(SC8) Acids and Alkalis

Question 1

Indicator table; Tell the colours the indicators will be if the solution is acidic/alkaline

Answer 1

Acids:
Litmus - red
Methyl orange - red
Phenolphthalein - colourless

Alkalis:
Litmus - blue
Methyl orange - yellow
Phenolphthalein - pink

Question 2

Polyatomic ions are…

Answer 2

formed when small groups of atoms, held together by covalent bonds, lose or gain electrons (eg. OH-; NO3-)

Question 3

What do acids and alkalis produce when they are dissolved in water?

Answer 3

Acids produce an excess of hydrogen ions

Alkalis produce an excess of hydroxide ions

Question 4

Common acids (formulas):

• hydrochloric acid
• sulfuric acid
• nitric acid

Answer 4

HCL
H2SO4
HNO3

Question 5

Common alkalis:

• sodium hydroxide
• potassium hydroxide
• calcium hydroxide

Answer 5

• NaOH
• KOH
• Ca(OH)2

Question 6

Concentrated solution…

Answer 6

contains a lot of dissolved solute per unit volume

Question 7

Dilute solution…

Answer 7

contains only a small amount of solute per unit volume

Question 8

Formula for concentration

Answer 8

amount dissolved/volume of solution

Question 9

1 pH = what difference in concentration of H+ ions

Answer 9

10

For example, hydrochloric acid with ph 0 is 10x10x10x10=10000 times more acidic than vinegar, with a pH of 4

Question 10

Strong acids…

Answer 10

their molecules dissociate completely into ions when they are dissolved in water, that’s why their concentration of hydrogen ions is high

Question 11

Weak acids…

Answer 11

their molecules do not dissociate completely, that’s why thei concentration of hydrogen ions is low and their pH is higher.

Question 12

Bases are…

Answer 12

substances that neutralise acids to form a salt and water only.

Question 13

Neutralisation reaction with metal oxides formula:

Answer 13

metal oxide + acid => salt + water

Question 14

What happens during neutralisation reaction?

Answer 14

Hydrogen reacts with oxide ions to form water. Hydrogen is replaced with metal to form salts. It removes hydrogen ions and so pH increases.

Question 15

Preparing soluble salts

Answer 15

Step 1
Add excess tin(II) oxide to hydrochloric acid to make sure that all the acid is used up.

Step 2
Gently warm the mixture up to speed up the reaction

Step 3
Filter to remove the unreacted solid from the solution

Step 4
Heat to evaporate water and concentrate the solution using the beaker with water in order to not evaporate any of the solution

Step 5
Leave to evaporate water slowly from the solution

Question 16

Preparing copper sulfate (formula)

Answer 16

Copper oxide(s) + sulfuric acid(aq) -> copper sulfate(aq) + water(l)

Question 17

Alkalis are…

Answer 17

soluble bases that form alkaline solution with pH value above 7

Question 18

The end point is…

Answer 18

when the indicator changes colour

Question 19

Describe titration…

Answer 19

Acid is added from a burette to a fixed volume of alkali in a conical flask. Pippete is used to meause out the alkali. Few drops of indicator are added to the alkali so you can follow the reaction. You need to stop when you reach the end point and then evaporate the water from the solution.

Question 20

Oxidation is…

Answer 20

loss of electrons

Question 21

Reduction is…

Answer 21

gain of electrons

Question 22

Reaction of acids with metal carbonates (equation)

Answer 22

Metal carbonate + acid -> salt + water + carbon dioxide

Question 23

Preparation of insoluble salts

Answer 23

Step 1
Silver nitrate solution is added to sodium chloride solution

Step 2
Use filtration to seperate silver chloride from sodium nitrate

Step 3
Add some water to silver chloride to wash it off