Chemical Changes Flashcards
Which ions make aqueous solutions acidic?
Hydrogen ions
Which ions make aqueous solutions alkaline?
Hydroxide ions
What is the pH scale?
The pH scale ranges from pH 0 to pH 14 and measures the acidity or alkalinity of a solution
What are pH ranges for acids and alkalis?
Acid - less than pH 7, Neutral - pH 7, Alkali - greater than pH 7
What can be used to measure pH?
Universal indicator and pH probe
What colour is phenolphthalein in acid and alkali?
Acid - colourless and Alkali - Pink
What colour is methyl orange in acid and alkali?
acid - red and Alkali - yellow
What colour is blue litmus paper in acid and alkali?
Acid - turns red and Alkali - stays blue
What colour is red litmus paper in acid and alkali?
Acid - stays red and Alkali - turns blue
What’s a problem with using universal indicator to test the path of a solution?
The colour of the solution is matched to a pH colour chart, this is quite subjective as people may disagree with which colour the solution matches and it doesn’t provide an exact pH value
If pH decreases by one unit, what happens to the concentration hydrogen ions?
The hydrogen ion concentration increases by a factor of 10
What is a neutralisation reaction?
Reaction between an acid and a base (in an acid-alkali neutralisation reaction H+ ions from the acid react with OH- ions from the alkali to form water
What is the ionic equation for a neutralisation reaction?
H+ + OH- -> H2O
What does concentrated and dilute mean when talking about acid?
Concentrated acids have more moles of acid per unit volume than dilute acids
What is a weak acid?
An acid that has partially dissociated in water
What is a strong acid?
An acid that has fully dissociated in water
What is a base?
Any substance that reacts with an acid to form salt and water only
What are the products when an acid reacts with a metal?
Acid + metal -> Salt and hydrogen
What are the products when an acid reacts with a metal oxide?
Acid + metal oxide -> salt + water
What are the products when an acid reacts with a metal hydroxide?
Acid + metal hydroxide -> salt + water
What are the products when an acid reacts with a metal carbonate?
Acid + metal carbonate -> salt + water + carbon dioxide
Why are metal oxides normally bases rather than alkalis?
Metal oxides are normally insoluble
What is the name of the salt formed from magnesium and sulphuric acid?
Magnesium sulfate
What is the name of the salt formed from zinc oxide and nitric acid?
Zinc nitrate
What is the name of the salt formed from calcium carbonate and hydrochloric acid?
Calcium chloride
What is the chemical test for hydrogen?
Insert a lot splint into a test tube of gas and a spewky pop will be heard if hydrogen is present
What is the chemical test for carbon dioxide?
Bubble the gas through limewater and limewater turns cloudy if carbon dioxide is present
When a soluble salt is prepared from an acid and an insoluble reactant, how and why is the excess reactant removed?
By filtration, to leave a pure solution of the salt
What method must be used to prepare a salt from an acid and a soluble reactant?
Titration, since both the reactants are soluble, a titration allows you to combine the reactants exactly and avoid adding an excess of either reactants as this would be hard to remove
What 3 steps are required when producing a pure dry salt from an acid and alkali?
Complete a titration to find the volume of acid that reacts exactly with a set volume of alkali, use the results from the titration to mix the acid and alkali in the correct proportions and evaporate the water from the solution, leaving pure dry salt crystals
How do you carry out an acid-alkali titration?
Use a pipettes to add a measured volume of acid to the conical flask then add a few drops of indicator, place on a white tile, fill the butter with the alkali, noting the initial volume, add the alkali to the conical flask, first complete a rough trial to find the end point, repeat, adding the alkali drop by drop near the end point and swirling the flask constantly to mix and record the final volume in the bursts, repeat until you have concordant results
What are the exceptions from chlorides being soluble?
Silver chloride and lead chloride
Are nitrates soluble?
Yes
Are sodiums, potassiums and ammonium salts soluble?
Yes
What are the exceptions from sulfates being soluble?
Lead, calcium and barium sulfate
What are the exceptions from carbonates and hydroxides being insoluble?
Sodium, potassium and ammonium
How could you prepare a pure, dry sample of an insoluble salt?
Mix two solutions required to form the salt, filter the mixture using filter paper, the residue on the filter paper is the insoluble salt and wash the salt with distilled water and leave to dry
What is an electrolyte?
An ionic compound in its molten or aqueous state
Why can an electrolyte carry charge?
An ionic compound in is molten or aqueous state has mobile ions which can carry charge
What is electrolysis?
A process which uses electrical energy to decompose electrolytes
What are cathode and anode?
Cathode - negative electrode and Anode - positive electrode
Where do charged ions in the electrolytes move to during electrolytes?
Cations move towards the cathode and anions move towards the anode
What happens at the anode during electrolysis?
The anions lose electrons to form their elements
What happens at the cathode during electrolysis?
Cations gain electrons to form their elements
What are the processes that occur at each electrode during electrolysis?
Oxidation and Reduction
What is formed at each electrode in electrolysis?
Positive electrode: non-metal and negative electrode: metal or hydrogen
How can you predict whether a metal or hydrogen will form at the negative electrode?
If hydrogen is above the metal in the reactivity series then the metal will form
What does oxidation mean?
Loss of electrons
What does reeducation mean?
Gain of electrons
How can electrolysis of copper sulfate can be used to purify copper?
Place 2 copper electrodes into copper sulfate solution, the anode should be impure copper and cathode should be pure copper, connect to a power supply and the copper in the impure anode is pulled towards the cathode to form pure copper, impurities form as sludge below the anode, Cu2+ ions from copper sulfate remain in solution
