9 - Calculations Involving Masses Flashcards
What is the empirical formula?
The simplest whole number ratio of atoms or ions of each element in a substance
What is the molecular formula?
The actual number of atoms of each element in one molecule
What is the relative formula mass of a substance?
The sum of the relative atomic masses of all the atoms or ions in its formula
How can you find the empirical formula of a compound from its mass
1) mass (g) / RAM
2) Divide answers by the smallest number to find the simplest ratio
How would you find the molecular formula from its empirical formula and RAM?
1) Find Relative formula mass of empirical formula
2) Divide Relative formula mass of that compound by its empirical formula
3) Multiply ans w/ empirical formula
What is concentration?
The amount of solute dissolved in a stated volume of a solution
What is a solute?
A solid substance that dissolves in a liquid
What is a solvent?
The liquid in which a solute is dissolved
What is a solution?
Forms when a solute dissolves in a solvent close solvent
How do you calculate concentration?
What are the units of concentration?
How many cm^3 is 1dm^-3?
1000cm^3 or 1L^3
How would you calculate the masses of products & reactants?
1) Write down the balanced equation for the reaction
2) Write the relative formula masses under the substances and add the units in the question
3) Multiply the relative formula masses by the coefficients in the equation
4) Find the mass of product for 1 g of reactant
5) Scale up for the mass given in the question
How is the percentage mass of an element in a compound calculated?
What is the law of conservation of mass?
States that no matter is lost or gained during a chemical reaction
Why must all chemical reactions be balanced?
Mass is always conserved
—> Total mass of the reactants = Total mass of the products
What is a precipitation reaction?
One in which two solutions react to form a precipitate
Describe the mass of a substance before & after the reaction in a closed system
Total mass of the reaction flask will remain constant
Describe the mass of a substance before & after the reaction in an open system
Total mass of the reaction flask will change
What is Avogadro’s constant?
What is the mole?
A unit which measures the amount of substance
What is the units for mole?
mol
What is molar mass?
1 mole of any element = FOR COMPOUNDS RAM of that element in grams OR FOR COMPOUNDS Relative formula mass in grams
What is the units for molar mass?
g/mol
What would the molar mass be of 1 mole of carbon atoms and why
Mass of 12 g (because the Ar of carbon is 12)
How do we find the mass of one mole of a compound?
We add up the RAMs
What is the relationship between moles, particles & the Avogadro’s constant?
What is the relationship between moles, mass & the RAM?
When does a chemical reaction stop?
When one of the reagents is used up
What is the limiting reagent?
- The reagent that is used up first
- Not present in excess in a reaction
What is the amount of product directly proportional to?
The amount of the limiting reagent added at the beginning of a reaction
How can we calculate masses of reactants and products from a chemical equation, being given the mass of one substance?
Why would you often use one reactant in excess in a chemical reaction?
To ensure that all of the other reactant is used
What is stoichiometry?
Refers to the balancing numbers in front of compounds/elements in reaction equations
Describe an experiment to determine the empirical formula of a simple compound such as magnesium oxide
1) Weigh some pure magnesium
2) Heat magnesium to burning in a crucible to form magnesium oxide, as the magnesium will react with the oxygen in the air
3) Weigh the mass of the magnesium oxide
//
Figure out mass of O2, moles of mag & o2
Calculate ratio of moles of magnesium to moles of oxygen
—> Use ratio to form empirical formula
