Chemistry: Chemical Reactions, Quantities, and Solutions

Comprehensive practice flashcards covering chemical reaction classifications, equation balancing, mole calculations, precipitation and solubility rules, gas evolution, redox, hard water chemistry, flame tests, and empirical formula determinations.

How is the mole defined in terms of pure carbon-12?

The mole is defined as the number of atoms in exactly $12\,\text{g}$ of pure carbon-12, which equals Avogadro's number ($6.022 \times 10^{23}\,\text{particles}$).

How does the molar mass of an element relate to its atomic mass?

The molar mass of an element in grams per mole ($\text{g/mol}$) is numerically equal to its atomic mass expressed in atomic mass units ($\text{amu}$).

What is the difference between an empirical formula and a molecular formula?

An empirical formula represents the simplest whole-number ratio of atoms of each element in a compound, whereas a molecular formula gives the actual number of atoms of each element in a molecule.

How is the integer multiplier $n$ calculated when determining a molecular formula from an empirical formula?

$$n = \frac{\text{molar mass}}{\text{empirical formula molar mass}}$$

What is the recommended daily intake limit for sodium recommended by the FDA, and what percentage of sodium chloride by mass is sodium?

The FDA recommends consuming less than $2.4\,\text{g}$ ($2400\,\text{mg}$) of sodium per day; sodium chloride ($\text{NaCl}$) is approximately $39\%$ sodium by mass ($39.34\%$).

What are the beneficial daily intake levels of fluoride for adults, and what condition can result from excess exposure?

Beneficial intake is about $1\text{ to }4\,\text{mg/day}$; excessive fluoride intake can cause dental fluorosis (mottled brown teeth) and skeletal fluorosis.

What five macroscopic observations provide evidence that a chemical reaction has occurred?

A color change, the formation of a precipitate (solid), the formation of a gas (bubbles), the emission or absorption of heat, and the emission of light.

Why is the bubbling of boiling water classified as a physical change rather than a chemical reaction?

Boiling forms gaseous steam, but both liquid water and steam consist of unchanged $\text{H}_2\text{O}$ molecules; only chemical analysis demonstrating that original substances transformed into new substances conclusively proves a chemical change.

What is the balanced equation for the combustion of octane ($\text{C}_8\text{H}_{18}$) in automobile engines?

$$2\text{C}_8\text{H}_{18}(l) + 25\text{O}_2(g) \rightarrow 16\text{CO}_2(g) + 18\text{H}_2\text{O}(g)$$

Which metal ions cause water hardness, and how does sodium carbonate ($\text{Na}_2\text{CO}_3$) soften hard water?

Hard water contains dissolved $\text{Ca}^{2+}$, $\text{Mg}^{2+}$, and $\text{Fe}^{3+}$ ions; sodium carbonate dissolves to yield carbonate ions ($\text{CO}_3^{2-}$), which precipitate these ions as insoluble calcium carbonate ($\text{CaCO}_3(s)$) and magnesium carbonate ($\text{MgCO}_3(s)$).

What is the order of precedence when balancing chemical equations containing polyatomic ions and free elements?

Balance intact polyatomic ions as single units, balance elements appearing in only one compound on each side first (metals before nonmetals), and balance free uncombined elements last by adjusting their coefficients.

What distinguishes a molecular equation, a complete ionic equation, and a net ionic equation?

A molecular equation shows complete neutral chemical formulas; a complete ionic equation dissociates all soluble strong electrolytes into their component ions; a net ionic equation omits spectator ions to display only species undergoing chemical change.

What are spectator ions, and which ions are spectator ions in the reaction between $\text{AgNO}_3(aq)$ and $\text{NaCl}(aq)$?

Spectator ions appear unchanged on both sides of a reaction; in this reaction, $\text{Na}^+(aq)$ and $\text{NO}_3^-(aq)$ are spectator ions, leaving the net ionic equation $\text{Ag}^+(aq) + \text{Cl}^-(aq) \rightarrow \text{AgCl}(s)$.

What is the net ionic equation for the neutralization reaction between a strong acid and a strong base?

$$\text{H}^+(aq) + \text{OH}^-(aq) \rightarrow \text{H}_2\text{O}(l)$$

What gas is produced when carbonates or bicarbonates react with an acid, and what intermediate decomposes to release it?

Carbon dioxide gas ($\text{CO}_2$) is produced via the decomposition of the intermediate carbonic acid ($\text{H}_2\text{CO}_3$).

What gases are evolved when acids react with sulfides or sulfites, and when ammonium salts react with strong bases?

Sulfides evolve hydrogen sulfide ($\text{H}_2\text{S}$); sulfites evolve sulfur dioxide ($\text{SO}_2$) via intermediate $\text{H}_2\text{SO}_3$; ammonium salts evolve ammonia ($\text{NH}_3$) via intermediate $\text{NH}_4\text{OH}$.

What are the electron-transfer definitions of oxidation and reduction, and what mnemonics are commonly used to remember them?

Oxidation is the loss of electrons and reduction is the gain of electrons; remembered by the mnemonics OIL RIG ("Oxidation Is Loss, Reduction Is Gain") and LEO GER ("Lose Electrons Oxidation, Gain Electrons Reduction").

How do chlorine atoms released from chlorofluorocarbons (CFCs) catalyze stratospheric ozone depletion?

UV light cleaves CFCs to produce atomic chlorine ($\text{Cl}$), which reacts with ozone ($\text{O}_3$) to form $\text{ClO}$ and $\text{O}_2$; subsequent reactions regenerate atomic chlorine, enabling a single chlorine atom to break down thousands of ozone molecules.

What are the four general classifications of chemical reactions based on atom movement?

Combination/synthesis ($\text{A} + \text{B} \rightarrow \text{AB}$), decomposition ($\text{AB} \rightarrow \text{A} + \text{B}$), single replacement/displacement ($\text{A} + \text{BC} \rightarrow \text{AC} + \text{B}$), and double replacement/displacement ($\text{AB} + \text{CD} \rightarrow \text{AD} + \text{CB}$).

What observations accompany the combustion of magnesium ribbon, and what balanced equation represents this reaction?

The magnesium ribbon ignites with an intense bright white flare and produces a dull white solid residue; represented by $2\text{Mg}(s) + \text{O}_2(g) \rightarrow 2\text{MgO}(s)$.

What observations confirm a single replacement reaction between zinc metal and copper(II) sulfate solution?

The blue color of the $\text{CuSO}_4$ solution fades and a reddish-brown solid of copper metal forms on the surface of the gray zinc strip ($\text{Zn}(s) + \text{CuSO}_4(aq) \rightarrow \text{ZnSO}_4(aq) + \text{Cu}(s)$).

What causes elements to emit characteristic flame colors during a flame test?

Thermal energy from the flame excites electrons to higher atomic energy levels; when these electrons transition back down to lower energy levels, they emit electromagnetic radiation of specific wavelengths and characteristic colors.

What is the structural difference between a hydrate and an anhydrate?

A hydrate contains water molecules chemically bound in its crystal matrix in a fixed stoichiometric ratio (e.g., $\text{CoCl}_2 \cdot 6\text{H}_2\text{O}$); an anhydrate is the dry compound remaining after all water is removed by heating.

Why is aluminum sulfate ($\text{Al}_2(\text{SO}_4)_3$) used as a flocculating agent in water purification?

It neutralizes charges and causes finely divided suspended clay and mud particles to aggregate into larger flocs that settle rapidly by sedimentation to the bottom of the settling tank.

According to solubility rules, which common cations form insoluble precipitates with sulfate ($\text{SO}_4^{2-}$) and chloride ($\text{Cl}^-$) anions?

Sulfate forms insoluble salts with $\text{Ba}^{2+}$, $\text{Pb}^{2+}$, $\text{Ca}^{2+}$, and $\text{Sr}^{2+}$; chloride forms insoluble salts with $\text{Ag}^+$, $\text{Pb}^{2+}$, and $\text{Hg}_2^{2+}$.

What are the balancing coefficients for the precipitation reaction between potassium phosphate and calcium nitrate: $\underline{\quad}\text{K}_3\text{PO}_4 + \underline{\quad}\text{Ca}(\text{NO}_3)_2 \rightarrow \underline{\quad}\text{Ca}_3(\text{PO}_4)_2 + \underline{\quad}\text{KNO}_3$?

$2, 3, 1, 6$, yielding $2\text{K}_3\text{PO}_4(aq) + 3\text{Ca}(\text{NO}_3)_2(aq) \rightarrow \text{Ca}_3(\text{PO}_4)_2(s) + 6\text{KNO}_3(aq)$.

What is the molar mass of magnesium phosphate, $\text{Mg}_3(\text{PO}_4)_2$?

$262.9\,\text{g/mol}$ (calculated as $3(24.31) + 2(30.97) + 8(16.00) = 262.87\,\text{g/mol}$).

How does temperature affect the solubility of potassium nitrate ($\text{KNO}_3$) in water, and what defines a saturated solution?

Solubility of $\text{KNO}_3$ increases as temperature rises; a solution is saturated when it contains the maximum dissolved solute possible at a given temperature in dynamic equilibrium with undissolved solid.