Chapter 3 - Quantitative Chemistry Flashcards
What is the relative formula mass
The relative formula mass of a compound is just all the relative atomic masses of all the atoms in the molecular formula added together
What is the mole
The mole is simply the name given to an amount not a substance
What is one mole equal to
6.02 x 10^23
This is known as the avogardo constant
Why do we use the mole
We use it because the mass of that number of atoms or molecules(the mole) of any substance is exactly the same number of grams as the relative atomic mass or relative formula mass of the element or compound
One mole of atoms or molecules of any substance will have a mass in grams equal to the relative formula mass for that substance
E.g.
Carbon has a relative atomic mass of 12, so one mole of carbon weighs exactly 12 g
How do we find the number of moles in a given mass
Number of moles = mass in grams (Of an element or compound)/relative (formula mass of the element or compound)
What does it mean if the mass increases in a reaction
If the mass increases is probably because one of the reactants is a gas that’s found in the air.
Before the reaction the gases floating around in the air. When the gas reacts to form part of the product it becomes contained inside the reaction vessel so the total mass of the stuff inside the reaction vessel increases
What does it mean if the mass decreases in a reaction
If the mass decreases is probably because one of the reactants is a gas and all the reactants are solids, liquids or aqueous
Before the reaction all the reactants are contained in the reaction vessel. If the vessel is an enclosed then the gas can escape from the reaction vessel as it formed therefore is no longer contain the reaction vessel you can’t account for its mass
How do you work out the concentration
Concentration = mass of solutes (in grams)/volume of solvent (in DM cubed)
