C3 - Quantitative Chemistry Flashcards
Relative Formula Mass (Mr)
The relative atomic masses of all the atoms in the molecular formula added together
(Equation) Mass of an Element in a Compound
% of mass in an element in a compound = Ar * number of atoms of elemnt / Mr of compound * 100
Mole
An amount of a substance
Avogadro constant
6.02 x 10^23
Describe what is 1 mole of any substance
An amount of that substance that contains an Avogadro number of particles
One mole of atoms == ?
A mass in grams equal to the relative formula mass (Carbon has an Ar of 12, so one mole of carbon weighs exactly 12g)
(Equation) Number of moles =
mass in g (of an element or compound) / Mr (of the element or compound)
Law of conservation of mass
During a chemical reaction, no atoms are destroyed and no atoms are created. This means there are the same number and types of atoms on each side of a reaction equation. Because of this, no mass is lost or gained - we say that mass is conserved during a reaction
Why might the mass during a chemical reaction seem to change?
- The reactants in the air can react with the substances (increase)
- If the mass decreases, one the products could be gas
How can you Balance Equations Using Reacting Masses
1) Divide the mass of each substance by its relative formula mass to find the number of moles
2) Divide the number of moles of each substance by the smallest number of moles in the reaction
3) If any of the numbers aren’t whole numbers, multiply all the numbers by the same amount so that they all become whole numbers
4) Write the balanced symbol equation for the reaction by putting these numbers in front of the chemical formulas
Limiting Reactants
A reactant in the reaction that completely gets used up
What graph type is the relationship between the amount of product formed and the amount of limiting reactant?
Directly Proportional (aka linear)
How to calculate the mass of a product formed in a reaction by using the mass of the limiting reactant and the balanced reaction equation?
1) Write out the balanced equation
2) Work out relative formula mass (Mr) of the reactant and product you want
3) Find out how many moles there are of the substance you know the mass of
4) Use the balanced equation to work out how many moles there’ll be of the other substance. In this case, that’
s how many moles of the product will be made of this many moles of reactant
5) Use the number of moles to calculate the mass
Concentration
The amount of a substance in a certain volume of a solution is called its concentration
Solute
The substance that’s dissolved
