Equations and Bonding Flashcards
What is the equation for working out relative atomic mass in isotopes?
Ar = total mass of atoms / total number of atoms
How do you work out relative atomic mass with isotopes?
To work out relative atomic mass you need to divide the total mass of the atoms by the total number.
Let’s use Chlorine as an example.
Chlorine has 2 isotopes (35/17 Cl (chlorine-35) and 37/17 Cl (chlorine-37)).
The abundance of chlorine-35 is 75% and the abundance of chlorine-37 is 25%. So, in every 100 chlorine atoms 75 of them have mass number 35 and 25 have mass number 37.
From here, you do 35 x 75 + 37 x 25 / 100 which would give you an answer of 35.5 rounded to 1dp.
How do you work out relative formula mass in complex ionic compounds?
To work out relative formula mass, you need to multiply the Ar of all the elements in the compound by how many molecules there are and add them together.
Let’s use aluminium sulphate (Al2(SO4)3) as an example. Aluminium has an Ar of 27, the Ar of sulphur is 32 and the Ar of oxygen is 16.
So from there the sun would be: 27 x 2 + 32 x 3 + 16 x 12 = 54 + 96 + 192 which would give you an answer of 342.
What is the equation for working out moles?
Number of moles = mass (g) / Ar (/) Mr
What is the equation for working out mass?
Mass (g) = no. of moles x Ar/Mr
How do you work out percentage yield?
The equation for percentage yield is: actual mass of product produced / maximum theoretical mass of product possible x 100.
To give an example, copper oxide reacts with sulphuric acid to make copper sulphate and water. In a experiment, 1.6 g of dry copper sulphate crystals are made. If the theoretical yield is 2.0 g calculate the percentage yield.
So from there you’d do: 1.6 / 2.0 x 100
which would give you an answer of 80%.
How do you work out percentage atom economy?
The equation for percentage atom economy is: total Mr of the desired product from equation / total Mr of all reactants.
Let’s give an example, hydrogen can be manufactured by reacting methane with steam: CH4(g) + H2O(g) —> 3H2(g) + CO(g). Calculate the atom economy for the reaction. (Ar of H = 1, C = 12 and O = 16).
First you need to work out the Mr’s of the reactants (methane and steam), hydrogen and the total. The Mr of methane = 12 + 4 = 16 and the Mr of steam = 2 + 16 = 18. So the total Mr would be: 16 + 18 = 34.
Also, the Ar of H2 = (2 x 1) = 2. So as there are 3 hydrogens in the equation, the total Mr of the desired product = 3 x 2 = 6.
From there, you’d do 6 / 34 x 100 which would give you an answer of 17.6 % to 3sf.
How would you work out concentration (g/dm3)?
The equation for concentration = amount of solute (g) / volume of solution (dm3).
For an example, 5.0 g of sodium hydroxide is dissolved in 250 cm3 of water. Calculate the concentration of the sodium hydroxide solution formed.
First, you need to convert the 250 cm3 into decimetres. For this you’d do: 250 cm3 = 250 / 1000 = 0.250 dm3.
As concentration equals mass / volume, next you’d do: 5.0 g / 0.250 dm3 which would give you an answer of 20 g/dm3.
What is metallic bonding?
An exchange that takes place during a chemical reaction. In this case atoms in metals loose electrons to form positive ions.
What is ionic bonding? Give the answer for both metals and non-metals.
Metals: Loose electrons to form positive ions.
Non-metals: Gain electrons to form negative ions.
What are the properties of ionic substances?
1) Ionic compounds have both high melting and boiling points. This is because they are giant atomic structures and have strong electrostatic forces of attraction in all directions.
2) They have many strong bonds and a large amount of energy is needed to break them.
3) They only conduct electricity when melted or dissolved in water. This is because the ions are free to move and so a charge can flow.
What is covalent bonding? How does this work in small molecules?
Two non-metals will share pairs of electrons. In small molecules, this takes effect of a small group of atoms sharing electrons.
What are the the properties of covalent substances in small molecules?
1) Small molecules have both relatively low melting and boiling points. This is because the molecules weak intermolecular forces are overcome when melting and boiling occur.
2) The bigger the size of the molecule the higher the melting and boiling points. This is because, the intermolecular forces increase with the size of the molecule.
3) They don’t conduct electricity because they have no overall electric charge.
What is covalent bonding? How does this work in giant structures?
Two non-metals will share pairs of electrons. In giant structures this takes the form of many atoms sharing electrons.
What are the properties of covalent substances in giant structures?
1) Polymers are solids at room temperature. This is because, intermolecular force increases with the size of the polymer molecules, which are very large.
2) Giant covalent compounds have high boiling and melting points. This is because, the atoms are linked by strong covalent bonds.
3) Diamond is very hard, has a very high melting/boiling point and doesn’t conduct electricity. This is because, each carbon is bonded to 4 others by strong bonds. There aren’t any free electrons.
4) Graphite is very hard, has a very high melting/boiling point and conducts electricity. This is because, each carbon is bonded to 3 others by strong bonds. It forms layers of hexagonal rings with free electrons.
5) Graphene is strong, light and an excellent conductor of thermal energy and electricity. This is because, it is a single layer of graphite so has free electrons.
6) Fullerenes are extremely strong and are excellent conductors of thermal energy and electricity because they have strong covalent bonds and free electrons.
