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DGS S4 Chemistry > Junior Secondary Chemistry (1A-1B) > Flashcards

Junior Secondary Chemistry (1A-1B) Flashcards

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1
Q

What is an atom?

A

An atom is the smallest part of an element and the smallest unit of matter that still retains its properties.

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2
Q

What is an element? How many elements are there and how can they be presented?

A

An element is a substance that contains only one kind of atom. There are 118 elements, all listed in the periodic table, with 92 being naturally occurring (up to uranium). Each element has their own chemical symbol, consisting of an upper case letter and sometimes a lowercase letter.

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3
Q

What are the chemical symbols of magnesium, lead, tin, mercury, silver, and gold?

A

Mg, Pb, Sn, Hg, Ag, Au

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4
Q

What are the elements represented by chemical symbols Al, Br, Ca, K, and P?

A

Aluminium, bromine, calcium, potassium, phosphorus

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5
Q

What are molecules?

A

Molecules are groups of non-metal atoms that make up some elements. They can be represented by chemical formulae indicating the number of atoms they contain.

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6
Q

What are the chemical formulae of hydrogen, ozone, phosphorus, nitrogen, and sulphur?

A

H2, O3, P4, N2, S8

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7
Q

What are common characteristics of metals and what are some exceptions?

A
  1. They are solids at rtp (room temperature & pressure) except for mercury which is a liquid.
  2. They are shiny when there is a large and smooth surface.
  3. They are usually strong and have a high density. (exception: sodium which is soft)
  4. They usually have high melting and boiling points. (exceptions: mercury being liquid and sodium having melting point of below 100C)
  5. They are good conductors of heat and electricity.
  6. They are malleable (can be pressed) and ductile (can be pulled into wires).
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8
Q

What are common characteristics of non-metals and what are some exceptions?

A
  1. They are either solids or gases at rtp except for bromine, which is a liquid.
  2. They are usually dull except for diamond (a form of carbon).
  3. They are usually brittle and have a low density.
  4. They usually have a low melting and boiling point except for diamond.
  5. They are poorly malleable or ductile, and they do not conduct heat well.
  6. They do not conduct electricity well except for graphite.
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9
Q

What is the meaning of brittle?

A

A brittle substance is hard and rigid on the surface but it breaks easily.

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10
Q

What are 2 examples of semi-metals and what are their characteristics?

A

Boron and silicon: They do not conduct electricity normally at rtp, but they conduct electricity well when mixed with impurities.
Silicon, as a semi-conductor, is used to make computer chips.

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11
Q

What are protons, electrons, and neutrons?

A

Protons, electrons, and neutrons are sub-atomic particles that exist in every atom, except for hydrogen (hydrogen has no neutron). Protons carry a relative charge of +1 and have relative mass of 1, while neutrons are neutral in charge and have relative mass 1. Electrons have a relative charge of -1 and their relative mass is negligible (about 1/1800 of that of a proton).

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12
Q

What is the nucleus of an atom and what are its properties?

A

The nucleus of an atom is made of protons and neutrons, having most of the atom’s mass. It occupies an extremely small amount of space relative to the atom, and the rest of the atom is mainly empty space. Electrons move freely around the nucleus.

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13
Q

What are atomic numbers and mass numbers?

A

The atomic number (Z) denotes the number of protons in an atom. Since there are an equal amount of protons and electrons in an atom, it represents the number of electrons in an atom as well.
The mass number (A) denotes the relative mass of the atom, that is the sum of the number of neutrons and protons in the atom.

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14
Q

What is an ion and what are the types of ions? How are they formed?

A

An ion is a charged counterpart of an atom. A positive ion, or cation, is formed when atoms lose electrons and the overall charge becomes positive. Meanwhile, a negative ion, or anion, is formed when atoms gain electrons and the overall charge becomes negative.

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15
Q

What is the relationship between the elements and the number of electrons they lose to form ions?

A

Metals form cations with overall charge equal to the group number in the periodic table. Non-metals form anions with overall charge equal to the difference between 8 and their group number. Hydrogen is the only non-metal that forms cations.

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16
Q

What are the characteristics of groups in the periodic table?

A

Groups in the periodic table are columns. Elements of the same group have similar chemical properties but differ in reactivity. For metals of groups I and II, the reactivity increases down the group, whereas for non-metals of groups IV to VII, the reactivity decreases down the group.

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17
Q

What are the characteristics of periods in the periodic table?

A

Periods in the periodic table are rows. From left to right across the period, elements are arranged from metals, semi-metals, to non-metals. Transition metals appear from period 4.

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18
Q

What are the usages of aluminium, chlorine, helium, and lithium?

A

Al: making soft drink cans
Cl: killing germs in water
He: filling balloons
Li: making lithium ion batteries for electronic devices

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19
Q

What are the usages of magnesium, oxygen, phosphorus, and silicon?

A

Mg: added to fireworks to produce brilliant white sparks
O: for patients with breathing difficulties
P: making matches
Si: making glass and computer chips

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20
Q

What are the characteristics of the electronic arrangements for elements 1-20?

A

Electrons are arranged in electron shells, while electron shells can hold different numbers of electrons. The maximum amount of electrons a shell can hold is 2n2, but for elements 1-20, starting from the 3rd shell, the outermost valent shell can only hold 8 electrons. The period of the element is the number of occupied electron shells, while the group is the number of electrons in the valent shell.

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21
Q

Why are some atoms stable?

A

Atoms are stable if their outermost shell is fully occupied/if they are in group VIII/0 (noble gases). Noble gases fulfill the duplet rule (He) or the octet rule (others) where the outermost shell is filled with 2 or 8 electrons.

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22
Q

Why do unstable elements form ions?

A

They bond to other atoms in order to gain the same arrangement of outer-shell electrons as a noble gas atom to become stable. Since it is easier for metals to lose ions to form a stable arrangement, they form cations and the charge is equal to the group number of the metal. Since it is easier for non-metals to gain ions to form a stable arrangement, they form anions and the charge is equal to 8-group number.

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23
Q

Why do metal reactivity increase down the group and why is it vice versa for non-metals?

A

Reactivity is determined by how easily the element forms ions.
For metals, since the attraction force between the outermost electrons are weaker when there are more occupied electron shells, it is easier for them to lose the electrons and form ions. Therefore, metal reactivity increases down the group.
For non-metals, since the attraction force between the outermost electrons are weaker when there are more occupied electron shells, it is harder for them to attract more electrons and form ions. Therefore, non-metal reactivity decreases down the group.

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24
Q

What are characteristics of simple ions from the first 20 elements?

A

A simple/monoatomic ion is derived from a single atom. All simple metal ions and H+ ions are cations, while all simple non-metal ions are anions with -ide ending. An atom and its ion have different physical and chemical properties because they have different numbers of electrons, while the identity of an element does not change after gaining or losing electrons as the number of protons stay the same.

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25
Q

What are the naming characteristics of polyatomic ions?

A

A polyatomic ion is derived form a group of ions. Those ending with -ide are simple anions except for OH- and CN- (hydroxide and cyanide ion). Those ending with -ite are polyatomic ions with less O atoms, while those ending with -ate are polyatomic ions with more O atoms. The same transition metal can form more than one simple cation with different charges.

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26
Q

What are the chemical formulas of hydrogen ion, calcium ion, nitride ion, fluoride ion, and phosphide ion?

A

Hydrogen ion: H+
calcium ion: Ca2+
nitride ion: N3-
fluoride ion: F-
phosphide ion: P3-

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27
Q

What are the chemical formulas of ammonium ion, silver ion, and zinc ion?

A

ammonium ion: NH4+
silver ion: Ag+
zinc ion: Zn2+

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28
Q

What are the chemical formulas of nitrate ion, nitrite ion, carbonate ion, and hydrogencarbonate ion?

A

nitrate ion: NO3-
nitrite ion: NO2-
carbonate ion: CO32-
hydrogencarbonate ion: HCO3-

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29
Q

What are the chemical formulas of sulphate ion, sulphite ion, and hydrogensulphate ion?

A

sulphate ion: SO42-
sulphite ion: SO32-
hydrogensulphate ion: HSO4-

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30
Q

What are the chemical formulas of chromate ion, dichromate ion, and phosphate ion?

A

chromate ion: CrO42-
dichromate ion: Cr2O72-
phosphate ion: PO43-

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31
Q

What are the chemical formulas of permanganate ion, cyanide ion, and hydroxide ion?

A

permangenate ion: MnO4-
cyanide ion: CN-
hydroxide ion: OH-

32
Q

What are the colours of chromate ion, dichromate ion, and chromium(III) ion in aqueous solution?

A

chromate ion: yellow
dichromate ion: orange
chromium(III) ion: green

33
Q

What are the colours of iron(II) ion, iron(III) ion, cobalt(II) ion, and copper(II) ion in aqueous solution?

A

iron(II) ion: pale green
iron(III) ion: yellow
cobalt(II) ion: pink (cobalt chloride paper)
copper(II) ion: blue

34
Q

What are the colours of manganese(II) ion, permanganate ion, and nickel(II) ion in aqueous solution?

A

manganese ion: pale pink
permanganate ion: purple
nickel(II) ion: green

35
Q

What are compounds and mixtures?

A

Compounds are pure substances that contain two or more elements chemically bonded together. It’s formation is a chemical change which involves formation of new substances; it can be broken down into its constituent elements by chemical methods.
Mixtures are impure; they are made up of two or more substances (elements or compounds) that are not chemically bonded together. It’s formation is a physical change, and components can be separated by physical methods.

36
Q

What are the chemical formulae of quartz, chalk, sulphuric acid, nitric acid, and limewater?

A

SiO2, CaCO3, H2SO4, HNO3, Ca(OH)2

37
Q

What are the features of a compound?

A
  1. constituent elements must be in fixed ratio indicated in the chemical formula.
  2. energy is usually taken in or released during formation.
  3. it’s properties are very different from its constituent elements.
  4. it has a sharp melting/boiling point because it is pure.
  5. it can only be separated to its constituent elements by chemical methods.
38
Q

What are the features of a mixture?

A
  1. variable proportion, concentration can be changed.
  2. no or little energy change when formed.
  3. properties similar to those of substances making up the moisture
  4. it does not have a sharp melting/boiling point as it is not pure.
  5. it’s constituent substances can be separated by physical methods.
39
Q

What are the chemical formulas and consituent elements of glucose, quartz and chalk?

A

glucose: C6H12O6, constituent elements are carbon, hydrogen, and oxygen
quartz: SiO2, consitituent elements are silicon and oxygen
chalk: CaCO3, constituent elements are calcium, carbon, and oxygen

40
Q

List three uses of aluminium and explain why.

A
  1. Aluminium is strong and has lower density, so it is suitable for making aircraft bodies.
  2. It is a good conductor of heat as well as malleable, so it is suitable for making kitchen foil (tin foil is aluminium).
  3. In addition, it is corrosion resistant and non-poisonous, these properties alongside with how aluminium is malleable and has low density makes it suitable for making soft drink cans.
41
Q

List three uses of copper and explain why.

A
  1. Copper is a good conductor of electricity, and it is ductile, meaning that it is suitable for making electric wires.
  2. It is non-poisonous and strong, so it is used to make water pipes.
  3. It is a good conductor of heat, so it is used for making cooking utensils.
42
Q

Suggest one use of lead and explain why.

A

Lead has a density much higher than that of water (11.3g/cm^3). It is suitable for making fishing sinkers.
(pencil lead is not made of lead; instead it is made of graphite since lead exposure is harmful)

43
Q

Suggest one use of iron and explain why.

A

Iron is a good conductor of heat and has a high melting point. Therefore, it is suitable for making cooking utensils.
(iron utensils are often coated with oil to prevent food from sticking and to slow down corrosion/rusting due to exposure to air.)

44
Q

List 5 metals that can only be extracted by electrolysis of molten ores in decreasing order of reactivity.

A

Potassium, sodium, calcium, magnesium, aluminium

45
Q

List 5 metals that are found as sulphides in decreasing order of reactivity, and the extraction method.

A

Zinc: zinc blende ZnS, lead: galena PbS, copper: copper pyrite CuFeS2, mercury: cinnabar HgS, silver: silver glance Ag2S. They can be extracted by heating in air.

46
Q

List 2 metals that can be extracted by heating with charcoal.

A

Iron: haematite Fe2O3, copper: copper oxide CuO (oxides)

47
Q

List 3 metals that are free in nature from the earliest discovered metal; how are they extracted?

A

Gold, platinum, silver; they are extracted through physical methods like panning.

48
Q

What is the reaction when metals are extracted from oxides through heating with carbon?

A

Carbon is oxidised by the metal oxide to form carbon dioxide, while the oxide is reduced by carbon to form the metal.

49
Q

List 3 metals that react with cold water in decreasing order of reactivity.

A

potassium, sodium, calcium

50
Q

List 4 metals that react with steam but not with cold water in decreasing order of reactivity.

A

magnesium, aluminium, zinc, iron

51
Q

List a metal that reacts with dilute acid but not with steam.

A

lead

52
Q

List 2 metals that react with oxygen in air but not with dilute acid in decreasing reactivity.

A

copper, mercury

53
Q

What is the word equation for metals’ reaction with oxygen?

A

metal + oxygen -> metal oxide

54
Q

What is the word equation for metals’ reaction with liquid water?

A

metal + water -> metal hydroxide + hydrogen gas

55
Q

What is the word equation for metals’ reaction with steam?

A

metal + water(g) -> metal oxide + hydrogen gas

56
Q

What is the word equation for metals’ reaction with dilute acid?

A

metal + dilute acid -> metal salt + hydrogen gas

57
Q

Which additional substance is used in the extraction of aluminium and why?

A

Cryolite is added to lower the melting point of aluminium as lower operation costs are needed for less heat energy.

58
Q

Why does bauxite have to be molten in order for electrolysis to take place?

A

Since the ore must be molten for ions to move freely, the ore must be heated to melt.

59
Q

What are alloys?

A

An alloy is a mixture of a metal and one or a few other elements. It is usually made by heating the metal and other elements together, causing them to melt and mix.
(metals do not form compounds with other metals, explaining why all alloys are mixtures.)

60
Q

What are the composition, properties and uses of steel and bronze?

A

steel: iron (>90%), carbon (0.2-5%): it is stronger than iron and more resistant to corrosion, so it is used to make motor car bodies and construction materials.
bronze: copper (~90%), tin (~10%): it is harder than copper and tin, and more resistant to corrosion. It is used to make statues.

61
Q

What is the difference between stainless steel and steel?

A

Stainless steel consists of ~20% of chromium and small amounts of nickel other than their common materials iron and carbon. This makes stainless steel stronger and more resistant to corrosion, so stainless steel is used to make cooking utensils and surgical tools. However, stainless steel is more expensive than steel as chromium is expensive.

62
Q

What are the similarities and differences between titanium alloy and duralumin?

A

Titanium alloys consist of mostly titanium with small amounts of aluminium and vanadium. Meanwhile, duralumin consists of mostly aluminium with small amounts of copper, magnesium, and manganese. Both alloys are very strong with low density, so are both used to make aircraft bodies. Titanium alloys can also be used to make glasses frames.

63
Q

What are the similarities and differences of brass and coinage metals?

A

Both alloys consist of copper and zinc. They are both harder than copper and more resistant to corrosion. However, coinage metals may also contain nickel in different proportions. In addition, brass is used to make musical instruments, doorknobs and keys, while coinage metals are mainly used for coins.

64
Q

What are the composition, properties, and uses of carat gold and solder?

A

carat gold: It consists of mainly gold with silver and copper in different proportions. It is harder and shinier than pure gold (24K). It is used to make ornaments and coins.
solder: it consists of ~50% of tin and lead each. It has a lower melting point but is harder than both composition metals. It is used for joining electronic parts in circuit boards.

65
Q

What is crude oil and its composition compounds?

A

Crude oil, or petroleum, is a thick, black liquid with a pungent odour. It is a mixture of many compounds, with most of them being hydrocarbons. Hydrocarbons are molecules only consisting of hydrogen and carbon atoms.

66
Q

What are the four simplest hydrocarbon molecules, and the general number of hydrogen atoms in hydrocarbons?

A

CH4: methane
C2H6: ethane
C3H8: propane
C4H10: butane
for hydrocarbons having n carbon atoms, they will have (2n+2) hydrogen atoms.

67
Q

How must crude oil be prepared to be used as a fuel and why?

A

When crude oil is burned directly, a lot of black smoke (soot) and harmful gases are produced. Therefore, crude oil cannot directly be used as a fuel and it must be refined first. Through fractional distillation, hydrocarbons with similar boiling points are separated into fractions, which refines crude oil.

68
Q

What is the working principle of industrialised fractional distillation of crude oil?

A

Crude oil is refined in fractionating towers divided into different levels, with each level keeping a particular range of temperatures.
In an oil refinery, crude oil is first heated to about 400°C in a furnace near the bottom of the fractionating tower. Then, the hot crude oil gas rises. As higher levels of the fractionating tower have lower temperatures, the crude oil is cooled as it rises. The larger hydrocarbons have a higher melting point, so they condense lower in the tower; smaller hydrocarbons condense at higher, cooler levels. The condensed liquid at each level is then collected separately as fractions of crude oil.

69
Q

For fractions of crude oil, what are the changes in properties for fractions having higher boiling points?

A

The higher the boiling point of the fraction:
1. the darker the colour (pale yellow -> brown)
2. the higher the viscosity
3. the lower the volatility
4. the lower the flammibility (the worse the fuel)
5. the more amount of black smoke produced when burning (more sooty flame)

70
Q

What are viscosity and volatility?

A

Viscosity: how sticky/thick a liquid is. The higher the viscosity, the thicker the liquid.
volatility: how easy a liquid evaporates. The higher the volatility, the easier for it to evaporate.

71
Q

As we go down the fractionating tower, what is the change in the length and boiling points of hydrocarbons condensed?

A

The lower the position, the larger the hydrocarbon molecules, the higher the boiling points.

72
Q

What are the names of crude oil fractions, from the lowest boiling point to the highest?

A

Liquefied Petroleum Gas (LPG) less than 40°C, petrol (gasoline) 40-70°C, naphtha 70-170°C, kerosene 170-250°C, diesel oil 250-350°C, fuel oil, lubricating oil, waxes, bitumen >350°C

73
Q

What are five types of crude oil fractions used as fuels for transportation?

A

LPG: fuels for taxis
petrol: furls for motor cars
kerosene: fuels for aeroplanes
diesel oil: fuels for heavy vehicles eg. lorries, buses
fuel oil: fuels for ships
Worse, less efficient fuels are used on larger transportation vehicles.

74
Q

What are the uses of naphtha, kerosene, fuel oil, and bitumen?

A

naphtha: raw materials for production of Town Gas, plastics and other chemicals
kerosene: aeroplane fuels, solvents
fuel oil: ship fuels, generation of electricity in power plants
bitumen: material for covering roads

75
Q

What are some products made from crude oil in daily life?

A

Plastic products, paints, detergents, solvents (to dissolve substances insoluble in water)

DGS S4 Chemistry (23 decks)

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