Unit 8 Flashcards
How can you tell if something is acidic
By how it affects litmus. Litmus is a purple dye. It can be used as a solution, or on paper.
Acids turn Litmus red
How can you tell if something is an alkali
It turns the litmus blue
What is litmus
It is an indicator because it indicates if something that is an alkali or acidic
And example of a substance that is neutral
Water
pH less than 7
Acidic
pH more than 7
Alkaline
pH that is exactly 7
Neutral
What makes acidic solutions acidic
Hydrogen ions
In a solution of strong ions
All molecules become ions.
In solution of weak acids
Only some molecules become acids
What does the higher concentration of hydrogen ions mean
The lower the pH and the stronger the acid
What does an alkaline solution contain
Hydroxide ions, this is what makes them alkaline
What is in a stronger alkali solution
Contains more hydroxide ions
What is in a weaker alkali solution
It contains less hydroxide ions
What does the higher concentration of hydroxide ions mean
That the pH is higher
How can you tell if a solution is weak or strong??
Measure their conductivity
A strong acid will show…
High conductivity and low pH
A weak acid will
Not conduct well and has a higher pH
A strong alkali will show
High conductivity and high pH
A weak acid will
Show low conductivity and low pH
What happens when an acid reacts will a metal
Hydrogen is displaced, leaving a salt in solution. It’s a redox reaction.
What are bases
Bases are a group of compound that reacts with acid, and neutralises them, giving a salt and water. Bases include alkalis, and insoluble metal oxides, hydroxides an carbonates.
Bases with alkalis
Acid + alkali –> salt + water
Bases with metal oxides
Acid + metal oxide —> salt + water
Bases with carbonates
Acid + metal carbonates —> salt + water + carbon dioxide.
Reactions of bases
Neutralising acids, giving salt and water. With carbonates carbon dioxide is produce too.
All the alkalis (except ammonia) will react with ammonium compounds, giving ammonia out
What is an ionic equation
An equation that shows only the ions that actually take part in the reaction. It leaves out the rest.
- First write down all the ions present in the equation
- now cross out any ions that appear, unchanged, on both sides of the equation.
- What’s left is the ionic equation for the reaction.
Proton donors and acceptors
Acids donate its protons to bases and bases except them.
For example:
Magnesium oxide is a insoluble base. The acid donates its H+ protons and the oxygen from magnesium oxide react with it to make water molecules.
Why do crops grow best when the pH of the soil is 7
If the soil is too acidic or too alkaline, crops grow badly or not at all
Why the soil being too acidic is usually the problem?
Because a lot of vegetation rotting in it or because too much fertiliser was used in the past.
How can you reduce the acidity?
The soil is treated with a base like limestone or quicklime or slaked lime
How is acid rain caused?
Is caused by factories, Power stations, homes who burn fossil fuels to make electricity. The waste gases from all these reactions include Sulphur dioxide, and oxides of nitrogen.they go into the air and react with air and water to produce so sulphuric acid and nitric acid which are strong acids
How can you make salts
By reacting metals ,insoluble bases or soluble bases with acids.
How to make salts with metals
1.add the zinc to the sulphuric acid in a beaker.
It will start to dissolve and hydrogen bubbles are given off. Stops when acid is used up.
- excess zinc is removed by filtering. This Leaves a aqueous solution of zinc sulphate.
- The solution is heated to evaporate some water . Then it is left to cool and crystals of zinc sulphate will start to form.
How to make salts with an insoluble base
It’s the same as the metal method but the metal will not react with the acid. So you must start with metal oxide
How to make salts won an alkali (soluble base)
- Put the alkali into a flask and add some drops of indicator
- add the acid fro, a burette, just a little bit at a time. Swirl the flask in o help the acid and the alkali mix .
- when the indicator turns green, stop adding acid.
- Calculate how much acid was used.
- Carry out the experiment again without the indicator and add the same amount of acid that was used before. They s is because the indicator will make the salt impure.
- Heat the solution from the flask and crystals will start to form.
What is the process that can help make insoluble salts
Precipitation
What salts are soluble
Sodium Potassium Ammonium All nitrates Chlorides Sulphates Sodium, potassium and ammonium carbonates
What salts are insoluble
Silver and lead chloride
Calcium barium and lead sulphate
All carbonates except sodium , potassium and ammonium
Preparing a barium sulphate
Barium sulphate is a soluble salt. You can make it b mixing solutions of barium chloride and magnesium sulphate
- make up solutions of barium chloride and magnesium sulphate
- Mix them. A white precipitate of barium sulphate forms at once
- filter the mixture. The precipitate is trapped in the filter paper
- Rinse the precipitate by running distilled water through it
- Then place it in a warm oven to dry
How do you precipitate an insoluble salt
Must mix the solution that contains its positive ions with one that contains its negative ions
