Exam questions Flashcards
state the meaning of the term bronzed-lowry acid
acid is a proton donator
write a expression for the acid dissociation constant Ka for ethnic acid
Ka = [H+][CH3COO-] / [CH3COOH]
write an equation for the dissociation of chloroethanoic acid in aqueous solution
ClCH2COOH ⇌ H+ + ClCH2COO-
suggest why chloroethanoic acid is stronger acid than ethnic acid
chlorine is electronegative so withdraws electrons from the O-H bond, so weakens it
write an expression for the acid dissociation constant (Ka) for the weak acid HX
Ka = [H+][X-] / [HX]
state which one is a strong base
ammonia or ethylamine
ethylamine is a stronger base
positive inductive effect
write an expression of pH
pH = -log[H+]
hydrogen carbonate ions act as a weak cid in aqueous solution. write an equation for this equilibrium
HCO3- ⇌ H+ + CO3^2-
use an equation to explain how the solution containing sodium hydrogencarbonate and sodium carbonate Cana its a buffer when small amount of acid or alkali are added
small amount of acid= shifts equilibrium to the left (HCO3- + H+)
small amount of alkali = shirt equilibrium to the right ( H+ + OH-)
overall [H+] stays the same
state the meaning of the term weak as applied to carboxylic acids
partially dissociated
two solutions, one with a pH of 4 and another one of 9, were left open to the air. the pH of 9 solution changed the most. suggest what substance might be present in the air to cause the pH to change
CO2
pH has decrees as it has reacted with the H+ ions in the solution
suggest why chloroethanoic acid is stronger acid than ethanoic acid
chloroethanic acid has a chlorine which is more electronegative than hydrogen, so withdraws electrons which weaken the O-H bond
the dissociation of methanoic acid in aqueous solution is endothermic. deduce whether the pH of a solution of methanoic acid will increase, decades or stay the same if the solution is heated.
decreases
if the forwards reaction is endothermic then more product is made to oppose the change of the increase in temperature. the equilibrium shifts to the left
the product formed exists as racemic mixture. state the meaning of the term racemic mixture and explain why such a mixture is formed in this reaction
50:50 ratio of an optical isomer
reagent can go either side of the C=O bond
state the meaning of the term stereoisomerism
two or compounds have the same structural formula, different arrangement of bonds in space
what type of isomerism is shown by but-2-ene
E-Z isomerism
define the term optically active
rotate plane of polarised light
why is a racemic mixture not optically active?
each isomer polars light in a direction and they cancel each other out
explain why a molecule can be optically active
the carbon is bond to four different chains
an ester was prepared by reacting (CH3)2CHOH with (CH3CO)2O
write an equation for this reaction and give the IUPAC name of the ester formed
(CH3)2CHOH + (CH3CO)2O —– CH3COOH + CH3COOCH(CH3)CH3
1-methyl,ethyl ethanoate
give the IUPAC name of glycerol
propane-1,2,3-triol
Ethnic acid, propyl ethanoate and propane-1-ol are all colourless liquids. esters do not give a positive result with any of the usual tests for functional groups. state how you could use chemical test to show the presence of ethnic acid and propane-1-ol in a mixture of the acid.
ethanoic acid
add NaCO3
bubbles observed as carbon dioxide given off
propane-1-ol
acidified K2Cr2O7
orange colour turns green with primary alcohols
a student prepared a sample of aspirin in the lab and attempted to purify it by recrystallisation. to check the purity of aspirin the student determined its melting point.
state two observations during the melting point process that would indicate that the sample is not pure
melt greatly before or after the given melting point
the meting point range would be wider
suggest why a pure sample of aspirin may sometimes appear to melt at a different from 135
the temperature on the thermometer is different from that of the sample
how many structural isomers (which are esters) have the molecular formula C4H5O2
4
state and explain how you could distinguish between the two enantiomers
use polarised light
rotated in opposite directions
why in practice KCN rather than HCN is added to the carbonyl compound
contraction is lower
weak acid
:CN- is very low
which one of the following statements abbey but-2-enal is not true
A-it has stereoisomers
B-shows a strong absorption in the infra-red at about 1700cm-1
C- turn an acidified solution of potassium dichromate green
D- dehydrated by concentrated sulphuric acid
D- dehydrated by concentrated sulphuric acid
state in terms of bonding why benzene is more stable than cyclohexane-1,3,5-triene
benzene is more stable because it has overlapping p-orbitals so the electrons delocalised
what is the difference in bonding between cyclohexane-1,4-diene and cyclohexane-1,3-diene
cyclohexa-1,3-dienece is more stable
double bons coller together
more p-orbitals overlapping
