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Chemsitry > Chemical changes (COGNITO) > Flashcards

Chemical changes (COGNITO) Flashcards

1
Q

what is a neutral ph

A

7

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2
Q

if ph is acidic then it is

A

below 7

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3
Q

if ph is alkaline it is

A

above 7

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4
Q

what is one way to measure ph

A

using indicators
those are different chemical diyes that change colour if they react with certain ph
most common example is universal indicator

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5
Q

what is another way to measure the ph

A

ph probe that is connected to a ph meter when we put the ph probe into the solution the meter tells us the exact number of ph

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6
Q

benefit of probe compare to indicator

A

more accurate and precise
don’t involve guessing shades
no human judgement

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7
Q

how do you define an acid

A

any substance that forms an aqueous solution with a pH less than 7
and the reason for that is because acid form h+ ions in water which makes it acididc

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8
Q

how do you denife bases

A

any substance with a ph greater than 7

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9
Q

how do you define alkalis

A

a base that dissolves in water toform a solution with a ph greater than 7

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10
Q

what ions do alkaline form in water

A

the form hydroxide ions oh-

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11
Q

what is a neutralizasion reaction and what it produces

A

neutralisation = acid + base
neutralisation = salt + water
eg HCl + NaOH - NaCl + H2O
another way H+ + OH - = H2O

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12
Q

name 3 common acids and their formula

A

hydrochloric HCl
sulfuric H2SO4
Nitric HNO3

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13
Q

name 2 common bases and their formula

A

sodium hydroxide NaOH
calcium carbonate CaCO3

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14
Q

what is a titration

A

A titration is an experimental technique used to find an unknown concentration of an acid or an alkali.

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15
Q

name 4 main titration equpment

A

A pipette to accurately measure a certain volume of acid or alkali (normally 25 cm3)
A conical flask to contain the liquid from the pipette
A burette to add alkali or acid to the the conical flask
A white tile to place the conical flask on

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16
Q

in 8 steps describe how the titration supposed to be done

A

1.Use the pipette to add 25 cm3 of alkali to a clean conical flask.
2.Add a few drops of indicator and put the conical flask on a white tile.
3.Fill the burette with acid and note the starting volume.
4.Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix.
5.Stop adding the acid when the end-point is reached (this is when the acid has neutralised the alkali and the indicator changes colour).
6.Note the final volume reading, and calculate how much acid you added in total.
7.Repeat the titration until you get ‘concordant results’, which means volumes of acid that are within 0.10 cm3 of each other.
8.Use the concordant results to calculate the mean volume of acid required to neutralise the alkali.

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17
Q

why is it important to swirl the flask

A

It is important to swirl the conical flask as you add the acid from the burette in order to evenly distribute it, and ensure that the colour change occurs as soon as neutralisation takes place.

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18
Q

why is it important to use white tile

A

It’s also important that you place the conical flask on a white tile, so you can more easily see when the colour change takes place.

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19
Q

There are 3 different type of indicators (and their respective colour changes) you should know:

A

Litmus is red in acidic solutions and blue in alkaline solutions
Phenolphthalein is colourless in acidic solutions and pink in alkaline solutions
Methyl orange in red in acidic solutions and yellow in alkaline solutions

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20
Q

what definese a strong acid

A

that they ionise completely which mena all of the acid particles will dissociate to release hydrogen ions
while weak ions dont fully ionise and they are revrsible

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21
Q

whats the difference between concentrated and strong acid

A

strenght is measured in how much the acid dissociates
while concentration measured in how much acid there is in a certain volume more concentrated solutions contain more acid per unit of volume

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22
Q

pH scale and H+ ions relashionship

A

ph is a measurment of how much h+ ions there are in the solutions
as the concentration of ions gets higher the ph gets lowereach decreade of 1 on ph scale is 10 X of H+
ph 5 to 3 = x 100

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23
Q

ph of strong and weak acid in relations with in cocnentration

A

at any given concentrain a strong acid will always have a lower ph than a higher acid
because a higher proportion of h ions will be dissociated

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24
Q

metal oxyde/ hydroxide + acid =

A

salt + water

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25
Q

acid + metal carbonate =

A

salt + water + CO2

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26
Q

if we want to make a soluble base we…

A

react acid with and isoluble base
like metal oxide/hydroxide/carbonate

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27
Q

Choose the correct balanced equation for the reaction of sulphuric acid and sodium oxide:

A

H2SO4 + Na2O ➔ Na2SO4 + H2O

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28
Q

Choose the correct balanced equation for the reaction of sulphuric acid and sodium oxide:

A

H2SO4 + Na2O ➔ Na2SO4 + H2O

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29
Q

During a neutralisation reaction, the positive ___________
ions from the acid react with the negative __________ ions from the alkali to form molecules of water.

A

During a neutralisation reaction, the positive hydrogen ions from the acid react with the negative hydroxide ions from the alkali to form molecules of water.

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30
Q

sodium oxide (Na2O) and hydrochloric acid (HCl) what is the formula?

A

sodium chloride (NaCl).

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31
Q

How to obtain soluble salt crystals from an acid-base reaction
Part 1

A

Part 1 - Obtain a solution of the soluble salt that we want

  • Place dilute acid in a beaker and heat gently.
  • Add the solid base bit by bit until it stops reacting, which means it’s in excess.
  • Isolate the salt solution by filtering out the excess solid base using filter paper and a funnel.
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32
Q

How to obtain soluble salt crystals from an acid-base reaction
Part 2

A

Part 2 - Isolate the soluble salt crystals from the solution

  • Heat the salt solution gently in a water bath until crystals start to form.
  • Let the solution cool further, which will cause more crystals to precipitate.
  • Filter out the soluble salt crystals using filter paper and funnel.
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33
Q

metal + acid =

A

salt + hydrogen gas (H2)

34
Q

heat and reactivity

A

the most reactive metals produce the most heat

35
Q

how to make reactvity test fair?

A

1.Use the same type and concentration of acid
2. use the same weight and SA of metal

36
Q

metal + water

A

metal Hydroxide and H2

37
Q

what is a displacement reaction

A

more reactive metals can displace less reactive ones

38
Q

what is oxydation and an equation

A

x = x + e
the process of gaining oxygen
loss of electrons

39
Q

what is a reduction reaction

A

the loss of oxygen
but gain of elect
x + e = x

40
Q

OIL RIG (only in terms of electrons)

A

oxydation is loss
reduction is gain

41
Q

how can pure metals be extracted

A

Pure metals can be extracted from metal oxides using the element carbon.The carbon causes the metal to lose its oxygen, so the metal becomes reduced.
This produces CO2, and can only work for metals less reactive than carbon.

42
Q

Why do we find pure gold in the ground, but not pure iron?

A

Gold is unreactive, so doesn’t react with any other elements
Iron is reactive enough to react with oxygen so is oxidised to iron oxide

43
Q

what is redox reaction

A

it is a reaction where both oxydation and reduction happen

44
Q

when metals react with acid in terms of oilrig

A

When a metal reacts with an acid, a redox reaction takes place.The metal ions lose electrons, so we say they’ve been oxidised.The hydrogen ions from the acid gain electrons, so we say they’ve been reduced.

45
Q

what is a spectator

A

A spectator ion is an ion that doesn’t take part in the reaction and so keeps the same charge.

46
Q

what happens at anode and cathode (oil rig)

A

anode = oxidised
cathode = reuced

47
Q

An electrolysis cell has two electrodes. What is the name of the positive electrode?

A

anode

48
Q

In electrolysis, which direction do the electrons travel?

A

Anode ➔ Cathode

49
Q

The electrodes in an electrolysis cell are normally made of inert carbon. What does the term ‘inert’ mean?

A

It is unreactive, so will not take place in the reaction.

50
Q

In electrolysis, why does the compound you’re trying to separate need to be molten or dissolved?

A

So that the ions are free to move around (and go to their respective electrode)

51
Q

Which two of the following chemical processes are used to extract metals from their ores?

A

Reduction with carbon
Electrolysis

52
Q

Why is electrolysis not used to extract all metals?

A

Electrolysis is expensive because it requires a large amount of electricity

53
Q

In the electrolysis of aqueous solutions, what is the rule for determining which ion will be oxidised (lose electrons) at the anode (positive electrode)?

A

It will always be the OH-, unless there is a halide ion (such as Cl-, or Br-) present

54
Q

In the electrolysis of aqueous solutions, what is the rule for determining which ion will be reduced (gain electrons) at the cathode (negative electrode)?

A

It will always be the H+ ion, unless Cu2+ is present (another way of phrasing it would be that it is always the ion of the least reactive element)

55
Q

In the electrolysis of aqueous copper nitrate, Cu(NO3)2 (aq), which four ions would be present in the electrolyte?

A

Copper ions (Cu2+)

Nitrate ions (NO3-)

Hydrogen ions (H+)

Hydroxide ions (OH-)

56
Q

Please
Stop
Calling
me
Careless
Zebra
instead
try
learning
how
copper
saves
gold

A

Pottasium
Sodium
Calcium
Magnesium
Carbon
Zinc
Iron
Tin
Lead
Hydrogen
Copper
Silver
Gold

57
Q

metal oxides dissolve in water to make
Non- metal oxides dissolve in water to make

A
  1. an alkali solution
    2.An acidic solution
58
Q

whata are native metals

A

metals found under groud that are unreactive eg gold and silver

59
Q

What condition causes corrosian to happen and why is it bad for the metal

A

Corrosion is caused by chemical reactions between the metal and substance in the oxygen.
The product of corrosion can affect the strenght of metal as well as its apperance.In extreme cases it can destroy the metal

60
Q

iron + oxygen + water =

A

Hydrated(|||) iron oxide

61
Q

how to prevent rust

A

coating iron with:
paint
oil
plastic
grease
a less or more reactive metal
(zinc is usually used)

62
Q

what is an ore

A

if a rock contains enough metals to make it economic to extract, it is called ORE

63
Q

what are three things that can affect the value of a metal?

A
  • how scare it is
  • How useful it is
  • How easy it is to extract
64
Q

what are adv and dis of ph probe and universal indicator

A

universal:
+ Easy to use no
+ not very expensive
+ quick
- does not tell you the most
- accurate and detailed results

pH probe:
+ record pH very accuratly
-Very expensive
- Not easily avilable

65
Q

what is an ionic equation for neutrialisation

A

H+ + OH- = H2O

66
Q

acid + alkali =

A

salt + water

67
Q

acid + base

A

salt + water

68
Q

Acid + Metal Carbonate

A

Salt + Water + CO2

69
Q

1 limitation of electrolysis

A

It only works at ioninc compound but never at covalent compunds because they do not conduct electricity

70
Q

What is inert electrode, D.C. and electrolyte

A

Electrolyte - substance that conducts electricity
D.C. - charge only flows into one direction
Inert Electrode - made up of graphite, unreactive

71
Q

in the electrolysis of aluminium oxide what is reduced

A

Alummion ions are reduced because they gain electrons therefor the reduction takes place

72
Q

what are half equations for electrolysis of Al2O3

A

2O-2 = O2 + 4e
Al3- + 3e = Al

73
Q

what is a halide

A

a halogen ( (F), (Cl), (Br), (I), (At), (Ts).) is a halogen atom bearing learning negative charge

74
Q

what is a bauxite

A

is aluminium and oxide

75
Q

what do aluminiom is mixed with and why

A

with cryolite and it is done to amke sure that the meting point of aluminiom is lower

76
Q

what is a test for hydrogen

A

If you put a burning splintinto hydrogen, it gives a pop

77
Q

What is a test for chlorine

A

Chlorine will bleah damp blue litmus paper ( turn it white)

78
Q

what is a test for oxygen

A

Oxygen will religh a glowing splint

79
Q

what is sodium hydroxide test

A

it is a strong alkali so it will turn universal indicator blue

80
Q

why is electrolysis of aluminiom so expensive

A

replacing anode
electricity bills
cost of extracting
high meting point

Chemsitry (4 decks)

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