O Last Minutes Flashcards
What is meant by a weak acid and bronsted Lowry theory?
Proton donor which which partially dissociates
Write the full equation for the reaction of C2H5COOH with sodium carbonate
C2H5COOH + Na2CO3 -> C2H5COONa + CO2 + H2O
Write the ionic equation for an acid + a hydroxide
H+ + OH- -> H2O
Explain in terms of equilibrium how the buffer solution would respond to the added NH3
NH3 is a base
So equilibrium shifts right
Alkali accepts H+
What is acid 2 usually?
The + ion
CH3COOH + H2O = ??
CH3COO- + H3O+
How can an aqueous solution of an acid contain hydroxide ions?
Water ionises
H2O -> H+ + OH-
How do you calculate the concentration of hydroxide ions?
Use Kw
Acid + carbonate ->?
Salt + CO2 + H2O
Because solution contains CH3COOH and CH3COO-
Acid + metal ionic equation
M + H+ -> M+ + H2
Ionic equation for acid + carbonate
Explain why a buffer solution forms when butanoic acid is added to sodium hydroxide?
CH3CH2CH2COO- forms
CH3CH2CH2CooH remains in excess
What is meant by the strength of an acid?
The proportion of dissociation
What does low pKa mean?
Low pH and strong acid
equation for acid + hydroxide
Salt + water
What do you do when there are 2 OH- ions?
Multiply the OH- conc by 2 when working out H+
What important factor does the student need to consider when deciding on the most suitable indicator for this titration?
The colour change of the indicator
Equation for the percentage molar dissociation
How do we know if a reaction is endothermic using Kw?
Endothermic because Kw increases with temperature
What is wring with using Kw?
Inaccurate results because Kw values with temperature
Plan an experiment that a student could carry out to measure the enthalpy change of neutralisation
Acid and alkali mix
Amount of acid and alkali stated
Temp taken at start and finish
Q = MCT
Energy scaled up from 1 mol of water
Hneut = - energy change
Suggest reasons for the difference between the enthalpy changes of solution of KF and RbF (KF has a smaller enthalpy change)
Ionic radius of K ion is smaller than
K+ has greater attraction
K+ has greater attraction to H2O
Enthalpy change of solution is affected more by LE than enthalpy change of hydration
Explain why ammonium nitrate in the cold pack dissolves spontaneously in water even though this process is endothermic.
Entropy increases
Total entropy change > change in enthalpy
Explain, with the help of an appropriate equation, how this buffer solution works when acid is added.
H+ moves equilibrium to the left
To maintain pH
Excess of salt ions
What else can [H+] be?
Moles of H
Describe what the students do and the measurements they make so that they can calculate the enthalpy change of solution.
Place known volume of water in a beaker
Add a known mass of solid
Add solid to water while stirring
Measure temp of water before and after
Percentage uncertainty for equipment
( Uncertainty x 2 / value ) X 100
Explain how an increase in the concentration of a greenhouse gas leads to an enhanced greenhouse effect.
Greenhouse gases absorb IR from Earth
So more IR would be absorbed
Describe the evidence for the relationship between the increased concentration of greenhouse gases and global warming.
There is a relationship between gas concentrations and temperature
Explain how greenhouse gas molecules are involved in the process of energy transfer that start with UV radiation from the sun and result in warming of teh troposphere
- Earth absorbs UV
- Earth emits IR
- Greenhouse gas molecules absorb IR
- Bonds vibrate
- KE becomes thermal energy
- and causes Earth’s temperature to rise
Write an equation for the reaction of ethanoic acid in water.
CH3COOH = CH3COO- + H+
i. Explain why the student decided to use a pH meter rather than universal indicator to determine the pH of the solution as the titration progressed.
Difficult to match colour with exact pH value using UI solution
Explain how a pH meter is calibrated
Use two buffer solutions of known pH
What is the unit for enthalpy during an entropy equation?
J
Which is the conjugate acid and which is the conjugate base?
What is [A-]/[HA] equal to?
Ka/[H+]
Explain why many ionic substances are soluble in water, naming the bonds which are made and broken
Ionic bonds are broken
Ion dipole bonds are formed
Hydrogen bonds in water are broken
Similar strength bonds are broken and made
Why is entropy of system negative?
Fewer moles on RHS
So less disorder
Explain the effect of raising the temp on the forward reaction
It would make entropy smaller
As the reaction would be less likely to occur
What should you always add to a question on how a buffer solution works?
And there’s a large conc of the negative salt ion
Eg HCO3-
What must you include in the equation for the ionisation of an acid?
reversible reaction sign
Draw a diagram of hydrogen bonding between two water molecules
Why can’t a weak acid act as a buffer?
No excess of A- ions
No equilibrium
Draw an enthalpy profile diagram for a soluble salt
Draw an enthalpy profile diagram for an insoluble salt
Why do ionic substances not dissolve in non-polar solvents?
- They do not have regions of psoitive and negative charge
- so do not interact strongly with ions
- Solution H is a large positive value and so dissolving is unlikely to occur
Equation for enthalpy change of solution
ΔHsol = ΔHhyd (cation) + ΔHhyd (anion) - ΔHLE
What is the equivalence point?
The centre of the vertical section of the titration curve
What indicator for an acid?
Methyl orange
What indicator for a base?
Phenolphthalein
Suggest, with reference to the pH curve on page 4, and the information in the table above, which indicator would be suitable for this titration.
Phenoplthalein as equivalence points are in alkaline conditions
Methyl orange would have already changed colour
Use ideas of inter-molecular forces to explain why carbon dioxide is only slightly
soluble in water, whereas sodium hydrogencarbonate (containing HCO3– ) is very
soluble
CO2 has IDIDBs between molecules
CO2 forms hydrogen bonds with water
Ions form ion dipole bonds with water
Water forms hydrogen bond with itself
The dissolving of sodium hydrogencarbonate is an endothermic process. What can you say about the sign and magnitude of the system entropy for this process?
Explain your answer.
Total entropy must be positive for process to occur
System entropy must be positive and greater than surrounding entropy
What does it mean if the calculated Ksp is > than Ksp?
The product made from the reactants will precipitate out of the solution as it is in excess
How do we know if a reaction is feasible?
Total S is positive
