Science - Chemistry - Chemical Changes - C4 Flashcards
what is the PH scale ?
a scale that measures how acidic or alkaline a solution is
what numbers - do the PH scale go between ?
0 -14
what kind of solution has a PH of less than 7 ?
acid
the lower the PH, the what ?
the more acidic the solution
what kind of solution has a PH greater than 7 ?
alkali
the higher the PH, the what ?
the more alkaline the substance is
what is a neutral substance ?
a substance that isn’t acidic or alkaline
what is the PH of a neutral substance ?
7
give an example of a neutral substance ?
pure water
how do you test the PH of a solution ?
by using an indicator
what is an indicator ?
a dye that changes color depending on whether it’s above or below a certain PH
what is a universal indicator ?
an indicator which contains a mixture of dyes so it can gradually change color over a broad range of PH’s
what are universal indicators useful for ?
estimating the PH of a solution
give an example of a solution with the PH of 1, red/orange PH ?
- car battery acid
- stomach acid
give an example of a solution with the PH of 3, orange PH
- vinegar
- lemon juice
give an example of a solution with a PH 4 / orange
- normal rain
give an example of a solution with a PH 5 / orange, yellow
normal rain
what solution has a PH of 7 ?
pure rain
what solution has a PH 8 / blue
washing up liquid
what solution has a PH 11 / purple ?
soap powder
how does a PH probe work ?
the probe is placed in the solution you are measuring and the PH is given on digital display as a numerical value
what solution has a PH 9 / dark blue
pancreatic juice
what solution has a PH of 12 / purple ?
bleach
what solution has a PH of 14 / dark purple ?
caustic soda ( drain cleaner )
what is a PH probe ?
a probe which can measure PH electronically
which is more reliable :
- an indicator
- a PH probe
- PH probe
what type of ions do acids form when dissolved in water ?
hydrogen ions (H+)
show the neutralization reaction equation
acid + alkali - salt + water
what happens in a neutralization reaction ?
hydrogen ions from the acid react with hydroxide ions from the alkali to produce water
show the neutralization reaction in terms of ions ?
H+ + OH-1 - H20
what determines whether a substance is an acid or an alkali ?
the type of ions are released when the substance is dissolved in water
what type of ions do alkalis form when dissolved in water ?
hydroxide ions (OH-1)
what is a neutralization reaction ?
when an acid reacts with an alkali to form a salt and water
what is the PH of the product formed from a neutralization equation ?
7
what is titration ?
an experiment that lets you see what volume of a reactant is needed to react completely with a certain volume of another reactant
give an example of when you’d use titration
to find out exactly how much acid is needed to neutralize a certain quantity of alkali
what can the results of a titration experiment show you ?
the concentration of one of the reactants
what does the strength of the acid tell you ?
about the proportion of acid particles that will dissociate to produce H+ ions in solution
what happens when acids are added to an aqueous solution ?
they ionise to produce H+ ions
what do weak acids do in water ?
partially ionise in water, only some of the acid molecules will ionise and release H+ ions
what do strong acids do in water ?
ionise completely, all the acid particles dissociate to release H+ ions
give examples of a strong acids
- sulfuric acid
- hydrochloric acid
- nitric acid
give examples of weak acids
- carboxylic acid
- carbonic acid
why can’t you use universal indicator in a titration experiment ?
the colour change is too gradual
what type of indicators are good for titrations ?
- phenolphthalein
- methyl orange
- litmus
they only have one colour changing compound so will have one distinct colour change at a particular PH
give a hazard when doing the titration experiment
acids and alkalis are often corrosive so you need to wear safety goggles to protect your eyes whilst using them
what is the dissociation of acids ?
when acids are added to an aqueous solution they ionise to produce H+ ions
give an example of a disassociation of acids ?
hydrogen chloride dissolves in water to form hydrogen chloride ions - HCl - H+ + Cl-
if the concentration of H+ ions are higher, the rate of reaction will be ?
faster
why will strong acids be more reactive than a weak acid of the same concentration ?
strong acids dissaociate more than weak acids so a strong acid will be more reactive than a weak acid of the same concentration
what does the PH measure with H+ ions in a solution ?
the concentration
the lower the PH, the what the concentration of H+ ions ?
higher
why will the concentration of H+ ions be higher with a lower PH ?
it is more acidic
why will the PH of a strong acid be lower than the PH of a weak acid with the same concentration ?
strong acids dissociate more than weak acids resulting in a larger concentration of H+ ions
for every decrease of 1 on the PH scale, the concentration of H+ ions increases by a factor of what ?
10
how do you calculate the change in H+ concentration ?
factor H+ ion concentration changes by = 10 - x
x = difference in PH
what does acid strength tell you ?
what proportion of the acid molecules ionise in water
what does the concentration of an acid measure?
the number of dissolved acid molecules there are in a certain volume of water, how watered down your acid is
the larger the amount of acid in a certain volume the what ?
more concentrated the acid is
the PH will decrease with —– what acid concentration ?
increasing
what are bases ?
substances that react with acids in neutralisation reactions
why are soluble metal hydroxides alkalis ?
they dissolve in water to form OH- ions
what are the products of a neutralisation reaction ?
a salt and water
what is the word equation for metal oxides or metal hydroxides ?
acid + metal oxide/ metal hydroxide - salt + water
give an example of a neutralisation reaction ?
hyrdochloric acid + copper oxide - copper chloride + water
reactions with hydrochloric acids give what ?
chlorides
reactions with sulfuric acid gives what ?
sulfates
reactions with nitric acid gives what ?
nitrates
metal carbonates react with acids to make what?
a salt, carbon dioxide, and water
what is the general equation for the reaction of metal carbonates and acids ?
metal carbonate + acid - metal salt + carbon dioxide + water
how can soluble salts be made ?
by reacting an acid with a metal or an insoluble base
what is the reactivity series ?
a list of metals that are arranged in order of how reactive they are
what is the reactivity of a metal ?
how easily it forms positive ions
a metal which easily forms positive ions are what ?
more reactive
which element is at the top of the reactivity series ?
potassium
which element is at the bottom of the reactivity series ?
copper
which 2 non - metals are in the reactivity series ?
carbon and hydrogen
why are carbon and hydrogen in the reactivity series ?
so you can compare where metals are in relation to them
how do you get a reactivity series ( investigation) ?
compare the relative reactivity of different metals with an acid or water and put them in order from most to least reactive
the higher a metal is in a reactivity series, the what ?
the more easily the metal is reacted with the water or the acid
how else can you determine a metals reactivity ( other than reacting them with water/ an acid) ?
- measure the temperature change of the reaction with an acid or water over a set time period
if you use the same mass and surface area of metal each time, the more reactive the metal, the greater what ?
temperature change
what is the reaction between metals and acids ?
metals and acids react to form a salt and a hydrogen
what is the equation for metals reacting with acids ?
acid + metal - salt + hydrogen
how can you tell how reactive different metals are when reacting with an acid ?
monitoring the rate of hydrogen production
when reacting an acid and a metal, how is the speed of reaction shown ?
- ## the rate of bubbles of hydrogen that are given off
give examples of metals that react explosively with acids
- potassium
- sodium
- lithium
- calcium
give examples of metals which react slowly with acids ?
-iron
-magnesium
-zinc
what test can be used to show the production of hydrogen?
the burning splint test
what is the burning splint test ?
where you put a lit splint in the mouth of the tube containing the metal and the acid, if the hydrogen is present you will hear a squeaky pop
the more reactive the metal, and the more hydrogen produced, the louder the what ?
squeaky pop
give an example of an element which reacts vigorously with cold dilute acids ?
magnesium
give an example of a cold dilute acid
hydrochloric acid
what does the name of the salt formed when mixing metals and acids depend on ?
the salt part depends on the name of the metal, and the second part comes from the acid which is used
give an example of a salt formed when reacting metals and acids ?
hydrochloric acid + magnesium - magnesium chloride + hydrogen
what type of salts does hydrochloric acid always produce ?
chloride salts
what type of salt does sulfuric acid always produce ?
sulfate salts
give the equation a metal reacting with water
metal + water - metal hydroxide + hydrogen
will metals that aren’t reactive such as zinc react with water ?
no
what is a displacement reaction ?
where a more reactive metal pushes the less reactive metal out of its compound
which metal is unreactive, and found in the earth itself, rather than in a compound ?
gold
how do you extract metals from the ground that are part of a compound ?
extract the metal from metal ores which are mined from the ground
what is a metal ore ?
a rock which contains metal inside of it to make it profitable to extract the metal from it
what are most metal ores ?
an oxide of the metal
what is a reaction that forms a metal oxide from its metal known as ?
oxidation
what is oxidation ?
the gain of oxygen by an element or compound
what is a reaction that separates a metal from its oxide called ?
reduction
what is reduction ?
the loss of oxygen from a compound
a metal below carbon in the reactivity series can be what ?
extracted from its ore by reducing it in a reaction with carbon
how can carbon be used to extract metals ?
the ore is reduced as oxygen is removed from it and carbon gains oxygen so is oxidized - displacement reaction
why can only metals below carbon use it to extract them from their ores ?
as carbon can only tale the oxygen away from metals that are less reactive than itself
what do metals that are more reactive than carbon use to extract them from their ores ?
electrolysis
what is the disadvantage of electrolysis ?
- expensive
what is a redox reaction ?
where electrons are transferred between substances
give an example of a redox reaction ?
- oxidation is a loss of electrons
- reduction is a gain of electrons
why are oxidation and reduction redox reactions ?
they happen at the same time
how is a displacement reaction a redox reaction ?
the metal ion gains electrons and is reduced, the metal atom loses electrons and is oxidized
what do ionic equations show ?
the particles that react and the products they form
what do ionic equations for redox reactions only focus on ?
the substances which are oxidized or reduced
what are redox reactions in acids and metals like ?
metal atoms lose electrons, hydrogen ions gain them
what is electrolysis ?
the process of breaking down a substance using electricity
what is an electrolyte ?
a liquid required during electrolysis, needed to conduct electricity
what do electrolytes contain ?
free ions
what do free ions in the electrolyte do to help with electrolysis ?
conduct electricity
what is an electrode ?
a solid that conducts electricity and is submerged into an electrolyte
how does electrolysis work ?
the electrodes are placed into the electrolyte and ions move from one electrode to the other, which conducts electricity through the circuit. The positive electrolyte goes towards the cathode and gains electrons and the negative ions in the electrolyte goes towards the anode and loses electrons. As ions lose or gain electrons they become atoms or molecules and are released
what is a cathode ?
a negative electrode
which type of ions go to the cathode ?
positive ions
what is an anode ?
a positive electrode
which type of ions go to the anode ?
negative ions
where does reduction occur in electrolysis ?
at the negative electrode as the positive ions are gaining electrons
where does oxidation occur in electrolysis ?
at the positive electrode as negative ions are losing electrodes
what are binary compounds ?
ionic compounds containing 2 elements which are ions- a positive metal and a negative metal ions
what happens during electrolysis of the molten binary compounds ?
gives the neutral metal and the non-metal elements, the metal ions will move to the cathode and gain electrons to become neutral and the non-metal ions will move to the anode to lose electrons and become neutral
what are half equations ?
an equation showing the reactions at electrodes
what is used to extract metals from their ores if it is more reactive than carbon ?
electrolysis
what is the disadvantage of electrolysis ?
it is expensive, requires lots of energy to melt the ore and produce the current
what is the main ore of aluminium ?
bauxite
because aluminium has a very high melting point of over 2000 degrees c, melting it would be very expensive, what is done instead ?
aluminium oxide is dissolved in a molten cryolite, which brings the melting point to 900 degrees c, saving energy
what can electrodes be made out of ?
carbon
in electrolysis with aluminium, what ions attract to the negative electrode ( cathode ) ?
positive aluminium ions
what happens between the cathode and aluminium 3 ions in electrolysis ?
the a3+ ions pick up 3 electrons and become neutral aluminium atoms, and sink to the bottom of the tank
what happens to the oxygen atoms 02- during electrolysis in aluminium?
they attract to the anode
when attracted to the anode, what happens to the negative o2- ions during electrolysis with aluminium ?
they lose 2 electrons and the neutral oxygen atoms combine to form 02 molecules
why does the positive carbon electrode sometimes have to be replaced when oxygen attracts to it ?
the oxygen and carbon react, forming carbon dioxide, which eats away at the electrode
at a negative electrode, if metal ions and H+ ions are present, what will happen to the metal ions ?
they will stay in the solution if the metal is more reactive than hydrogen because the more reactive an element, the more likely it is to stay as ions - so hydrogen will be produced unless metal is less reactive than it
what will happen at the positive electrode if OH- and halide ions are present ?
molecules of chlorine, bromine or iodine will be formed
what would happen if no halide ions are present with OH- ions and a positive electrode ?
OH- ions are discharged and oxygen and water will be formed
what is the experiment carried out when investigating electrolysis of an aqueous solution ?
- get 2 inert electrons, clean their surfaces using emery paper
- place both electrodes into a beaker filled with your electrolyte and position them so they are inside inverted test tubes containing the aqueous solution
- connect electrodes to power supply
- collect gases formed during experiment in test tubes
what gases may be produced when doing electrolysis in an aqueous solution ?
- chlorine
- hydrogen
- oxygen
how do you test to see if chlorine was formed when doing electrolysis in an aqueous solution ?
- it bleaches damp litmus paper turning it white
how do you test to see if hydrogen was formed when doing electrolysis in an aqueous solution ?
- it makes a squeaky pop with a lit splint
how do you test to see if oxygen was formed when doing electrolysis in an aqueous solution ?
- will relight a glowing splint
