Quantitive Chemistry Flashcards
What is the symbol of relative atomic mass?
Aᵣ
How do you work out the Aᵣ?
- Multiply Aᵣ with number of elements
- Add them all up
How do you find out the % Mass of an element in a compound?
% mass of an element in a compound = Aᵣ X number of atoms in that element / Mᵣ of compound X 100
What does the Aᵣ of an element mean?
the mean mass of all of the isotopes of an element.
Avogadro constant
6.02 X 10²³
Formula for mass (g)
Mass (g) = Mᵣ X Number of moles
What is the conservation of mass?
Mass is the same for the reactants and products - mass is conserved
Why might the mass increase?
One of the reactants is a gas
Why might the mass decrease?
One of the products is a gas
Formula for concentration using moles and volume
Concentration (gdm-3) = Mass (grams)/ Volume (dm3)
How many cm3 is there is dm3
1000
How would you convert 480cm3 to dm3
Divide by 1000 = 0.48dm3
Formula for volume of gas
Vol of gas (dm3) = 24 X Moles
Atom economy formula
Atom economy = Mr/ Mass of desired products/ Mr/Mass of all reactants X 100
What is atom economy?
Tells you how much of the mass of the reactants that end up as useful products when manufacturing a chemical = high needed
What does 100% atom economy mean?
Means all the atoms in the reactants have been turned into useful products
What does a low atom economy mean?
Low mass of useful products
Why is it important to consider atom economy?
- Raw materials are expensive, if waste is produced = less profitable
- Less sustainable - Large quantities of reactants -> small amounts of products
- Waste products - expensive to dispose of
Solutions to atom economy
- Use a more efficient reaction
- Find use of waste products
Factors to find out how profitable a reaction is
- % Yield
- Cost of raw materials
- Rate of reaction
- Cost of maintaining the right conidtions
- Temperature
- Pressure
What is percentage yield?
Amount of product you get from a reaction
Difference between actual and theoretical yield?
Actual yield = amount we actually get
Theoretical yield = what you expect
Reasons why we might not make as much product
- Reversible reaction - some products may turn into reactants
- Side reactions may occur = unwanted products
- Some lost during separation eg some left on filter paper
- Some product may be a gas = escapes
- Evaporation = if liquid
How to calculate percentage yield
actual yield (g)
/
max theooretical yield
X 100
What is concentration?
Shows how much solute (grams or mols) are in a certain volume of a liquid
Titration Method
- Collect HCL in a beaker and label it
- Rinse burette with distilled water and then with some HCL
- Fill burette with the HCL beyond the 0 mark and let soolution run out until botto m of meniscus is exacltly on the 0 mark - all bubbles should be removed from the jet
- Collect sodium hydroxide in a beaker and label it
- Rinse 25cm3 pipette with distilled water and then with sodium hydroxide
- Use pipette and pipette filler to transfer 25cm3 of NaOH into a clean dry conical flask
- Add 3/4 drops of phenolphthlein indicator into the flask and swirl. Place conical flask on the white tile directly under burette
- Record initial burette reading in the table below ( show be 0.00cm3)
- Carry out a rough titration by adding the acid to the alkali in small amountd at a time.Swirl flask after every addition and continue until indicator permanently turns pink
- Repeat titration accurately by adding the acid drop-wise near the end point.
- Repeat titration until you have 2 concondant results (within 0.10cm3)
- Record readings in table
How should you read the meniscus? Where is it?
- It is in a burette
- the bottom bit is where you take reading
- must be done at eye level
- need 3 readings that are consistent
What happens to the conc. if you increase the mass of the solute and keep the volume the same?
Conc increases
What happens to the conc is the volume of the solution increases and the mass of the solute stays the same?
Conc decreases
What is phenolphthalein in acidic and alkaline solutions?
acidic + neutral = colourless
alkaline = pink/red
How do you do titration calculations
- Calc number of moles
- Find molar ratio
- Convert cm3 to dm3 = divide 1000
- Calc number of moles using known conc using formula
- Identify number of moles and using ratio find out no of moles for other reactant
- calc conc using same formula
conc and mol fomrula (2)
1 mol of any gas takes up what volume?
24dm3
In a titration calculation, how would you turn moles/dm3 to g/dm3
multiply conc by the Mr
How can you balance equations?
Work out number of moles in a ratio and divide by the least
Name indicators for titrations
- Phenolphthalein
- Methyl Orange
- Litmus
Phenolphthalein
- Acid = colourless
- neutral = colourless
- alkakline = pink
Methyl orange
- Acid = red
- Neutral = orange
- alkaline = yellow
Litmus
- Acid = red
- Neutral = purple
- Alkaline = blue
In a reaction, one reactant has to be ____ and the other has to be ______
- in excess - makes sure of the other reactant used up
- limiting - limits amount of products made
What is the rule of 1 mole of any gas?
- They occupy the same vol under the same conditions of temp and pressure
- room temp = 20 , pressure = 1 atmos
- Takes up a vol of 24cm3
Formula for number of moles of a gas
vol of gas (dm3) / 24dm3
How would you decrease the volume in general?
place under high pressure
Why is having a high atom economy important?
- sustainable development
- economic reasons
- reduce waste
How would you use Avogadros constant to calculate the number of particles?
moles X constant
