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CHEM 1411 > Book: Ch. 4 > Flashcards

Book: Ch. 4 Flashcards

1
Q

Define solute and solvent

A

A solution consists of a smaller quantity of one substance, the solute, dissolved in a larger quantity of another, the solvent

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2
Q

On the atomic scale, water’s great solvent power arises from _____

A

the uneven distribution of electron charge and its bent molecular shape

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3
Q

What are the three properties of polar molecules?

A
  1. Uneven charge distribution. Recall from Section 2.7 that the electrons in a covalent bond are shared between the atoms. In a bond between identical atoms—as in H2, Cl2, O2—the sharing is equal and electron charge is distributed evenly between the two nuclei. In covalent bonds between different atoms, the sharing is uneven because one atom attracts the electron pair more strongly than the other atom does.
  2. Bent molecular shape. The sequence of the H—O—H atoms in water is not linear: the water molecule is bent with a bond angle of 104.5º.
  3. Molecular polarity. The combination of polar bonds and bent shape makes water a polar molecule: the region near the O atom is partially negative, and the region between the H atoms is partially positive.
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4
Q

In an ionic solid, oppositely charged ions are held together by _____

A

electrostatic attractions

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5
Q

Water separates the ions by _____.

A

replacing these attractions with others between several water molecules and each ion

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6
Q

Dissolution occurs because _____.

A

the attractions between each type of ion and several water molecules outweigh the attractions between the ions

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7
Q

What does it mean for ions to be solvated?

A

Dissociated. They are surrounded closely by solvent molecules and then move randomly in the solution.

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8
Q

What causes certain ionic compounds to not dissolve in water?

A

For an ionic compound that doesn’t dissolve in water, the attraction between ions is greater than the attraction between the ions and water.

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9
Q

What happens to the electrical conductivity of a solution when ions are dissolved?

A

It increases dramatically.

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10
Q

When the ionic compound dissolves, the separate solvated ions _____ the electrode of opposite charge.

A

move toward

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11
Q

What is an electrolyte?

A

A substance that conducts a current when dissolved in water.

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12
Q

Soluble ionic compounds are strong electrolytes because _____.

A

they dissociate completely and conduct a large current

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13
Q

From the formula of the soluble ionic compound, we know _____ of each ion in solution.

A

the number of moles

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14
Q

What are nonelectrolytes?

A

Soluble covalent substances that do not separate into ions, but remain intact molecules. Their aqueous solutions do not conduct an electric current.

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15
Q

What is the concentration of a solution?

A

The quantity of solute dissolved in a given quantity of solution (or of solvent).

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16
Q

Concentration is an _____ property.

A

intensive

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17
Q

What is Molarity (M)?

A

The most common unit of concentration: M = (mols of solute)/(L of solution)

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18
Q

How do you go between mass, number of entities, amount, and volume of a solution with molarity?

A
  1. mass and amount are related through molar mass.
  2. entities and amount are related through Avogadro’s number.
  3. amount and volume are related through molarity.
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19
Q

What are the steps for preparing a solution of a solid solute?

A
  1. Weigh the solid. Calculate the mass of solid needed by converting from volume (L) to amount (mol) and then to mass (g)
  2. Transfer the solid. We need 0.500 L of solution, so we choose a 500-mL volumetric flask (a flask with a fixed volume indicated by a mark on the neck), add enough distilled water to fully dissolve the solute (usually about half the final volume, or 250 mL of distilled water in this case), and transfer the solute. Wash down any solid clinging to the neck with some solvent.
  3. Dissolve the solid. Swirl the flask until all the solute is dissolved. If necessary, wait until the solution is at room temperature.
  4. Add solvent to the final volume. Add distilled water to bring the solution volume to the line on the flask neck; cover and mix thoroughly again.
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20
Q

A concentrated solution (higher molarity) is converted to a dilute solution (lower molarity) by _____.

A

adding solvent

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21
Q

dilute solution contains _____ solute particles per unit volume

A

fewer

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22
Q

The relationship between a dilute solution molarity and a stock solution molarity is given by _____

A

M_dil x V_dil = amount (mol) = M_conc x V_conc

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23
Q

The molecular equation shows _____

A

all the reactants and products as if they were intact, undissociated compounds.

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24
Q

The total ionic equation shows _____

A

all the soluble ionic substances as they actually exist in solution, where they are dissociated into ions.

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25
Q

What are spectator ions?

A

Appear unchanged on both sides of the total ionic equation equation.

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26
Q

What is the net ionic equation?

A

Eliminates the spectator ions and shows only the actual chemical change.

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27
Q

What is a precipitation reaction?

A

Two soluble ionic compounds react to form an insoluble product: a precipitate.

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28
Q

The key event in a precipitation reaction is _____.

A

the formation of an insoluble product through the net removal of ions from solution

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29
Q

Three steps help us predict if a precipitate forms: _____

A
  1. Note the ions in the reactants.
  2. Consider all possible cation-anion combinations.
  3. Decide whether any combination is insoluble.
    - Eliminate all the spectator ions to get the net ionic equation.
30
Q

What are metathesis reactions?

A

(aka double displacement reactions) are when ions exchange partners.

31
Q

What are the steps for analyzing the stoichiometry of a precipitation reaction?

A
  1. Balance the equation.
  2. Find the amount (mol) of one substance using its molar mass (for a pure substance) or the volume and molarity (for a substance in solution).
  3. Relate that amount to the stoichiometrically equivalent amount of another substance.
  4. Convert to the desired units.
32
Q

For solutions A and B, what are the relationships between their masses, amounts, volume, and number of entities?

A
  1. mass of A ↔ amount of A via molar mass.
  2. mass of B ↔ amount of B via molar mass.
  3. Amount of B ↔ amount of A via molar ratio from balanced equation.
  4. amount of A or B ↔ volume of A or B via molarity.
  5. amount of A or B ↔ entities of A or B via Avogadro’s number.
33
Q

Acid-base reaction (also called a neutralization reaction) occurs when _____

A

an acid reacts with a base: an acid is a substance that produces H+ when dissolved in water, and a base is a substance that produces OH-

34
Q

Acidic solutions arise when _____. They are related to polar bonds in that _____.

A
  1. Certain covalent H-containing molecules dissociate into ions in water
  2. In every case, these molecules have polar bonds to H in which the other atom pulls much more strongly on the electron pair
35
Q

Explain the mechanism in which hydronium ions are produced during acid-base reactions.

A

When acids dissociate, they produce H+ ions, which are just protons. The protons get attracted to the negative pole of water molecules and form hydronium ions that associate with other water molecules.

36
Q

What does it mean for an acid or a base to be strong?

A

Strong acids and bases dissociate completely into ions.

37
Q

What does it mean for acids and bases to be weak?

A

Weak acids and bases dissociate very little into ions.

38
Q

Explain how weak or strong acids and bases relate to electrolytes.

A

Strong acids and bases are strong electrolytes that conduct a large current, whereas weak acids and bases are weak electrolytes.

39
Q

Explain the defining structural features of acids and bases

A

Acids have one or more H atoms which dissociate into protons, and bases have either O^2- or OH^- as part of their structure.

40
Q

The key event in aqueous reactions between a strong acid and a strong base is that _____

A

An H^+ ion from an acid and an OH^- from the base form a water molecule.

41
Q

Like precipitation reactions, acid-base reactions occur through _____ (by what physical mechanism?)

A

The electrostatic attraction of ions and their removal from solution as the product.

42
Q

The ionic compound resulting from reaction of an acid and a base is called a _____

A

Salt

43
Q

In an aqueous neutralization reaction, the products are _____

A

A salt and a water molecule

44
Q

Acid-base reactions are _____ reactions

A

Metathesis

45
Q

In an acid-base reaction, the cation for the salt comes from _____ while the anion comes from _____.

A
  1. Base

2. acid

46
Q

For strong acid-base reactions, the elimination of spectator ions reveals that the reaction is a _____ process

A

proton-transfer

47
Q

What happens in a proton-transfer process between acids and bases?

A

An acid donates a proton and a base accepts it.

48
Q

The defining characteristic of reactions of acids with carbonates or sulfites is _____

A

they are gas-forming reactions that produce H2

49
Q

What is the key difference between a strong acid-base reaction and a reaction between a weak acid and a strong base?

A

There is still proton-transfer, but the total ionic equation is written differently. On the left side, the acid appears as an undissociated, intact molecule.

50
Q

What is a titration?

A

The known concentration of one solution is used to determine the unknown concentration of another.

51
Q

The two stages of a titration reaction are _____ (name and explain them)

A
  1. The equivalence point: when amount of H+ ions in the original volume of acid has reacted with the same amount of OH- from the buret.
  2. End point: when a tiny excess of OH- changes the indicator permanently to its base color.
52
Q

In stoichiometry acid-base reactions, we usually assume the amount of base needed to reach the end point is _____ to amount needed to reach equivalence point.

A

equal

53
Q

Examples of oxidation-reduction (redox) reactions include _____

A

formation of a compound from its elements, the reverse of that, all combustion processes, the generation of electricity with batteries, the production of cellular energy.

54
Q

The key chemical event in a redox reaction is _____

A

the net movement of electrons from one reactant to another.

55
Q

The movement of electrons in redox reactions results from _____

A

the reactant with less attraction for electrons to the losing electrons to the reactant with more attraction for electrons

56
Q

Explain the mechanism for covalent redox reactions and ionic redox reactions.

A
  1. For ionic compounds, you get a transfer of electrons away from the metal to the nonmetal.
  2. For covalent compounds, electrons are shifted, not transferred. That is, no ions are formed.
57
Q

Oxidation refers to _____ while reduction refers to _____.

A
  1. loss of electrons

2. gain of electrons

58
Q

The oxidizing agent is the _____ while the reducing agent is the _____.

A
  1. species doing the oxidizing (causing electron loss)

2. species doing the reducing (causing electron gain)

59
Q

In a redox reaction, the oxidizing agent is _____ while the reducing agent is _____.

A
  1. reduced

2. oxidized

60
Q

What is an oxidation number (aka oxidation state)?

A

The charge the atom would have if its electrons were transferred completely, not shared.

61
Q

In terms of oxidation number, oxidation shows as _____ in the O.N., while reduction is _____ in the O.N.

A
  1. increase

2. decrease

62
Q

The electrons are _____ [free or never free] in a redox reaction. Why?

A
  1. never free

2. Because the reducing agent loses electrons and the oxidizing agent gains them simultaneously.

63
Q

What are combination redox reactions?

A

X + Y → Z

64
Q

In the formation of an ionic compound, the reducing agent is _____ and the oxidizing agent is _____

A
  1. the metal

2. the nonmetal

65
Q

What are decomposition redox reactions?

A

Z → X + Y

66
Q

Explain the two types of decomposition redox.

A

Thermal decomposition: when the energy absorbed for the bonds to break is through heat.
Electrolytic decomposition: when the energy absorbed is through electrical energy.

67
Q

What are displacement redox reactions?

A

In displacement reactions, the number of substances on the two sides of the equation remains the same, but atoms or ions exchange places.

68
Q

What are the two types of displacement reactions?

A
  1. Double-displacement (or metathesis): such as precipitation and acid-base reactions, two compounds exchange places for their atoms. These are NOT redox reactions.
  2. Single-displacement: one of the substances is an element; therefore, all of these are redox processes.
69
Q

In solution, single-displacement reactions occur when ____. If metal is involved, the atom _____ and if it involves nonmetals, _____.

A
  1. an atom of one element displaces the ion of another
  2. reduces the ion
  3. the atom oxidizes the ion
70
Q

Combustion is the process of _____

A

combining with oxygen

71
Q

Are all combustion reactions redox processes?

A

yes

72
Q

What does it mean for a reaction to reach dynamic equilibrium?

A

Two opposing reactions are taking place simultaneously, the forward reaction continues, but the reverse reaction occurs just as fast. No further changes appear in the amounts of reactants or products. The reaction is static, but it is dynamic on the molecular level.

CHEM 1411 (19 decks)

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