- Side reactions
- Loss of gas products
What is atom economy?
A measure of how many atoms are wasted in a reaction.
What does 100% atom economy indicate?
Only one product is formed.
How is apparatus uncertainty calculated?
Uncertainty of apparatus x 100 / Reading.
What is experimental error?
Difference between your value and the correct value x 100 / Correct value.
