chemical changes Flashcards
What does the pH scale go from?
0 to 14
If the pH is less than seven, what is the substance?
An acid
Acids form what ion in water?
H+
As the concentration of hydrogen irons increase does the pH decrease or increase?
In decrease
What is a base?
A substance that reacts with an acid to produce salt and water
What is an alkaline?
Base that is soluble in water
What ions alkalis form?
OH-
In alkaline solutions, the higher the concentration of OH- ions, does the pH increase or decrease?
Increase
What is an indicator?
A dye that changes colour depending on whether it’s above or below a certain pH
What are some examples of indicators?
Litmus, methyl orange, phenolphthalein
What is litmus in acidic solutions neutral solutions and alkaline solutions?
Acidic - red
Neutral - purple
Alkaline - blue
What is methyl orange in acidic solutions neutral solutions and alkaline solutions?
Acidic - red
Neutral and alkaline - yellow
What is phenolphthalein in acidic solutions neutral solutions and alkaline solutions?
Acidic and neutral - colourless
Alkaline - pink
Acids and bases do what?
Neutralise each other
What does a neutralisation reaction produce?
Salt and water
When an acid neutralises a base, the product are neutral, they have a pH of seven, the concentration of hydrogen ions is what to the concentration of hydroxide ions?
Equal
How was your carry out a neutralisation reaction between calcium oxide (a base) and a dilute hydrochloric acid?
Start by measuring out a set volume of dilute hydrochloric acid into a conical flask use a prepare or measuring cylinder for this
Measure out fix mass of calcium oxide using a mass balance
Add the calcium oxide to the hydrochloric acid
Wait for the base to completely react then record the pH of the solution using either a pH probe or universal indicator paper
Repeat until all the acid has reacted - you’ll know when you’ve reached this point when you get unreacted calcium oxide sitting at the bottom of the flask
You can then photograph to see how pH changes within the mass of the base added
Explain how water is produced in a neutralisation reaction
The H+ ions from the acid react with the OH- irons from the alkalis form water
Acids produce hydrogen ions in what?
Water
What does it mean to ionise an acid?
Acids splitting up to produce a hydrogen ion, H+, and another ion
Do strong acids completely ionise in water?
Yeah
Large proportion of acid molecules ionise to release H+ ions
Tend to have low pH (0-2)
Do weak acids fully ionise in water?
No
Small proportion of the acid molecules ionise to release H+ ions
pH tend to be around 2-6
Ionisation of weak acids are what reaction
Reversible
Key points about concentrated acids
Concentration measures how much acid that is in a litre of water
An acid with a large number of acid molecules compared to the volume of water is said to be concentrated. an acid with a small number of acid molecules compared to the volume of waters had to be dilute
Describes the total number of dissolved acid molecules
The more grams of acid per DM3 the more concentrated the acid is
If the concentration of H plus irons increases by factor of 10, what does the pH decreased by?
1
If the H plus iron concentration increases by factor of 100, what is the pH decreased by ?
2
If you decrease the H plus iron concentration by factor of 10, what would the pH be increased by?
1
A solution with a hydrogen iron concentration of 0.001 mole/dm has a pH of four. What would happen to the pH if you increase the hydrogen ion concentration to 0.01 mol/DM3?
The H plus concentration has increased by a factor of 10 so the pH would decreased by one.
So the new pH would be 4 - 1 = 3
When do salts form?
Acids reacting with bases
What does an acid and metal oxide form
Salt and water
Give examples of acid + metal oxide - salt + water
2HCl + CuO - CuCl2 + H2O (copper chloride)
H2SO4 + ZnO - ZnSO4 + H2O (zinc sulfate)
What does an acid and metal hydroxide form?
Salt and water
Give examples of acid + metal hydroxide - salt + water
HCl + NaOH - NaCl + H2O (sodium chloride)
H2SO4 + Zn(OH)2 - ZnSO4 + 2H2O (zinc sulfate)
What does an acid and metal form
Salt and hydrogen
What are examples of acid + metal - salt + hydrogen
2HCl + Mg - Mg l2 + H2 (magnesium chloride)
H2SO4 + Mg - MgSO4 + h2 (magnesium sulfate)
How do you test for hydrogen?
Squeaky pop test
What does an acid and metal carbonate form?
Salt and water and carbon dioxide
What are some examples of acid + metal carbonate - salt + water + carbon dioxide
2HCl + Na2CO3 - 2NaCl + H2O + CO2 (sodium chloride)
How can you test for a carbon dioxide?
Bubble gas through lime water
If the gas is carbon dioxide the limewater return cloudy
Are common salts of sodium potassium and ammonium soluble?
Yes
Are nitrates insoluble?
No
Are common chloride soluble?
Yes, except silver chloride and lead chloride
Are common sulphate soluble?
Yes, except leadbarium and calcium sulfate
Are common carbonate and hydroxide soluble?
No, except for sodium, potassium and ammonium
How do we get a dry sample of an insoluble salt?
Precipitation
How would you get a dry sample of an insoluble salt through a precipitation reaction?
Add one spatula of lead nitrate to a test tube add water to dissolve it you should. Use the ionised water to make sure there are no other irons involved.. shake it thoroughly to ensure that all the lead nitrate has dissolved then in a separate test tube do the same with one spatula of sodium chloride
Tip the two solutions into a small beaker and give it a good start to make sure it’s all mixed together the light chloride should precipitate out.
Put a folded piece of filter paper into a filter funnel and stick the funnel into a chronicle flask
Pour the contents of the beaker into the middle of the filter paper make sure that the solution doesn’t go above the filter paper otherwise some of the solid could triple down the side
Swell out the beaker with more deionised water and tip this into the filter paper
Rinse the contents of the filter paper with ionised water to make sure that all the so all soluble sodium nitrate has been washed away
Scrape the lead chloride onto fresh filter paper and leave it dry in an oven or a desiccator
How can we make soluble salts?
With an acid and an insoluble base
How to remake a soluble salt with an acid and an insoluble base
You can make a soluble salt by reacting in acid that contains one of the ions you want in the salt with an insoluble base that contains the other iron you need
By heating the acid in a water bath this speed up the reaction between the acid and the insoluble base do this in a fume cupboard to avoid releasing acid fumes in the room
Then at the base to the acid the base and acid will react to produce a soluble salt and water. Make sure you don’t have any leftover acid in your product.
Filter of the excess solid to get a solution containing only the salt and the water
Heat the solution gently using a Bunsen burner to slow evaporate off some of the water the solution to allow the salt to crystallise filter of the solid salt and leave to dry
How do you make a soluble salt?
Using acid/alkaline reactions
How do you make a soluble salt using an acid/alkaline reaction?
Measure out to set amount of acid into a chronical flask using a pippette. Add a few drops of indicator.
Slowly add alkaline to the acid using a burette until you reach the end point - this is when the acids been exactly neutralised and indicated changes colour.
Then carry out the reaction using exactly the same volumes of alkaline and acid but with no indicator so the salt won’t be contaminated with indicator .
The solution that remains when the reaction is complete contains only the salt and water
Slowly evaporate off some of the water then leaves the solution to crystallise . Filter off the solid and dry it you’ll be left with a pure and dry salt.
OILRIG
Oxidation is loss of
Reduction is gain
Electrolysis is what?
Breaking down of a substance using electricity.
What are the positive ions?
Cations
What is the cathode
Negative electrode
What is the negative ions ?
Anions
What is the anode?
Positive electrode?
At the anode does oxidation happen or reduction?
Oxidation
At the cathode, does oxidation happen or reduction?
Reduction
If your electrolyte is a solution how would you carry this out?
Get two unreactive electrodes
Clean the surfaces of the electrodes using some sand paper
From this point and be careful not to touch the surfaces of the electrode with your hands
Placeboth electrodes into a beaker filled with your electrolyte
Connect the electrodes to a power supplies using crocodile clips and wires when you turn the power supply on a current will flow through the cell
How would you carry out electrolysis if your electrolytes is a molten ionic substance?
Put your solid ionic substance in a crucible
Heat the crucible with a bunsen burner until the solid molten you should do this in a fume cupboard to release any toxic fumes
What’s the solid molten dip to clean and unreactive electrodes into the electrolyte
Then connect the electrodes to power supplies using wires and clips
Can an ionic solid be electrolysed, explain why?
No, because the ions are in fixed positions and can’t move
Can molten ionic compound be electrolysed? Explain why?
Yes, as the ions can move freely and conduct electricity
Can electrolysis be involved in aqueous solutions?
Yes
Explain how an electrolysis of aqueous solutions
Solutions as well as the ions from the ionic compound, there will be hydrogen ions and hydroxide irons from the water.
At the cathode if H plus ions and metal ions are present, hydrogen gas will be produced if the metal is more reactive than hydrogen
If the metal is less reactive than hydrogen, then a solid layer of the pure metal will be produced instead
If ions are present molecules of chlorine brooming or iodine will be formed if no halide ions are present then oxygen will be formed
Give an example of electrolysis of aqueous solutions
Solution of sodium chloride contains four different ions and A+, Cl-, OH- and H+.
Sodium methyl is more reactive than hydrogen so at the cathode hydrogen gas is produced
Chloride ions are present in the solution so the chlorine gases produced
What does electrolysis of copper sulphate with unreactive electrodes produce?
Oxygen
Electrolysis of copper sulfate
The reaction continues the mass of the unable decrease and the mass of the cord will increase. This is because copper is transferred from the anode to the cathode.
The reaction takes 30 minutes to get decent change in mass
The mass of your electrodes has changed during an experiment by finding the difference between the masses of the electrodes before and after the experiment
You should make sure the electrodes are dry before weighing them
If you increase the current will increase the rate of electrolysis this means there will be a bigger difference between the mass of the two electrodes after the same amount of time
The electrical supply act by pulling electrons of copper atoms at the anode and offering electrons at the cathode to nearby Cu2+ ions
If we extract copper from its core by reduction with carbon, it’s impure, we use electrolysis. Is it pure?
Yes
Purifying copper with electrolysis
The anode starts up as a big lump of impure copper
The cathode starts off as a thin piece of pure copper
The imperial copper unloaded is oxidised dissolving into the electrolyte to form copper ions
The copper ions are reduced that the pure copper covered and added to a layer of pure copper
Any impurities from the pure copper and sink to the bottom of the cell forming a sludge
A student added a strong acid to a solution with a pH of 6. The new solution had a pH of 3. State whether the concentration of H+ ions had increased or decreased and by what factor?
It increased by a factor of 1000
Write a balanced chemical equation for the reaction of hydrochloric acid with calcium carbonate
2HCl + CaCO3 - CaCl2 + H2O + CO2
Suggest two reactants you could use to form barium sulphate in a precipitation reaction
Barium chloride and copper sulphate
Suggest two reactants you could use to form barium sulphate in a precipitation reaction
Barium chloride and copper sulphate
A student covers out electrolysis on molten calcium chloride. What is produced at the anode and the cathode
Anode : Chlorine gas
Cathode : calcium atoms
State whether silver would displace iron from iron chloride solution and explain your answer
So would not displace iron from iron chloride solution because it’s lower down than iron in the reactivity series
Lithium sits between sodium and calcium in the reactivity series state whether the lithium would display zinc from zinc sulphate solution and explain your answer
Lithium would displace sink from zinc sulphate solution as it higher than zinc in the reactivity series
Write a balanced equation for the reduction of lead oxide, PbO, by carbon, C.
2PbO + C - 2Pb + CO2
How would you extract tin from its metal ore?
Tin is less reactive than carbon so you could extract tin from its ore by reducing it with carbon
Use the reactivity series to predict whether aluminium or iron would be more expensive to extract from its ore
Aluminium would be more expensive to extract than iron as aluminium is more reactive than carbon, so it has to be extracted using electrolysis, where is iron can be extracted by reduction with carbon. Extracting metals using electrolysis is much more expensive than using reduction with carbon as it requires high temperatures to melt the metal ore which is expensive.
Material X is a metal. To recycle material X you need 110% of the energy used to extract and refine it. Explain why it still might be a better idea to recycle material X.
Metals are non-renewable, so recycling metals is important to conserve finite resources of the metal. Also non-recycled material has to be disposed of in landfill sites which take up space and can pollute the surroundings.
