[AK] acids and alkali

Question 1

what is an acid?

Answer 1

an acid is a substance that dissociates into ions in water to produce hydrogen ions

Question 2

what do all acids contain?

Answer 2

all acids contain hydrogen ions

Question 3

do all compounds containing hydrogen qualify as acids?

Answer 3

nope

Question 4

what are the four physical properties of acids?

Answer 4

• sour taste
• turns blue litmus paper red
• pH <7 (the lower the pH, the higher the acidity!)
• conducts electricity when dissolved in water

Question 5

what are the two chemical properties of acids?

Answer 5

1. acid + reactive metal -> hydrogen gas + salt
2. acid + metal carbonate -> carbon dioxide + salt + water

Question 6

what are the non-reactive metals?

Answer 6

copper, gold, silver

Question 7

what test do you use to test for hydrogen gas?

Answer 7

lighted splint test

Question 8

what are the observations when hydrogen gas is present

Answer 8

• effervescence is observed
• a colourless and odourless gas is produced
• gas extinguishes lighted splint with a “pop” sound

Question 9

what test do you use to test for carbon dioxide?

Answer 9

limewater test

Question 10

what are the observations when carbon dioxide is present?

Answer 10

• effervescence is observed
• colourless and odourless gas is produced
• white precipitate is formed in limewater

Question 11

what are bases?

Answer 11

bases are metal oxides and metal hydroxides

Question 12

what are alkalis?

Answer 12

alkalis are aqueous solutions containing hydroxide ions

Question 13

what are the four physical properties of alkalis?

Answer 13

• 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

Question 14

what are the chemical reactions of alkalis?

Answer 14

1. alkali + acid = salt + water (neutralisation)
2. alkali + ammonium salt = salt + water + ammonia gas

Question 15

what test is used to detect ammonia gas?

Answer 15

litmus paper test

Question 16

what are the observations when ammonia gas is present?

Answer 16

• colourless and pungent gas is produced
• gas turns damp red litmus paper blue

Question 17

what is pH?

Answer 17

it is the measure of acidity or alkalinity in a solution

Question 18

how is pH related to the concentration of hydrogen ions in a solution?

Answer 18

the smaller the pH value, the higher the concentration of hydrogen ions
the larger the pH value, the lower the concentration of hydrogen ions

Question 19

what are indicators?

Answer 19

indicators are substances with different colours in acidic and alkaline solutions (they change colour depending on the pH of the solution

Question 20

how does litmus paper indicate acidity and alkalinity?

Answer 20

red litmus paper turns blue in alkaline solutions and remains red in acidic solutions

Question 21

what are some of the other common indicators beside litmus paper?

Answer 21

phenolphthalein, bromothymol blue and methyl orange

Question 22

what is universal indicator?

Answer 22

universal indicator changes colour when added to solutions with different acidity and alkalinity

Question 23

what colour does universal indicator turn in a strong acid?

Answer 23

red

Question 24

what colour does universal indicator turn in a neutral solution?

Answer 24

green

Question 25

what colour does universal indicator turn in a strong alkaline?

Answer 25

purple