chemical changes (seneca) Flashcards
Acids are substances that —– when they dissolve in water (aqueous solutions).
form hydrogen (H+) ions
Acids are substances that form hydrogen (H+) ions when they …
dissolve in water (aqueous solutions).
Alkalis are substances that form —— when they dissolve in water (aqueous solutions).
hydroxide (OH-) ions
Alkalis are substances that form hydroxide (OH-) ions when
they dissolve in water (aqueous solutions)
The pH scale is used to measure …
how acidic or alkaline a substance is.
Acids and alkalis are on the opposite ends of the ——. They combine to form —— , which is…
pH scale
water
neutral.
hydrogen ion+hydroxide ion=
water
——- ion+——- ion=water
hydrogen
hydroxide
An oxidation reaction involves gaining …
oxygen
Oxidation reactions can also involve losing…
electrons.
When metals react with oxygen, …
metal oxides are produced
A reduction reaction involves losing…
oxygen
A reduction reaction involves ——oxygen
losing
Oxidation reactions can also involve —- electrons.
losing
when metal oxides lose oxygen,
they return to their atomic form
A mnemonic (memory aid) for remembering what happens to electrons during oxidation and reduction reactions is
OIL RIG
Metals reacting with oxygen to form metal oxides is an example of
an oxidation reaction
When reacting with other substances, metal atoms always form …
positive ions.
The reactivity of a metal is linked to …
how easy it is for a metal to form its positive ion.
highly unreactive metals are found in …
the Earth’s crust as pure metals.
highly unreactive,pure metals that are found in the Earth’s crust are also called
native metals.
A metal can only displace another metal from a compound if
it is located above it in the reactivity series.
1 reactive substances can displace (replace) 2 reactive substances from compounds.
1.More
2.less
what does spectator ions mean?
ions that are unchanged in the reaction
Potassium, sodium and lithium all react quickly with cold water to produce
a metal hydroxide and hydrogen gas.
Potassium, sodium and lithium all react quickly with ——– to produce a metal hydroxide and hydrogen gas.
cold water
Potassium reacting with cold water is the 1. so reacts 2.The hydrogen produced 3. and the metal also sets alight, sparking and burning with a 4.
1.most reactive
2.very quickly
3.ignites instantly
4.lilac flame.
Sodium, when reacting with cold water, 1. and 2. that 3.
1.fizzes rapidly
2.melts to form a ball
3.moves around on the water surface.
Lithium,when reacting with cold water, 1. and 2., becoming 3.
1.fizzes steadily
2. floats
3.smaller until it eventually disappears.
The metals that react with dilute acids but not cold water are…
magnesium, aluminium, zinc, iron and lead (iron and lead react slowly).
Metals don’t have to be —— to react with dilute acids.
that reactive
The only metals that aren’t reactive enough,to react with dilute acids, are …
copper, silver, gold and platinum.
Most metals react with dilute acids to give…
a salt (e.g. aluminium chloride) and hydrogen gas.
Reducing a metal with carbon will result in the …
extraction of the metal if the metal is lower in the reactivity series than carbon.
Most metals are only found as 1. because the metal has 2. Because of this,3…
1.compounds
2.reacted with other elements in the past
3. the metal has to be extracted from the ore (rock) where the metal compound is found.
In the reduction, the metal oxide —– oxygen to form a pure metal.
loses
Reduction with carbon normally involves 1, which is often used in the form of 2.
1.heating the metal oxide in the presence of the carbon
2.coal
Carbon is used in reduction because it is…
cheap and abundant
What form is carbon often used in when reducing metal oxides?
Coal
Potassium down to aluminium are more reactive than carbon and so …
cannot be extracted by reduction with carbon.
Silver, gold and platinum are either found as ——— or can be …
natural elements
simply extracted by heating directly in air
The remaining metals - zinc, iron, and copper - are all commonly extracted by …
reduction with carbon.
What are the metals that react with dilute acids but not cold water?
lead
aluminium
iron
magnesium
zinc
In a reduction reaction with carbon, a metal oxide loses —– to form a pure metal.
oxygen
Reducing a metal with carbon will result in the extraction of the metal if the metal is ——- in the reactivity series.
lower
what metals that can’t react with dilute acids?
-platinum
-copper
-silver
-gold
When zinc is reacted with calcium carbonate, no reaction occurs. Explain why.
Zinc does not react with calcium carbonate because zinc is not as reactive as calcium.
Metal + Acid ->
Salt + Hydrogen
what is the chemical formula of calcium
Ca 2+
what is the chemical formula of carbonate
CO3 2-
what is the chemical formula of sodium
Na +
what is the chemical formula of bromide
Br -
what is the chemical formula of sulfate
SO4 2-
what is the chemical formula of chloride
Cl-
what is the chemical formula of hydrochloride acid?
HCl
Redox reactions involve …
a reduction reaction (one reactant gains electrons) and an oxidation reaction (one reactant loses electrons).
Spectator ions are not present in the …
ionic equations
what is the acronym for what happens during oxidation and reduction reactions?
Oxidation
Is
Loss (of electrons)
Reduction
Is
Gain (of electrons)
Reactions that involve both a reduction and oxidation are called …
redox reactions
Acids can be neutralised by …
reacting with bases (an alkali is a base that dissolves in water)
Metal carbonates, metal oxides and metal hydroxides are all examples of …
bases.
—————————— are all examples of bases.
Metal carbonates, metal oxides and metal hydroxides
Acid + carbonate →
salt + water + carbon dioxide
Acid + hydroxide →
salt + water
Acid + metal oxide →
salt + water
magnesium carbonate+nitric acid→
magnesium nitrate+carbon dioxide+water
When acids are neutralised by metal carbonates, what is formed?
salt + water + carbon dioxide
when the acid Hydrochloric acid becomes a salt it becomes
Chloride
when the acid nitric acid becomes a salt it becomes
nitrate
when the acid sulfuric acid becomes a salt it becomes
sulfate
What is the name given to ions that remain unchanged during redox reactions, and aren’t included in the ionic equation?
Spectator ions
Soluble salts are …
salts which dissolve in water.
We can produce soluble salts through a reaction between …
acids and solid, insoluble substances
such as pure metals, metal oxides, metal hydroxides, or metal carbonates.
What must be reacted together to produce a soluble salt?
- Solid, insoluble substance
- acid
what is a word that means ‘does not dissolve in water’
insoluble
what is a word that means ‘dissolves in water’
soluble
The aim of Required Practical - Separating Mixtures is to produce …
a pure, dry sample of a soluble salt from an insoluble oxide or carbonate.
what does preparation entail for Required Practical - Separating Mixtures
Use a Bunsen burner to gently warm the acid.
Add the insoluble solid (with stirring) until the reaction no longer happens.
what does filtration entail for Required Practical - Separating Mixtures
Filter the solution to remove the excess insoluble solid.
This will leave a solution of the salt dissolved in water.
what does crystallisation entail for Required Practical - Separating Mixtures
-Heat the solution in an evaporating basin above a beaker of water.
-The ‘water bath’ ensures gentle heating.
-Let the solution cool and allow more water to evaporate.
-As water evaporates, the solution will become more concentrated and the salt will begin to crystallise.
Crystallisation separates a …
dissolved solid (the solute) from a liquid (the solvent)
what method do you use to separate a mixture of insoluble solid and liquid?
filtration
what method do you use to separate a Mixture of soluble solid and liquid (solution)
crystallisation
what method do you use to separate a Mixture of liquids
-Simple distillation
-Fractional distillation
what method do you use to separate a Mixture of dissolved solids
Chromatography
Double displacement reactions are
reactions in which two chemical substances react by exchanging ions to produce two new molecules.
what are the steps for crystallisation
1.Heat the solution in an evaporating basin above a bunsen burner.
2.The ‘water bath’ ensures gentle heating.
3.Leave the solution to cool and allow more water to evaporate.
4.As water evaporates, the solution will become more concentrated and the salt will begin to crystallise.
The acidity or alkalinity of a solution is measured using the —–, which ranges from 0 to 14.
pH scale
The acidity or alkalinity of a solution is measured using the pH scale, which ranges from …
0 to 14.
pH of exactly 7 is a
neutral
pH less than 7 is a …
acid
Strong acids have a pH close to …
0
Acids form —— when they dissolve in water.
hydrogen (H+) ions
Acids form hydrogen (H+) ions when they …
dissolve in water.
pH more than 7 is a …
alkali
Strong alkalis have a pH close to …
14.
Alkalis form hydroxide (OH-) ions when they …
dissolve in water.
Alkalis form —— when they dissolve in water.
hydroxide (OH-) ions
whats an example of an acid?
acid rain
whats an example of a neutral?
pure water
whats an example of an alkaline?
washing-up liquid
Universal indicator changes to a particular …
colour depending on the pH of a solution.
A pH probe returns a —– that represents the pH of a solution.
number
The numerical pH scale is a measure of the …
For every increase of - in pH, the ——— gets …
concentration of H+ ions in a solution.
1
concentration of H+ ions
divided by 10:
At pH 0, the concentration of H+ ions is
1 mol/dm3.
At pH 1, the concentration of H+ ions is
0.1 mol/dm3.
At pH 2, the concentration of H+ ions is
0.01 mol/dm3.
Increase pH by 1 →
divide H+ concentration by 10
Red cabbage contains a chemical called …
anthocyanin.
Red cabbage act as …
natural litmus paper.
Red cabbage molecules change ——- in acidic or alkaline conditions and this changes…
shape
the molecules’ colour.
A neutralisation reaction happens when …
an alkali is reacted with an acid
The 1 from the acid combine with 2 from the alkali to give 3.
1.hydrogen ions
2.hydroxide ions
3.water
A ———- reaction happens when an acid reacts with an alkali
neutralisation
Titration is a technique that measures …
the volumes of acid and alkali solutions that are needed in a neutralisation reaction.
If, for example, we were neutralising an alkali with an acid, titration could be used to calculate the concentration of the alkali if we knew:
1.The concentration of the acid to be added.
2.The volume of the alkali.
Indicators show the end point of titrations by…
suddenly changing colour when the solution turns from acidic to alkaline, or alkaline to acidic.
When choosing an indicator, the strength of the acid and alkali must be considered.
If both the acid and alkali are strong, suitable indicators would be:
Methyl orange (yellow in alkali → red in acid).
Phenolphthalein (pink in alkali → colourless in acid).
in a titration, we gradually add the acid to the alkali until the …
indicator changes colour
All acids ionise (become ions) in …
aqueous solutions
All acids ——– in aqueous solutions
ionise (become ions)
The strength of an acid is determined by…
how much it ionises in water.
Strong acids fully ionise in water, meaning that …
all of the acid molecules break up to form H+ ions.
give three examples of strong acids
hydrochloric acid
Sulfuric acid
nitric acid
when ionising in hydrochloric acid (strong acid) produce the equation
HCl →
H+ + Cl-
Weak acids 1 ionise in water, meaning that …
1.only partially
not all of the acid molecules break up to form H+ ions.
when ionising in water ethanoic acid (weak acids) produce the equation
CH3COOH ⇌
CH3COO- + H+
——– are weak acids.
Most acids
what colour does the indicator phenolphthalein?
pink
What ions are formed when acids ionise?
H+
When ionic compounds are melted or dissolved in water,
the ions (charged particles that have gained/lost electrons) are free to move around, and the liquid/solution will conduct electricity.
Ionic compounds that dissolve in water to make a solution that conducts electricity are called …
electrolytes.
what are electrolytes?
Ionic compounds that dissolve in water to make a solution that conducts electricity
When a voltage (direct current) is applied across an electrolyte, …
the charged ions are attracted to the electrode with the opposite charge to the ion.
Positively charged ions are attracted to …
the negative electrode (cathode).
Negatively charged ions are attracted to …
the positive electrode (anode).
another name for a positive electrode is…
anode
another name for a negative electrode is…
cathode
When an ion touches an electrode,
electrons can be transferred, producing elements.
If copper ions (Cu2+) are in a solution and a voltage is applied,——-
When they touch the cathode, each Cu2+ ion will …
they’ll move to the cathode (negative electrode)
gain 2 electrons and form a copper metal.
What happens when ionic compounds are dissolved in water?
The charged ions become free to move
The liquid/solution will conduct electricity
Since non-metals ions are —— (anions), they will be —— to the ————(anode), …….
negative
attracted
positive electrode
where the non-metal (element) will form
Since metals ions are —– (cations), they will be —— to the —–(cathode), …
positive
attracted
negative electrode
where the metal (element) will form
the metal and non-metal ions within the molten ionic compound become …
free to move so the liquid can undergo electrolysis
Positive metal ions are called cations. They are always attracted to the …
cathode
Positive metal ions (cations) are attracted to …
negative electrode (cathode)
Negative non-metal ions (anions) are attracted to …
positive electrode (anode)
Electrolysis is the process that
splits ionic compounds into the different elements that they are made of.
Electrolysis happens using a solution that …
conducts electricity.
Electrolysis is used to …
extract reactive metals from molten ores (melted materials containing metals)
Electrolysis is used to …
extract metals such as aluminium, which are higher in the reactivity series than carbon.
What happens at the anode? (Extracting Metals)
Oxygen forms at the carbon anode. The carbon and oxygen react to give carbon dioxide.
The anode is usually made of carbon because it is a good conductor and is cheap.
(Extracting Metals)Oxygen forms at the 1. The carbon and oxygen react to give 2.
1.carbon anode
2.carbon dioxide.
What happens at the cathode? (Extracting Metals)
The element is formed at the cathode.
The anode is usually made of carbon because it is a 1. and is 2.
1.good conductor
2.cheap
Electrolysis is a process in which
electrical energy, from a direct current (dc) supply, breaks down electrolytes
What are the disadvantages of electrolysis?
-Lots of energy is needed to:
Melt the solid ionic compound to allow the ions to flow.
Produce the electrical current.
-expensive
Electrolysis is used to extract reactive
1. from 2.
metals
molten ores
how would you extract a metal that is less reactive than carbon and less reactive than copper
Found as natural element
Heat directly in air
how would you extract a metal that is less reactive than carbon and more reactive than copper
Reduction with carbon
how would you extract a metal that is More reactive than carbon
Electrolysis
Which ions are attracted to which electrode?
cations -> cathode
anions-> anode
When a 1 is applied across an electrolyte, the charged ions are attracted to the oppositely charged 2.
- voltage
2.electrode
What aspects of using electrolysis to extract metals require lots of energy?
-providing the electrical current
-melting the solid ionic compound
2 ——- are submerged in an electrolyte, and a …
electrodes
voltage is applied across the electrodes using a power supply.
Electrolysis requires large amounts of —- to melt the solid ionic compound and to provide the —–
energy
electrical current
The products of the electrolysis of aqueous solutions are difficult to predict because …
the water molecules in the solution split up to give hydrogen (H+) and hydroxide (OH-) ions.
What is formed at the cathode depends on the —— of the metal
reactivity
At the cathode (negative electrode) (electrolysis of aqueous Solutions), ——- is produced if the metal is higher than hydrogen in the reactivity series.
hydrogen
At the cathode (negative electrode) (electrolysis of aqueous Solutions), ——- is produced if the metal is lower than hydrogen in the reactivity series.
the metal
At the anode (positive electrode) ,(electrolysis of aqueous Solutions),If there are halide ions present, …
the respective halogen forms.
What is formed at the anode depends on if there are …
halide ions present
At the anode (positive electrode) ,(electrolysis of aqueous Solutions), if there are no halide ions, …
oxygen forms
An aqueous solution of copper(II) sulfate (CuSO4) contains Cu2+, SO42-, H+ and OH- ions. What happens when it is electrolysed?
At the anode, oxygen is produced as there are no halide ions present:
4OH- → O2 + 2H2O + 4e-
At the cathode, copper is produced as it is lower in the reactivity series than hydrogen:
Cu2+ + 2e- → Cu
During electrolysis, different reactions take place …
at the different electrodes
The reactions that happen at each electrode can be shown using …
half equations
At the cathode (negative electrode), —– reactions happen i.e. …
Reduction
positively charged ions gain electrons
At the anode (positive electrode), —— reactions happen i.e. …
oxidation
negatively charged ions lose electrons
Half equations are …
equations that show one-half of a redox reaction.
A redox reaction is a reaction in which …
both oxidation and reduction occur
2Br − →Br 2+2e −
In the electrolysis of lead bromide, …
bromide ions are oxidised at the anode to give bromine and electrons.
at the anode, ——– reactions takes place
oxidation
at the cathode, ——- reactions takes place
reduction
In the electrolysis of aqueous solutions, what products can form at the anode?
Oxygen gas
A halogen
the product formed at the anode depends on on wether there’s
a halide ions present or absent
the product formed at the cathode depends on whether the metal involved is
more reactive or less reactive than hydrogen
What region of the pH scale would a substance that forms H+ be on?
red 1 or 2
Which substances would be in the purple region of the pH scale?
bases
alkali
what characteristic makes a metal react easily
a metal that produces a positive ion more easily
Give 2 reasons why carbon is used to extract metals from their oxides
Carbon is cheap
Carbon is abundant
not all acids break up to realease…
H+
