Chemistry Last Minute

Front 1

function of the boiling chips

Back 1

to ensure smooth boiling of the mixture

Front 2

isotopes definition

Back 2

isotopes are atoms of the same element with the same number of protons and electrons, but different numbers of neutrons.

add on: same chemical properties, but slightly different physical properties

Front 3

difference between a mixture and a compound in terms of its composition and separation methods

Back 3

mixture has no fixed composition, can be separated into its different components by physical separation methods.

compound have a fixed composition, cannot be separated into its different components by physical separation methods, only chemical.

Front 4

one example of a compound and mixture each.

Back 4

compound -> water

mixture -> air

Front 5

describe in terms of electrons, how a chlorine atom becomes a chloride ion.

Back 5

a chlorine atom will gain one valence electron to become a chloride ion

Front 6

explain why ionic bonds have high melting points

Back 6

it has strong electrostatic forces of attractions between the opposite charged ions

Front 7

why sodium chloride has to be dissolved in water or molten before it will conduct electricity

Back 7

to form molten that can carry charges to conduct electricity.

solid = cannot conduct electricity

Front 8

this change always occurs when a metal atom turns into an ion.

Back 8

it becomes positively charged

Front 9

explain why the reaction stops.

Back 9

the reaction stopped as all the calcium present completely reached with water, hence no more hydrogen gas is produced.

Front 10

element

Back 10

a pure substance that cannot be broken down into two or more simpler substances by chemical processes

Front 11

compound

Back 11

a pure substance containing two or more elements that are chemically combined in a fixed ratio.

Front 12

mixture

Back 12

made up of two or more substances that are not chemically combined

Front 13

ion

Back 13

in an atom, the number of protons is the same as the number of electrons. an imbalance in the number of protons or electrons returns in ions.

Front 14

carbonate , ammonia and nitrate

Back 14

CO32- , NH3 , SO42-

Front 15

ionic bonds

Back 15

the strong electrostatic forces of attraction between positive and negative ions

Front 16

covalent bonds

Back 16

are a bond formed by the sharing of electrons between the two non-metallic atoms

Front 17

relative atomic mass Ar, defined by comparing the mass of one atom with the mass of another atom. what is that atom ?

Back 17

Carbon -12 or 12C

Front 18

relative formula mass

Mr of MgSO4 = ?

Back 18

Mr of MgSO4 = 24 + 32 + 4(16)

= 120

Front 19

the mole and avogadro’s no.

Back 19

one mole of any substance contains 6X10 power 23 particles

Front 20

mole calculations

Back 20

no. of moles (mol) = mass of substance over molar mass of substance ( mol = mass over Mr )

Front 21

maximum mass produced

Back 21

moles X Mr

Front 22

acids and bases

Back 22

an acid is a substance that produces hydrogen ions, H+ , in aqueous solution.

Front 23

properties of acids

Back 23

-> sour taste

-> dissolve in water to form solution which conduct electricity

-> turns blue litmus paper red (blue -> red)

Front 24

test for hydrogen gas

Back 24

test : place a lighted splint at the mouth of the test tube.

reaction : if there is hydrogen gas present, hydrogen gas will extinguish the lighten splint with a ‘pop’ sound.

Front 25

metal + acid -> salt + hydrogen

carbonate + acid -> salt + water + carbon dioxide

hydrogen carbonates + acid -> salt + water + carbon dioxide

Back 25

metal oxide + acid -> salt + water

metal hydroxide + acid -> salt + water

base + acid -> salt + water

alkali + acid -> salt + water

Front 26

test for carbon dioxide

Back 26

test : bubble the gas through limewater

reaction : carbon dioxide forms a white precipitate with limewater.

Front 27

bases

Back 27

a base is any metal oxide or hydroxide that reacts with an acid to produce a salt and water only.

Front 28

alkali (a base that is soluble in water)

Back 28

an alkali is a substance that produces hydroxide ions, OH- , in aqueous solution

Front 29

when ammonia gas dissolves in water, ammonia ions and hydroxide ions are formed.

Back 29

ammonia + water ≈ ammonia ion + hydroxide ion

Front 30

properties of alkalis

Back 30

-> bitter taste and feel soapy

-> turns red litmus paper blue (red -> blue)

Front 31

neutralisation reaction

Back 31

H+ (aq) + OH- (aq) -> H20 (l)

Front 32

alkalis, when heated with ammonia salts, causes ammonia gas to be given off.

Back 32

alkali + ammonium salt -> salt + water + ammonia

ammonia gas can be recognised by its characteristic pungent smell

Front 33

test for ammonia gas , NH3

Back 33

test : place damp red litmus paper into the gas

observation : it turns blue in the presence of ammonia

Front 34

universal indicator

Back 34

ROYGBIV

red, orange, yellow = acidic (pH0-6)

green = neutral

blue, indigo, violet = alkaline (pH 8-14)

Front 35

colour change

Back 35

litmus paper :

strong acidic solution -> red

strong alkaline solution -> blue

universal indicator :

strong acidic solution -> red

strong alkaline solution -> violet

Front 36

controlling pH of soil

Back 36

it is important to control the pH of soil because it will affect the growth and development of plants. most plants grow best in neutral or slightly acidic/alkaline soils.

Front 37

pH of soil may become unsuitable for plants to grow due to:

Back 37

-> too much fertilisers added to the soil.

-> environmental pollution such as acid rain.

Front 38

way to treat acidity in soil

Back 38

add calcium hydroxide (slaked lime) or calcium oxide (quick lime). this process known as ‘slaking’. these bases neutralise the acid in the soil.

Front 39

classification of oxides

Front 40

acidic oxides

Back 40

- non-metallic oxides

- often gases at room temperature (low bp)

- most dissolve in water to form acids (H+ ions)

-react with bases to form a salt and water only

Front 41

neutral oxides

Back 41

- insoluble in water

- show neither acidic nor basic properties. do not react with neither acids nor bases.

- e.g h20, NO (nitric oxide), CO (carbon monoxide)

Front 42

basic oxides

Back 42

- metallic oxides

- often solids at room temp (high mp and bp)

-some dissolves in water to form alkalis

- react with acids to form a salt and water only.

- can be soluble or insoluble.

Front 43

amphoteric oxides

Back 43

- react with acids to form a salt and water, behaving like a base.

- react with bases to form a salt and water, behaving like an acid

only 3 amphoteric oxides

- lead(II) oxide (Pb0), aluminium oxide (AL2O3) , zinc oxide (ZnO)

Front 44

test that can be carried out on each sample, to show that the solution had changed from alkaline to acidic.

Back 44

test : add a few drops of universal indicator to a sample of the solution.

observation before : universal indicator turns blue or purple in an alkaline solution.

observation after : universal indicator turns red, orange or yellow in an acidic solution.

Front 45

explain in terms of the chemistry involved, the effect this chemical has on the soil

Back 45

calcium hydroxide or calcium oxide is a base that will neutralise the acids in the soil and raise its pH so that the soil becomes less acidic.

Front 46

composition by volume of clean, dry air

Back 46

78% nitrogen

21% oxygen

10% other gases (noble gases (argon) and carbon dioxide)