Chemistry Waiver Exam-Official Study Guide Info

These were taken straight from the ACS study guide

Which equation is used to determine the number of moles of product given a specific number of moles of a reactant?

Moles of product = moles of product x (coefficient of product/coefficient of reactant)

What is a limiting reactant?

The limiting reactant is the substance that is completely consumed in a reaction, stopping the reaction from continuing and determining the maximum amount of product that can be produced (bread analogy) 

Which equation is used to determine the mass of a starting material needed to produce a given amount (in moles) of a product?

Mass of reactant = mass of product x (coefficient of reactant/coefficient of product) x molar mass of product

How to find the theoretical yield given moles?

Use the equation that finds the moles of product for both molecules. Whichever molecule has the lowest product will be the theoretical yield.

What does theoretical yield mean?

The amount of product predicted by stoichiometry from the limiting reactant?

Which equation is used to determine the mass of a product formed (theoretical yield) given the mass of each of the reactants/

Theoretical yield (g) = (mass of reactant/molar mass of reactant) x (coefficient of product/coefficient of reactant) x molar mass of product

What is the relationship between number of molecules and moles?

Number of molecules = moles x 6.022×10²³

Moles = number of molecules/6.022×10²³

How to determine the limiting reagent using the number of molecules? (3 steps)

1) convert molecules to moles

moles = number of molecules/6.022×10²³

2) Use the mole ratio for the balanced equation

3) The reactant with less product is the limiting reagent

How to determine the limiting reagent from a graphic?

Divide the number of each reactant shown by its coefficient in the balanced equation

What is an isotope?

a form of chemical element that has the same number of protons but a different number of neutrons

What is an ion?

An atom that has a charge because it gained or lost electrons

If an atom gains electrons what is the charge and what is it called?

Negative charge, anion

If an atom gains electrons what is the charge and what is it called?

Positive charge, cation

What does mass number represent?

number of protons and neutrons

What does atomic number represent?

number of protons

What is relative abundance?

The percentage of each isotope of an element found in nature. Will always add up to 100% and is used to calculate average atomic mass.

How to calculate a weighted average? 

Average mass= (Mass1*Isotope1%)/100% and so on with the rest of the isotopes

Where to find the average atomic mass?

Bottom number on the periodic table

What are the seven diatomic molecular elements?

H₂,N₂,O₂,F₂,Cl₂,Br₂, and I₂

Charge of ions in group 1?

+1

Charge of ions in group 2?

+2

Charge of ions in group 17?

-1

Charge of ions in group 16?

-2

Charge of ions in group 15?

-3

Charge of ions in transition metals?

Variable charges so use roman numerals. Ex: Fe²⁺ = iron (II)

Which term best describes the relation of hydrogen (¹H) to deuterium (²H)?

A) allotropes

B) isomers

C) isotopes

D) polymers

A) allotropes

B) isomers

C) isotopes

D) polymers

In all neutral atoms, there are equal numbers of? 

electrons and protons

Which statement is true?

A) The nucleus of an atom contains neutrons and electrons

B) The atomic number of an element is the number of protons in an atom

C) The mass number of an atom is the number of protons in the nucleus plus the number of electrons outside

D) The number of electrons outside the nucleus is the same as the number of neutrons in the nucleus

B) The atomic number of an element is the number of protons in an atom

Lithium has two naturally occurring isotopes, 6Li and 7Li, with masses of 6.015 amu and 7.016 amu,

respectively. What is the relative abundance of each isotope?

(A) 6Li = 7.49% and 7Li = 92.51%

(B) 6Li = 25.31 %and 7Li = 74.69 %

(C) 6Li = 46.16% and 7Li = 53.84%

(D) 6Li = 92.51 % and 7Li = 7.49 %

(A) 6Li = 7.49% and 7Li = 92.51%

Which group contains nonmetals, metalloids, and metals?

(A) 1 (B) 13 (C) 15 (D) 18

C) 15

What is a main group element?

(A) Pu (B) Mg (C) Sc (D) Fe

B) Mg

The halogens are found in group

(A) 1 (B) 15 (C) 17 (D) 18

 (C) 17

Which statement below is correct?

A) Chlorine is a transition metal

B) Oxygen is a metal

C) Sodium is a metalloid

D) Phosphorus is a nonmetal

D

Which of the following is an example of an open system and why?

I) an insulated coffee cup with a lid

II) a plastic soda bottle with a lid

III) a glass of water without a lid

Because

IV) energy, but not matter, can transfer between the system and surroundings

V) both energy and matter can transfer between the system and surroundings

VI) neither energy nor matter can transfer between system and surroundings

III and V

Which of the following is true when an intramolecular force is formed between two molecules?

A) ΔH_sys is negative and heat is absorbed into the system.

B) ΔH_sys is negative and heat is released into the surroundings.

C) ΔH_sys is positive and heat is absorbed into the system.

D) ΔH_sys is positive and heat is released into the surroundings.

B

Consider the following reaction:

C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g)

What happens to the entropy of the system during this reaction and why?

A) Entropy decreases because there are more ways to arrange the reactants.

B) Entropy decreases because there are more ways to arrange the products.

C) Entropy increases because there are more ways to arrange the reactants.

D) Entropy increases because there are more ways to arrange the products.

D

Consider a process that is thermodynamically favorable in which the entropy of the system increases.

Which of the following statements is true?

A) ΔG is positive but we cannot tell if the entropy of the surroundings increases or decreases.

B) ΔG is positive and the entropy of the surroundings increases.

C) ΔG is positive and the entropy of the surroundings decreases.

D) ΔG is negative but we cannot tell if the entropy of the surroundings increases or decreases.

E) ΔG is negative and the entropy of the surroundings increases.

F) ΔG is negative and the entropy of the surroundings decreases.

D

Consider the following reaction:

CaCO3(s) → CO2(g) + CaO(s)

For this reaction at 298 K, ΔH° is 178 kJ/mol and ΔS° is 161 J/K•mol). Is this reaction thermodynamically favorable at this temperature? Why or why not?

A) No, because this reaction is endothermic.

B) Yes, because this reaction is exothermic.

C) No, because the entropy of the system decreases during this reaction.

D) Yes, because the entropy of the system increases during this reaction.

E) No, because the Gibbs Free Energy change is positive.

F) Yes, because the Gibbs Free Energy change is negative.

E

You have a 0.50 M aqueous solution of NaCI. You take 100 mL of the 0.50 M NaCI solution and add enough water to make 1.0 L of a new solution. How would you describe the new solution?

A) The new solution is more dilute than the 0.50 M solution.

B) The new solution is more concentrated than the 0.50 M solution.

C) The new solution has the same concentration as the 0.50 M solution.

D) There is not enough information provided to compare the new solution to the 0.50 M solution.

A

A 2.5 M solution is made by dissolving KOH in enough water to make 100 mL of solution. How many grams of KOH are in this solution?

A) 1400 g

B) 0.250 g

C) 4.46 g

D) 44.6 g

E) 14.0 g

F) 2.24 g

E

What is bond dissociation energy?

BDE= broken-formed

Arrhenius acid

Produces H⁺ ions in aqueous solution.

Arrhenius base

Produces OH⁻ ions in aqueous solution.

Bronsted–Lowry acid

Proton donor (gives H⁺).

Bronsted–Lowry base

Proton acceptor (takes H⁺).

Lewis acid

Electron-pair acceptor.

Lewis base

Electron-pair donor.

Kw definition

Ion-product constant for water: Kw = [H₃O⁺][OH⁻].

Numerical value of Kw at 25°C

1.0 × 10⁻¹⁴.

Why Kw changes with temperature

Water ionization is endothermic; Kw increases as t

Formula for pH

pH = –log[H₃O⁺].

Formula for pOH

pOH = –log[OH⁻].

Relationship between pH and pOH

pH + pOH = 14 (only at 25°C).

Neutral solution definition

[H₃O⁺] = [OH⁻], not necessarily pH = 7 unless 25°C.

The 7 strong acids

HCl, HBr, HI, HNO₃, HClO₄, HClO₃, H₂SO₄ (first proton).

Strong base list

Group 1 hydroxides + Ca(OH)₂, Sr(OH)₂, Ba(OH)₂.

Why strong acids have weak conjugate bases

Their conjugate bases are extremely stable and do not accept protons.

Acid dissociation equilibrium

HA + H₂O ⇌ H₃O⁺ + A⁻.

Ka expression

Ka = [H₃O⁺][A⁻] / [HA].

Relationship between Ka and acid strength

Larger Ka → stronger acid → more dissociation.

Base dissociation equilibrium

B + H₂O ⇌ BH⁺ + OH⁻.

Kb expression

Kb = [BH⁺][OH⁻] / [B].

Ka–Kb relationship

Ka × Kb = Kw.

Conjugate acid strength rule

Stronger acid → weaker conjugate base.

Conjugate base strength rule

Stronger base → weaker conjugate acid.

Conjugate bases of strong acids in water (Cl⁻, Br⁻, NO₃⁻)

Neutral in water — NO BASICITY.

Conjugate bases of weak acids in water (F⁻, CN⁻)

basic in water