In depth Triple Chemistry (4)
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- Created by: HarveyCB
- Created on: 06-10-18 17:08
What is the pH scale
A measure of how acidic or alkaline a solution is
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What does the pH scale go up to
0-14
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What type of solution has a pH lower than 7
An acid
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What happens the lower down the pH scale you go
It gets more acidic
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What type of solution has a pH higher than 7
An alkali
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What happens the higher up the pH scale you go
It gets more alkaline
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Why type of solution has a pH of 7
A neutral solution
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Give an example of a neutral solution
Pure water
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What is one way to test pH
Using an indicator
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What is an indicator
A dye that changes colour depending on whether its above or below a certain pH
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What do some indicators contain
A mixture of dyes, so they gradually change colour over a range of pHs
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What do you call an indicator that contains multiple dyes
Wide range indicators
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Give an example of a wide range indicator
Universal indicator
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What colour does neutral show as using universal indicator
Green
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What colour do acids show as using universal indicator
Yellow to red (red being very acidic)
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What colour do alkalis show as using universal indicator
Blue to violet (violet being very alkaline)
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List some examples of acids, from least to most acidic
Normal rain, acid rain, vinegar and lemon juice, and car battery acid and stomach acid
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List some examples of alkalis, from least to most alkaline
Washing up liquid, pancreatic juice, soap powder, bleach, and caustic soda (drain cleaner)
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What is another method of testing pH
By using a pH probe attached to pH meter
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Why is it better to use a pH probe and meter
It gives the pH as a numerical value, and is therefore more accurate than indicator
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Whether a substance is acid or alkali depends on what
The type of ions that are released when the substance is dissolved in water
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What ions do acids form when dissolved in water
H+ (hydrogen)
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What ions do alkalis form when dissolved in water
OH- (hydroxide)
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Acid + alkali --> ?
Salt + water
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What do you call a reaction between an acid and an alkali
A neutralisation reaction
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How would you write a neutralisation reaction in terms of H+ and OH- ions
H+ (aq) + OH- (aq) --> H2O (l)
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What is a titration
An experiment that let's you see what volume of a reactant is needed to react completely with another reactant
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How can we use titration
To found out how much acid is needed to neutralise a certain quantity of alkali (or vice versa)
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Why does it matter what indicator you use in titration
It can affect the accuracy of your results
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Evaluate universal indicator for titration
It can turn a wide range of colours, which is helpful when estimating pH, but for titration you want an indicator that gives a definite colour change so you know the exact point where the acid is neutralised
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What are three good indicators for titration
Phenolphthalein, methyl orange and litmus (these are all single indicators)
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What are single indicators
Indicators that only contain one colour changing compound, so they change only at a specific pH
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Describe phenolphthalein
It is pink in alkalis, but colourless in acids, so if you're adding acid to an alkali the end point is when the solution turns clear
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Describe methyl orange
It is yellow in alkalis, but red in acids, so if you're adding acid to an alkali the end point is when the solution turns red
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Describe litmus
Litmus is blue in alkalis, but red in acids, so if you're adding acid to an alkali the end point is when the solution turns red
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What would the end point be if you were adding an alkali to an acid
For each indicator the colour change would be reversed
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What are the main hazards in titration
The acid and the alkali
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What happens when acids are added to an aqueous solution
They ionise to produce H+ ions
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What does the strength of an acid tell you
The proportion of acid particles that will dissociate to produce H+ ions in a solution
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What happens when strong acids are dissolved in water
All the acid particles dissociate completely to form H+ ions
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Give an example of some strong acids
Sulfuric acid and hydrochloric acid
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What happens when weak acids are dissolved in water
Only some of the acid particles dissociate to form H+ ions
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Give some examples of some weak acids
Citric and carbonate acids
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What type of reaction is the ionization of weak acids
A reversible reaction. Since only a few of the particles dissociate, the position of the equilibrium lies well to the left
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How does acid strength affect reactivity
If the concentration of H+ ions is higher, the rate of reaction will be faster. Since strong acids dissociate more than weak acids, a strong acids will more more reactive than a weak acid of the same concentration
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What is pH a measure of
The concentration of H+ ions in a solution. Lower pH= higher H+ concentration= stronger acid
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Why will a strong acid have a lower pH than a weak acid at the same concentration
The strong acid dissociates more than the weak acid resulting in a larger H+ concentration
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What happens to the concentration of H+ ions with every decrease of 1 on the pH scale
The concentration increases by a factor of 10
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How can you calculate the change in H+ concentration
The factor that the H+ ion concentration changes by= 10 to the power of -x (x being the difference in pH)
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How are acid concentration and strength different
Concentration is how much of the acid there is in a volume of water, strength what proportion of the acid molecules ionise in water
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What are bases
Substances that react with acids in neutralisation reactions
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What are two types of base
Metal oxide and metal hydroxide
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What kind of base is an alkali
Metal hydroxides because they dissolve in water to form OH- ions
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What is the equation for an acid reacting with metal oxide or metal hydroxide
Acid + metal oxide/hydroxide --> salt + water
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What types of acids give what salts
Hydrochloric gives chlorides, sulfuric gives sulphates, and nitric gives nitrates
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What is another type of base
Metal carbonates
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What is the equation for an acid reacting with a metal carbonate
Acid + metal carbonate --> metal salt + carbon dioxide + water
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How do you make soluble salts
By reacting an acid with a metal or insoluble base (such as metal oxide/hydroxide/carbonate)
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What is the reactivity series
A list of metals that are arranged in order of how reactive they are, with the most reactive at the top, and the least reactive at the bottom
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What is the reactivity of a metal derived from
How easily if forms positive ions (loses electrons). A metal which easily forms positive ions is more reactive
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Which two non metals are often included in the reactivity series and why
Carbon and hydrogen, so you can compare where the metals are in relations to them
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List the reactivity series from most to least reactive
Potassium, sodium, lithium, calcium, magnesium, carbon, zinc, iron, hydrogen and copper
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What is the equation for a metal reacting with an acid
Acid + metal --> salt + hydrogen
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How can you test metals reactivity with acid
By observing the amount of bubbles produced, and using the squeaky pop test to test for hydrogen
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What is the squeaky pop test
You put a lit splint at the mouth of the tube containing metal and acid. If hydrogen is present, you will hear a squeaky pop. The more hydrogen, the louder the pop
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How else can you test a metals reactivity
By reacting it with water, the more vigorous the reaction, the more reactive the metal
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What is the equation for a metal reacting with water
Metal + water --> metal hydroxide + hydrogen
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What is a displacement reaction
When one metal replaces another one out of a compound
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What is the rule for displacement reactions
A more reactive metal will displace a less reactive metal from its compound
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Unreactive metals are found in the Earth as a pure metal, but how are the others found
In a compound called metal ores
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What are most metal ores
Oxides
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How do we get the metal from an ore
Extraction
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What is the reaction that forms a metal oxide from its metal
Oxidation, which is the gain of oxygen, or the loss of electrons from a compound
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What is the reaction that separates a metal from its metal oxide
Reduction, which is the loss of oxygen, or the gain of electrons from a compound
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What type of reduction do we use to extract metals
Electrolysis and reduction by carbon
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When can we use reduction by carbon
When the metal is less reactive than carbon, so it is displaced, and the carbon becomes oxidised (CO2)
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When do we use electrolysis
When the metal is more reactive than carbon
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Why don't we use electrolysis for everything
Because its expensive
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What is a redox reaction
A reaction when electrons are transferred between substances (REDuction and OXidation)
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Why do we use the term redox
Because both reduction and oxidation are happening at the same time
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What are displacement reactions a type of
Redox reactions
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What always happens in a displacement reaction
The metal ion gains electrons and is reduced, the metal atom loses electrons and is oxidised
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What are ionic equations
Equations that show ionic compounds and an ions charge
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What do we do when writing an ionic equation for a redox reaction
We don't include the ions that don't change (the ions that are in both the reactant and product compound)
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What type of reaction is that between an acid and a metal
Redox, as the metal loses electrons (oxidised), and the hydrogen ions gain them (reduced)
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What is electrolysis
If you pass an electric current through an ionic substance that is molten or dissolved, the ions will move towards to electrodes, where they can react, causing the ionic substance to decompose
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What do we call the liquid involved in electrolysis
The electrolyte
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What do electrolytes contain
Free ions, which conduct electricity and allow the whole thing to work
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What is an electrode
A solid that conducts electricity and is submerged in the electrolyte
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What do you call the negative electrode
The cathode
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What do you call the positive electrode
The anode
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What is a common material to make the electrodes out of
Carbon (graphite)
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How does electrolysis work
A current is run through the electrodes and electrolyte. Positive ions move to the cathode and gain electrons, and negative ions move to the anode and lose electrons. As the ions gain or lose electrons they become atoms or molecules and are released
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What does electrolysis always involve
An oxidation and reduction reaction. Reduction occurs at the cathode and oxidation occurs at the anode
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What are binary compounds
Ionic compounds containing two elements which are ions, a positive metal ion and a negative non metal ion
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What does electrolysis of molten binary compounds give
The neutral metal and non metal ions
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What are half equations
The equations for what happens at each electrode
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How do you write a half equation for the negative electrode
Write the symbol for the positive ion on the left hand side, and the symbol for the neutral atom or molecules on the right. Balance the equation by balancing the number of atoms, and then by adding or subtracting electrons (shown as e-1)
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How do you write a half equation for the positive electrode
Write the symbol for the negative ion on the left hand side, and the symbol for the neutral atom or molecules on the right. Balance the equation by balancing the number of atoms, and then by adding or subtracting electrons (shown as e-1)
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How do we extract metals from a metal ore using electrolysis
By melting the metal ore, which requires a lot of energy so it's very expensive
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Why is electrolysis different in molten and aqueous solutions
In aquaous solutions there are H+ and OH- ions as well as those present in the metal compound
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How do we predict the products of electrolysis of aqueous solutions at the negative electrode
If the metal is more reactive than hydrogen, hydrogen is produced. If the metal is less reactive, the metal is produced
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How do we predict the products of electrolysis of aqueous solutions at the positive electrode
If halide ions are present (halogens), they are produced. If not, then the OH- ions are discharged and oxygen and water is produced
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How can you test the products of electrolysis with an aqueous solution
Squeaky pop test for hydrogen, seeing if chlorine gas is present to bleach damp litmus paper, and oxygen will light a glowing splint
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Other cards in this set
Card 2
Front
What does the pH scale go up to
Back
0-14
Card 3
Front
What type of solution has a pH lower than 7
Back
Card 4
Front
What happens the lower down the pH scale you go
Back
Card 5
Front
What type of solution has a pH higher than 7
Back
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