Topic 3 - Quantitive Chemistry Flashcards
Whats the equation for %mass of an element in a compound?
%mass of an element in compound = (Ar x number of atoms of that element / Mr of the compound) x 100
What is the avogadro constant?
6.02 x 10^23
This is how many particles of 1 mole of a substance has
Whats the formula for number of moles?
Number of moles = Mass(g) / Mr
What is the conservation of mass?
Mass of products always equals mass of reactants.
What explanations are there for mass changing during a reaction?
1) One of the reactants was a gas. At the beginning it wasnt contained in the reaction vessel so you couldnt account for its mass.
After it reacts to become part of the product, it becomes contained in the reaction vessel so the mass increases.
2) if mass decreases it could be because gas escaped from the reaction vessel if its not enclosed.
What is the limiting reactant in an equation?
The reactant thats used up. (because it limits the amount of product formed)
Product formed is directly proportional to limiting reactant
Whats the equation to find the volume of a gas at room temperature?
Volume of gas(dm^3) = (Mass of gas(g) / Mr of gas) x 24
What is concentration?
The amount of a substance in a certain volume.
Whats the equation for concentration?
Concentration(g/dm^3) = mass of solute(g) / volume of solvent(dm^3)
Concentration(mol/dm^3) = moles of solute(mol) / volume of solvent(dm^3)
Whats the equation for atom economy?
Atom economy = (formula mass of desired products / formula mass of all reactants) x 100
What is atom economy?
Percentage of desired products
What is percentage yield?
The amount of product made.
Whats the equation for percentage yield?
Percentage yield = (mass of product made(g) / maximum theoretical mass of product(g) ) x 100
Why are percentage yields never 100%?
1) Not all reactants react to make the product. In reversible reactions the products can turn back to reactants so never 100% yield.
2) Might be side reactions eg some may react with gases in the air.
3) Lose product when you transfer something from one container to another.
