Exam Cards - Unit 1: Atoms & Reactions Flashcards
Define isotopes.
Atoms of an element with the same number of protons but different numbers of neutrons.
Define relative atomic mass (Ar).
The mass of each atom in 1 mole of an element compared to every atom in 1 mole of carbon-12.
Define relative isotopic mass.
The mass of each atom in 1 mole of an isotope compared to every atom in 1 mole of carbon-12.
Define relative molecular mass (Mr).
The average mass of a molecule compared with one atom of carbon-12.
How is the relative molecular mass calculated?
By adding up the relative atomic mass values of all the atoms in the molecule.
How is relative atomic mass calculated from isotopic abundances?
Example: 76% of Cl atoms have a relative isotopic mass of 35, while 24% of Cl atoms have a relative isotopic mass of 37. What is the relative atomic mass (Ar)?
- Multiply each relative isotopic mass by its % relative isotopic abundance and add up the results: (76 x 35) + (24 x 37) = 3548
- Divide by 100: 3548/100 = 35.5 (1 d.p)
What is Avogadro’s Constant?
6.02 x 1023
What is the formula for calculating the number of moles from the number of atoms or molecules?
Number of moles = Number of particles you have/Number of Particles in a mole (Na)
Example: There are 1.5 x 1024 carbon atoms. How many moles of carbon is this?
Number of moles = 1.5 x 1024/6.02 x 1023 = 2.49 moles
What is molar mass (M) and what is it equal to?
Molar mass is the mass of one mole of something. It is equal to relative molecular mass (Mr).
How do you calculate the number of moles using the mass of a substance and molar mass?
Number of moles = mass of substance/ molar mass
n = m/M
How do you calculate the number of moles using concentration and volume?
Number of moles = concentration x volume (in dm3)
n = cv
How do you calculate the number of moles of a gas at r.tp?
Number of moles = volume in dm3/24
or Number of moles = volume in cm3/24000
Define empirical formula.
The smallest whole number ratio of atoms in a compound.
Define molecular formula.
The actual numbers of atoms in a molecule.
How do you work out the molecular formula of a molecule using the empirical formula?
Example: A molecule has a empirical formula of C4H3O2 and a molecular mass of 166g. Work out the molecular formula.
- Work out the empirical mass. Example: (4 x 12) + (3 x 1) + (2 x 16) = 83g
- Divide the molecular mass by the empirical mass. Example: 166/83 = 2 empirical units
- Multiply the empirical formula by the empirical units. Example: C4H3O2 x 2 = C8H6O4
How do you caluculate the empirical formula from experimental results?
Example: When a hydrocarbon is burnt in excess oxygen, 4.4g of carbon dioxide and 1.8g of water are produced. What is the empirical formula of this hydrocarbon?
- Work out the number of moles of the product. Example: n (CO2) = 4.4/44 =0.1mol n (H2O) = 1.8/18 = 0.1mol
- 1 mol of H2O contains 2 H atoms, so you must have started with 0.2mol of H atoms
- C:H = 0.1:0.2
- Divide by the smallest = 1:2
- Empirical formula = CH2
How do you work out the empirical formula from percentages?
- Assume you have 100g of substance so the percentages can be converted t mass
- Work out the number of moles in each element
- Divide each number of moles by the smallest number to find a ratio
Are acids proton donors or acceptors and why?
Proton donors because they produce H+ ions in an aqeuous solution.
Are bases proton donors or acceptors and why?
Proton acceptors because they remove H+ions from an aqeuous solution.
What are the products when an acid reacts with a metal?
Acid + Metal -> Metal Salt + Hydrogen
What are the products when an acid reacts with a metal carbonate?
Acid + Metal -> Metal Salt + Carbon Dioxide + Water
What is the difference between a hydrated and anhydrous salt?
Hydrated salts contain water of crystallisation and anhydrous salts do not.
Define alkali.
A base which dissolves in water.
Define oxidation.
The loss of electrons.
Define reduction.
The gain of electrons.
What term is used for a reaction which has oxidation and reduction happening simultaneously?
A redox reaction.
What is the oxidation state for an uncombined element?
0
What is the oxidation state for a simple monatomic ion? (e.g. Na+)
The oxidation state is equal to its charge (e.g. Na+ = 1)
What is the oxidation state of compounds or compound ions? (e.g. SO42-)
The oxidation number is the ion charge. (e.g. SO42- = -2)
What is the oxidation state for a combined oxygen?
-2 (except in O2, where it’s 0)
What is the oxidation state for a combined hydrogen?
+1 (except in H2, where it’s 0)
What do all ions with the suffix -ate contain?
Oxygen.
What is a reducing agent?
Something that donates electrons and gets oxidised.
What is a oxidising agent?
Something that accepts electrons and gets reduced.