Definition of an acid
- 'sour'- a substance which ionises/dissociates hydrogen ions when dissolved in water
What is the role of water in chemical properties of acids?
- substance has acidic properties only when dissolved in water to form an aq solution - presence of water essential for the acid molecules to produce H+ ions which is the only ion responsible for the acidic properties
Common acids to memorise (3 types)
1. Hydrochloric acid HCl2. Sulfuric acid H2SO43. Nitric acid HNO3
Chemical properties of acids and alkalis (4 types of reactions )
1. Acid-metal reactionAcid + reactive metal -> salt + hydrogen2. Acid-carbonate reactionAcid + carbonate -> salt + water + carbon dioxide3. Acid-base reaction (neutralisation reaction)Acid + base -> salt + water4. Alkali-ammonium salt reaction Alkali + ammonium salt -> salt + water + ammonia
Is a salt always formed in any acid or alkali reaction?
Yes
Which is the only reaction which has no gas released?
Neutralisation reaction, acid-base reaction
What is a salt? How is it formed?
- compound formed when an acid reacts with a base - an ionic compound in which the +ve ion comes from the base and -ve ion comes from the acid- compound formed when hydrogen (H+) in an acid is replaced by a metal cation or NH4 +
Test for hydrogen gas (result)
Effervescence of colourless and odourless gas extinguishes the lighted splint with a 'pop' sound
Test for oxygen gas (result)
Effervescence of colourless and odourless gas relights the glowing splint
Test for carbon dioxide gas (result)
Effervescence of a colourless, odourless gas forms a white precipitate in limewater (calcium hydroxide solution)
Test for ammonia gas (result)
Effervescence of a colourless, pungent gas that turns moist red litmus paper blue
What are bases?
a compound which reacts with an acid to form a salt and water only
What are some examples of bases? (3 general egs)
1. Metal oxides (O)2. Metal hydroxides (OH)3. (NH4OH): ammonia solution/ammonium hydroxide/aq ammonia
How do acids and alkalis differ in taste?
Acids: sour tastealkalis: bitter taste
Should both acids and alkalis be corrosive?
Yes
Can both acids and alkalis sq solution conduct electricity?
Yes
Do alkalis have slippery touch?
Yes
What are alkalis?
- soluble (in water) bases
Egs of alkalis (what grp number)
Grp 1: all metal oxides and hydroxides are solubleGrp 2: metal oxides and hydroxides are partially soluble, solubility increases down the grp
What do alkalis produce when dissolved in water?
Hydroxide ions (OH -)
How do the values of pH scale (3 main grps) show acidic/neutral/alkaline?
0-6: acidic7: neutral8-14: alkaline
How do the colours of the litmus paper show acidic/neutral/alkaline?
Red: acidicblue: alkalineno change: neutral
How do the colours of the methyl orange show acidic/neutral/alkaline?
Red: acidicyellow: alkalinepH colour change: 4
How do the colours of the universal indicator relate to the pH value?
0-1: red2-5: orange6: yellow7: green8: green blue9: blue10-11: blue-purple12-14: purpleJust remember: red -> green -> blue -> purple
How to confirm if an unknown solution contains an acid/alkali
Using indicators:1. Use a piece of moist red and blue litmus paper- blue turns red: acid- red turns blue: alkali2. Add a few drops of Universal Indicators- red/orange/yellow: acid- blue/violet: alkaliBy chemical reaction:Test for acid1. Add a metal (acid-metal reaction)2. Add a carbonate (acid-carbonate reaction)Test for alkali1. Add ammonium salt (alkali-ammonium salt reaction)
Why is the reaction btw an acid and base not used to test for acids and alkalis?
No visible change, not suitable
Why are there pieces of magnesium left in the solution after a reaction?
- The acid has reacted completely - there is no more acid to continue reacting with the magnesium- the acid is the limiting reagent - magnesium is in excess