Topic 3 - Chemical Changes Flashcards
Acids in solution are a source of
Hydrogen ions(H+ ions). The higher the concentration of H+ ions, the lower the pH.
Alkalis in solution are a source of
Hydroxide ions(OH- ions). The higher the conc of OH- ions, the higher the pH.
Neutral, acidic and alkali solution pH
Neutral - 7
Acidic - <7
Alkali - >7
A base is
A substance that reacts with an acid to make a salt and water
Alkalis are
Bases that are soluble in water
Acids and alkali effect on litmus paper
In an acid, blue litmus turns red
In an alkali, red litmus turns blue
Acids and alkali effect on methyl orange
Turns red in an acid and yellow in an alkali
Acid and alkali effect on phenolphthalein
Colourless in acid, pink in alkalis
The higher the concnetration of H+ ions in an acid,
The stronger the acid and lower the pH
The higher the concentration of OH- ions in an alkali,
The stronger the alkali and higher the pH
An increase by a factor of 10 to H+ concentration leads to
A decrease in pH by 1
The steps of the neutralisation practical between calcium oxide and dilute hydrochloric acid
Measure out a certain amount of hydrochloric acid using a pipette.
Measure a fixed mass of calcium oxide
Mix them
Wait for the calcium oxide to all react, then measure the pH and add more.
Repeat until there is an excess
Dilute means
There is a low concentration of a substance in the solution
Concentrated means
There is a high concentration of a substance in a solution
What makes an acid strong
They ionise almost completely in water. A large proprotion of the acid molecules dissociate to release H+ ions. Low pH
What makes an acid weak
The dont fully ionise in solution. A small amount of molecules dissociate into H+ ions. Higher pH.
The difference between strong and concentrated acids
Concentration shows how much acid is in the water but strength shows how many acid molecules ionise in water.
A reaction between an acid and a base is called
A neutralisation reaction
A salt is
An ionic compond
Acid+Metal oxide ->
Salt+Water
Acid + Metal Hydroxide ->
Salt+Water
Acid + Metal ->
Salt+Hydrogen
Acid+ metal carbonate ->
Salt + Water+ Carbon dioxide
Steps of hydrogen test
Put a lighted splint into the test tube.
If hydrogen is present there will be a squeaky pop
Steps of Carbon dioxide test using limewater
Bubble the CO2 gas through limewater. If it turns cloudy, CO2 is present
In an acid-alkali neutralisation reaction what reacts
H+ ions and OH- ions react to make water
You can make a soluble salt by
Reacting an acid with an insoluble base
Reacting an acid with a soluble base(alkali)
Steps of making a soluble salt with an acid and insoluble base
Add excess reactant to remove all acid
Filter off excess to get a solution of the salt and water
Steps of making a soluble salt with an acid and alkali
A titration must be used because you cant tell if there is an excess
They need to be mixed in the correct proportions because it is soluble so will contaminate it in excess
Once they neutralise using an indicator, there iso nly the salt and water remaining
Steps of turning a solution of copper sulfate to crystals
Add to evaporating dish and evaporate some of the water with a water bath.
Then leave to evaporate until pure dry crystals of copper sulfate are produced
Steps of titration practical for an acid-alkali neutralisation to make crystals
Measure out a set amount of alkali into a flask using a pipette
Add a bit of indicator to flask
Fill a burette with an acid of known concentration
Add a little at a time to the flask, until the indicator shows it has been neutralised
Then use the method of making crystals in an evaporating dish
All common salts of sodium, potassium and ammonium are
Soluble
Nitrates are
Soluble
Common chlorides are… except
Soluble(except silver and lead chloride)
Common sulfates are…except
Soluble(except lead, barium and calcium sulfate)
Common carbonates and hydroxides are…except
Insoluble(except sodium, potassium and ammonium)
A precipitate forms if
An insoluble salt and water is formed.
An insoluble salt is formed
By two certain soluble salts react
Steps of preparing a pure dry sample of an insoluble salt
Mix two soluble salts in solution together.
A precipitate should form in water.
Filter through filter paper so the water goes int othe beaker and insoluble salt gets stuck.
Leave the salt to dry on a piece of filter paper in the oven
Electrolytes are
Ionic compounds either molten or aqueous
Electrolysis is
The breaking down of a substance using electricity
Cathode
negatively charged electrode
Anode
positively charged electrode
During electrolysis ions move to where
Positve ions move to the cathode
Negative move to the anode
When a molten substance is electrolysed, the products are
The same as the substance originally
When an aqueous solution is electrolysed, the products are
Can be metal ions or hydrogen ions at the cathode, so the product is either a metal or hydrogen gas
Can be halide ions or OH- at the anode, so either halide molecules or oxygen is formed
In aqueous solutions, the product at the cathode depends on
If the metal is more reactive than hydrogen. If it is more reactive, hydrogen is formed. if its not, then a solid layer of the pure metal will form.
In aqueous solutions, th product at the anode depends on
If halide ions are present, a haldie molecule is formed. If there is no halide ions, then oxygen is formed
Copper chloride solution products
Cathode - copper
Anode - Chlorine
Sodium sulfate solution products
Cathode - hydrogen
Anode - Oxygen
Water acidified with sulfuric acid electrolysis products
Cathod - Hydrogen
Anode - Oxygen
During electrolysis the processes are
Reduction - A gain in electrons
Oxygen - A loss of electrons
Reduction occurs at the
Cathode
Oxidation occurs at the
Anode
Hlaf equations show
The elctrons lost or gained by ions resulting in the product during electrolysis
Copper sulfate solution products elctrolysis when inert electrodes are used
Cathode - Copper
Anode - Oxygen
Core practical of copper sulfate solution electrolysis uses electrodes made of
Copper
When copper electrodes are used in a solution of copper sulfate, th result is
Copper getting transferred form the anode to the cathode. This makes the mass of the cathode increase and the mass of the anode decrease.
Electrolysis of copper sulfate solution using copper elctrodes steps
Set up like normal, and leave for 30 misn for copper to move through the solution
Measure original mass and final mass of elctrodes
