CC8 Acids Flashcards
What does soluble mean? What does insoluble mean?
Dissolves in water. Does not dissolve in water
Define acid in terms of pH
A substance with a pH of less than 7
Define acids in terms of ions
A substance which releases H⁺ ions in solution
State the three common acids and give their formulae
Hydrochloric acid, HCl(aq), Sulphuric acid, H₂SO₄(aq), Nitric acid, HNO₃
Define pH in terms of ions
Below pH 7 the lower the pH the higher the concentration of H+ ions. Above pH 7 the higher the pH the higher the concentration of OH- ions
What is a neutral solution?
A solution with a pH of 7. Water is an example.
How do you measure pH?
With an indicator or pH probe.
What is a base?
A metal oxide, hydroxide or carbonate that will neutralise an acid. E.g. copper oxide
What is an alkali?
A soluble base. E.g. sodium hydroxide
Which ions are always present in a solution of an alkali?
OH⁻
What type of salts are formed by the three main acids?
Hydrochloric acid produces chlorides, sulphuric acid = sulphates, nitric acid = nitrates
What causes some metals not to completely react with an acid?
A layer of the salt produced (which is insoluble) formed on the surface of the metal blocking the acid from the metal
What is a precipitate?
A product formed from a chemical reaction of two liquids that is solid
What do you see if a precipitate forms?
turn cloudy, see the solid particles
What do you see if carbon dioxide or hydrogen is formed?
bubbles/ effervescence because they are gasses
What is a neutralisation reaction?
A reaction involving an acid that results in a neutral solution.
Write an ionic equation for neutralisation.
H⁺ + OH⁻ → H₂O
Which ions always react together in a neutralization reactions between acids and alkalis?
H⁺ and OH⁻
metal + acid →
→ salt + hydrogen gas
metal hydroxide + acid →
→ salt + water
metal oxide + acid →
→ salt + water
metal carbonate + acid →
→ salt + water + carbon dioxide
How do you make a soluble salt from an acid?
React the acid with a base. E.g. to make copper sulphate react copper oxide with sulphuric acid
If a salt is in solution, how do you extract it as a solid?
Allow the water to evaporate off and it will leave the salt behind as a solid.
What is a strong acid?
An acid which completely splits up into its ions in water. E.g. when HCl is in water all the HCl molecules split up into H⁺ and Cl⁻.
What is a weak acid?
An acid which will have some molecules which do not split up into their ions. E.g. in ethanoic acid only some of the molecules will have split up into the ethanoate ion and H⁺ ions.
What is the relationship between an acid of pH2 and an acid of pH 3?
pH 2 is 10 times more hydrogen ions than pH 3
What is a concentrated acid?
An acid where there are lots of acid particles in the water.
What is a dilute acid?
An acid where there are fewer acid particles in the water.
How is pH measured?
pH is related to the concentration of H⁺ in a solution.
How can hydrogen be tested for?
Makes a squeaky pop when a splint is placed in it
How can carbon dioxide be tested for?
Bubble through limewater, turns it milky (cloudy)
What colour is litmus in acid and alkali?
Acid – red, alkali – blue
What colour is methyl orange in acid and alkali?
Acid – red, alkali – yellow
What colour is phenol phthalein in acid and alkali?
Acid – colourless, alkali – pink
How do you prepare a sample of a soluble salt from an insoluble base and an acid?
Neutralisation with excess insoluble base, filtration, crystallisation
How do you prepare a sample of a soluble salt from an acid and an alkali?
Titration, repeat titration without indicator, crystallisation
How do you prepare a sample of an insoluble salt from two solutions
Combine, filtration, rinse with distilled water, dry
