O Last Minutes

Question 1

What is meant by a weak acid and bronsted Lowry theory?

Answer 1

Proton donor which which partially dissociates

Question 2

Write the full equation for the reaction of C2H5COOH with sodium carbonate

Answer 2

C2H5COOH + Na2CO3 -> C2H5COONa + CO2 + H2O

Question 3

Write the ionic equation for an acid + a hydroxide

Answer 3

H+ + OH- -> H2O

Question 4

Explain in terms of equilibrium how the buffer solution would respond to the added NH3

Answer 4

NH3 is a base
So equilibrium shifts right
Alkali accepts H+

Question 5

What is acid 2 usually?

Answer 5

The + ion

Question 6

CH3COOH + H2O = ??

Answer 6

CH3COO- + H3O+

Question 7

How can an aqueous solution of an acid contain hydroxide ions?

Answer 7

Water ionises
H2O -> H+ + OH-

Question 8

How do you calculate the concentration of hydroxide ions?

Answer 8

Use Kw

Question 9

Acid + carbonate ->?

Answer 9

Salt + CO2 + H2O

Question 10

Answer 10

Because solution contains CH3COOH and CH3COO-

Question 11

Answer 11

Question 12

Acid + metal ionic equation

Answer 12

M + H+ -> M+ + H2

Question 13

Ionic equation for acid + carbonate

Answer 13

Question 14

Explain why a buffer solution forms when butanoic acid is added to sodium hydroxide?

Answer 14

CH3CH2CH2COO- forms
CH3CH2CH2CooH remains in excess

Question 15

What is meant by the strength of an acid?

Answer 15

The proportion of dissociation

Question 16

What does low pKa mean?

Answer 16

Low pH and strong acid

Question 17

equation for acid + hydroxide

Answer 17

Salt + water

Question 18

What do you do when there are 2 OH- ions?

Answer 18

Multiply the OH- conc by 2 when working out H+

Question 19

What important factor does the student need to consider when deciding on the most suitable indicator for this titration?

Answer 19

The colour change of the indicator

Question 20

Equation for the percentage molar dissociation

Answer 20

Question 21

How do we know if a reaction is endothermic using Kw?

Answer 21

Endothermic because Kw increases with temperature

Question 22

What is wring with using Kw?

Answer 22

Inaccurate results because Kw values with temperature

Question 23

Plan an experiment that a student could carry out to measure the enthalpy change of neutralisation

Answer 23

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

Question 24

Suggest reasons for the difference between the enthalpy changes of solution of KF and RbF (KF has a smaller enthalpy change)

Answer 24

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

Question 25

Explain why ammonium nitrate in the cold pack dissolves spontaneously in water even though this process is endothermic.

Answer 25

Entropy increases Total entropy change > change in enthalpy

Question 26

Explain, with the help of an appropriate equation, how this buffer solution works when acid is added.

Answer 26

H+ moves equilibrium to the left To maintain pH Excess of salt ions

Question 27

What else can [H+] be?

Answer 27

Moles of H

Question 28

Describe what the students do and the measurements they make so that they can calculate the enthalpy change of solution.

Answer 28

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

Question 29

Percentage uncertainty for equipment

Answer 29

( Uncertainty x 2 / value ) X 100

Question 30

Explain how an increase in the concentration of a greenhouse gas leads to an enhanced greenhouse effect.

Answer 30

Greenhouse gases absorb IR from Earth So more IR would be absorbed

Question 31

Describe the evidence for the relationship between the increased concentration of greenhouse gases and global warming.

Answer 31

There is a relationship between gas concentrations and temperature

Question 32

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

Answer 32

- Earth absorbs UV - Earth emits IR - Greenhouse gas molecules absorb IR - Bonds vibrate - KE becomes thermal energy - and causes Earth’s temperature to rise

Question 33

Write an equation for the reaction of ethanoic acid in water.

Answer 33

CH3COOH = CH3COO- + H+

Question 34

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.

Answer 34

Difficult to match colour with exact pH value using UI solution

Question 35

Explain how a pH meter is calibrated

Answer 35

Use two buffer solutions of known pH

Question 36

What is the unit for enthalpy during an entropy equation?

Answer 36

J

Question 37

Which is the conjugate acid and which is the conjugate base?

Answer 37

Question 38

What is [A-]/[HA] equal to?

Answer 38

Ka/[H+]

Question 39

Explain why many ionic substances are soluble in water, naming the bonds which are made and broken

Answer 39

Ionic bonds are broken Ion dipole bonds are formed Hydrogen bonds in water are broken Similar strength bonds are broken and made

Question 40

Why is entropy of system negative?

Answer 40

Fewer moles on RHS So less disorder

Question 41

Explain the effect of raising the temp on the forward reaction

Answer 41

It would make entropy smaller As the reaction would be less likely to occur

Question 42

What should you always add to a question on how a buffer solution works?

Answer 42

And there’s a large conc of the negative salt ion Eg HCO3-

Question 43

What must you include in the equation for the ionisation of an acid?

Answer 43

reversible reaction sign

Question 44

Draw a diagram of hydrogen bonding between two water molecules

Answer 44

Question 45

Why can’t a weak acid act as a buffer?

Answer 45

No excess of A- ions No equilibrium

Question 46

Draw an enthalpy profile diagram for a soluble salt

Answer 46

Question 47

Draw an enthalpy profile diagram for an insoluble salt

Answer 47

Question 48

Why do ionic substances not dissolve in non-polar solvents?

Answer 48

- 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

Question 49

Equation for enthalpy change of solution

Answer 49

ΔHsol = ΔHhyd (cation) + ΔHhyd (anion) - ΔHLE

Question 50

What is the equivalence point?

Answer 50

The centre of the vertical section of the titration curve

Question 51

What indicator for an acid?

Answer 51

Methyl orange

Question 52

What indicator for a base?

Answer 52

Phenolphthalein

Question 53

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.

Answer 53

Phenoplthalein as equivalence points are in alkaline conditions Methyl orange would have already changed colour

Question 54

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

Answer 54

CO2 has IDIDBs between molecules CO2 forms hydrogen bonds with water Ions form ion dipole bonds with water Water forms hydrogen bond with itself

Question 55

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.

Answer 55

Total entropy must be positive for process to occur System entropy must be positive and greater than surrounding entropy

Question 56

What does it mean if the calculated Ksp is > than Ksp?

Answer 56

The product made from the reactants will precipitate out of the solution as it is in excess

Question 57

How do we know if a reaction is feasible?

Answer 57

Total S is positive