Topic 3 Flashcards
How do you work out the relative formula mass Mr of a compound?
Add all the relative atomic masses Ar of all the atoms in the formula together.
How do you work out the % mass of an element in a compound?
% mass of an element in a compound =
Ar x number of atoms of the element
_______________________________________ x 100
Mr of the compound
What is the mole?
The mole is simply the name given to an amount of a substance
What is the Avogadro constant
_________23
6.02 x 10
What is the formula to find the number of moles in a given mass?
number of moles =
mass in g (of an element or compound)
___________________________________________
Mr (of the element or compound)
What is conserved during a chemical reaction?
The mass as no atoms are lost or destroyed.
In some cases why does the mass increase in a chemical reaction?
It’s probably because one of the reactants is a gas that’s found in air and all the products are solids, liquids or aqueous
Explain why In some cases the mass increase in a chemical reaction?
Before the reaction, the gas is floating around in the air. It’s there but it’s not contained in the reaction vessel, so you can’t account for it’s mass. When the gas reacts to form part of the product, it becomes contained inside the reaction vessel - so the mass increases.
In some cases why does the mass decrease in a chemical reaction?
It’s probably because one of the reactants is a gas that’s found in air and all the products are solids, liquids or aqueous
Explain why In some cases the mass decrease in a chemical reaction?
Before the reaction, all the reactants are contained in the reaction vessel. If the vessel isn’t enclosed then the gas can escape from the reaction vessel as it formed. Its no longer contained in the reaction vessel so you can’t account for its mass - the total mass of the stuff inside the reaction vessel decrease.
What’s a limited reaction?
When 1 reactant gets used up before the rest so the reaction stops.
What is a limiting reactant?
The reactant that gets used up in a limiting reaction because it limits the amount of product that is formed.
What is the volume any gas will occupy if it’s at the same temperature (20 degrees), pressure and has the same number of moles?
——–3
24dm at 20 degrees
What is the formula to calculate the volume of gas?
volume of gas = mass of gas
_____________ x 24
Mr of gas
What is concentration a measure of?
How crowded things are
How does solute effect concentration?
The more solute there is in a given volume, the more concentrated the solution is.
What is solute?
The substance that’s dissolved
What is the formulas to calculate the concentration?
concentration (in g) = mass of solute (g)
________________
volume of solvent (dm cubed)
concentration (in mol) = number of moles of solute (mol)
_____________________________
volume of solvent (dm cubed)
What are titrations?
Experiments that let you find the volumes needed for two solutions to react together completely.
What is atom economy?
the percentage of reactants forming useful products
What is the formula to work out the atom economy?
Atom economy= relative formula mass of desired product
_________________________________________ x100
relative mass of all reactants
What is meant by yield?
The amount of product you get.
What is the formula to work out the percentage yield?
Percentage yield = mass of product actually made (g)
_________________________________ x100
maximum theoretical mass of product (g)
What are percentage yields always between?
0% and 100%
