Topic 3 - Quantitive Chemistry Flashcards
What’s the formula for percentage mass of an element in a compound
((Ar x number of atoms in that element) ÷ Mr of the compound ) × 100
What is one mole of any substance
An amount of that substance that contains an avogadro’s number of particles
What’s the value of avogadro’s constant
6.02 × 10^23
What is the mass of one mole of atoms in any substance equal to
The relative formula mass
What’s the equation linking mass, moles, and Mr
Moles = mass÷ Mr
What is the law of conservation of mass
During a chemical reaction no atoms are destroyed and no atoms are created - due to this no mass is lost or gained
Why might the mass seem to change in a reaction
- if there is a gas involved and the reaction happens in an unsealed reaction vessel
In a symbol equation, what tells us how many moles of each substance there are
The big numbers in front of the chemical formulas
When is a reactant limiting
When it is used up before the others - any other reactant is it excess
What is the amount of product formed dependent on
The amount of the limiting reactant
At room temperature and pressure how much does one mole of gas occupy
24 dm^3
What’s the formula for the volume of a known mass at r.t.p
Volume = (mass of gas ÷ Mr of gas) × 24
What’s the equation for concentration of a solution
Mass of solute or number of moles of solute ÷ volume of solvent
How do you calculate the mass of a solute in a solution
Concentration x volume
How do you convert cm^3 to dm^3
Divide by 1000
How to convert mol/dm^3 to g/dm^3
Use the equation mass = moles x Mr
What’s the equation for atom economy
Atom economy =( relative formula mass of desired product ÷ relative formula mass of all reactants) × 100
Why are reactions with a higher atom economy better
- reactions with a low atom economy use up resources quickly making them unsustainable and unprofitable
- they don’t produce as much waste products
What reactions typically have the highest atom economy
The ones that only have one product
What’s the equation for percentage yield
(Mass of product actually made ÷ maximum theoretical mass of product) × 10p
Why is a higher percentage yield better
Reduced waste and reduced cost
Why are yields below 100 percent
1) not all reactants react to make a product
2) there may be side reactions
3) you may lose some product when you separate it from the reaction mixture
