Concepts Test 2

Question 1

Reagent vs. reactant

Answer 1

• Reagent is “off the shelf”.
• A reactant is a substance consumed in the course of a chemical reaction.

Question 2

Solvent vs. solute

Answer 2

• Solvent - more of it. Assume that it is an aqueous solution and that the solvent is water.
• Solute - have less of it, can be a solid, liquid or gas.

Question 3

Solubility

Answer 3

• The # grams of solute that can dissolve in 100g of solvent at room temperature, to make a saturated solution
• When a compound has reached it’s maximum solubility and there is solid is present in the solution, the solution is SATURATED.

Question 4

Coulomb’s Law

Answer 4

• Force of attraction or repulsion is directly proportional to the magnitude of the charges, and inversely proportionally to the distance between the particles. So as ion charges increase, the force increases. As distance increases, the force decreases.
• The sign of the charges matter for showing us the direction - attraction or repulsion

Question 5

What happens to ionic compounds in water?

Answer 5

• The compound dissolves, dissociates. The ions separate break up into cations and anions. The ions move freely in the water, and the solution is able to conduct electricity.
• The electrolytic solution can be strongly acidic or strongly basic

Question 6

Strong electrolyte vs. weak electrolyte vs. nonelectrolyte

Answer 6

• A strong electrolyte is an ionic compound that 100% dissociates in aqueous solution.
• A weak electrolyte partially dissociates.
• When a nonelectrolyte (like sugar) dissolves in water, molecules remain intact. The solution carries no electrically charged particles.

Question 7

What is the formula for the dissociation of calcium chloride?

Answer 7

CaCl₂ (s) –> Ca²⁺ (aq) + 2Cl^- (aq)

Write the formulas of the ions separately, to show that they are independent of each other.

Question 8

Describe the 3 types of equations for a reaction between solutions of electrolytes

Answer 8

• Molecular equation keeps the molecules together.
• Ionic equation separates the ions (except for individual polyatomics) and shows their charges
  
  • Keep in molecular form if the ionic substance is insoluble
  • Weak acids and bases are always written in molecular way, never in ionic way
  • To be balanced, need same net charge on both sides of equation
• Net ionic equation eliminates the spectator ions, focus on the chemical change

Question 9

ionic compounds vs. molecular compounds

Answer 9

• Ionic compounds are between metals and nonmetals or between metals and polyatomic ions or between polyatomics. When an ionic substance is dissolved in aqueous solution, it ALWAYS ionizes and the ions always have a charge.
  
  • Ex: sodium chloride NaCl, magnesium nitrate Mg(NO₃)_2, ammonium sulfate (NH₄)₂SO₄.
  • Remember to never split apart a polyatomic ion. NH₄NO₃ ionizes into NH4+ and NO3¯.
• Molecular compounds involve only nonmetals. Molecular substances never ionize in solution, they exist as complete molecules and never have a charge.
  
  • Ex: sulfur trioxide (SO₃), carbon dioxide (CO2), water (H2O) and glucose (C6H12O6).

Question 10

Solubility rules for ionic compounds in water:

What are the rules for soluble compounds?

Answer 10

• If one ion from the Soluble Compound list is present in a compound, the compound is water soluble.

Write in dissociated form:

1. All compounds of the alkali metals (Group 1A) are soluble.
2. All salts containing NH₄⁺ , NO₃^- , ClO₄ ^- , CLO₃^- , and C₂H₃O₂ - are soluble.
3. All chlorides, bromides, and iodides (salts containing Cl^- , Br^-, or I^-) are soluble EXCEPT when combined with select transition metals: Ag+ , Pb²⁺ and Hg₂²⁺
4. All sulfates (salts containing SO₄^2-) are soluble EXCEPT those of Pb²⁺ Ca²⁺, Sr²⁺, Hg₂²⁺ and Ba²⁺

Question 11

Solubility rules for ionic compounds in water:

What are the rules for insoluble compounds?

Answer 11

1. Most salts of carbonate CO₃^2-, phosphate PO₄^3-, sulfite SO₃^2-, sulfide S^2-
   
   1. EXCEPT for salts of NH₄⁺ and the Group 1 alkali metal cations
2. Most metal hydroxides and oxides
   
   1. EXCEPT for those of Group 1A, Ca, Sr, Ba

Question 12

Dissolve vs. dissociate vs. ionize

Answer 12

• To dissolve is to become part of a solution. (Any soluble compound.)
• To dissociate is to break up into ions which already exist in a compound. (Ionic compounds only.)
• To ionize is to produce new ions by gain or loss of electron. (Covalent compounds or neutral metals only, since they didn’t have ions before.)

Question 13

What does is mean to be soluble?

Answer 13

Soluble means it dissolves

and in the case of electrolytes, dissociates

(breaks up into its ions).

Different from miscible.

Question 14

What are strong and weak electrolytes?

Answer 14

• An electrolyte is an ionic compound that conducts electricity in aqueous solutions because it dissolves and dissociates in water.
• Strong electrolytes dissociate completely.
  
  • Soluble salts, strong acids, strong bases.
  • Ex: CuCl₂ (s) –> Cu²⁺ (aq) + 2Cl^- (aq)
• Weak electrolytes dissociate only to a small extent
  
  • Weak acids, weak bases, partially soluble salts
  • Ex: acetic acid. CH₃CO₂H (aq) ⇄ CH₃CO₂^- (aq) + H⁺(aq)
• Nonelectrolytes dissolve, but do not dissociate
  
  • Ex: insoluble compounds.

Question 15

Salt

Answer 15

An ionic compound that is neither an acid nor a base

Question 16

Acid

Answer 16

Acids are ionic compounds that increase the concentration of H₃O+ in water.

Question 17

Base

Answer 17

• Bases are ionic compounds that increase the concentration of OH- in water. Proton acceptor.
  
  • When you see OH, be careful to notice what its attached to. If it isn’t attached to a cation, it isn’t a base.

Question 18

What are types of reactions?

Answer 18

• Exchange (aka double displacement, displacement, metathesis): ionic reaction in which cations and anions change partners.
  
  • Precipitation formation (Due to low solubility - use solubility rules to predict)
  • Acid-base neutralization
  • Gas formation
• Combustion (compound with C and H + O₂ –> CO₂, H₂O
• Single replacement from lab
  
  • Magnesium reacts with hydrochloric acid according to the equation: Mg (s) + 2 HCl (aq) –> MgCl 2 (aq) + H 2 (g) This demonstration can be used to illustrate the characteristic reaction of metals with acid, a single replacement reaction, or to demonstrate the generation of hydrogen gas.
• Redox (oxidation-reduction) reactions
• Ionization reaction - ions form where they didn’t exist before. (Covalent compounds or neutral metals only)
• Ionic reaction - a reaction between ions

Question 19

When is there no reaction?

Answer 19

• If everybody is soluble, nothing happens in the beaker. The ions just keep floating around.
• Write no reaction “ –> NR”.

Question 20

What are gas forming reactions?

Answer 20

• Strong driving force to create gas.
• Do exchange reaction and recognize gas products: CO₂, NH₃, SO₃, H₂S, HCN

Question 21

What is molarity, and its relevant equations?

Answer 21

• Molarity (M) is how we define concentration in aqueous solution
• Molarity = moles of solute / liters of solution
• moles = Molarity • Volume
• M₁V₁ = M₂V₂
  
  • Molaritystock • Volumestock = Mdilution • Vdilution

Question 22

What are the important pH equations?

Answer 22

• pH = -log[H+]
  
  • interchangeable with [H₃O+]
• [H+] = 10^-pH
• pH + pOH = 14
• [H+][H₃O+]= 10^-14