Chapter 4: Three Major Classes of Chemical Reactions

Merged flashcards from Chapter 4 of Chemistry: The Molecular Nature of Matter and Change.

Solution

A homogenous mixture with a uniform composition and no visible component boundaries, consisting of a dissolved solute and dissolving solvent

Aqueous solution

A solution where water is the solvent

Concentration

The quantity of solute dissolved in a given quantity of solution

• This is an intensive property, independent of volume

Molarity (M)

The most common unit of concentration, expressing moles of solute per liter of solution

• Can be used as conversion factor to find other values

• Requires solution (not solute) volume

• Calculate the mass of solid needed for the desired volume and molarity.

• Transfer the solid to the flask, and add enough solvent (typically half of the final volume) to dissolve the entire mass of solid first.

• Dissolve the solid by swirling.

• Add the remaining amount of solvent needed, and mix again.

How would I prepare a solution?

Dilution

The addition of more solvent to lower the concentration and molarity of a solution

Stock solution

A highly concentrated solution which is stored for future use in dilution

• First, find the amount in moles needed in the dilute solution.

• Next, find the amount of stock solution needed to obtain that same amount in moles.

• Finally, add enough solvent to the calculated amount of stock solution to obtain the desired volume of the dilute solution. Check your answer with the molarity equation.

How would I prepare a dilute solution from a concentrated solution?

M_concV_conc = M_dilV_dil = constant mol of substance

What is the equation to solve for molarities or volumes given a constant amount of substance?

Water

A polar, unevenly-charged molecule with two positive H atoms and one negative O atom that forms a bent molecular shape

• These forces can break apart bonds in certain ions, should the attraction between the ions be lower than the attraction towards the water molecules

Solvation

The close surrounding of ions by solvent molecules, allowing them to move randomly in solution

• This allows for a dramatic increase in conductivity due to this new available movement of charged particles

• May also occur to covalent compounds, but only between molecules and not individual ions with no conductivity

Electrolyte

A substance that conducts a current when dissolved in water, as ions move towards the electrode of opposite charge

• Higher ionic dissociation results in stronger variants of these, like NaCl

Nonelectrolytes

Substances that do not conduct electric current when dissolved in water

• Includes many covalently-bound molecules

Precipitation reactions

Reactions where two aqueous ionic compounds are combined to form a solid

• Results from a newly made cation-anion attraction that is stronger than those in water

• May be expressed through a molecular, total ionic, or net ionic equation

Molecular equation

An equation that depicts all reactants and products as if they were undissociated substances, after balancing charges

• 2AgNO_3(aq) + Na₂CrO_4(aq) → Ag₂CrO_4(s) + 2NaNO_3(aq)

Total ionic equation

An equation that depicts all substances as they actually exist in solution, typically as ions, combining to potentially form a solid precipitate

• 2Ag⁺_(aq) + 2NO^-_3(aq) + 2Na⁺_(aq) + CrO₄^2-_(aq) → Ag₂CrO_4(s) + 2Na⁺_(aq) + 2NO₃^-_(aq)

Net ionic equation

An equation that depicts only the changed ions in a total ionic equation, without spectator ions

• 2Ag⁺_(aq) + CrO₄^2-_(aq) → Ag₂CrO_4(s)

Spectator ions

Ions that remain unchanged in the combination of two aqueous ionic substances

Solubility rules

These are required to determine if the compounds that are formed will be soluble in water

Metathesis reactions (double-displacement reactions)

Reactions in which the reactant ions change partners

• Includes precipitation and acid-base reactions

Hydronium

The name for the the H₃O⁺ ion formed between an H⁺ ion and a water molecule

Gaseous reactions

Reactions that form a gas and sometimes a water

• Includes reactions with carbonates, sulfites, and bisulfates for an equation resembling CO₂

• Includes reactions with sulfides for H₂S

• Includes reactions with ammonium for NH₃

1. Note the color changes of the indicator in acids and bases

2. Measure out a known volume of acid (or base) with indicator

3. Add drops of base (or acid) to replace H⁺ (or OH^-), observing a temporary change in color that goes away when swirled

4. Stop when the endpoint is reached, where a color is effected even after swirling

How would I perform a titration?

Acid

A substance that increases the concentration of H⁺ when dissolved in water

Base

A substance that increases the concentration of OH^- when dissolved in water

• Can either dissociate to form OH^- (when strong) or remove an H⁺ ion from water (if weak)

Acid-base reaction

A reaction between an acid and a base with water acting as a solvent, product, or reactant

Strong acid

An acid with a strong tendency to dissociate into ions in water, allowing for high electrolytic capacity

• Includes hydrogen and N-ate, S-ate, Cl-+ate, Br, and I, which are soluble

Weak acid

An acid with a low tendency to dissociate into ions in water, creating low electrolytic capcity

• Written as undissociated compound decomposing into ions in ionic equations

Strong base

A base with a strong tendency to dissociate in to OH^- and another substance in water

• Includes OH^- and group 1 and 2 metals, of which ones are soluble

Weak base

A base that does not readily dissociate in water and instead forms OH^- through the attraction of an H⁺ ion from water

• Typically includes nitrogen, like in NH₃⁺ (ammonia)

Electrolytic capacity

This is increased when a salt, strong acid, or strong base dissociates into water

• Allows for the use of molarity as a conversion factor

Metathesis reactions (double-displacement reactions)

Reactions where cation and anion partners switch

Molecular equation

An equation where all compounds are shown as undissociated substances

Total ionic equation

An equation where all compounds are shown as they exist in solution, potentially as ions for a salt, strong base, or weak base

Net ionic equation

An equation where only changed ionic compounds are shown in solution

• Does not include spectator ions

Spectator ions

Ions that do not participate in a reaction and are left out in the net ionic equation

Equivalence point

When the moles of OH^- equal the moles of H⁺ in a solution for complete neutralization

End point

When the moles of either H⁺ or OH^- in a solution are slightly greater than the other, effecting a change in an indicator that does not disappear when swirling

• Sometimes treated as equivalent to the equivalence point due to only slight difference

Redox reaction

A reaction involving the oxidation and reduction of two substances at the same time

• Contributes to both ionic and covalent compounds as electrons are transferred or shifted

• Seen with 2Na⁺ + Cl₂^- → 2NaCl, as Na loses a negative charge (oxidized) and Cl gains a negative charge (reduced)

Electron transfer

What occurs between atoms in an ionic compound

Electron shift

What occurs between atoms in a covalent compound, with no ions formed yet still a difference in charge

Oxidation

The loss of electrons to an oxidizing agent

• In 2Na⁺ + Cl₂^- → 2NaCl, Na has this done to it as it loses negative electrons to Cl

Reduction

The gain of negatively-charged electrons from a reducing agent

• Term refers to the total positive charge going down

• In 2Na⁺ + Cl₂^- → 2NaCl, Cl has this done to it as it gains negative electrons from Na

Oxidizing agent

What receives the negatively-charged electrons from an oxidized atom, thus becoming reduced with more negative charges

• Term refers to the other substance’s change after losing electrons

• In 2Na⁺ + Cl₂^- → 2NaCl, Cl is this as it removes electrons from Na

  • Makes something more positive by becoming more negative

Reducing agent

What loses electrons to a reduced atom, thus becoming oxidized with fewer negative charges

• Term refers to the other substance’s change as it gains negatively-charged electrons

• In 2Na⁺ + Cl₂^- → 2NaCl, Na is this as it contributes electrons to Cl

  • Makes something more negative by becoming more positive

Oxidation number (ON)

A number stating the charge an individual atom would have, if all its shared electrons were transferred to the atom that attracts them more strongly

• Sum of multiplied charges must equal 0 or stated charge

• Written as (+2) and not (2+)

Ion charge

What is the oxidation number for each element in a binary ionic compound?

What must the sum of all multiplied oxidation numbers be in an equation?

0 or the stated charge

Oxidation rules

The oxidation number for each element in a covalent compound is determined by these

What is the oxidation number for an atom in its elemental form, like Na or C?

0

What is always the oxidation number for F?

-1

What is the oxidation number for O, when in a peroxide?

-1

What is the oxidation number for O outside of a peroxide or compounds with F?

-2

What is the oxidation number for H when bound to a nonmetal?

+1

What is the oxidation number for H when bound to a metal or B?

-1

What is the oxidation number for elements in group 17, when bound to metals, non-O nonmetals, and non-F halogens?

-1

Write out the oxidation numbers for each of the elements in a reaction, then compare.

How would I find out which elements are oxidized or reduced in a reaction?

Add enough ion indicator to a substance such that the substance changes color at the end point, signifying that the moles of electrons lost are equal to the moles of electrons gained. Then, use the chemical equation to perform extended calculations.

How would I perform a redox titration?

Combination reaction

A reaction in the form X + Y → Z

• Includes ionic compounds and covalent bond formation

Decomposition

A reaction in the form Z → X + Y

• Can be achieved through heating or electricity

Displacement

A reaction in the form:

• AB + CD → AD + BC (double)

• X + YZ → XZ + Y (single)

Metal activity series

How metals are ranked for displacement ability based on their ability to displace H₂; those that are closer to Li have generally higher abilities

Halogen activity series

How halides are ranked for displacement ability, similar to metals, except for those closer to F

Combustion

A reaction involving a substance and O₂ to produce heat