chem1013-quiz 6: chapter 5

When ionic solutes form a solution with water, what do ions undergo?

hydration (water molecules surround each ion)

What is dissociation?

solute ions break their attraction to each other and are attracted to the water molecules and disperse into the water (solvent)

ie: NaCl (s) → Na⁺ (aq) + Cl^- (aq)

What happens to molecular solutes when they form solutions with solvents?

molecular solutes can also form solutions with solvents, but molecules only separate from each other (no dissociation, no bonds breaking)

ie: CH₃OH (l) → CH₃OH (aq)

What are electrolytes?

Substances that dissociate into ions in solution, conducting electricity.

What are strong electrolytes?

completely dissociate into ions when dissolved in water

mostly ionic compounds

ie: NaCl

What are non electrolytes?

do not dissociate into ions when dissolved in water

do not conduct electricity

mostly molecular compounds

ie: C₁₂H₂₂O₁₁

*not acids

Explain how sugar dissolves and how that differs from a sodium chloride solution?

sugar dissolves because the attraction between sugar and water molecules overcome the attraction of sugar molecules to each other. So, unlike a sodium chloride solution (which breaks up into Na⁺ and Cl^- ions), a sugar solution contains intact C₁₂H₁₂O₁₁ molecules homogeneously mixed with water molecules

What is a strong acid?

completely ionize in solution, strong electrolytes, single →
ie: HCl → H⁺ + Cl^-

What is a weak acid?

do not completely ionize in water, weak electrolytes, use double arrow (⇌) in equations, eg: CH₃COOH ⇌ H⁺ + CH₃COO⁻

What is solubility?

grams solute that can be dissolved in 100 g solvent (water) at a temperature in Celsius, to be said simpler: whether something dissolves or not

What does it mean if something is soluble?

dissolves in water

What does it mean if something is insoluble?

does not dissolve in water

How do you determine solubility?

look at the given paper and see the rules and exceptions

What are precipitation reactions?

a solid (precipitate) forms when two solutions mix

*only insoluble compounds form precipitates

*if both possible products are soluble, no reaction occurs and no precipitate forms

What do you do when no reaction occurs?

write “no reaction,” cross out the arrow, and do not write the products

How do you write a precipitate reaction?

1. write formulas of two compounds as reactants

2. write products that could form by combining cations and anions

3. use solubility rules to determine if products are insoluble (s)

4. if all possibly products are soluble, write no reaction; if soluble, write (aq), if insoluble, write (s)

   1. balance

What is a molecular equation?

complete neutral formulas for each compound

In actual solutions of soluble ionic compounds, how are dissolved substances presented?

as free ions, not as intact compounds

What is the complete ionic equation?

all of ions present (reactants and products) and shows states for each

ie: shows all soluble ions separated, indicating their participation in the reaction.

strong electrolytes are represented as their component ions in ionic equations— weak electrolytes are not
*liquids and solids do not break up, only aqueous

Write an example complete ionic equation for the reaction between lead (II) nitrate and potassium chloride.

The complete ionic equation shows the dissociation of lead (II) nitrate and potassium chloride in aqueous solution, resulting in lead (II) ions, potassium ions, and chloride ions, while maintaining the solid state of lead (II) chloride. It can be represented as: Pb^{2+} (aq) + 2 K^{+} (aq) + 2 Cl^{-} (aq) → PbCl_{2} (s) + 2 K^{+} (aq).

What are spectator ions?

do not participate in the reaction (same on both sides of the arrow)

What is the net ionic equation?

only species that actually change during the reaction and exclude spectator ions.

Write the net ionic equation for the  reaction between lead (II) nitrate and potassium chloride.

The net ionic equation is Pb^{2+} (aq) + 2 Cl^{-} (aq) → PbCl_{2} (s).

What is an acid-base reaction?

“neutralization reaction,” acid reacts with base and they neutralize each other, producing water (sometimes weak electrolyte)

What is a gas-evolution reaction?

gas forms, bubbling (many are acid-base reactions)

What is the Arrhenius definition of an acid?

produces H⁺ (or H₃O⁺) in an aqueous solution

What is the Arrhenius definition of a base?

produces OH^- in an aqueous solution

What are strong acids?

dissociate completely, single arrow

What are weak acids?

do not dissociate completely, double arrow

What are polyprotic acids?

have more than 1 ionizable proton, release them sequentially

ie: H₂SO₄ → H⁺ + HSO₄^-

HSO₄^- → H⁺ + SO₄^2-

What happens when you mix acids and bases (weak or strong)?

H⁺ (aq) from the acid combines with OH^- (aq) form the base to form H₂O (l) and usually an ionic compound, called a salt

What are the six strong acids?

The six strong acids are

H₂SO₄, HI, HBr, HNO₃, HCl, HClO₄

They completely dissociate in water.

What is a way to remember the six strong acids?

One mnemonic is "So I Brought No Clean Clothes" which stands for: HCl, HBr, HI, HNO₃, HClO₄, and H₂SO₄.

Any acids that are not the six strong acid list are considered what?

weak acids

What do strong bases include that weak bases do not have?

OH

What is an example of a weak base?

Ammonia (NH₃)

What is the rule for the net ionic equation for any acid-base reaction with a strong acid?

H_⁺ (aq) + OH^- (aq) → H₂O (l)

What is the rule for the net ionic equation for any acid-base reaction with a weak acid?

The weak acid donates protons partially, resulting in a reversible reaction with water and its conjugate base.
Do not break up the weak acid when writing the net ionic equation
Double arrow

Example of an acid-base reaction with a weak acid:
HF (aq) + NaOH (aq) double arrow H2O (l) + NaF (aq)
How do you write its net ionic equation?

HF (aq) + OH^- (aq) ⇌ H₂O (l) + F^- (aq)

the sodium ion cancels because it is a spectator ion

What is titration?

substance in a solution of known concentration is reacted with another substance of unknown concentration

What is the equivalence point?

point in titration when the number of moles OH- is equal to the number of mole of H+
*consider molar ratios from the chemical equation

What is an indicator?

dye whose color depends on acidity or basicity of solution, signals the equivalence point

What is titration in general terms?

the concentration of 1 reactant solution is unknown, concentration of other reactant is known, carefully measure volume of each solution required to reach the equivalence point, then determine the concentration of unknown solution

How do you do a titration question?

1. write the chemical equation (and balance it)

2. write what is given: M can be mol/ L conversion

3. use M as a conversion

4. Calculate moles of unknown
   start with volume of known

   1. calculate unknown concentration using M= mol/L

What are oxidation-reduction (redox) reactions?

electrons transfer from 1 reactant to another

What is oxidation?

lose electrons

What is reduction?

gain electrons

What is the oxidation state or oxidation number?

given to each atom based on electron assignments, the “charge” it would have if all shared electrons were assigned to the atom with the greatest attraction

What are the rules for assigning oxidation states? MUST GO IN ORDER

1. free element = 0

2. monatomic ion = charge

3. sum of oxi # of all atoms in neutral compound = 0
   ion = charge

4. metals have positive oxidation #
   IA = +1, IIA = +2

5. nonmetals:

   1. F = -1

   2. H = +1

   3. O = -2

   4. 7A = -1

   5. 6A = -2

   6. 5A = -3

note: when H is paired with nonmetal, it is +1

when with metal, it is -1

What does the oxidation state of each element depend on?

what other elements are present in the compound (except: 1A and 2A metals are always +1 and +2)

Rule 3 must always be followed for oxidation (sum = 0 for neutral or sum = charge of ion). So, what do you give priority to first to assigning other elements?

nonmetals:

F = -1

H = +1

O = -2

7A = -1

6A = -2

5A = -3

How do you determine the oxidation state of elements that are not listed in the rules?

use the sum charge and known oxidation states to use algebra to determine the oxidation state

How do you identify a redox reaction?

one thing is oxidized (lose electrons, ox # increases)

one thing is reduced (gain electrons, ox # decreases)

How do you determine what is oxidized and what is reduced?

Identify changes in oxidation states for the elements involved; oxidation occurs when an element's oxidation state increases, while reduction occurs when its oxidation state decreases.

write which element is oxidized and which is reduced

How do you determine oxidizing and reducing agents, and how do you write them?

The oxidizing agent is the species that gains electrons (is reduced), and the

reducing agent is the species that loses electrons (is oxidized).

write down the entire reactant, not just the element

What is pressure?

amount of force per unit area (result of molecular collisions)

pressure exerted by a gas = force exerted by its particles/ surface area that they strike

P = F/A

What does the total pressure depend on?

several factors, including the concentration of gas particles in the sample (lower concentration means lower pressure)

What is a barometer?

measures atmospheric pressure

What is a manometer?

measures gas sample pressure

What are the four properties of a sample of gas?

pressure (P)

volume (V)

temperature (T)— must be in Kelvin!

amount (n)— moles

What is Boyle’s Law?

inverse relationship between volume and pressure

V ~ 1/p when temperature and n are constant

P1V1 = P2V2

when the volume of a gas decreases, more collisions with walls occur and therefore an increase in pressure

What is Charle’s Law?

direct relationship between volume and temperature

V ~ T when P and n are constant

V1/T1 = V2/T2

when the temperature of a sample increases, the gas particles more faster and collide more often with the walls, causing an increase in volume.

What is Avogadro’s Law?

direct relationship between volume and amount of gas

V ~ n when T and P are constant

V1/n1 = V2/n2

when the amount of gas in a container increases, the volume also increases if the temperature and pressure remain constant.

What is Gay-Lussac’s Law?

direct relationship between pressure and temperature

P ~ T when V and n are constant

P1/T1 = P2/T2

when the temperature of a gas increases, the pressure also increases if the volume and amount of gas remain constant.