AQA AS CHEMISTRY PAPER 2 MARKING SCHEME 2020
Define Relative Atomic Mass (Ar) [1] - (answer)the average mass of an element÷ 1/12th the mass of a
C12 atom
Define Relative Molecular/Formula Mass (Mr) [1] - (answer)Average mass of one molecule ÷ 1/12th the
mass of a C12 atom
What is meant by the Avogadro constant? [1] - (answer)The number of atoms in 12g of carbon.
Give the formula for moles. [1] - (answer)moles= mass÷Mr
Give the formula for concentration in mol/dm³ [1] - (answer)concentration = moles÷volume
State the Ideal Gas Equation, what each symbol represents and the units for each symbol. [9] -
(answer)PV= nRT
where...
P= Pressure measured in Pa
V= Volume measured in m³
n= number of moles
R= The molar gas constant- 8.31JK^-1mol^-1
T= Temperatures measured in K
Define Empirical Formula [1] - (answer)The simplest whole-number ratio of atoms of each element in a
compound.
Define Molecular Formula [1] - (answer)The actual number of atoms of each element in a compound.
What are the four state symbols? [4] - (answer)Solid (s), liquid (l), gas (g), aqueous solution (aq)
Describe how to perform a titration. [5] - (answer)1. Fill a burette with the acid of known concentration,
,2. Accurately measure 25cm³ of the alkali solution using a pipette and transfer it to a conical flask.
3. Add a few drops of a suitable indicator to the alkali. eg phenolphthalein.
4. Slowly add the acid from the burette into the conical flask, swirling constantly. As soon as the indicator
changes colour the solution has turned neutral so stop adding the acid.
5. Record the volume of acid added.
6. Repeat the process until you achieve concordant results. The mean of these results is used to calculate
the average titre.
State the formula for percentage atom economy. [1] - (answer)
State the formula for percentage yield. [1] - (answer)
Describe how to make up a standard solution [7] - (answer)1. Weigh the sample bottle containing the
solid on a balance.
2. Transfer solid to a beaker and reweigh the sample bottle.
3. Record the difference in mass.
4. Add distilled water and stir with a glass rod until the solid has dissolved.
5. Transfer to a volumetric flask with washings.
6. Makeup to the 250cm³ mark with distilled water.
7. Shake flask.
What is an ionic bond? [1] - (answer)The strong electrostatic attraction between oppositely charged ions.
Describe the melting and boiling point of an ionic compound. [3] - (answer)- Strong electrostatic
attraction between ions.
- This requires a lot of energy to overcome.
- Giving ionic compounds high melting and boiling points.
Describe the electrical conductivity of an ionic compound. [3] - (answer)- Can conduct electricity when
molten or in solution.
, - When compound is solid the ions are held in fixed position and cannot flow.
- When compound is molten/in solution, the ions are free to move and carry charge.
Describe the structural properties of an ionic compound. [2] - (answer)- Brittle, shatter easily.
- As if the rows of ions slide past one another and like charges are adjacent, the two fragments repel one
another.
What is meant by covalent bond? [1] - (answer)A shared pair of electrons between two atoms.
Why do covalent substances not conduct electricity? [1] - (answer)Electrons used in forming covalent
bonds and cannot carry charge.
What is meant by coordinate bond? [1] - (answer)A shared electron pair which have both come from the
same atom.
When do coordinate bonds occur? [2] - (answer)- One atom requires at least two electrons in order to fill
its outer shell, and is electron deficient.
- One atom has a lone pair, which it donates.
What is meant by metallic bonding? [1] - (answer)The strong electrostatic attraction of positive metal
ions surrounded by a sea of delocalised electrons.
Why is the metallic bonding in magnesium stronger than in sodium? [3] - (answer)- Mg has a greater
charge of 2+
- Mg has twice as many electrons in the sea of delocalised electrons
- Mg ions are smaller, meaning that there is a grater charge density.
Describe the conductivity of metals. [3] - (answer)- All metals are good electrical and thermal conductors
- Delocalised electrons help transfer energy through the metal very efficiently.
- Delocalised electrons can flow and carry charge- so metals conduct electricity.
Define Relative Atomic Mass (Ar) [1] - (answer)the average mass of an element÷ 1/12th the mass of a
C12 atom
Define Relative Molecular/Formula Mass (Mr) [1] - (answer)Average mass of one molecule ÷ 1/12th the
mass of a C12 atom
What is meant by the Avogadro constant? [1] - (answer)The number of atoms in 12g of carbon.
Give the formula for moles. [1] - (answer)moles= mass÷Mr
Give the formula for concentration in mol/dm³ [1] - (answer)concentration = moles÷volume
State the Ideal Gas Equation, what each symbol represents and the units for each symbol. [9] -
(answer)PV= nRT
where...
P= Pressure measured in Pa
V= Volume measured in m³
n= number of moles
R= The molar gas constant- 8.31JK^-1mol^-1
T= Temperatures measured in K
Define Empirical Formula [1] - (answer)The simplest whole-number ratio of atoms of each element in a
compound.
Define Molecular Formula [1] - (answer)The actual number of atoms of each element in a compound.
What are the four state symbols? [4] - (answer)Solid (s), liquid (l), gas (g), aqueous solution (aq)
Describe how to perform a titration. [5] - (answer)1. Fill a burette with the acid of known concentration,
,2. Accurately measure 25cm³ of the alkali solution using a pipette and transfer it to a conical flask.
3. Add a few drops of a suitable indicator to the alkali. eg phenolphthalein.
4. Slowly add the acid from the burette into the conical flask, swirling constantly. As soon as the indicator
changes colour the solution has turned neutral so stop adding the acid.
5. Record the volume of acid added.
6. Repeat the process until you achieve concordant results. The mean of these results is used to calculate
the average titre.
State the formula for percentage atom economy. [1] - (answer)
State the formula for percentage yield. [1] - (answer)
Describe how to make up a standard solution [7] - (answer)1. Weigh the sample bottle containing the
solid on a balance.
2. Transfer solid to a beaker and reweigh the sample bottle.
3. Record the difference in mass.
4. Add distilled water and stir with a glass rod until the solid has dissolved.
5. Transfer to a volumetric flask with washings.
6. Makeup to the 250cm³ mark with distilled water.
7. Shake flask.
What is an ionic bond? [1] - (answer)The strong electrostatic attraction between oppositely charged ions.
Describe the melting and boiling point of an ionic compound. [3] - (answer)- Strong electrostatic
attraction between ions.
- This requires a lot of energy to overcome.
- Giving ionic compounds high melting and boiling points.
Describe the electrical conductivity of an ionic compound. [3] - (answer)- Can conduct electricity when
molten or in solution.
, - When compound is solid the ions are held in fixed position and cannot flow.
- When compound is molten/in solution, the ions are free to move and carry charge.
Describe the structural properties of an ionic compound. [2] - (answer)- Brittle, shatter easily.
- As if the rows of ions slide past one another and like charges are adjacent, the two fragments repel one
another.
What is meant by covalent bond? [1] - (answer)A shared pair of electrons between two atoms.
Why do covalent substances not conduct electricity? [1] - (answer)Electrons used in forming covalent
bonds and cannot carry charge.
What is meant by coordinate bond? [1] - (answer)A shared electron pair which have both come from the
same atom.
When do coordinate bonds occur? [2] - (answer)- One atom requires at least two electrons in order to fill
its outer shell, and is electron deficient.
- One atom has a lone pair, which it donates.
What is meant by metallic bonding? [1] - (answer)The strong electrostatic attraction of positive metal
ions surrounded by a sea of delocalised electrons.
Why is the metallic bonding in magnesium stronger than in sodium? [3] - (answer)- Mg has a greater
charge of 2+
- Mg has twice as many electrons in the sea of delocalised electrons
- Mg ions are smaller, meaning that there is a grater charge density.
Describe the conductivity of metals. [3] - (answer)- All metals are good electrical and thermal conductors
- Delocalised electrons help transfer energy through the metal very efficiently.
- Delocalised electrons can flow and carry charge- so metals conduct electricity.
