Topic 1: Fundamentals of Chemistry and Planet Earth Flashcards

Question

What are the state symbols of solid, liquid, gas and when a substance is dissolved in water (aqueous solution)?

Answer 1

Solid (s); Liquid (l); Gas (g); Aqueous solution (aq)

Answer 2

**Physical change** is a change in which no new substance is formed. **Chemical change** is a change in which new substance(s) is (are) formed (a chemical reaction is involved). Evidences for a chemical change can be: * Change in odour * Change in colour * Change in temperature of the reaction mixture * Formation of gases, which often appears as bubbles in aqeuous solution * Formation of insoluble substances

Answer 3

**Chemical properties** of a substance are the properties of the substance in chemical reactions, e.g. chemical reactivites towards the reaction with water and oxygen. **Physical properties** of a substance are the properties which can be measured/observed without chemically changing the substance into something else. Examples of physical properties: 1. **Appearance**: It includes how a substance looks like and its physical state. 2. **Colour** 3. **Odour** 4. **Solubility**: It describes whether and to what extent a substance is soluble in a particular solvent (e.g. water). 5. **Density**: It is the mass of a substance per unit volume. 6. **Melting point**: It is the temperature at which the substance changes state from solid to liquid (melting point = freezing point, which is the temperature at which the substance changes state from liquid to solid. 7. **Boiling point**: It is the temperature at which the substance changes state from liquid to gas (boiling point = condensation point, which is the temperature at which the substance changes state from gas to liquid. 8. **Viscosity**: It is the ease of a substance to flow. 9. **Electrical conductivity**: It is the ability of a substance to conduct electric current. 10. **Thermal conductivity**: It is the ability of a substance to conduct heat.

Answer 4

1. Place a Bunsen burner on an insulating mat. 2. Turn the collar to close the air hole. 3. Light a match and bring it over the burner. Then turn on the gas tap. 4. Open the air hole. 5. Adjust the height of the Bunsen flame by turning the gas tap.

Answer 5

If the burner is lighted without closing the air hole, striking back will occur and it is dangerous. The **flame burns inside the chimney** with a **hissing sound**. The collar becomes **very hot**. When it occurs, turn off the gas tap immediately and report to the teacher.

Answer 6

(left: When air hole is closed; right: When air hole is opened) 1. Colour of the flame: yellow; blue 2. Brightness of the flame: luminous; non-luminous 3. Shape of the flame: irregular; regular 4. Temperature of the flame: lower; higher 5. Sound of the flame: quiet; noisy Note: A yellow flame contains unburnt carbon particles which will blacken glasswares.

Answer 7

**Explosive** (e.g. hydrogen): / **Flammable** (e.g. hydrogen, town gas, LPG, reactive metals): Fire extinguisher standby; No flame nearby **Oxidizing**: Wear safety goggles and protective gloves **Toxic**: Wear safety goggles and protective gloves; Carry out the experiment in a fume cupboard **Corrosive**: Wear safety goggles and protective gloves **Carcinogenic**: Wear safety goggles and protective gloves; Carry out the experiment in a fume cupboard **Harmful**: Wear safety goggles and protective gloves; Carry out the experiment in a fume cupboard **Irritant** (including dilute acids and alkalis): Wear safety goggles and protective gloves; Carry out the experiment in a fume cupboard

Answer 8

Air is a **mixture of gases**, which make up the atmosphere. Composition of air: 78% Nitrogen (N₂), 21% Oxygen (O₂), 0.93% Argon (Ar), 0.03% Carbon dioxide (CO₂), 0.04% Other noble gases (e.g. helium and neon) *Approximate percentage by volume

Answer 9

1. N₂ gas (together with H₂ gas) is used to make **ammonia** (NH₃), which is then used to make **fertilizers** (e.g. ammonium sulphate and ammonium nitrate). 2. N₂ gas is used to provide a **chemically inert** (unreactive) environment, e.g. food is packaged in gaseous nitrogen to **increase its shelf life** (potato chip packages are filled with N₂ gas to **prevent oxidation** of the chips). 3. Liquid N₂ is used to provide a low temperature (-196°C) to **store biological sample** (e.g. cells) and **freeze food**.

Answer 10

1. O₂ gas is essential for respiration (i.e. making **oxygen tanks** for medical purpose, divers and firemen). 2. O₂ gas **supports combustions** of fuels (e.g. hydrogen gas, coal, petrol, town gas).

Answer 11

1. CO₂ is the **raw material** for photosynthesis. 2. **Dry ice (solid CO₂)** is used to provide a low temperature (-78°C) for different purposes (e.g. **storing ice-creams**). 3. CO₂ can be used to make **fire extinguisher** because it **does not support combustion** and is **denser than air**. 4. CO₂ can be used in **soft drinks** (a large amount of CO₂ dissolves in water at high pressure).

Answer 12

**Helium (He) gas** is used to fill **balloons and airships** as it is chemically inert / unreactive and lighter than air. * Exceptions: Hydrogen gas (H₂) cannot be used because it is flammable and explosive; Ne(g) and Ar(g) are not used. Although Ne(g) has a density lower than air, its density is not low enough for flying high. Ar(g) has a higher density than air. **Neon (Ne)** is used to make neon light / advertising signs as it emits red light at a high temperature (when electricity passes through). * Notes: He(g) and Ar(g) can be used. Different noble gases give out lights of different colours. **Argon (Ar)** is used to fill up the space in a light bulb to prevent air oxidation of the tungsten metal.. * Exceptions: He(g) and Ne(g) cannot be used. Light bulb is cheap. He(g) and Ne(g) are more expensive that Ar.

Answer 13

Oxygen and nitrogen are useful **industrial materials**. The main source of oxygen and nitrogen is **air** (O₂ = 21% and N₂ = 78% by volume). Oxygen and nitrogen (together with argon) are separated from air by **fractional distillation**.

Answer 14

Fractional distillation is a method used to separate **a mixture of miscible liquids** which have **different boiling points (b.p.)**. Note: Air must be **liquefied / converted to liquid** first before carrying out fractional distillation.

Answer 15

1. The air is **purified** to remove dust, CO₂, water vapour and etc. (dust is filtered, CO₂ and water vapour are removed as solids at suitable temperature and pressure). 2. The purified air is **cooled to -200°C** (by repeated compression and rapid expansion) - purified air is changed to **liquid**. 3. The liquid air at -200°C is introduced to the lower part of the fractionating tower (or fractionating column). 4. The liquid air is **warmed slowly** and the gases are collected on by one. At -190°C, nitrogen (b.p. = -196°C) vaporizes and is separated from the liquid mixture first. Argon (b.p. = -186°C) vaporizes next and oxygen (b.p. = -183°C) follows at a higher temperature and are then collected.

Answer 16

Since oxygen **supports combustion**, oxygen gas can **relight a glowing splint**. Preparation of a glowing splint: Light a wooden splint; Blow out the flame, but make sure that the splint has reddish, glowing tip.

Answer 17

Sea water is a **mixture** containing salts, dissolved gases and water. Composition of sea water: 96.5% Water, 2.4% Sodium chloride (NaCl), 0.5% Magnesium chloride (MgCl₂), 0.4% Sodium sulphate (Na₂SO₄), 0.1% Calcium chloride (CaCl₂), Other salts (Very small amount) *Approximate % by mass

Answer 18

NaCl is also known as **common salt**, **rock salt** or **table salt**.

Answer 19

Solute = sodium chloride (NaCl), magnesium chloride (MgCl₂) ... other dissolved gases Solvent = water

Answer 20

Sodium chloride (NaCl) can be extracted from sea water by ... Method 1: 1. Filtration: to remove large particle impurities. 2. Evaporation by heating to **dryness** - NaCl(s) (impure) because it contains impurities (e.g. MgCl₂), which are originally presented in sea water Method 2: 1. Filtration: to remove large particle impurities. 2. Evaporation of water by heating until a **saturated solution** is obtained: heat the filtrate to evaporate away some water to make sea water more concentrated and finally get a saturated solution. 3. Crystallization: allow the saturated solution to cool down at room conditions; the solubility of NaCl in water decreases with decreasing temp. Thus, NaCl crystals are formed upon cooling. 4. Filtration, wash and dry: NaCl crystals are filtered and washed with small amount of **cold distilled water**; NaCl crystals are allowed to dry on **filter**. - NaCl(s) (pure) Method 3: 1. Filtration: to remove large particle impurities. 2. **Slow evaporation of water at room temperature**: the amount of water (the solvent) becomes less and less as a result of evaporation. 3. Crystallization: when a saturated solution is formed, the amount of water is **merely enough to dissolve all NaCl**. Further evaporation of water causes crystallization to occur. Crystals are formed. 4. Filtration, wash and dry: NaCl crystals are filtered and washed with small amount of cold distilled water; NaCl crystals are allowed to dry on filter. - NaCl(s) (pure)

Answer 21

(Refer to notes p.33,36)

Answer 22

Filtration is a method used to separate **(an) insoluble solid(s)** (with large or small particle size) from **a liquid/solution**.

Answer 23

Evaporation is a method used to separate **dissolved solid(s)** (solute), with **higher boiling point** than that of the solvent, from a solution. Upon heating, the **solvent of the solution is lost** as a result of evaporation and **the high boiling solid(s) is/are left over**. Evaporation can also be used to **remove some solvent** (most commonly water) from a solution. The resulting solution will be **more concentrated or become saturated**.

Answer 24

Crystallization is a method used to **separate a dissolved solid (solute) from a solution**. * A saturated solution is obtained by heating the solution to evaporate away some solvent (most commonly water). * **Large crystals** of the dissolved solid will form upon **slow cooling of the saturated solution** (e.g. standing in air). This is because **the solubility of the solid in the solvent decreases with decreasing temperature**.

Answer 25

Crystal or crystalline solid is a **solid** with particles (atoms, ions or molecules) **arranged in an orderly repeating pattern**.

Answer 26

It is a solution containing **the maximum amount of solute** at a certain temperature.

Answer 27

1. Lower the **temperature** of the solution. 2. Decrease the **volume** of solvent in the solution.

Answer 28

* Obtain by **crystallization** instead of evaporation by heating to dryness * **Slow cooling** of the saturated solution (smaller and less pure crystals will form if cooled by ice-water bath)

Answer 29

Dip a glass rod into the solution, take it out to see if **small crystals** appear on the rod.

Answer 30

Hydrogen: flammable, explosive Oxygen: oxidizing

Answer 31

Simple distillation is a method used to separate dissolved solid(s) (solute), with higher boiling point than that of the solvent, from a solution. **Pure water** can be isolated from the solution (sea water) by simple distillation. * The water from the solution (sea water) **vaporizes** (boiling point = 100°C) upon heating, the water vapour escapes and passes through the condenser. The vapour is **cooled** by the cold water flowing around the condenser. The water vapour **condenses to form liquid water**, which is then collected as **distillate**. * The dissolved solid(s) (i.e. NaCl) **will not vaporize** (NaCl has very high melting point and boiling point) and remain in the flask and eventually isolated as the **solid residue**. ^Remarks: A round bottomed flask is used, anti-bumping granules are added, water should enter the condenser from the bottom.

Answer 32

A round-bottomed flask is used to ensure **even heating**.

Answer 33

Anti-bumping granules are added to ensure **smooth boiling**.

Answer 34

Water should enter the condenser from the **bottom** to ensure **the jacket of the condenser is fully filled with water**. This results in a **better cooling effect** to condense water vapour.

Answer 35

**Flame test** (for identification of metal ions) Many metal ions give **characteristic flame colour** upon heating over a Bunsen flame.

Answer 36

Sodium ion (Na+): Golden yellow Potassium ion (K+): Lilac Calcium ion (Ca2+): Brick-red Copper(II) ion (Cu2+): Bluish green

Answer 37

1. A **platinum (or nickel / nichrome) wire** is cleaned by soaking in concentrated hydrochloric acid [HCl(aq)] and heated in a non-luminous flame until it does not give a characteristic coloured flame. 2. The cleaned platinum wire is put into **concentrated hydrochloric acid [HCl(aq)]**. 3. It is then dipped into the solid sample. 4. The wire with the bound solid sample is heated in a **non-luminous flame** and the flame colour is recorded. Alternatively, the **solid sample can be dissolved in concentrated hydrochloric acid [HCl(aq)]** first and the cleaned platinum (or nickel) wire is put into the resulting solution and then heated in a non-luminous flame.

Answer 38

Chloride ion (Cl-) in the sea water can be identified by addition of **acidified silver nitrate solution** [silver nitrate solution + nitric acid (not hydrochloric acid / sulphuric acid)]. After addition, **white precipitate** (沈澱物) will be formed. Procedure: 1. Dilute nitric acid (HNO₃) is added to the **sample solution** (sea water) until the solution is **acidic** (tested with **pH paper or blue litmus paper**). 2. Silver nitrate (AgNO₃) solution is then added. Chemical equation: * AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq) colourless, colourless, white precipitate, colourless

Answer 39

**Dilute nitric acid** (not hydrochloric acid / sulphuric acid) is used to **remove carbonate ions (and other anions)** which can also form white precipitate with silver nitrate.

Answer 40

1. Water can turn **blue anhydrous cobalt(II) chloride (anhydrous CoCl₂) solid** to pink. * Water can be identified by **blue dry cobalt(II) chloride paper** [colour change: blue → pink] 2. Water can also turn **white anhydrous copper(II) sulphate (anhydrous CuSO₄) solid** to blue.

Answer 41

Electrolysis is the **decomposition of an electrolyte** by an **electric current** (a chemical method).

Answer 42

Sea water→ Hydrogen gas + Chlorine gas + Sodium hydroxide Diagram: Refer to notes p.44

Answer 43

H₂(g): * NH₃(g) (for fertiliser production) * Making fuel (rocket fuel) Cl₂(g) + H₂(g): * HCl(g) → HCl(aq): Hydrochloric acid Cl₂(g): * Sterilization of drinking (/ swimming pool) water * Making PVC (a plastic) NaOH(aq) + Cl₂(g): * Making bleaching solution NaOH(aq): * Making soap, detergents * Making paper * Waste water treatment

Answer 44

A rock (岩石) is a **solid** containing **one or more minerals**. It needs not have a specific chemical composition. * e.g. Limestone = Calcium carbonate (mainly) + Silicon dioxide + Other constituents

Answer 45

A mineral (礦物) is a **naturally occuring inorganic solid**, which has a characteristic chemical composition and a highly ordered crystalline structure. A mineral can be: 1. **an uncombined element** (e.g. graphite and gold) 2. **a compound**; made up of different elements (e.g. quartz = silicon dioxide, rock salt = sodium chloride, calcite = calcium carbonate)

Answer 46

An ore (礦石) is a rock from which a **valuable constituent (usually metal)** can be extracted through **mining** and **refined for uses**.

Answer 47

Name of ore, Compound present, Extracted metal: * **Rock salt**, Sodium chloride (NaCl), Sodium (Na) * **Haematite**, Iron(III) oxide (Fe₂O₃), Iron (Fe) * **Bauxite**, Aluminium oxide (Al₂O₃), Aluminium (Al) * **Malachite**, Copper(II) carbonate (CuCO₃), Copper (Cu) * **Calcite**, Calcium carbonate (CaCO₃), Calcium (Ca) * **Iron pyrite**, Iron(II) disulphide / Iron(II) persulphide (FeS₂), Iron (Fe) * **Copper pyrite**, Copper-iron sulphide (CuFeS₂), Copper (Cu) * **Galena**, Lead(II) sulphide (PbS), Lead (Pb) * **Zinc blende**, Zinc sulphide (ZnS), Zinc (Zn) * **Cinnabar**, Mercury(II) sulphide (HgS), Mercury (Hg) ^ Exceptions (non-metal) : **Quartz**; Silicon dioxide; Silicon

Answer 48

1. Mining of ore (by digging) 2. Purification of ore (removal of waste) 3. Extraction of metal by ... * (i) Physical separation (e.g. platinum, gold) * (ii) Heating the ore (e.g. mercury, silver) * (iii) Heating the ore with carbon (e.g. zinc, iron, lead, copper) * (iv) Electrolysis (e.g. potassium, sodium, calcium, magnesium, aluminium) 4. Purification of the impure metals extracted

Answer 49

Chalk, limestone and marble are **rocks** made up of mainly **calcite / calcium carbonate (CaCO₃)**.

Answer 50

**Chalk** Process of formation: * Sea animals with shells died → shells fell to sea bed and built up a deposit→ under high pressure, deposit is converted to chalk after millions of years. Hardness: Soft Use: White pigment in paper, plastics and paints **Limestone** Process of formation: * Under higher temperature and pressure, chalk is converted to limestone. Hardness: Hard Use: Materials for construction, e.g. limestone + clay = cement; limestone + water + sand + stone = concrete **Marble** Process of formation: * Under much higher temperature and pressure, chalk/limestone is converted to marble. Hardness: Hardest Use: Materials for construction, e.g. making floor, monuments

Answer 51

Calcium carbonate (CaCO₃) is **insoluble in water**. Chemical equation: CaCO₃(s) + H₂O(l) → no reaction / insoluble

Answer 52

Calcium carbonate reacts with **hydrochloric acid [HCl(aq)]** to form **calcium chloride [CaCl₂(aq)], water and carbon dioxide**. Chemical equation: * CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g) Calcium carbonate + Hydrochloric acid → Calcium chloride + Water + Carbon dioxide Calcium carbonate also reacts with **nitric acid** to form **calcium nitrate [Ca(NO₃)₂(aq)], water and carbon dioxide**. Chemical equation: * CaCO₃(s) + 2HNO₃(aq) → Ca(NO₃)₂(aq) + H₂O(l) + CO₂(g) Calcium carbonate + Nitric acid → Calcium nitrate + Water + Carbon dioxide

Answer 53

Calcium carbonate **decomposes** upon heating to give **white calcium oxide [CaO(s)] and carbon dioxide**. Chemical equation: * CaCO₃(s) -heat→ CaO(s) + CO₂(g) Calcium carbonate -heat→ Calcium oxide + Carbon dioxide

Answer 54

The calcium ion in calcium carbonate can be identified by a **flame test**. This is because a calcium compound gives a characteristic **brick-red flame colour** upon heating over a Bunsen flame.

Answer 55

1. The carbonate ion in calcium carbonate can be identified by addition of **dilute hydrochloric acid (HCl)** [or **dilute nitric acid (HNO₃)**, but not sulphuric acid (H₂SO₄) - CaSO₄ insoluble; stops reaction]. After addition, **colourless gas bubbles evolve** / effervescene occurs (due to CO₂) and the CO₂ gas **turns clear limewater [Ca(OH)₂(aq)] milky** due to the formation of **insoluble calcium carbonate [CaCO₃(s)]**. Chemical equation: * CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g) Calcium carbonate + Hydrochloric acid → Calcium chloride + Water + Carbon dioxide * Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water 2. The carbonate ion in calcium carbonate can also be identified by **heating the solid in a test tube and put a lighted match / burning splint into the tube**. Since calcium carbonate decomposes on heating to give CO₂ gas, which does not support combustion → the fire / flame will be **extinguished**. Chemical equation: * CaCO₃(s) → CaO(s) + CO₂(g) Calcium carbonate → Calcium oxide + Carbon dioxide

Answer 56

If excess CO₂(g) is bubbled into the milky suspension, the mixture turns to **colourless/clear**. Chemical equation: * CaCO₃(s) + CO₂(g) + H₂O(l) → Ca(HCO₃)₂(aq) * Calcium carbonate + Carbon dioxide + Water → Calcium hydrogencarbonate

Answer 57

(Refer to notes p.50)

Answer 58

Lime cycle: Refer to notes p.52 (Remark: Ca(OH)₂(s) is only slightly soluble in water, CaCO₃(s) is insoluble in water) Chemical equation: * Calcium carbonate(s) ***limestone / chalk / marble*** (^heat) → Calcium oxide(s) ***quicklime*** + Carbon dioxide(g) * Calcium oxide(s) ***quicklime*** + Water(l) → Calcium hydroxide(s) ***slaked lime*** * Calcium hydroxide(s) ***slaked lime*** (^water) → Calcium hydroxide(aq) ***limewater*** * Calcium hydroxide(aq) ***limewater*** + Carbon dioxide(g) → Calcium carbonate(s) + Water(l) * Calcium carbonate(s) + Water(l) + (excess) Carbon dioxide(g) → Calcium hydrogencarbonate(aq)

Answer 59

Clear limewater is prepared by **adding excess water** to CaO(s) / Ca(OH)₂(s) followed by **filtration** to remove any undissolved Ca(OH)₂(s).

Answer 60

Weathering is the process where rock is **dissolved**, **worn away** or constantly broken down into **smaller particles** by physical and chemical processes.

Answer 61

Erosion is the process where weathered rock materials are **carried away by water, wind or gravity**.

Answer 62

1. **Change in temperature** causes repeated cooling and expansion of rocks → Cracks are formed on rocks 2. When **water gets into the cracks of rocks**, and is changed to **ice** at low temperature, it **expands** and causes further cracking of the rocks.

Answer 63

1. **Normal rain water** is acidic (pH = 5.6) ∵ CO₂(g) in air is dissolved in the rain water to form **carbonic acid (H₂CO₃)**. Carbonic acid will react with calcium carbonate [CaCO₃(s)] limestone to form **water-soluble calcium hydrogencarbonate [Ca(HCO₃)₂(aq)]**, calcium carbonate is thus broken down. Chemical equations: * CO₂(g) + H₂O(l) → H₂CO₃(aq) Carbon dioxide + Water → Carbonic acid (碳酸) * H₂CO₃(aq) + CaCO₃(s) → Ca(HCO₃)₂(aq) Carbonic acid + Calcium carbonate → Calcium hydrogencarbonate 2. **Acid rain** also causes breaking down of calcium carbonate. 3. Calcium carbonate decomposes slowly at **elevated temperature** to form calcium oxide and carbon dioxide. Chemical equations: * CaCO₃(s) (^heat) → CaO(s) + CO₂(g) Calcium carbonate (^heat) → Calcium oxide + Carbon dioxide

Answer 64

Acid rain is formed as a result of **presence of air pollutants** nitrogen oxides (nitrogen monoxide (NO), and nitrogen dioxide (NO₂)) and sulphur oxides (SO₂) in air.

Answer 65

Shake a mixture of calcium carbonate and sodium chloride with **water**. [1M] **Filter the mixture** using a **funnel** with **filter paper** and the residue is calcium carbonate. [1M] **Evaporate** the filtrate and the solid formed is sodium chloride. [1M]

Topic 1: Fundamentals of Chemistry and Planet Earth Flashcards

(89 cards)