OCR chem paper 2- Synthesis and Analytical
Techniques in answering questions
Which statement is correct for the different rates of hydrolysis of RCl and
RBr? - Ans>>RBr is hydrolysed faster because the C-Cl bond enthalpy is
greater than C-Br.
The compound below reacts with hydrogen gas to form a saturated
compound. What is the volume of hydrogen, measured at room temperature
and pressure, that reacts with 0.0500 mol of the compound? - Ans>>Since
there are 2H2 for each double c-c bond
and 2H2 for triple C-N bond so 4H2.
1:4 ratio
- 0.05 x 4 = nH2 = 0.2 mol
- 0.2 x 24dm^3 = 4.8 4m^3
Describe a Chemical Test to confirm the presence of a carbonyl group -
Ans>>Use 2,4-DNP
- positive result causes an orange precipitate
- Crystallise and compare melting points with database
The reaction of aqueous methanoic acid with magnesium - Ans>>2HCOOH +
Mg → (HCOO)2Mg + H2
What chemical tests could be used to confirm the presence of the phenol
group in compounds K and L? - Ans>>Add bromine, positive test causes a
white precipitate
Formation equation for a chlorine catalyst - Ans>>Cl2 + AlCl3 -> Cl+ +
AlCl4-
Regeneration of AlCl3 - Ans>>H+ + AlCl4- -> AlCl3 + HCl
Why do phenol's react more readily halogens than benzene? - Ans>>(In
phenols) a (lone) pair of electrons on O is (partially) delocalised into the π-
system
Electron density increases
Phenols are more susceptible to electrophilic attack
How can you show acidified potassium dichromate in a reaction? - Ans>>[O]
Techniques in answering questions
Which statement is correct for the different rates of hydrolysis of RCl and
RBr? - Ans>>RBr is hydrolysed faster because the C-Cl bond enthalpy is
greater than C-Br.
The compound below reacts with hydrogen gas to form a saturated
compound. What is the volume of hydrogen, measured at room temperature
and pressure, that reacts with 0.0500 mol of the compound? - Ans>>Since
there are 2H2 for each double c-c bond
and 2H2 for triple C-N bond so 4H2.
1:4 ratio
- 0.05 x 4 = nH2 = 0.2 mol
- 0.2 x 24dm^3 = 4.8 4m^3
Describe a Chemical Test to confirm the presence of a carbonyl group -
Ans>>Use 2,4-DNP
- positive result causes an orange precipitate
- Crystallise and compare melting points with database
The reaction of aqueous methanoic acid with magnesium - Ans>>2HCOOH +
Mg → (HCOO)2Mg + H2
What chemical tests could be used to confirm the presence of the phenol
group in compounds K and L? - Ans>>Add bromine, positive test causes a
white precipitate
Formation equation for a chlorine catalyst - Ans>>Cl2 + AlCl3 -> Cl+ +
AlCl4-
Regeneration of AlCl3 - Ans>>H+ + AlCl4- -> AlCl3 + HCl
Why do phenol's react more readily halogens than benzene? - Ans>>(In
phenols) a (lone) pair of electrons on O is (partially) delocalised into the π-
system
Electron density increases
Phenols are more susceptible to electrophilic attack
How can you show acidified potassium dichromate in a reaction? - Ans>>[O]
