unit 4 - chemistry

physical change

If only IMFs/attractions are broken/formed, than is it likely a physical or chemical change?

chemical change

If only chemical bonds are broken/formed, than is it likely a physical or chemical change?

Na⁺, K⁺, NH₄⁺, and NO₃⁻

What salts are always soluble in water?

Strong acids/bases

Are strong or weak acids/bases going to be soluble in water?

Covalent compounds, weak base/acids, liquids, solids, insoluble ionics

What compounds do you NOT split up to write a net ionic eqn?

The positive charges of the cations and the negative charges of the anions MUST be equal.

What do you have to make sure your particulate diagram contains in regards to charges?

e.g. NaCl is in excess. Limiting is AgNO₃

If Cl- is the participating ion, then that ion would be shown in the diagram. Limiting reactant has the Ag+ participating, and so there'd be no Ag+ ions in the diagram.

** Spectator ions would also be shown, with the precipitate at the bottom.

If a question mentions that a compound is in excess, what does that mean for your particulate diagram?

H⁺ + OH⁻ → H₂O

What's always the net ionic eqn for a strong acid and a strong base?

Don't separate the weak base and removing the spectator ions

e.g. HCl + NH₃ → NH₄Cl

NIE: H⁺ + NH₃ → NH₄⁺

What does a net ionic eqn look like with a strong acid and a weak base?

Don't separate the weak acid and remove spectator ions.

e.g. HF + NaOH → NaF + H₂O

HF + OH⁻ → F⁻ + H₂O

What does the net ionic eqn look like with a weak acid and a strong base?

Don't separate the acid or the base. Just donate the H+.

e.g. HF + NH₃ → F⁻ + NH₄⁺

What does the net ionic eqn look like with a weak acid and a weak base?

There should be a mixture of reactants and products still.

In a particulate diagram, if the reaction is reversible, would all the particles become products or not?

The NIE shows how a solid is formed, and the spectator ions are removed because they do not change in this reaction.

Why would a reaction be best represented by a net-ionic equation?

To make sure that all water has been removed so that the mass stays constant

What's the purpose of drying and weighing the filter paper with the precipitate multiple times?

it would not change the mass percent because the additional water is removed by filtration and drying --> the mass of the dry precip. should be the same

In an filtration experiment, if a larger amount of water was used to make a solution, would it change the mass percent of a particular ion?

It's the reactant that limits your reaction by producing less product than your other reactant. (to solve: using stoichiometry find out how much product each reactant makes; smaller amt of product made is the limiting reactant.)

What is a limiting reactant?

the maximum amount produced by the limiting reactant.

What is theoretical yield?

MaVa = MbVb

If there is a 1-to-1 mole ratio between the acid and the base, you can also which equation?

donates a proton (an H⁺)

What is a Bronsted-Lowry acid?

accepts a proton (an H⁺)

What's a bronsted-lowry base?

an ionic salt and water

What are often the products of a Bronsted-Lowry Acid-base rxn?

The charge on the ion

e.g. Al³⁺ --> Oxid # is +3

For a monoatomic ion, what's the oxid #?

it it always -1 in ANY compound

What is always the oxidation # of F?

it would be positive

e.g. NaBrO₃

Na = +1

Br = +5

O = -2

When (Cl, Br, or I) is bonded to O or F, is the Oxid# +/-?

+1

e.g. NaH

Na = +1

H = -1

When H is bonded to a metal, what is its oxid #?

-1

e.g. H₂O₂

H = +1

O = -1

In peroxide, what is the Oxid # of O?

Make sure the amount of e- being gained/lost are the SAME. Multiply by a coefficient if needed, then add 2 eqns 2tog.

e.g. (Mg → Mg²⁺ + 2 e⁻) X 2

4 e⁻ + O₂ → 2 O²⁻

= 2 Mg + O₂ → 2MgO

How do you combine an Oxid half-reaction and a reduction half-reaction together?

actual yield from lab/theoretical yield X 100 =

How do you find percent yield to measure efficiency?

Divide # of moles of reactant with it's coefficient. LR will be the one w/ less moles rxn.

e.g. 2 C₂H₆ + 7 O₂

.449 mol C₂H₆ --> .449/2 = .225 mol rxn

1.41 mol O₂ --> 1.41/7 = .201 mol rxn

O is the LR

Shortcut for finding limiting reactant?

when the exact amt of base has been added to neutralize the acid (indicator.) --> 1 mol base =1 mol acid

what is the equivalence point?

pH = 7

What's always the EQ point of a strong acid and strong base?

the charge of the polyatomic atom

e.g. NH₄⁺… O#'s should = +1

If assigning Oxid#'s for a polyatomic atom, the sum of the #'s should equal…

Strong acid --> weak conj base

Strong base --> weak conj acid

(same for the opposite)

If an acid or base is strong, what does that mean for its conjugate?

Base & Conj. Acid

Acid & Conj. Base

e.g. NH₃ & NH₄⁺

H₂O & OH⁻

What is a conjugate pair?

Smaller K value --> weaker acid/base, stronger conj

How does Ka or Kb describe a base/acid?