Calculations Involving Masses Flashcards
Substance that are made of simple molecules also have a molecular formula. What does the molecular formula represent?
Represents the actual number of atoms in one molecule
What is the relative formula mass?
The relative formula mass (Mr), of a substance is the sum of the relative atomic masses (Ar) of all the atoms or ions in its formula
How can you find the empirical formula?
The empirical formula can be calculated from the masses of the elements used to make it
Go to p73
And look at the empirical formula table
How do you work out the relative atomic mass?
(Mass ✖️ atomic number) ✖️ (mass ✖️ atomic number) ➗ 100
What the the law of conservation of mass?
When a solute is dissolved in a solvent to make a solution, the mass of the solution is equal to the mass of the solvent and the mass of the solute, the overall mass of the substance does not change.
What is concentration?
The amount of solute dissolved in a stated volume of a solution. The units are usually grams per cubic decimetre written as g dm 3. 1 dm3 is the same as 1 litre or 1000 cm3
How do you calculate the concentration of a solution?
Concentration = mass of solute in g ➗ volume of solution in dm3
In concentration if the solution is given in cm3 what do you need to do?
Convert it to dm3 by dividing by 1000
What is closed system?
When substances cannot enter of leave an observed environment
What is a non-closed system?
Another term for an open system
What happens in all systems?
The mass of the products is always the same as the mass of the reactants
Go to page 75
See how to work out the masses of reactants
What is the Avogadro constant (or 1 mol)
6.02 ✖️ 10 to the power of 23
How do you work out the number of moles in a substance?
Mass of a substance (g) ➗ Ar or Mr
What is the limiting reactant?
The amount of product formed determined by the amount of product formed that is not in excess
What is the empirical formula?
This is the simplest whole number of ratio of atoms or ions of each element in a substance
If you know the mass of each substance in a reaction what can you calculate?
You can calculate the number of moles of each and deduce the balanced equation. The ratio of the moles of each substance is the stoichometry of the reaction
Go to page 77
And look at the example
What is the stoichometry?
The molar ratio of the reactants and products in a chemical reaction
