Topic 3 - Acids And Alkalis Flashcards
Where is an acid on the pH scale.?
pH lower than 7
Where is an alkali on the pH scale?
pH above 7
Where is neutral on the pH scale?
pH of 7
What colour does litmus paper turn when acidic?
Blue to red
What does phenolphthalein turn when acidic?
From pink to colourless
What do acids produce when they dissolve in water?
An excess of hydrogen ions H+
What is formed when hydrogen chloride gas is dissolved in water?
Hydrochloride acid - the gas splits into H+ ions and Cl- ions
What is produced when an alkali dissolves in water?
An excess of hydroxide ions (OH-)
What happens if the concentration of hydrogen ions goes up?
The more acidic the solution becomes and the pH lowers
What happens if the concentration of hydroxide ions increases?
The more alkaline the solution becomes and the higher the pH
What makes the solution neutral?
When there are equal amounts/ concentrations of hydrogen and hydroxide ions
How to calculate concentration?
Amount dissolved / volume of solution
What happens to the pH is the concentration of hydrogen ions is increased by a factor of 10?
The pH decreases by 1
What happens to the pH if the concentration of hydrogen ions decreases by a factor of 10
The pH increases by 1
If HCL has a factor of 0, how many more times acidic is it then vinegar with a pH of 4?
X10 x10 x10 x10 which is 10,000 more hydrogen ions from 0 - 4
What is a strong acid?
Fully dissociate into water
I.e. their molecules break up (dissociate) completely into ions when dissolved in water
They produce high concentrations of hydrogen ions
E.g. HCl
What are weak acids?
Acids that only partially dissociate when dissolved in water (not fully)
E.g. Ethanoic acid
What is a BAWS reaction?
Base + acid —> water + salt
What is metal oxide neutralisation equation?
Metal oxide + acid —> salt + water
What happens during neutralisation (metal oxide)?
The hydrogen ions in the acid combine with the oxide ions to form water because this removes the hydrogen ions which increases the pH (become more neutral)
How are the salts produced?
By replacing the hydrogen ions with metals ions
What is the experiment to make soluble salts by reacting an acid and an insoluble salt?
Add the insoluble salt to an acid (e.g. hcl) in excess as this makes sure all the acid is used up
Gently heat the mixture to speed up the reaction (by water bath e.t.c)
Filtered the mixture to remove the insoluble substances from the solution
Heat the new solution in an evaporating basin over a beaker of boiling water
Then leave it to evaporate slowly for crystallisation to occur and create a soluble salt
What is the Core Practical for making copper sulfate crystals?
Measure 20cm cubed of sulfuric acid and place into a conical flask
Then use a water bath to gently heat the solution until around 50degrees
Add a little copper oxide powder and stir - stop when the powder is in excess
Filter the mixture so you get rid of any insoluble substances and only have copper sulfate solution
Put the solution in an evaporating basin and heat it by placing it over a beaker of boiling water which is being heated by a Bunsen
Stop heating when crystals start to form
Leave the solution to dry/the water to evaporate so you obtain pure, dry crystals
How is water formed in a neutralisation reaction?
It’s formed from the OH in the alkali and the H in the acid
What is the Core Practical for neutralisation?
Add 50cm cubed of HCl into a beaker
Record the pH by placing the end of a glass rod into the acid and then tap it on some universal indicator paper and compare the colour shown to the pH colour chart
Measure out 0.3g of calcium hydroxide paper on a weighing boat
Keep recording the pH after adding 0.3 and keep going until 2.4g has been added.
Then plot a graph with pH and mass as your axis
What are sources of hydrogen ions?
Acids e.g. hydrochloride acid
What are sources of hydroxide ions?
Alkalis e.g sodium hydroxide
What is the equation for water?
+ -
H + OH ——> H20
The ions are (aq)
What happens to the other ions left in solution?
They form together to create a salt when the water evaporates
E.g. if sodium hydroxide and hydrochloride acid reacted, water would be made and then the Na ions and the Cl ions would form to create sodium chloride (a salt) when the water evaporates
How do you do a titration experiment?
Rinse the Burette with the acid your using and then close the tap and fill it with the same acid and record the initial volume
Rinse a pipette with the alkali your using and then measure out 25cm cubed of that alkali with the pipette, and put it into a conical flask.
Place this conical flask on a white tile and add a few drops of phenolphthalein which will turn the solution pink to show it is an alkali solution.
Slowly add the acid until the solution turns colourless and record the final volume of acid in the burette.
Then repeat for concordant results
What happens when a metal reacts with an acid?
It will produce salt and a hydrogen which you will see as effervescing (use squeaky pop test to test the gas)
The first part of salt comes from the metal and second part comes from acid.
E.g. magnesium + sulphuric acid — magnesium sulfate
What is the half equation for hydrogen?
2H + 2e ——> H
2
What is reduction?
Gain of electrons ( the electrons will be on the left of the half equation)
What is oxidation?
Loss of electrons (electrons will be on right of half equation)
What is a CAWCS reaction?
Carbonate + acid —> Carbon dioxide + water + salt
How can you test for carbon dioxide?
Lime water test - Bubble the gas through limewater. If carbon dioxide is present, it turns the limewater cloudy from clear/colourless
Which substances are ALL soluble in water?
All sodium, potassium and ammonium salts
All nitrates
What substances are MOSTLY soluble in water?
Most chlorides
Most sulfates
What are the exceptions?
Silver and lead chlorides
Lead, barium and calcium sulfates
What substances are MOSTLY INsoluble?
Most carbonates
Most hydroxides
What are the exceptions (which are soluble)
Sodium, potassium and ammonium carbonates
Sodium, potassium and ammonium hydroxides
What is a precipitation?
An insoluble substance (can’t be dissolved in water)
I.e. (s) state symbols
How are all salts similar and why?
All salts are ionic
When two soluble salts react, their ions swap.
E.g Copper sulfate + Potassium carbonate
The copper swaps with the potassium and is now Copper Carbonates
The potassium swaps with the copper and is now Potassium sulfate
When will a precipitate not form?
If both products are soluble
How do you prepare insoluble salts?
You mix two soluble salts together in a solution
Filter the mixture as the salts swap names e.g silver nitrate is mixed with sodium chloride - neither are insoluble but because they’re ionic they’re ions swap so we now have sodium nitrate and silver chloride. Silver chloride is insoluble so it won’t be filtered.
Pour a little distilled water over the precipitate in the funnel and carefully remove the filter paper and leave the precipitate to dry or dry it in an oven
