[AK] acids and alkali Flashcards
what is an acid?
an acid is a substance that dissociates into ions in water to produce hydrogen ions
what do all acids contain?
all acids contain hydrogen ions
do all compounds containing hydrogen qualify as acids?
nope
what are the four physical properties of acids?
- sour taste
- turns blue litmus paper red
- pH <7 (the lower the pH, the higher the acidity!)
- conducts electricity when dissolved in water
what are the two chemical properties of acids?
- acid + reactive metal -> hydrogen gas + salt
- acid + metal carbonate -> carbon dioxide + salt + water
what are the non-reactive metals?
copper, gold, silver
what test do you use to test for hydrogen gas?
lighted splint test
what are the observations when hydrogen gas is present
- effervescence is observed
- a colourless and odourless gas is produced
- gas extinguishes lighted splint with a “pop” sound
what test do you use to test for carbon dioxide?
limewater test
what are the observations when carbon dioxide is present?
- effervescence is observed
- colourless and odourless gas is produced
- white precipitate is formed in limewater
what are bases?
bases are metal oxides and metal hydroxides
what are alkalis?
alkalis are aqueous solutions containing hydroxide ions
what are the four physical properties of alkalis?
- bitter taste and soapy touch
- turns red litmus paper blue
- pH >7 (the higher the pH, the higher the alkalinity)
- conducts electricity when dissolved in water
what are the chemical reactions of alkalis?
- alkali + acid = salt + water (neutralisation)
- alkali + ammonium salt = salt + water + ammonia gas
what test is used to detect ammonia gas?
litmus paper test
what are the observations when ammonia gas is present?
- colourless and pungent gas is produced
- gas turns damp red litmus paper blue
what is pH?
it is the measure of acidity or alkalinity in a solution
how is pH related to the concentration of hydrogen ions in a solution?
the smaller the pH value, the higher the concentration of hydrogen ions
the larger the pH value, the lower the concentration of hydrogen ions
what are indicators?
indicators are substances with different colours in acidic and alkaline solutions (they change colour depending on the pH of the solution
how does litmus paper indicate acidity and alkalinity?
red litmus paper turns blue in alkaline solutions and remains red in acidic solutions
what are some of the other common indicators beside litmus paper?
phenolphthalein, bromothymol blue and methyl orange
what is universal indicator?
universal indicator changes colour when added to solutions with different acidity and alkalinity
what colour does universal indicator turn in a strong acid?
red
what colour does universal indicator turn in a neutral solution?
green
