Chemical Reactions Flashcards
How does magnesium react with oxygen?
Rapidly
Releases a great deal of heat and light
Vigorous reaction
How does iron react with oxygen?
Slowly, could take weeks or months
What happens when metals react with oxygen?
Form a metal oxide
Oxidation reaction takes place, because the metal has gained oxygen
Metal atoms have been oxidised
How do you compare the reactivity of magnesium, zinc, iron and copper?
Use a dilute acid because they don’t react with water
What determines how rapidly a metal reacts?
When metals react, they lose electrons and form a positive ion.
So the reactivity of a metal depends on its ability to lose an electron and form a positive ion.
How are unreactive metals such as gold found?
In the earth as the metal itself.
How do you extract a metal from a compound?
Use a displacement reaction.
Most of the time carbon is used because it is extremely cheap.
What is oxidation in terms of electrons?
Loss of electrons
What is reduction in terms of electrons?
Gain of electrons
What do acids produce in aqueous solution?
Hydrogen ion H+
What are bases?
Chemicals which can neutralise acids, producing a salt and water.
They are usually metal oxides or metal hydroxides.
Some examples are copper oxide, iron (III) hydroxide and sodium hydroxide.
What are bases that are soluble in water?
Alkalis.
This means that copper oxide and iron (III) hydroxide are bases only, because they are insoluble in water.
Sodium hydroxide is soluble in water, so it is both a base and an alkali.
What is a neutralisation reaction?
When a base reacts with an acid to neutralise it, producing salt and water.
What do alkalis produce in aqueous solution?
Hydroxide ions (OH-)
What is the pH of acids?
0-6
What is the pH of neutral solutions?
7
What is the pH of alkalis?
8-14
Difference between a pH probe and universal indicator
pH probe determines it electronically- so you are given a numerical value.
Universal indicator changes colour depending on whether the solution is an acid, alkali or neutral.
Green-neutral
Red- very acidic
Purple-very alkaline
Neutralisation reaction between an acid and an alkali.
The acid will proceed hydrogen ions and the alkali will produce hydroxide ions.
The hydrogen ions react with the hydroxide ions to produce water
Formula for hydrochloric acid
HCl
Formula for sulfuric acid
H2SO4
Formula for nitric acid
HNO3
Why does magnesium react rapidly with acids?
Higher than magnesium on the reactivity series, so it is a lot more reactive.
Magnesium can easily displace hydrogen from acids.
Why does iron react slowly with acids?
Iron is only slightly more reactive than hydrogen
What are salts?
They contain a positive ion which comes from the base or alkali.
Also contain a negative ion which comes from the acid.
What are salts?
They contain a positive ion which comes from the base or alkali.
Also contain a negative ion which comes from the acid.
Metal carbonates:
sodium carbonate - Na2CO3
calcium carbonate - CaCO3
potassium carbonate - K2CO3
Required Practical 1: Making soluble salts using an acid.
Equipment:
- beaker
- gauze
- tripod
- bunsen burner
- heatproof mat
- Start with a fixed volume of dilute sulfuric acid. This is our limiting reactant. We don’t want any acid remaining in the end because it would contaminate the salt.
- Gently heat the acid until it’s almost boiling.
- Use a spatula to add small amounts of copper oxide to the acid.
- Stir the solution using a glass rod.
- The copper oxide will react and seem to disappear.
- Continue adding copper oxide if the solution continues to be clear blue.
- Stop adding copper oxide if some powder remains after stirring.
- The reaction has stopped because all the acid has reacted. Solution of copper sulphate is now neutral.
- We must remove the unreacted copper oxide. Use filtration as it is insoluble.
- Filter funnel and filter paper.
Now to make the crystals of copper sulfate:
- Place the copper sulphate solution and place this in an evaporating basin.
- Heat this gently over a beaker of boiling water.
- Do this until half the solution remains.
- Leave the solution for 24 hours in a cool place so the crystals can form.
- Scrape the crystals onto a paper towel and pat them dry.
Required Practical 1: Making soluble salts using an acid.
Why can’t you react copper with sulphuric acid?
Copper isn’t reactive enough for the reaction to actually take place.
Where could the metal ion in the salt come from?
The metal itself.
Metal oxide.
Metal hydroxide.
Metal carbonate.
Where does the negative ion in the salt come from?
The acid.
Strong acids vs weak acids.
Strong acids fully ionise in aqueous solutions and we know this as the arrow goes in one direction only.
Examples are hydrochloric acid, sulfuric acid and nitric acid.
Weak acids partially ionise in aqueous solutions. Reversible reactions.
Examples are carbonic acid, ethanoic acid and citric acid.
Strong acids vs weak acids.
Strong acids fully ionise in aqueous solutions and we know this as the arrow goes in one direction only.
Examples are hydrochloric acid, sulfuric acid and nitric acid.
Weak acids partially ionise in aqueous solutions. Reversible reactions.
Examples are carbonic acid, ethanoic acid and citric acid.
What does the pH scale do?
Gives us an idea of the concentration of hydrogen ions produced by an acid.
Strong acids have a lower pH than weak acids for a given concentration.
As the pH scale decreases by one unit, the concentration of hydrogen ions increases by ten times. This is one order of magnitude.
So for example, pH 1 has a 100x greater concentration of hydrogen ions than pH 3. This is two orders of magnitude.
Concentrations of acids.
This tells us the amount of acid molecules in a given volume of a solution.
A dilute acid will have fewer acid molecules in a given volume than a concentrated acid even if the strength of the acid is the same.
Required Practical 2: Carrying out a titration
- Use a pipette to transfer 25cm^3 of sodium hydroxide solution into a conical flask.
- Add 5 drops of indicator such as methyl orange to the alkali in the conical flask.
- Place the conical flask on a white tile so we can see a colour change more clearly.
- Fill a burette with sulfuric acid.
- Add acid to the alkali until the solution is neutral. When we see a colour change, we now add acid drop by drop until it is neutral.
- Swirl the solution so it mixes.
- The colour change will be from yellow to permanently red.
- Read the volume of acid added from the burette. Make sure your eye is level with the surface of the liquid as there is a meniscus.
Read from the bottom of the meniscus. - Repeat the titration several times until we get two readings within 0.1cm^3.
- Take a mean of these for a final volume.
Why can’t solid ionic compounds conduct electricity?
The ions are locked in place and are not free to move.
They are held in place by strong electrostatic forces of attraction.
When an ionic compound is melted or dissolved in water, the forces of attraction are broken and the ions are free to move.
These liquids can now conduct electricity. These are called electrolytes.
