Chemistry: The Atmosphere, The Ocean, and Matter

Comprehensive practice flashcards covering classification of matter, atmospheric components and liquefaction, sea water composition, separation techniques, flame tests, chloride tests, and electrolysis.

What are the three main regions of the Earth's surface from which natural resources are obtained?

The crust, the ocean, and the atmosphere.

How is matter defined in physical science?

Matter is anything which has a mass and occupies space.

What is the scientific definition of an element?

An element is a substance which cannot be broken down into anything simpler by chemical methods.

Approximately how many elements are known, and what proportion of them occur naturally on Earth?

There are about $112$ known elements, and over $80\%$ of them can be found naturally on Earth.

What is the scientific definition of a compound?

A compound is a substance made up of two or more elements chemically joined together.

How can water and molten common salt be decomposed into their constituent elements?

By passing electricity through them, breaking water into hydrogen and oxygen, and molten salt into sodium and chlorine.

How does composition by mass differ between a mixture and a compound?

Components in a mixture can exist in any proportion, whereas the constituent elements in a compound must exist in a fixed ratio.

How do the melting and boiling points of a mixture compare with those of a compound?

A mixture does not have a fixed melting or boiling point, whereas a compound has a sharp melting and boiling point.

In which layer of the atmosphere do humans live, and what is its position relative to Earth?

The troposphere, which is the layer closest to the Earth.

What is the approximate composition of clean air by percentage volume?

Nitrogen ($78\%$), oxygen ($21\%$), and small amounts of carbon dioxide, water vapour, and noble gases (about $1\%$).

Which five noble gases are present in the Earth's atmosphere?

Argon, helium, neon, krypton, and xenon.

What is the difference between physical properties and chemical properties?

Physical properties can be measured without changing the chemical composition of a substance (e.g., colour, melting point), while chemical properties describe its ability to form new substances (e.g., burning in air).

What is the fundamental difference between a physical change and a chemical change?

During a physical change, no new substance is formed; during a chemical change, new substance(s) are produced.

What term describes the phase change where a solid turns directly into a gas?

Sublimation.

Which separation method is used to separate two miscible liquids?

Fractional distillation.

Which apparatus is used to separate a mixture of two immiscible liquids such as oil and water?

A separating funnel.

What are the three stages of separating nitrogen and oxygen from air?

Stage A: Purification (removal of dust, water vapour, and carbon dioxide); Stage B: Liquefaction of air; Stage C: Fractional distillation of air.

During the liquefaction of air, to what temperature does the air fall after repeated compression and expansion cycles?

$-200\,^\circ\text{C}$.

What are the boiling points of nitrogen and oxygen during fractional distillation of liquid air, and where are they collected in the column?

Nitrogen boils at $-196\,^\circ\text{C}$ and exits at the top of the column; oxygen boils at $-183\,^\circ\text{C}$ and is collected at the lower part.

What percentage of the Earth's surface is covered by sea water, and what percentage of dissolved salts does it typically contain?

Sea water covers over $70\%$ of the Earth's surface and contains about $3.5\%$ of dissolved solids.

What is the most abundant dissolved salt in sea water, and what is its percentage by mass of total salts?

Sodium chloride (common salt), making up $68\%$ by mass of dissolved salts.

What are the percentages by mass of magnesium chloride, sodium sulphate, and calcium chloride in a typical sample of sea water salts?

Magnesium chloride: $14.6\%$; Sodium sulphate: $11.4\%$; Calcium chloride: $3.1\%$.

What is the definition of a saturated solution?

A solution that contains the maximum amount of solute dissolved in a given volume of solution at a given temperature.

What is decantation, and when is it typically used?

Decantation is a quick physical method used to separate a much heavier insoluble solid from a liquid, such as coarse sand from sea water.

In filtration, what are the names given to the solid left on the filter paper and the liquid that passes through?

The solid left on the filter paper is called the residue, and the liquid that passes through is called the filtrate.

Why is common salt obtained by complete evaporation of sea water not pure sodium chloride?

Because soluble impurities present in the sea water will also turn into solids once all the solvent is evaporated.

How is crystallization carried out by cooling a solution?

A dilute solution is heated until concentrated or saturated, then cooled down so crystals precipitate because solute solubility decreases at lower temperatures.

How is crystallization carried out by slow evaporation at room temperature?

A dilute solution is kept in a beaker covered with perforated filter paper; as the solvent evaporates slowly, the concentration rises to saturation, forming solid crystals.

Why are solid crystals obtained by crystallization purer than solids obtained by evaporation?

Crystallization leaves soluble impurities dissolved in the remaining solvent, whereas evaporation dries everything, leaving all impurities behind.

What is distillation, and what formula expresses the relationship between its constituent processes?

Distillation is the process of evaporating a liquid and subsequently condensing the vapour ($\text{distillation} = \text{evaporation} + \text{condensation}$).

What is the purpose of adding anti-bumping granules to a distillation flask?

They ensure even boiling and avoid the bumping of liquid molecules.

In a distillation condenser, where must the cooling water enter and leave?

Cooling water enters at the bottom inlet and leaves through the top outlet.

Why is a nichrome wire dipped in concentrated hydrochloric acid before performing a flame test?

To clean the wire of impurities; nichrome is used because it does not react and has a high melting point.

What flame colour does a sodium compound produce in a flame test?

Golden-yellow.

What characteristic flame colours are produced by compounds of potassium, calcium, and copper?

Potassium produces lilac, calcium produces brick-red, and copper produces bluish-green.

What procedure is carried out to test for the presence of chloride ions in a solution?

Add excess dilute nitric acid followed by silver nitrate solution.

What positive observation indicates the presence of chloride ions in the silver nitrate test?

A white precipitate appears.

What chemical test confirms the presence of water using cobalt(II) chloride paper?

Water turns blue cobalt(II) chloride paper pink.

What are the definitions of electrolysis and electrolytes?

Electrolysis is a chemical change caused by passing electricity through a substance; electrolytes are substances that can be decomposed by passing electricity through them.

What three products are formed during the electrolysis of sea water?

Chlorine gas, hydrogen gas, and sodium hydroxide solution.