Amount Of Substance Flashcards
Define the mole. (3)
The amount of substance that contains as many elementary particles as there are in 12g of carbon-12
Equation involving moles mass and Mr?
Moles= mass divided by Mr
Remember mass
Mr moles
What is the equation for percentage yield
Actual mass/mol of product divided by theoretical mass/mol of product all multiplied by 100
Give 3 reasons why full percentage yields are rarely obtained
• the reaction may be reversible- reaction takes place at equilibrium
• the reactants may be impure, leading to side reactions
• some reactants or products may be lost when preparing and purifying a compound
Give the equation for atom economy
Mr desired product divided by Mr all products multiplied by 100
What does it mean if a reaction has high atom economy?
Less waste product is produced
Why is a higher atom economy desirable in chemistry?
Increases sustainability as more useful products are made
What is meant by solvents solutes and solutions?
A solute is the solid which is dissolved in the solvent (the liquid which dissolves the solid). This produces a solution
What is the unit of concentration? (M)
moldm^-3
What is the equation for concentration?
Moles divided by volume (in dm^3)
How many cm in 1dm?
1000
What is reached at the end of a titration? (1) what do we assume this is? (2)
The end point- where we assume the moles of H+ ions from the acid equal the moles of OH- ions from the alkali, so the neutralisation equation takes place
What is the equation for neutralisation?
H+ + OH- -> H2O
Describe how to prepare a standard solution for volumetric analysis. (5)
1• Accurately weigh the solid using a weighing boat and measuring scales
2• Dissolve the solid in a beaker with distilled water until no more solid can be seen
3• Carefully transfer the solution to a volumetric flask, rinsing the boat and beaker thoroughly with distilled water. Add rinsings to the VF.
4• Fill the volumetric flask with distilled water up until the bottom of the meniscus is exactly in line with the graduation mark
5• Invert the flask several times with a stopper fitted
What to remember involving burette readings? (2)
Always to 2 decimal places and end in a 5 or a 0 (e.g 0.45 or 2.10)
What are meant by concordant results?
Burette titres within 0.1cm^3 of each other
State the equation triangle involving moles, volume and molar gas volume
volume
24dm^3 moles
Remember ‘24,moles,volume’
What are the assumptions of ideal gas?
• no intermolecular forces
• negligible size
• elastic collisions
• random motion
What is the ideal gas equation? When is it used?
pV=nRT
when conditions are outside of the norm
What is the ideal gas equation? When is it used?
pV=nRT
when conditions are outside of the norm
What is standard room temperature and pressure?
298K (25 degrees Celsius)
101KPa (101000Pa)
What is volume of gas measured in in the ideal gas equation? What would this be equal to 10000cm^3?
m^3
1m^3=1000000cm^3 so
10000cm^3=0.01m^3
What is gas molar volume?
The volume per mole of gas- dm3/mol
What is concentration of a solute?
The amount of solute (in moles) dissolved in 1dm^3 of solvent (volume)
What is relative formula mass? (3)
The weighted mean mass of the formula unit of a compound compared to 1/12th of an atom of carbon-12
What is Avogadro’s constant?
6.02x10^23
What is stoichiometry?
The balancing number giving the ratio of the amount, in moles of each substance in a balanced equation
What is meant by empirical formula? (1)
The simplest whole number ratio of atoms of each element in a compound
How to work out empirical formula?
•Place the percentage by masses of each element in a table
•divide this by Ar
•divide by the element which has the smallest value
•see ratio
What is meant by molecular formula? (1)
The actual number of atoms of each element in a molecule
What is the term for the water present in a compound giving the compound a crystalline appearance?
Water of Crystallisation (xH2O)
Define hydrated (1)
When water of crystallisation is present in a crystal compound
Define anhydrous (1)
When the waters of crystallisation have been removed from a compound
You have the exact value for the moles of water lost in crystallisation, as well as the moles of the entire salt before heating. What should be done to find the initial formula of the salt?
•mol water lost divided by mol entire salt
•this is n for how many moles of water lost
•add this to equation to get initial formula
What is meant by volumetric analysis?
A technique used to find the volume of one solution which is needed to react with a measured volume of another solution
What is meant by a standard solution?
The concentration of one of the solutions must be known exactly
A standard solution has been accurately prepared. Describe how a student should carry out an acid base titration now. (6)
1• Place 25cm3 of solution from the volumetric flask into a conical flask using a pipette
2• Add a few drops of indicator (methyl orange) to the conical flask
3• Add acid to burette
4• Slowly open burette and add acid to the conical flask, drop wise near the end point until the indicator changes from red to yellow
5• Record final burette reading to nearest 0.05cm3
6• Repeat until at least two concordant results are achieved
What is the Mr of SrCl2•6H2O?
266.6- water is locked within the compound so the Mr of H2O is included
When should balancing numbers be taken into account when calculating Mr? (2 examples)
•For atom economy (e.g 4H2=8)
•For water of crystallisation
When calculating atom economy, what would be the Mr of 3Na?
69gmol-1
Tips to remember which reactant is limiting?
• When the reactants do not have equal moles, e.g if
