Topic 3 - Chemical Changes Flashcards
Aqueous Solutions
Something that has been dissolved in water
( can either be acid, alkaline or neutral )
PH scale
Mesures how acidic or alkaline something is
0 - 6 = Acid
7 = Neutral
8 - 14 = Alkaline
Indicators
Substances that change color depending on the PH
What are 3 common Universal Indicators?
Litmus, Methyl Orange and Phenolphthalein
What is the color range of Litmus in PH ?
Alkaline = blue
neutral = purple
Acidic = Red
What is the color range of methyl orange in PH?
Alkaline / = Yellow
Acid = Red
What is the color range of phenolphthalein in PH
Alkaline = Pink
Acid / Neutral = Colorless
Ion
An atom that has a net charge through loosing or gaining electrons
( metals always make a + ion)
Polyatomic Ions
Groups of atoms held together by covalent bonds, has a net charge.
What do acids do when in water? How does this cause their Ph?
They dissociate/ ionise - they form H+ ions in water. As the concentration of H+ ions increases, the Ph decreases
What is the formula for hydrochloric acid?
HCl
What is the formula for sulfuric acid?
H2SO4
What is the formula for nitric acid?
HNO3
What is the formula for sodium hydroxide
NaOH
What is the formula for Potassium hydroxide
KOH
What is the formula for Calcium hydroxide?
Ca(OH)2
How does Hydrochloric acid dissociate when in water?
HCL –> H+1 + Cl-4
How does Sulfuric acid dissociate when in water?
H2SO4 —-> H+2 + SO-2
How does nitric adis dissociate when in water?
HNO3 –> H+ + NO3 -
What do acids produce when dissociating in water?
Hydrogen ions
H+
What do alkalis produce when dissociating in water?
Hydroxide ions
OH-
What is Ph a mesure of ?
How many hydrogen ions are in a solution.
More H+ = Higher concentration = lower PH = More acidic
More hydroxide = more alkaline
hydrigen ions are equal to hydroxide ions = neutral PH
What is the Equation for concentration?
Con (g/dm3) = Amount dissolved / Volume of solution
what is the unit for concentration?
Grams per decimetre cubed or g/dm3
What is a dm3
cm3 times 1000
What difference is there between different PH?
x 10 or / 10
PH 6 x 10 = PH 7
Bases
substances that reacts with (neutralises) acids to form a salt and water only
What is the equation or bases and salts?
Metal oxide + acid —-> salt + water
Neutralisation
The chemical reaction in which a base is mixed with and acid to form a water and salt
How does an acid become neutal in neutralisation?
During neutalisation, hydrogen ions in the acid combine with oxide ions to form water. this removes the hydrogen and so the ph increases
How is a solution more acidic?
That solution will have a higher concentration of hydrogen ions
( as the concentration of H+ increases, the PH decreases)
What is a common base?
Metal Oxides ( they are basic/ alkaline)
What does acid strength tell you?
what proportion of the acid molecules ionise in water
more ionise = higher concentration of Hydrogen ions = lower PH
What are some strong acids?
Nitric, sulfuric, hydrochloric
What are some weak acids?
Carbonic, ethonic, boric
What do strong acids do in water?
They almost completeky ionise, a large proportion of the acid molecules dissociate to release h + ions
this cannot be reversed
What do weak acids do in water?
they do not fully ionise in solution, only a small proportion of the acid molecules dissociate to release H + ions
These dissociations can be reversed
What does concentration mesure?
How much acid there is in a litre of water ( how watered down your acid is)
What is an acid with a larger number of acid molecules compared to the volume of water called?
concentrated acid
what is the opposite of concentrate?
dilute
Why is extra base always added when prepping soluble salts?
to make sure all the acid is used up
Why is the extra reactant/ base always filtered out?
so you are left with just salt and water so you can have pure crystals
Why is the filtered solution in a soluble salts experiment alwats just salt and water?
through the base added to the acid in exess, then filtered out, we can make the solution fully neutalised, leaving only salt and water
what is effervesence?
Bubbles
metal + acid =
salt + hydrogen
metal oxide/ hydroxide + acid =
salt + water
how are soluble salts produced?
the reaction between an acid and an insoluble metal OXIDE
how are insoluble salts produced
the reaction between an acid and a metal HYDROXIDE
what is the ionic equation for neutralisation?
H+ + OH- = H20
How do you test for hydrogen
The squeaky pop text
take a lit splint and hold it over the test tube, if it pops, there is hydrogen
How to test dor carbon dioxide
Bubble it through limewater, it will turn the water cloudy
how to test for oxygen?
Glowing splint test
but a just burnt out match into the test tube, it is re lit if there is oxygen
How to test for chlorine
it turns litmus papar white
What are spectator ions?
the ions that dont change in the reaction
What are the spectator ions in
metal + acid -> salt + hydrogen?
the non H+ ions in the acid
e.g. Cl, N, S,O
WHat do half equations show?
what happens to the electrons
What happens in an oxidiation reaction?
a loss of electrons
What is reduction reaction?
a gain of electrons
What happens in electrolysis
The breaking down of a substance using electricity. An electric current is passed through an electrolyte, causing it to decompose
Oxidation or Reduction
What is an electrolyte
a molten or dissolved ionic compound
Cations
Positive ions
Anions
negative ions
ELECTOLYSIS
which Stick do the cations (+) move to?
The cathode (-)
They Gain electrons
REDUCED
ELECTROLYSIS
which Stick do the anions (-) move to?
The anode
They loose electrons
OXIDISED
What happens to the ions as they reach the anode/cathode?
As they gain/loose electrons they form uncharged substances and are dicharged from the electrolyte
Why cant an ionic solid be electrolysed?
The Ions are in fixed positions and cannot move, therefore cannot conduct electricity
Molten ionic substances can be electrolysed as the ions can move freely and conduct electricity
What are metal ions?
+ or -
+
What do positive metal ions do in electrolysis?
They are reduced to metal atoms at the cathode
What do negative ions do in electrolysis?
Oxidised to atom or molecules at the anode
What forms at the cathode when the electolysis is in SALT WATER
or aqueous solution
If there is gold, silver or copper that will be produced. IF not hydrogen
( if the metal is less reactive than hydrogen it will be produced)
What forms at the anode when the electolysis is in SALT WATER
or aqueous solution
if a halide is present the halogen will be produced
If not then its oxygen
What metals are less reactive than hydrogen?
gold, copper, platinum, silver
in order, what metals are more reactive than carbon?
K
Na
Ca
Mg
Al
C
What metals are more reacitve than H but less reactive than C? in order.
Zn
Fe
H
Metal carbonate + Acid ->
→ Salt + carbon dioxide + water
What is an alkalai?
A base that is soluble in water
Ph of more than 7 as they form OH- ions in water
WHat is the reaction between an acid and a base called?
Neutralisation
Acid + Base =
Salt + Water
What does the ionic equation look like for Neutralisation in Aqueous solution?
H+ + OH- = H20
What do strong acids do in water?
They Ionise completely in water- A large proportion of the acid molecules dissociate to release H+ ions.
e.g Sulfuric, Hydrochloric, nitric
Ph 0-2
what do weak acids do in water?
They dont fully ionise in solution - A small proportion of the acid molecules dissociate to release H+ ions.
e.g Ethanoic, citric, carbonic
Ph 2-6
How do the reactions of Strong and weak acids differ in reversibility?
Ionisation of weak acids is reversible -Sets up an equilibrium, lies well to the leftnsince only a few of the cid releases H+ ions
Acid + Metal oxide/Hydroxide =
Salt + Water
Acid + Metal =
Salt + Hydrogen
Acid + Metal Carbonate =
Salt + water + Carbon Dioxide
What will form in a reaction for an insoluble salt?
A precipitate
What will form for a reaction for a soluble salt?
Salt formed in solution
What common salts are soluble?
Soluble
1) Common salts of sodium, potassium, and ammonium
2) Nitrates
3) Common chlorides ( exept silver and lead chloride)
4) Common sulfates ( exept lead, barium, and calcium chloride)
What common salts are insoluble?
Insoluble
1) Common carbonates and hydroxides (Exept for sodium, potassium and ammonium ones)
What reaction takes place to make an insoluble salt?
Precipitation reactions
2x soluble salts (not all a correct pick) -> Insoluble salt
Insoluble salts
Lead nitrate + Sodium chloride ->
both soluble salts
Lead chloride + Sodium nitrate
Lead chloride is an insoluble salt and the sodium nitrate is solution
How are soluble salts made?
A reaction of an acid and an insoluble base
(Acid + Alkalai)
What is electrolysis?
the breaking down of a substance using electricity
What is the rule for oxidation and reduction?
OILRIG
What is an electrochemical cell
A circuit, made up of the anode, cathode, electrolyte, a power source and the wires that connect the two electrodes
How do you set up an electrochemical cell for electrolysis in solution?
1) Get two intert electrodes and clean their surfaces using some emery paper (sandpaper)
2) Dont touch the electrodes from that point - grease transfer nono
3) Place both electrodes in a beaker filled with your electrolyte
4) Connect the electrodes to a power supply using crocodile clips and wires. When you turn the power supply on, a current will flow through the cell
What can electrodes be made out of for them to be inert?
Graphite or platinum
How do you set up an electrochemical cell for electrolysis with a molten ionic substance?
1) Put your solid ionic substance ( which will become your electrolyte) in a crucible
2) Heat the crucible with a bunsen burner untill the solid is molten - do this in a fume cupboard to avoid releasing any toxic fumes into the room
3) Once the solids molten, dip two clean, inert electrodes into the electrolyte
4) Then, connect the electrodes to a power supply using wires and clips - you should get a current flowing through the cell once you turn it on
In molten electrolysis what is produced at each electrode?
Cathode
Metal ion (reduced) -> Metal
Anode
Negative ions (oxidised) -> Non-metal subtance (no charge)
