C3- Quantative Chemistry Flashcards
Mass number
The total number of protons and neutrons
Atomic number
The number of protons or the number of electrons
Relative atomic mass
The number of protons or the number of electrons
State the law of conservation of mass?
No atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants.
What is relative formula mass (Mr)?
The relative formula mass (Mr) of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula.
Why may some reactions appear to have a change in mass?
Some reactions may appear to involve a change in mass but this can usually be explained because a reactant or product is a gas and its mass has not been taken into account.
What is the Avogadro constant?
The number of atoms, molecules or ions in a mole of a given
substance is the Avogadro constant. The value of the Avogadro constant is 6.02 x 1023 per mole.
What is a limiting reactant?
The reactant that is completely used up is called the limiting reactant because it limits the amount of products.
Percentage yield equation?
% Yield = (Mass of product actually made / Maximum theoretical mass of product) × 100
What is atom economy?
The atom economy (atom utilisation) is a measure of the amount of starting materials that end up as useful products.
Percentage atom economy equation?
(Relative formula mass of desired product / Sum of relative formula masses of all reactants from equation) × 100
What is the volume of 1 mole of gas at room temperature?
The volume of one mole of any gas at room temperature and pressure (20C and 1 atmosphere pressure) is 24 dm3
What is electrolysis?
Electrolysis breaks down ionic compounds (salts) into their element using electricity.
Ions must be _ for electrolysis to work?
free to move
Cations?
+ ions (formed by metals)
Anions?
- ions (formed by non-metals)
3 things electrolysis is used for?
To extract reactive metals from their ores, to purify metals, electroplating.
How is aluminum extracted from it’s ore?
Bauxite contains alumina -> it’s refined to produce ammonia -> ammonia is melted with cryolite to lower it’s melting point -> using electrolysis aluminium is formed.
What are the 2 rules for electrolysis?
- At the cathode, the ion of the least reactive element will be discharged.
- At the anode, if a halide (group 7) is present that’s the one that gets discharged. If there is not one present the hydroxide ion is discharged, and oxygen is produced.
What is an ore?
An ore is a material containing enough metal for it to be economically worth extracting.
Equation linking moles, mass and formula mass?
Moles (mol) = mass (g) / formula or atomic mass (g/mol)
Equation linking concentration, amount of solute, and volume of solution.
Conc. = amount of solute (moles) / volume of solution
Why is a higher atom economy desired?
It’s more sustainable, less waste products and therefore less pollution, use fewer raw materials (natural resources) and therefore less energy.
Why is 100% yield unattainable?
-Reversible reactions (doesn’t reach completion)
-Errors can be made
-Unexpected reactions occur (reactions are not 100% pure)
-Product is lost during separation or transfer
What is uncertainty?
When measuring quantities, there is always some degree of error known as uncertainty.
What is resolution?
The smallest measurement that a piece of equipment can measure.
What is the uncertainty of an analogue measurement?
Half the resolution.
What is the uncertainty of a digital measurement?
Half the last digit shown on it’s display.
What is the uncertainty for a set of repeat measurements?
+- half the range
