Chapter 4 - ME

Question 1

What is an electrolyte solution?

Answer 1

An electrolyte solution is a solution where the solute fully or partially dissociates into ions. This process can happen with ionic compounds such as NaCl or non-ionic compounds such as sugar or ethanol.

Question 2

What are electrolytes?

Answer 2

Electrolytes are substances that when dissolved in water dissociate into ions, specifically cations and anions.

Question 3

What is the role of ions in an electrolyte solution?

Answer 3

Ions are responsible for the conductivity of electrolyte solutions. Because the ions can move in an electric field, they can carry electric current and thereby conduct electricity

Question 4

What is the difference between strong and weak electrolytes?

Answer 4

Strong electrolytes are substances that are fully dissociated into ions when dissolved in water, while weak electrolytes only partially dissociate into ions.

Question 5

What are examples of strong electrolytes?

Question 6

What are examples of weak electrolytes?

Question 7

What is the Arrhenius definition of acids and bases?

Answer 7

According to the Arrhenius definition, acids are substances that give off H+ ions (protons) when dissolved in water, while bases are substances that give off OH- ions (hydroxide ions) when dissolved in water.

Question 8

What is the Brønsted definition of acids and bases?

Answer 8

The Brønsted definition expands on the Arrhenius definition by defining acids as substances that donate protons (H+ ions) in a chemical reaction, while bases are substances that accept protons.

Question 9

Weak acids - all other acids:

Answer 9

HF
HNO2 (nitrous acid)
H2CO3 (carbonic acid, really CO2+H2O)
H2SO3 (sulfurous acid)
H3PO4
HClO (hypochlorous acid)
All “organic” acids, e.g. acetic acid CH3COOH → CH3COO− + H+

Question 10

Strong acids

Answer 10

HCl, HBr, HI: e.g. HCl(aq)→ H+(aq) + Cl−(aq) fully dissociated
HNO3 HNO3 (aq) → H+ + NO3−
H2SO4 (but see special case of sulfuric acid in section 4.3)
HClO3
HClO4

Question 11

Strong bases:

Answer 11

Alkali metal hydroxides (LiOH, NaOH, KOH, etc.),
Earth alkali hydroxides insofar soluble, Ba(OH)2

All other bases are weak, the most common weak base: ammonia, NH3

Question 12

Soluble are:

Answer 12

All alkali metal and ammonium (NH4+) salts are soluble, no exceptions
All nitrates (NO3−), bicarbonates (HCO3−), chlorates (ClO3−) and perchlorates (ClO4−) are soluble, no exceptions.
All halides (Cl−, Br−, I−) are soluble, with exception salts with Ag+, Pb2+, Hg22+
All sulfates (SO42−) are soluble, with exceptions salts with Ag+ Ca2+, Sr2+, Ba2+, Pb2+, Hg22+

Question 13

Insoluble are:

Answer 13

Carbonates (CO32−), phosphates (PO43−), chromates and dichromates (CrO42−,Cr2O72−), sulfides (S2−)
Exceptions of course are the alkali metal salts of these anions (e.g. K2CrO4 is soluble)
Hydroxides (OH−), with exceptions the alkalimetal hydroxides but also Ba(OH)2 is soluble.

Question 14

A precipitation reaction

Answer 14

when two solutions of soluble compounds are mixed, but a new combination of ions produces an insoluble compound

Question 15

What are spectator ions?

Answer 15

Spectator ions are ions that do not participate in a chemical reaction and remain unchanged throughout the reaction. They are typically present in solutions as salts or other ionic compounds.

Question 16

What is a net ionic reaction?

Answer 16

A net ionic reaction is a chemical reaction in which only the species that actually participate in the reaction are shown. This is in contrast to a complete ionic equation, which shows all the ions that are present in the reaction, including spectator ions that do not participate. The net ionic equation allows for a clearer understanding of the chemical reaction and the behavior of the reacting species.

Question 17

What is a monoprotic acid?

Answer 17

A monoprotic acid is an acid that can donate one proton (H+) in a chemical reaction.

Question 18

What is the difference between a diprotic acid and a triprotic acid?

Answer 18

The main difference between a diprotic acid and a triprotic acid is the number of protons that they can donate in a chemical reaction. Diprotic acids can donate two protons, while triprotic acids can donate three protons. This difference can affect the acidity and basicity of the acid, as well as its behavior in various chemical and biological processes.

Question 19

Oxidation
Reduction

Answer 19

Oxidation: to lose electrons
Reduction: to gain electrons

Question 20

Rules for assigning oxidation numbers

Answer 20

1. Neutral elements have ox# = 0: Fe, Cl2, O2, N2, S8: ox# of all these is 0.
2. Monoatomic ions have ox# = charge:
   Na+ = +1, Fe3+ = +3, Cl− = − 1, O2− = −2, S2− = −2, Zn2+ = +2, Al3+ = +3, etc. All alkali metals in compounds always are +1, earth alkaline metals always are +2, Al always = +3.
3. Fluorine is always −1
4. O is always −2 (except in peroxides, such as H2O2 where it is −1)
5. H is always +1 (except in metalhydrides such as AlH3 or NaH where it is −1)

Then comes the rule that tells us the oxidation number of elements not mentioned in rules 1-5:
6. The sum of oxidation numbers in a neutral compound = 0, in an ion it equals the charge of the ion. In equation form: Σ(Ox.#) = net charge

Question 21

Oxidation numbers across the periodic table

Answer 21

For the main group metals:
Group 1 (alkalimetals) always +1, they lose 1 electron
Group 2 (earth alkaline metals) always +2, they lose 2 electrons
Group 13 Al always +3
For the non-metals:
Group 17 (halogens) −1 as monoatomic ions, but in oxyanions they can lose a maximum of 7 electrons, e.g. Cl in ClO4− = +7
Group 16 −2 as monoatomic ions (S2−, O2−), but in oxyanions they can lose a maximum of 6 electrons, e.g. S in SO42− = +6
Group 15 -3 as monoatomic ions (e.g. N3−, the nitrides), but in oxyanions they can lose a maximum of 5 electrons, e.g in NO3 N = +5, in PO43− P = +5
Group 14 no monoatomic ions exist, but in oxyanions they can lose a maximum of 4 electrons, e.g. in CO32− C = +4, also in CO2 and SiO2,C and Si are +4 respectively.

The transition metals can have a range of oxidation numbers, as shown in the periodic table on p. 136. We will come back to the regularities for the transition metals in chapter 8.

Question 22

What is a combination reaction?

Answer 22

A combination reaction is a type of redox reaction in which two or more elements or compounds combine to form a single product. In a combination reaction, one or more elements or compounds may be oxidized or reduced. For example, the reaction 4Fe + 3O2 → 2Fe2O3 is a combination reaction in which iron is oxidized and oxygen is reduced.

Question 23

What is a decomposition reaction?

Answer 23

A decomposition reaction is a type of redox reaction in which a single compound breaks down into two or more simpler substances. In a decomposition reaction, one or more elements or compounds may be oxidized or reduced. For example, the reaction 2KClO3 → 2KCl + 3O2 is a decomposition reaction in which chlorine is reduced (from +5 to −1) and oxygen is oxidized (from −2 to 0).

Question 24

What is a displacement reaction?

Answer 24

A displacement reaction is a type of redox reaction in which an atom or ion is displaced by another element. In a displacement reaction, one element or ion is oxidized while another is reduced. For example, the reaction Ca + 2H2O → Ca(OH)2 + H2 is a displacement reaction in which calcium replaces the hydrogen in its combination with oxygen.

Question 25

What is a disproportionation reaction?

Answer 25

A disproportionation reaction is a type of redox reaction in which the same element is both oxidized and reduced. In a disproportionation reaction, a single compound is transformed into two different compounds, one in which the element is oxidized and one in which it is reduced. For example, the reaction H2O2 → H2O + O2 is a disproportionation reaction in which hydrogen peroxide is both oxidized and reduced.

Question 26

What is a combustion reaction?

Answer 26

A combustion reaction is a type of redox reaction in which a substance reacts with oxygen to produce energy in the form of heat and light. In a combustion reaction, one or more elements or compounds may be oxidized or reduced. For example, the reaction CH4 + 2O2 → CO2 + 2 H2O is a combustion reaction in which methane is oxidized and oxygen is reduced