Topic 4 Using Spec Flashcards
What are acids in terms of ions
Substances that form hydrogen ions when dissolved in water
What are alkalis in terms of ions
Substances that form hydroxide ions when dissolved in water
Type of base
On the ph scale describe acids alkalis and water
Neutral is 7 which is water and it’s what acids and alkalis combine to form
Acidic solutions have a lower pH
Alkaline solutions have a higher pH
Describe the effect of high concentration of hydrogen ions In an acidic solution
Higher the concentration of hydrogen ions in an acidic solution the lower the pH
Describe the effect of high concentration of hydroxide ions In an alkaline solution
The higher the concentration of hydroxide ions in an alkaline solution, the higher the pH
What are the three types of indicators
Methyl orange
Phenolphthalein
Litmus paper
What colour does methyl orange go
Red in acid
Yellow in alkali
What colour does phenolphthalein go
Colourless in acid
Pink in alkali
What colour does litmus paper go
Red in acid
Blue in alkali
Measuring change in pH practical
Measure out mass of a base onto a piece of paper
Add powdered calcium hydroxide into the beaker of a fixed volume of dilute hydrochloric acid
Stir and then estimate and record the pH of the mixture
Repeat until a maximum pH 14
How could you improve this practical
Use a pH probe date logger so u don’t have to judge the colour of each value of pH
What is the independent and dependent variable
Independence-Amount of base added
Dependant - pH of liquid
What does the term ‘concentrated’ mean
Concentrated solution contains a relatively large amount of the solute in the same volume of solvent
What does dilute mean
A dilute solution contains a relatively small amount of the solute in a given volume of solvent.
How can acids be neutralised
By reacting with a base
General reaction of metal hydroxides
Acid + hydroxide -> salt + water
Eg hydrochloric acid + sodium hydroxide-> sodium chloride + water
General reaction for metal carbonates
Acid + carbonate-> salt + water + carbon dioxide
General reaction for metal oxides
Acid + oxide -> salt + water
Describe the test for hydrogen
Place a lit splint close to the mouth of a test tube that contains a gas.
If the gas is hydrogen, a “squeaky pop” sound will be produced.
Describe the test for carbon dioxide
Take an aqueous solution of limewater (calcium hydroxide) and bubble through the gas.
If the gas is carbon dioxide, the limewater solution will turn from clear to cloudy.
What is the product of a neutralisation reaction
Water
How do acids and alkalis react to form water
They go through a neutralisation reaction where the hydrogen ions react with the hydroxide ions
If soluble salts are prepared from an acid and an insoluble reactant explain why excess of the reactant is added
To make sure all of the acid has reacted
This is done by filtering, filtering removes the unreacted insoluble reactant from the salt solution so that only salt and water remains
If soluble salts are prepared from an acid and an insoluble reactant explain why excess of the reactant is removed
To remove impurities from the salt that has been prepared
If soluble salts are prepared from an acid and an insoluble reactant explain why the solution remaining is only salt and water
Because you have reacted all the acid and removed all the impurities
Explain why if soluble salts are prepared from an acid and a soluble reactant, why titration must be used
Because there is no insoluble excess reactant that could be removed by filtration
Explain why if soluble salts are prepared from an acid and a soluble reactant why the acid and soluble reactants are mixed in the correct proportions
As we want a precise amount of the salt and no excess acid or any of the other reactants
How are blue copper sulfate crystals formed
by adding black copper oxide to sulfuric acid
Practical for producing pure dry sample of a double salt
Use a Bunsen burner to warm the acid and then add the insoluble solid
Filter the solution to remove excess insoluble solid
Heat the solution in an evaporating basin above a beaker of water (water baths ensure gentle heating)
Allow solution to cool and more water to evaporate
As water evaporates solution will become more concentrated and salt will begin to crystallise
Acid-alkali titration practical
Using pipette add set volume of strong alkali to a conical flask and add few drops of indicator
Place strong acid of known concentration in a burette
Gradually add the acid to the alkali and as you get closer to end point start to add the acid at a slower rate
As soon as indicator changes colour, stop adding acid
What are we trying to work out in a titration experiment
Volume of acid needed to neutralise the alkali
What common salts are soluble
Sodium , potassium and ammonium
What chlorides aren’t soluble
Silver and lead
What sulfates aren’t soluble
Lead , barium, calcium
Potassium sulfate solution is mixed with barium chloride solution. Predict whether a precipitate will be formed and name it
barium sulfate will be formed as barium is insoluble
