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 definition of Avogadro’s constant?
Number of particles/atoms/ions in one mole of a substance
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
What are standard conditions?
25°C/298K
1 atm/ 100kPa
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
