Quantitative Chemistry
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What is relative formula mass (Mr)?
Masses of all atoms in molecular formula added together
One mole contains how many atoms/molecules i.e. what’s “the Avogadro constant”?
6.02 x 1023
How do you work out 1 mole of substance?
Work out its relative formula mass
In a chemical reaction, mass is ___ ______
Always Conserved
During a chemical reaction, are atoms are destroyed and created?
NO
How do we know mass is conserved during a reaction?
Same no. + types of atoms on each side of reaction equation (& total of Mr of all reactants = total Mr of products)
When may you observe a change of mass?
When the reaction takes place in an unsealed reaction vessel
If mass increases in a reaction, what’s likely to have happened?
• Reactant = gas - not contained in reaction vessel = can’t account for its mass • Gas reacts to form part of product = becomes contained inside reaction vessel
If mass decreases in a reaction, what’s likely to have happened?
• Product = gas - before reaction, all reactants contained in reaction vessel • Vessel isn’t enclosed = gas escapes from reaction vessel as it’s formed ∴ can’t account for its mass
What is the volume of one mole of any gas at room temperature and pressure?
24 dm3
When does a reaction stop?
When all of one reactants is used up
E.g. Reaction with 2 reactants: Why might one reactant be added in excess?
To make sure other reactant is used up
What is a limiting reactant?
Reactant that’s used up in a reaction
Amount of ____ _____ is ____ ______ to amount of limiting reactant
product formed is directly proportional
Why is the amount of product formed directly proportional to amount of limiting reactant?
Because if you add more reactant there will be more reactant particles to take part in the reaction = more product particles
What is concentration?
Amount of substance (e.g. mass or the number of moles) in a certain volume of a solution
How increase the concentration of solution, in given a volume?
Increase amount of solute
1ml = ….
1cm3
Why are yields are always less than 100%?
• Reversible reactions may not go to completion (i.e. Not ALL the reactants react to make a PRODUCT) • Some reactants may react in an expected way (i.e. there may be SIDE REACTIONS) • Some product may be lost when you SEPARATE IT from the reaction mixture
Why should industrial processes have as high percentage yield as possible?
To reduce waste and costs
State how to get from: m3 → dm3 → cm3
m3 (x1000)→ dm3 (x1000)→ cm3
State how to get from: cm3 → dm3 → m3
cm3 (÷1000)→ dm3 (÷1000)→ m3
Name the formula for working out concentration (mass) and state the units
Concentration = Mass of Solute ÷ Voume of Solvent c = m/v c = g/dm3 m = g v = dm3
Name the formula for working out concentration (moles) and state the units
Concentration = No. of Moles of Solute ÷ Voume of Solvent c = /v c = mol/dm3 or mol/dm-3 n = mol v = dm3