5.2 - Calculations using moles and the Avogadro's constant Flashcards
What is a mole?
A mole is the amount of substance that contains the same number of particles as the number of carbon atoms in exactly 13g of the 12C isotope.
What is the value for Avogadro’s constant?
This number allows for the number of particles present in a sample of a substance with a known mass to be found.
How is the number of particles calculated using Avogadro’s constant?
Number of particles = Amount of substance (moles) x Avogadro’s constant.
What is the first equation for calculating moles?
Moles = Mass/Molar mass
n=M/Mr
How are equations balanced?
Reacting ratios must be correct. For chemical equations to be balanced it must have the same number and type of each atom present on both sides of the equation. Also include state stables.
How are ionic equations completed?
Ionic equations show atoms or molecules involved. Only ions that react together not the spectator ion.
Start with full equation
Replace the formulae of ionic compounds with their separate ions
Delete any ions that don’t appear on both side
How are reacting masses equations calculated?
First calculate the number of moles by n=M/Mr. Then complete the ratio to figure out if the next step is dividing or multiplying. Finally to find the mass use the equation m= N x Mr
How are equations worked out from reacting masses?
Calculate the molar masses of the relevant substances.
Calculate the amount of these substances or moles.
Use these amounts or moles found to calculate the simplest whole number ratio for these substances.
Use this ratio to work out the equation for the reaction.
What is Avogadro’s Law/
Avogadro’s Law states that equal volumes of gases under the same conditions of temperature and pressure contain the same number of molecules
How are Avogadro’s Law equations calculated?
Make sure the ratios of the volumes of reacting gases are in a whole number ratio.
For example is 1 mole of Nitrogen reacts with 3 moles of hydrogen 2 forms of ammonia will form.
How is Avogadro’s Law equations calculated using reacting volume of gases?
Given an equation showing reacting gases. Can workout the volumes that are involved.
If 100cm3 of H2 Mixed with 100cm3 of cl2 in the equation
H2 + Cl2 > 2HCl
it would react to form 200cm of hydrogen chloride because it is in the ratio 1:1:2
What is Molar volume?
The volume of the gas that contains one mole of that gas. Same for all gases. Varies with temp and pressure.
Value is usually 24.0dm3
What are the calculations using the molar volume equation?
Vm/24.0 = Volume (dm3)/ Amount in mol
24 = V/N
How is molar volume calculated if the equation involves a gas and solid or liquid?
Combine the 2 calculations, can interconnect between the amount and volume for gases. For solids and liquids can interconvert between amount and mass.
Step 1: Calculate amount in moles from either the mass or the volume depending on what is given.
Step 2: Is to use the relevant reaction ratio in the equation to calculate the amount of another substance.
Step 3: Is to convert this amount to a mass or volume depending on what questions asks.
