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Chemistry > Chapter 4: Acid and Redox > Flashcards

Chapter 4: Acid and Redox Flashcards

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1
Q

what element do all acids contain?

A

hydrogen

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2
Q

what happens to acids when dissolved in water?

A

acids releases hydrogen ions as protons (H+)

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3
Q

equation for HCl + aq:

A

HCl (g) + aq → H+ (aq) + Cl- (aq)

+ symbol shows excess water is present
- the equation is hydrogen chloride gas dissolving to form aqueous solution

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4
Q

example of strong acid:

A

HCl

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5
Q

what do strong acids do?

A

releases all its hydrogen atoms into solution as H+ ions and completely dissociates into aqueous solutions
HCl (aq) → H+ (aq) + Cl (aq)

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6
Q

example of a weak acid:

A

ethanoic acid (CH3COOH)

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7
Q

what do weak acids do?

A

only release small proportion of it’s availed hydrogen atoms into solution as H+ ions
- weak acid partially dissociates into aqueous aqueous solutions
CH3COOH (aq) →← H+ (aq) + CH3COO- (aq)

  • forward reaction is incomplete
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8
Q

what does each molecule of ethanoic acid contain?

A

four hydrogen atoms but only one of COOH group is released as H+
- most organic acids are weak

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9
Q

base examples:

A

me take oxides, metal hydroxides, metal carbonates, ammonia (NH3)

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10
Q

what does a base neutralise?

A

neutralises an acid to form aqueous salt

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11
Q

alkali definition:

A

a base that dissolves in water releasing hydroxide ions (OH-) into solution

NaOH (s) + aq → Na+ (aq) + OH- (aq)

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12
Q

common bases that are metal oxides:

A

MgO
CaO
CuO

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13
Q

common bases that are metal carbonates:

A

Na2CO3
CaCO3
CuCO3

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14
Q

common bases that are alkalis:

A

NaOH
KOH
NH3

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15
Q

what happens in neutralisation of an acid?

A

H+ (aq) ions react with a base to form aqueous salt and neutral water

H+ ions from acid are replaced by metal or ammonium ions from the base

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16
Q

HCl and its salts

A

type: chloride
name of salt: sodium chloride (NaCl)

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17
Q

sulfuric acid (H2SO4) and its salt

A

type: sulfate
salt name: sodium sulfate (Na2SO4)

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18
Q

nitric acid (HNO3) and its salt:

A

type: nitrate
salt: calcium nitrate Ca(NO3)2

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19
Q

ethanoic acid (vinegar/CH3COOH) and its salt

A

type: ethanoate
salt: ammonium ethanoate (CH3COONH4)

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20
Q

what is an acid neutralised by?

A

a metal oxide or metal hydroxide to form only salt and water

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21
Q

equation for neutralisation of sulfuric acid and HCL by copper (II) oxide to form a salt and water only:

A

CuO (s) + H2SO4 (aq) → CuSO4 (aq) + H2O (l)
CuO (s) + 2HCl (aq) → CuCl2 (aq) + H2O (l)

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22
Q

how are reactants in alkalis?

A

in solution form

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23
Q

formula for metal oxides:

A

acid + alkali → salt + water

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24
Q

full and ionic for neutralisation of H+ (aq) ions by OH- (aq) ions to form neutral water:

A

HCl (aq) + NaOH (aq) → NaCl (aq) + H2O (l)

ionic:
H+ (aq) + OH- (aq) → H2O (l)

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25
what do carbonates neutralise?
acids to form salt, water and CO2
26
neutralisation of carbonates by sulfuric acid and HCl:
ZnCO3 (s) + H2SO4 (aq) → ZnSO4 + H2O (l) + CO2 (g) MhCI3 (s) + 2HCl (aq) → MgCl2 (aq) + H2O + CO2 (g)
27
what type of acid is sulfuric acid?
strong acid but this is only true for one of the hydrogen atoms - when mixed with water each molecule dissociates + released one of its two hydrogen atoms as H+ ion H2SO4 (aq) →H+ (aq) + H2SO4- (aq) resulting in H2SO4- (aq) ions only partially dissociating: HSO4- (aq) → ← H+ (aq) + SO42- (aq)
28
how does sulfuric acid behave when dissociated?
as a strong acid HSO4- ions behave as a weak acid - other string acids containing more than one hydrogen atom behave similarly
29
what are titrations:
a technique used to accurately measure the volume of one solution that reacts exactly with another solution
30
why are titrations used?
- to find concentration of a solution - identification of unknown chemicals - finding purity of a substance
31
why is checking the purity of a substance important?
medicines, food, cosmetics - small impurity in a drug can be harmful
32
what is a standard solution?
a solution of a known concentration
33
what is used to make standard solutions?
volumetric flasks to make solution accurate
34
tolerances of volumetric flasks:
100cm3 =3.52 UK fl oz +- 0.20cm3 250cm3 = +- 0.30cm3
35
steps for preparing a standard solution:
1. solid is weighed 2. solid dissolved in beaker using less distilled water than needed to fill volumetric flask to mark 3. solution is transferred to volumetric flask. last traces of solution are rinsed into flask with distilled water 4. flask carefully filled to graduation line by adding distilled water a drop at a time until bottom of meniscus 5. volumetric flask inverted several time to mix solution thoroughly + makes results more consistent
36
acid base titration steps:
solution of an acid is titrated against a solution of a base using pipettes + burette
37
tolerances for pipettes:
10cm3 = +- 0.004cm3 25cm3 = +-0.06cm3
38
burette tolerances:
50cm3 = +- 0.10 cm3
39
reading of burette for tolerances:
- always to two d.p - last place being either 0 or 5
40
steps for acid base titration:
1. add measured volume of one solution to a conical flask using a pipette 2. add other solution to burette + record initial burette reading to nearest 0.05cm3 3. add a few drops of indicator to conical flask 4. run solution in burette into conical flask + swirl to mix two solutions. indicator will change colour at end point of titration
41
steps for recording titration:
5. record burette reading, the vol of solution added from burette is the titre, calculated by final - initial burette reading 6. trial titration is carried out to find approx titre 7. titration repeated accurately, adding so,ruin dropwise as the endpoint is approached 8. further titrations carried out until two accurate titres are concordance (within 0.10cm3)
42
what does the table for recording titrations contain?
final burette reading cm3 initial burette reading cm3 titre cm3 mean titre 3 trials
43
which titres are used to calculate the mean?
- only the closest accurate titres - relating titres until two agree writhing 0.10cm3 + reject inaccurate ones or accuracy is lost
44
what will you know from the titration results?
- both concs and reacting volume of one solution - reacting volume of the other solution
45
titration calculations:
Step 1: Work out the amount, in mol, of the solute in the solution for which you know both the concentration c, and volume V Step 2: Use the equation to work out the amount, in mol, of the solute in the other solution. Step 3: Work out unknown information about solute in other solution.
46
steps for identifying a carbonate:
1. prepare unknown solution of carbonate X2CO3 in volumetric flask 2. using pipette, measure 25.00cm3 of prepared solution into conical flask 3. using burette, titrate this solution using 0.100moldm-3 HCl 4. analyse results to identify carbonate
47
steps for analysis of titrations:
1. calculate mol of HCl reacted 2. determine mol of X2CO3 that reacted 3. work out unknown info by scaling up to find mol in 250cm3 solution + find molar mass of X2CO3 3. use M(X2CO3) to identify X
48
rules of oxidation numbers for elements:
- oxidation number is always zero - in pure elements, any bonding is to atoms of the same element - in H2, O2, P4, S8, Na, Fe
49
rules of oxidation numbers for compounds and ions:
each atom in a compound has an oxidation number - has a sign (+ -) placed before number
50
oxidation number for oxygen:
-2 e.g in H2O, CaO
51
oxidation number for H:
+1 e.g NH3, H2S
52
oxidation number for F:
-1 e,g HF
53
oxidation number for Na+ and K+
+1 e.g NaCl, K2O
54
oxidation number for Mg2+ and Ca2+
+1 e,g NaCl, K2O
55
oxidation number for Mg2+ and Ca2+
+2 e.g MgCl2, CaO
56
oxidation number for Cl-, Br, I-
-1 e,g HCI, KBr, CaI2
57
special cases of oxidation numbers:
H in metal hydrides = -1 e.g NaH, CaH2 O in peroxides = -1 e.g H2O2 O bonded to F = +2 e.g F2O
58
sum of oxidation numbers =
total charge
59
why are roman numerals used in compounds of elements names?
shows the oxidation number of the element without the sign
60
what does iron (II) represent?
Fe2+ with oxidation number +2
61
what does iron (III) represent?
Fe3+ with oxidation number +3
62
modern names of poly atomic ions:
NO2- oxidation number: +3 common name: nitrite modern name: nitrate (III) NO3- oxidation number: +5 common name: nitrate modern name: nitrate (V)
63
where does the roman numeral come from?
- the common ion usually with more oxygen atoms - nitrate is assumed to be No3- - sulfate is assumed to be SO42-
64
oxidation and reduction definitions:
oxidation - addition of oxygen reduction - loss of oxygen
65
what is a redox reaction?
involves oxidation and reduction at the same time
66
reduction definition in terms of electrons:
gain of electrons
67
what do roman numerals show?
oxidation numbers
68
NO2- common name, oxidation number and modern name:
common name: nitrite oxidation number : +3 modern name: nitrate (III)
69
NO3- common name, oxidation number and modern name:
common name: nitrate oxidation number: +5 modern name: nitrate (V)
70
what is nitrate assumed to be?
NO3-
71
what is sulfate assumed to be?
SO42-
72
what also undergoes redox reactions?
dilute acids metal + acid → salt + hydrogen
73
what are redox reactions?
involve reduction and oxidation
74
what is reduction?
gain of electrons
75
what is oxidation?
loss of electrons
76
do redox reactions need oxygen?
no. they can happen if electrons are lost or gained
77
ions of FeCl3:
Fe3+ and Cl-
78
reduction in terms of oxidation number:
- reduction is the decrease in oxidation number - oxidation is an increase in oxidation number
79
what do the changes in each oxidation number apply to?
changes apply to each atom - the total changes in oxidation number balance
80
reaction of zinc with dilute HCl:
Zn (s) + 2HCl (aq) → ZnCl2 (aq) + H2 (g)
81
Reaction of aluminium with dilute sulfuric acid:
2Al (s) + 3H2SO4 (aq) → Al2(SO4)3 (aq) + 6H2 (g)

Chemistry (18 decks)

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