Topic 3 - chemical change Flashcards
What is an acid?
A substance with a pH less than 7
What ions do acids form in water?
H+ ions
What is an alkali?
A base that is soluble in water. pH more than 7
What ions do alkalis form in water?
OH- ions (Hydroxide ions)
What is the pH of a neutral solution?
pH 7
What is an indicator?
A dye that changes colour depending on whether it’s above or below a certain pH.
Explain the effect of acidic, neutral and alkaline solutions on litmus
Red in acidic, purple in neutral, blue in alkaline
Explain the effect of acidic, neutral and alkaline solutions on methyl orange.
Red in acidic, yellow in neutral and alkaline solutions
Explain the effect of acidic, neutral and alkaline solutions on phenolphthalein
Colourless in acidic and neutral solutions, pink in alkaline
What’s the effect of increasing the concentration of hydrogen ions in an acidic solution?
The solution becomes more acidic so the pH decreases
What’s the effect of increasing the concentration of hydroxide ions in an alkaline solution?
The pH increases so becomes a stronger alkaline.
What happens to the pH of a solution when hydrogen ion concentration is increased?
As hydrogen ion concentration increases by a factor of 10, the pH of the solution decreases by 1
What does concentrated mean for an acid?
An acid with a large number of acid molecules compared to the volume of water
What does dilute mean for an acid?
An acid with a small number of acid molecules compared to the volume of water.
What are strong acids?
Acids that ionise almost completely in water ie. a large proportion of the acid molecules dissociate to release H+ ions.
What are weak acids?
Acids that don’t fully ionise in solution ie. only a small proportion of the acid molecules dissociate to release H+ ions.
What is a base?
Any substance that reacts with an acid to form a salt and water only.
What is a neutralisation reaction?
A reaction between an acid and a base
What is the chemical test for hydrogen?
Use a lighted splint and if hydrogen is present you will hear a squeaky pop due to hydrogen burning with oxygen in the air to form water.
What is the chemical test for carbon dioxide using limewater?
To see if a gas is carbon dioxide bubble it through with limewater. If the gas is carbon dioxide the limewater will turn cloudy.
What happens in an acid-alkali neutralisation reaction?
Hydrogen ions (H+) from the acid react with hydroxide ions (OH-) from the alkali to form water.
Why must titration be used if soluble salts are prepared from an acid + soluble reactant?
because there is no insoluble excess reactant that could be removed by filtration
What common substances are soluble in water?
All common sodium, potassium + ammonium salts
All nitrates
Most common chlorides
Most common sulphates
What common substances are insoluble in water?
Silver + lead chlorides
Lead, barium + calcium sulfate
Most common carbonates + hydroxides except those of sodium, potassium + ammonium
Why is excess of the reactant added when making soluble salts prepared from an acid + an insoluble reactant?
So you don’t have any leftover acid in your product
Why is the excess reactant removed when making soluble salts prepared from an acid + an insoluble reactant?
To get a solution containing only the salt and water
Why must the acid + soluble reactant be mixed in the correct proportions when soluble salts are prepared from an acid + and a soluble reactant?
Because the salt is soluble and would be contaminated with the excess alkali
Describe the method used to prepare a pure, dry sample of an insoluble salt
1- mix two suitable solutions
2- use filtration to separate precipitate as a residue from solution
3- wash precipitate with distilled water while it’s in the filter funnel
4- leave washed precipitate aside or in warm oven to dry
How is a salt formed?
During a neutralisation reaction (a reaction between an acid + base)
What salts do the general acids produce?
Hydrochloric acid produces chloride salts
Sulfuric acid produces sulfate salts
Nitric acid produces nitrate salts
Explain the general reactions of aqueous solutions of acids with metals
Acid + metal -> salt + hydrogen
Eg 2HCl + Mg -> MgCl2 + H2
Explain the general reactions of aqueous solutions of acids with metal oxides
Acid + metal oxide -> salt + water
Eg 2HCl + CuO -> CuCl2 + H2O
Explain the general reactions of aqueous solutions of acids with metal hydroxides
Acid + metal hydroxide -> salt + water
Eg HCl + NaOH -> NaCl + H2O
Explain the general reactions of aqueous solutions of acids with metal carbonates
Acid + metal carbonate -> salt + water + carbon dioxide
Eg 2HCl + Na2CO3 -> 2NaCl + H2O + CO2
