Principles of Chemistry: Particulate Theory, Atomic Structure, and Mixtures

Comprehensive practice flashcards covering particulate theory, states of matter, atomic structure, solubility curves, types of mixtures, separation techniques, and industrial sucrose extraction.

According to the particulate theory of matter, what is matter composed of?

Matter is made of tiny particles that are constantly moving, have spaces between them, and attract one another.

What three scientific phenomena provide direct evidence supporting the particulate theory of matter?

Diffusion, osmosis, and Brownian motion.

What is the scientific definition of diffusion?

Diffusion is the spontaneous movement of particles of a substance from a region of higher concentration to a region of lower concentration, until the particles are evenly distributed.

What is observed when a potassium permanganate ($\text{KMnO}_4$) crystal is placed in water, and what does this demonstrate?

The purple color slowly spreads throughout the water until the solution is uniformly purple. This demonstrates that liquid particles move and have spaces between them, supporting the particulate theory of matter.

In the demonstration shown below, why does the ring of white ammonium chloride ($\text{NH}_4\text{Cl}_{(s)}$) form closer to the concentrated hydrochloric acid ($\text{HCl}$) end of the tube?

Ammonia ($\text{NH}_3$) particles diffuse more quickly along the tube than hydrogen chloride ($\text{HCl}$) particles because ammonia particles are lighter, allowing them to travel farther before colliding and reacting to form the white ring at point C.

What is osmosis?

Osmosis is the movement of water molecules from a region of higher water concentration to a region of lower water concentration through a partially permeable membrane.

How do potato or yam cells respond when placed in distilled water versus a concentrated salt or sugar solution?

In distilled water, water enters the cells by osmosis, causing them to become turgid (firm). In a concentrated salt or sugar solution, water leaves the cells by osmosis, causing them to become flaccid (soft).

What is Brownian motion, and what causes it?

Brownian motion is the random, jerky movement of visible particles suspended in a fluid (gas or liquid). It is caused by collisions with invisible, fast-moving particles of the surrounding fluid.

How do salt and sugar function as preservatives against food-spoiling microorganisms?

They draw water out of microorganisms by osmosis, reducing the internal water available for their survival and growth.

How do solids, liquids, and gases differ in terms of particle arrangement, movement, and kinetic energy?

Solids have particles closely packed in a regular arrangement that vibrate about fixed positions and have the lowest kinetic energy. Liquids have particles packed close together in a less regular arrangement that slide past each other with medium kinetic energy. Gases have particles far apart in a random arrangement that move rapidly in all directions with the highest kinetic energy.

What is the difference between sublimation and deposition?

Sublimation is the direct change of state from a solid to a gas without passing through the liquid phase (e.g., dry ice, iodine). Deposition is the reverse process, where a gas changes directly into a solid.

What physical processes are occurring during the horizontal segments $B \text{ to } C$ and $D \text{ to } E$ in the heating curve shown below?

Segment $B \text{ to } C$ represents melting, where solid changes to liquid at a constant melting point. Segment $D \text{ to } E$ represents boiling/vaporizing, where liquid changes to gas at a constant boiling point.

What state changes are taking place along the flat horizontal portions $B \text{ to } C$ and $D \text{ to } E$ of the cooling curve shown below?

Segment $B \text{ to } C$ represents condensation (gas changing to liquid), and segment $D \text{ to } E$ represents freezing (liquid changing to solid).

Why do drops of water develop on the outside of cold beverage bottles left to stand in a warm room?

Water vapor present in the surrounding air cools down upon contacting the cold bottle surface, loses kinetic energy, and condenses into liquid water droplets.

What are the location, relative charge, and relative mass of the three subatomic particles in an atom?

Protons are located in the nucleus with a relative charge of $+1$ and a relative mass of $1$. Neutrons are located in the nucleus with no charge ($0$) and a relative mass of $1$. Electrons are located in shells around the nucleus with a relative charge of $-1$ and a negligible relative mass of $0$.

Why is an isolated atom electrically neutral?

Because the number of positively charged protons in the nucleus is always equal to the number of negatively charged electrons in the shells.

Define atomic number ($Z$) and mass number ($A$).

The atomic number ($Z$) is the number of protons in the nucleus of an atom. The mass number ($A$) is the total number of protons and neutrons in the nucleus of an atom.

How many protons, neutrons, and electrons are present in a potassium atom represented as $^{39}_{19}\text{K}$?

It contains $19$ protons, $19$ electrons, and $20$ neutrons ($39 - 19 = 20$).

What are isotopes?

Isotopes are atoms of the same element that have the same number of protons (same atomic number) but different numbers of neutrons (different mass numbers).

How is the Relative Atomic Mass (R.A.M.) of chlorine calculated given its isotopes $^{35}_{17}\text{Cl}$ ($75\%$) and $^{37}_{17}\text{Cl}$ ($25\%$)?

Using the weighted mean of naturally occurring isotopes: $\text{R.A.M.} = (0.75 \times 35) + (0.25 \times 37) = 26.25 + 9.25 = 35.5$.

Define the solubility of a solute in a solvent.

Solubility is defined as the mass of a solute that dissolves in $100\,g$ of a solvent at a particular temperature to form a saturated solution.

What differentiates unsaturated, saturated, and supersaturated solutions?

An unsaturated solution contains less than the maximum amount of solute that can dissolve at that temperature. A saturated solution contains the maximum amount of solute that can dissolve at that temperature. A supersaturated solution contains more than the maximum amount of dissolved solute reached at an elevated temperature.

According to the solubility curve shown below, what is the solubility of sodium bicarbonate at $20\,^\circ\text{C}$ and at $50\,^\circ\text{C}$?

At $20\,^\circ\text{C}$, the solubility is about $9.6\,g$ per $100\,g$ of water. At $50\,^\circ\text{C}$, the solubility is about $14.3\,g$ per $100\,g$ of water.

If a saturated solution of sodium bicarbonate in $100\,g$ of water is cooled from $50\,^\circ\text{C}$ ($14.3\,g$ dissolved) to $20\,^\circ\text{C}$ ($9.6\,g$ dissolved), what mass of solute crystallizes out?

$14.3\,g - 9.6\,g = 4.7\,g$ of sodium bicarbonate will crystallize out of solution.

Why is potassium nitrate ($\text{KNO}_3$) soluble in water but insoluble in pentane?

Potassium nitrate is an ionic compound and water is a polar solvent, so the strong ionic forces are overcome by polar water molecules ('like dissolves like'). Pentane is a non-polar solvent and cannot overcome the ionic bonds in $\text{KNO}_3$.

How do pure substances differ from mixtures in composition and separation methods?

A pure substance contains only one type of particle, has a fixed composition, definite properties, and cannot be separated by physical methods. A mixture contains two or more physically combined substances, has variable composition, retains constituent properties, and can be separated by physical methods.

How do solutions, colloids, and suspensions compare regarding particle size and settling?

Solutions have very small particles ($< 1\,nm$) that never settle. Colloids have medium-sized particles ($1\,nm \text{ to } 1000\,nm$) that generally do not settle. Suspensions have large particles ($> 1000\,nm$) that settle upon standing.

What is the Tyndall effect and what is it used for?

The Tyndall effect is the scattering of a beam of light in many directions by dispersed particles in a colloid, whereas a true solution does not scatter light. It is used to distinguish a true solution from a colloid.

What is the distinction between an aqueous solution and a non-aqueous solution?

An aqueous solution uses water as the solvent (indicated by $\text{(aq)}$, such as salt water), whereas a non-aqueous solution uses a solvent other than water (such as iodine dissolved in alcohol).

What are the eight sequential steps in the industrial extraction of sucrose from sugar cane shown in the diagram below?

1. Harvesting and washing, 2. Crushing, 3. Clarification, 4. Evaporation, 5. Crystallization, 6. Centrifugation, 7. Drying, and 8. Refining (for white sugar).

During the extraction of sucrose from sugar cane, what is the fibrous residue remaining after crushing called, and what is extracted?

The fibrous residue is called bagasse, and the extracted liquid is juice containing dissolved sucrose.

Why is lime ($\text{CaO}$ or $\text{Ca(OH)}_2$) added to sugar cane juice during the clarification stage?

Lime is added to neutralize organic acids and to precipitate impurities, which are subsequently removed by filtration or settling.

How are solid sucrose crystals separated from molasses following crystallization?

They are separated using a centrifuge (centrifugation), which forces the liquid molasses away from the solid sugar crystals.

In the filtration apparatus shown below, identify the roles of the 'residue' and the 'filtrate'.

The residue is the insoluble solid (sand) that remains trapped on the filter paper, while the filtrate is the liquid (water) that passes through the filter paper into the conical flask.

Why can filtration NOT be used to separate dissolved table salt from water?

Dissolved salt particles are extremely small (at the molecular/ionic scale) and pass freely through the pores of ordinary filter paper along with the water molecules.

What is the physical principle underlying simple distillation, and when is it applied?

It separates components based on significant differences in boiling points ($> 25\,^\circ\text{C}$), such as recovering pure water from a salt water solution.

When is fractional distillation preferred over simple distillation?

When separating two or more miscible liquids that have closer boiling points (difference $< 25\,^\circ\text{C}$), such as ethanol and water, or separating crude oil into fractions.

How does a separating funnel separate an immiscible mixture of oil and water?

Oil and water do not mix and form two distinct layers based on density. The denser liquid (water) forms the bottom layer and is drained off first by opening the tap, leaving the less dense liquid (oil) in the funnel.

Using the diagram below, write the formula for the Retention Factor ($R_f$) and calculate the $R_f$ value for the red dye.

$R_f = \frac{\text{distance moved by substance}}{\text{distance moved by solvent front}}$. For the red dye: $R_f = \frac{7\,cm}{10\,cm} = 0.7$.

How can a solid mixture of ammonium chloride and sand be separated?

By sublimation; when heated, ammonium chloride changes directly from a solid into a gas, leaving the non-subliming sand behind, and the ammonium chloride vapor condenses back to a solid upon cooling.