5. Mocks revision

Question 1

How does a change in volume and pressure affect the equilibrium/K?

Answer 1

if V increases/decreases and p follows, the equilibrium will shift to the left, if V increases/decreases and p does the opposite, the equilibrium will shift to the right
additionally, if there is a natural decrease in V as well as an artificial increase, the equilibrium will shift to the left, but if there is a natural increase in V as well as an artificial increase, the equilibrium will shift to the right, doesn’t affect K value

Question 2

How does a change in temperature affect the equilibrium/K?

Answer 2

exo: T increase causes a shift to the left (K decrease), T decrease causes a shift to the right (K increase) – endo: T increases causes a shift to the right, T decrease causes a shift to the left

Question 3

What effect does a catalyst have on the equilibrium/K?

Answer 3

no effect as it speeds up both reactions equally, and K is only affected by temperature

Question 4

Formula showing the relationship between ΔG and K

Answer 4

ΔG=-RTlnK
greater K means more negative ΔG (more spontaneous reaction), if K<1 (R favored), ΔG will be positive (non-spontaneous reaction)

Question 5

Different definitions of acids and bases

Answer 5

1| Arrhenius (only when dissolved in water): acids produce H+ and bases produce OH-
2| Bronsted-Lowry (dissolved in any solvent): acids donate H+ and bases accept H+
3| Lewis: acids accept an e- pair and bases donate an e- pair

Question 6

Formula for when hydrogen ion dissolves in water

Answer 6

H+ + H2O -> H3O+ (hydronium ion)

Question 7

The Bronsted-Lowry concept

Answer 7

a reactant base produces a conjugate acid by accepting a H+ and a reactant acid produces a conjugate base by donating a H+

Question 8

Lewis concept example with ammonia
Lewis acid examples

Answer 8

H+ (e- pair acceptor) + NH3 (e- pair donor) -> NH4+
Al2Cl6, BF3-, transition metals

Question 9

Properties of acids

Answer 9

1| Produce H+
2| Taste sour, destroy body tissue
3| Turn blue litmus paper red
4| Electrolytes in solution form
5| Neutralize solutions containing hydroxide ions (e.g. bases)
6| When reacting with some more reactive metals release H2 (corrosion) and when reacting with carbohydrates and hydrogencarbonates release CO2

Question 10

Strong acids, examples

Answer 10

get completely ionized in water (go from polar covalent molecules into ions), strong electrolytes and conductors, cause severe burns to body tissue
HCl (hydrochloric acid), HNO3 (nitric acid), H2SO4 (sulphuric acid), HI, HBr, HClO4, HClO3

Question 11

Weak acids, example

Answer 11

don’t completely ionize in water (mainly stay as molecules after dissociation), weak electrolytes and conductors
CH3COOH (acetic acid), H2CO3 (carbonic acid), and H3PO4 (phosphoric acid)

Question 12

Properties of bases

Answer 12

1| Produce OH- (hydroxide)
2| Taste bitter and have a slippery, soapy feel, dissolve fatty/lipid material
3| Turn red litmus paper blue
4| Electrolytes in solution form
5| Neutralize solutions containing hydrogen ions (e.g. acids)
6| Displace ammonia from ammonium salts

Question 13

Strong bases

Answer 13

get completely ionized in water (go from metal hydroxides (1A elements) into ions), strong electrolytes and conductors, cause severe damage to skin and eyes
NaOH (sodium hydroxide), KOH (potassium hydroxide), Ba(OH)2 (barium hydroxide), LiOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2

Question 14

Weak bases

Answer 14

do not contain OH- but when dissolved in water produce a small amount of it – weak electrolytes/conductors
NH3 (ammonia), C2H5NH2 (amines), CO32, HCO3-, HPO42-

Question 15

Experiments to distinguish between strong and weak acids and bases

Answer 15

1| pH measurements
2| conductivity measurements – strong acids and bases have higher conductivity (equally concentrated solutions)
3| the rate of reaction of strong acids with metals, metal oxides, metal hydroxides, metal hydrogen carbonates and metal carbonates will be greater than that of weak acids

Question 16

What is the pH scale determined by?

Answer 16

the ion product of water (pure H2O at 25°C)
H2O <-> H+ + OH- [H+] = [OH-] = 10-7 M
ion product: [H+] [OH-] = 10-14 M

Question 17

How does the value of Kw change with temperature?

Answer 17

proportionally because the dissociation of water into ions is endothermic

Question 18

The formula connecting pH with H+ concentration and the same for bases

Answer 18

pH = -log [H+] and pOH = -log [OH-] pOH + pH = 14

Question 19

Indicators

Answer 19

weak acids or bases in which the dissociated form is a different color than the undissociated form – acids: methyl orange (pKin=3.7, pH range 3.1-4.4) and blue litmus paper – bases: phenolphthalein (pKin=9.6, pH range 8.3-10.0) and red litmus paper

Question 20

When does the color of the indicator change (related to pH)?

Answer 20

pH = pKin, and Kin=[H+]x([In-])/([HIn])

Question 21

Acidity of rain

Answer 21

rain is naturally acidic because of CO2 but when sulfur dioxide and nitrogen oxides dissolve in water they produce acid rain:

Question 22

Environmental effects of acid rain

Answer 22

1| Increase the acidity of the soil (decreased nutrients)
2| Increases lake acidity
3| Erode buildings
4| Increases incidence of respiratory diseases in humans

Question 23

Methods for lowering the effects of acid rain

Answer 23

1| Lower the amount of NOx and SOx (improve engine design)
2| Switch to renewable energy sources
3| Neutralizing lake acidity

Question 24

Acid-base neutralization

Answer 24

to completely neutralize each other they must have equal C
when they are equal in strength (SA and SB or WA and WB) the equivalence point is at pH 7
when WA and SB the equivalence point is above pH 7
when SA and WB the equivalence point is below pH 7

Question 25

NaCl, CH3COONa, NH4Cl acidic/basic and prove it by chemical equations

Answer 25

neutral (SA + SB)
basic (WA + SB) like CH3COONa
acidic (SA + WB) like NH4Cl 1) CH3COONa→ Na+ + CH3COO-, H2O ↔H+ + OH- 2
NH4Cl→NH4+ + Cl-, H2O ↔H+ + OH-

Question 26

A buffer solution

Answer 26

also called pH buffer, an aqueous solution consisting of a mixture of a weak acid and its conjugate basic salt, or a weak base and its conjugate acidic salt used to prevent changes in the pH of a solution (its difficult to change its pH)

Question 27

How are acidic and how are basic buffers made?

Answer 27

1| Adding excess WA into a SB so that a WA and its basic salt are produced as the buffer solution (e.g. CH3COONa → Na+ + CH3COO-, CH3COOH ↔ H+ + CH3COO-)
2| Adding excess WB into a SA so that a WB and its acidic salt are produced as the buffer solution (e.g. NH4Cl → NH4+ + Cl- , NH3 + H2O ↔ NH4+ + OH-)