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Sciene Chem > chemical changes 4 > Flashcards

chemical changes 4 Flashcards

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1
Q

what is the PH scale

A

a measure of how acidic or alkaline a solution is
the lower the PH the more acidic
the higher the more alkaline

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2
Q

what is indicator

A

a dye that changes colour depending on weather it’s above or below a certain PH
some indicators contain a mixture of dys that means they gradually change colour over a broad range of PH

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3
Q

ways to measure PH

A

PH probe

measure electronically

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4
Q

what is an acid

A

a susbstance that forms aqueous solutions with PH of less than 7
Acids form H plus ions

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5
Q

what is a base

A

a substance with a PH level greater than 7

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6
Q

Base(alkali)

A

base that dissolves in water to form a solution with PH greater than 7
form OH minus ions

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7
Q

acid + base =

A

salt + water

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8
Q

H plus + OH minus =

A

H2O

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9
Q

what do reactions of strong acids and alkali help calculate

A

reactions of a strong acids and alkalis to calculate the concentration by titration

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10
Q

what PH does a neutral substance have

A

PH 7

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11
Q

what do strong acids do in water

A

ionise completely in water

all acid particles dissociate to release H plus ions

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12
Q

what do weak acids do in water

A

do not fully ionise

only a small proportion of particles dissociate to reales H plus ions

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13
Q

what kind of reaction is a weak acid

A

reversible reaction which sets up an equillibrium between the undissociated and dissociated ions.
lies on the left because only few H plus ions are released

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14
Q

what happens when the concentration of H plus ions increase

A

rate of reaction will be faster if strong acid

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15
Q

what is the PH of acid or alkali and what happens when the scale decreases

A

a measure of the concentration of H plus ions

for every decrease of 1 on the PH scale the concentration increases by a factor of 10

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16
Q

general rule when ion concentration changes

A

factor h plus ion concentration changes by 10-x (x is difference in PH)

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17
Q

what does acid strength tell you

A

what proportion of the acid molecules ionise in water

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18
Q

what is acid concentration

A

how much acid there is in a certain volume

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19
Q

metal oxides or metal hydroxide + acid =

A

salt + water

20
Q

how you make a salt

A

metal + acid

21
Q

acid + metal carbonate =

A

salt + water + carbon dioxide

22
Q

what is the reactivity series

A

lists metals in order of their reactivity

23
Q

how is metal reactivity measured

A

how easily they lose there electrons and form positive ions

24
Q

acid + metal =

A

salt + hydrogen

25
Q

how do you measure reactivity

A

react it with an acid

the speed of the reaction is indicated by the amount of hydrogen gas given off

26
Q

metal + water =

A

metal hydroxide + hydrogen

27
Q

what is a redox reaction

A

a reaction that separates a metal from it’s oxide

28
Q

Formation of metal ore =

A

Oxidation = gain of oxygen

29
Q

extraction of metal ore =

A

Reduction = loss of oxygen

30
Q

how is metal extracted with carbon

A

by reduction

ore is reduced as oxygen is removed from it and carbon gains oxygen so is oxidised

31
Q

how are metals higher than carbon extracted

A

electrolysis

32
Q

how are metals below carbon extracted

A

reduction using carbon

33
Q

what is oxidation

A

a loss of electrons

34
Q

what is reduction

A

a gain of electrons

35
Q

OIL RIG

A

oxidation is loss reduction is gain

36
Q

what are displacement reactions

A

involve one metal kicking another one out of it’s compound

37
Q

rule of displacement reaction

A

A more reactive metal will displace a less reactive metal

38
Q

what gains the electrons and what loses the electrons during a displacement reaction

A 
metal ion (reduced)
metal atom (oxidised)
39
Q

what is an ionic equation

A

only show particles that react and the products produced not the spectator ions

40
Q

what and how does electrolysis do/work

A

an electric current is passed through an electrolyte

positive ion in the electrolyte will move towards the cathode and gain electrons

negative ions in the electrolyte will move towards the anode and loses electrons

this creates a flow of charge through the electrolyte as the ions travel to the electrode

41
Q

why electrolysis only works on molten ionic solids

A

ionic solid can’t be electrolysised because ions are in a fixed position and don’t move

molten ionic compounds can be electrolysed because the ions can move freely

positive ions are reduced to the element at the cathode

negative ions are oxidised to the element at the anode

42
Q

how is aluminium extracted using electrolysis

A

aluminium is extracted from the ore bauxite by electrolysis

aluminium oxide has a very high melting temperature so it’s mixed with cryolite to lower the melting point

The molten mixture contains free ions

the positive 3 plus AL ions are attracted to the negative electrode where they pick up three electrons and turn into neutral aluminium atoms

the negative 2 minus O ions are attracted to the positive electrode where they each lose two electrons

43
Q

overall equation of extracted aluminium

A

aluminium oxide = aluminium + oxygen

44
Q

what do half equations show

A

show the reactions at the electrodes.

45
Q

electrolysis of aqueous solutions what else is produced

A

as well as the ions produced from the compound there will be hydrogen ions and hydroxide ions from the water.

at the cathode if the hydrogen ion is less reactive than the metal hydrogen gas is formed otherwise the metal ion coats the cathode

at the anode if hydroxide ions are present, molecules of chlorine, bromine or iodine will be formed
if no halide ions are present then the hydroxide ions are discharged and oxygen will be formed

46
Q

reactivity series

A 
potassium k
sodium Na
lithium Li
calcium Ca
magnesium Mg
carbon C
zinc Zn
iron Fe
hydrogen H
copper Cu

Sciene Chem (14 decks)

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