Unit 1: Section 2 - Amount of Substance Flashcards
What is the Avogadro’s constant equation? (This is really helpful because you always forget it)
Number of particles = Number of moles x Avogadro’s constant
What is the moles, mass equation?
Mass of substance = Number of moles x Mr
What is the moles, concentration equation?
Number of moles = Concentration x Volume
What is the Ideal Gas equation including the units?
pV=nRT
p - pressure in Pa
V - volume in m^3
n - number of moles
R - gas constant in JK^-1mol^-1
T - temperature in K
How do you write an ionic equation?
- Write the balanced symbol equation
- Identify the soluble compounds using the solubility rules or the aqueous state symbol
- Split up the soluble compounds into ions
- Cancel ions that appear on both sides of the equation
- Write out the resulting ionic equation
How to make a standard solution (Using sodium hydroxide)?
- Work out how many moles of NaOH you need using moles = concentration x volume
- Work out how many grams of NaOH you need using mass = moles x Mr
- Use weighing by difference to find the precise mass of the solid used and add to beaker making sure to rinse the washings
- Add distilled water to the beaker and stir
until all NaOH has been dissolved - Tip the solution into a volumetric flask using a funnel
- Rinse the beaker and stirring rod with distilled water and add that to the flask, making sure there’s no solute left over
- Use distilled water to fill the flask up to the line, making sure the bottom of the meniscus is lined up
- Stopper and invert the flask a few times to ensure it’s all been mixed
How to set up a titration
- Use a pipette to measure a set volume of the solution you want to know the concentration of, and put it in a flask
- Add a few drops of indicator
- Then fill a burette with a standard solution of the acid that you know the exact concentration of
- Use a funnel to carefully pour the acid into the burette, always doing this below eye level
How to carry out a titration
- Do a rough titration to get an idea where the end point actually is
- Take an initial reading to see exactly how much acid is in the burette, then run the acid within 2cm^3 of the rough titre, then add it dropwise, swirling the flask until the colour just changes
- Work out the amount of acid required to neutralise the alkali
- Repeat until you have three concordant results
- Calculate a mean value
What are the titration indicators?
Methyl orange - red in acid and yellow in alkali
Phenolphthalein - colourless in acid and pink in alkali
Use a white tile to be bale to see the colour change easier
What is the empirical formula?
The simplest whole number ratio of atoms of each element in a compound
What is the molecular formula?
Gives the actual numbers of atoms of each element in a compound
What is theoretical yield?
The mass of product that should be formed in a chemical reaction, it assumes no chemicals are ‘lost’ in the process.
You can use the masses of reactants and a balanced equation to calculate it
How to calculate percentage yield
Percentage Yield = Actual Yield / Theoretical Yield x 100
What is percentage yield?
Tells you how wasteful a process is, based on how much product is lost during the process
What is atom economy?
The measure of the proportion of reactant atoms that become part of the desired product rather than the by-products in the balanced chemical equation
