Chemical changes.4

Question 1

Method for investigating inks

Answer 1

Draw a pencil line near the bottom of the chromatography paper. Apply a small spot of ink and then place the paper into a boiling tube containing a little solvent replace the bung and allow the solvent to travel through the paper

Question 2

Properties of acids

Answer 2

pH if there aqueous solutions is less than 7

Source of hydrogen ions, H+ (aq) in a solution

Hydrochloric acid releases H+ ions :
HCl(aq) -> H+ (aq) + Cl- (aq)

Ethanoic acid releases H+ ions:
CH3COOH(aq) -> CH3COO- (aq) + H+ (aq)

The higher the concentration of H+ (aq) ions, the lower the pH of the acidic solution

Question 3

What are the alkali properties

Answer 3

pH of their aqueous solutions is more than 7

Source of hydroxide ions OH- (aq) in solution

Sodium hydroxide release OH- ions:
NaOH(aq) -> Na+ (aq) + OH- (aq)

Ammonia produces OH- ions in solution:
NH3 (g) + H2O (l) -> NH4+ (aq) + OH- (aq)

The higher the concentration of OH- (aq) ions, the higher the ph of the alkaline solution

Question 4

What’s the pH scale

Answer 4

A measure of the acidity or alkalinity of a solution (how acidic or alkaline it is)

From 0-14

Neutral = 7

Question 5

What are indicators

Answer 5

Substances that have different colours, depending on their pH

Question 6

What colour does litmus go in acid

Answer 6

Red

Question 7

Litmus turns in alkaline

Answer 7

Blue

Question 8

What colour does phenolphthalein go in acid

Answer 8

Colourless

Question 9

What colour does phenolphthalein go in alkaline

Answer 9

Pink

Question 10

Methyl orange in acid

Answer 10

Red

Question 11

Methyl orange in alkaline

Answer 11

Yellow

Question 12

Red litmus in acid

Answer 12

Red

Question 13

Red litmus in alkaline

Answer 13

Blue

Question 14

Blue litmus in acid

Answer 14

Red

Question 15

Blue litmus in alkaline

Answer 15

Blue

Question 16

For a given volume a concentrated solution :

Answer 16

Has a greater amount of dissolved solute particles than a dilute solution

Question 17

You can change a dilute solution to a more concentrated solution by

Answer 17

Dissolving more solute in it

Evaporating some of the water

Question 18

Strong acids

Answer 18

Hydrochloride acid and sulfuric acid are strong acids because they fully dissociate unto ions in solution
All their molecules release H+ (aq) ions :

HCL (aq) -> H+ (aq) + Cl- (aq)
H2SO4 (aq) -> 2H + (aq) + SO2-4 (aq)

Question 19

Weak acids

Answer 19

Ethanoic acid is a weak acid because it partially dissociates into ions in solution

Only a few molecules release H+ (aq) ions:

CH3COOH (aq) (reverresible) CH3COOH-(aq) + H+ (aq)

Question 20

At a given concentration of acid:

Answer 20

A strong acid has a higher concentration of H+ ions than a weak acid

A strong acid has a lower pH than a weaknacid

Question 21

The pH increases by 1 when the H+ ion concentration decreases by a factor of

Answer 21

10

Question 22

An alkali is a

Answer 22

Soluble base

Question 23

What does a soluble bass mean

Answer 23

One tht will dissolve in water

Question 24

A base is

Answer 24

Any substance that reacts with an acid to form a salt and water only

Question 25

What are examples of bases

Answer 25

Metal oxides and metal hydroxides

Question 26

In general base + acid ->

Answer 26

Salt + water

Question 27

Examples of reactions of acids with bases

Answer 27

NaOH(aq) + HCL(aq) -> NaCL(aq) + H2O (l) CuO(s) + 2HNO3 (aq) -> Cu(NO3)2 (aq) + H2o (l)

Question 28

When does a salt form

Answer 28

When hydrogen ions in an acid are replaced by metal ions or ammonium ions

Question 29

What is the first name of a salt

Answer 29

The metal in the base

Question 30

What’s the second part of naming a salt

Answer 30

From the acid used

Question 31

Metals + acid ->

Answer 31

Salt + hydrogen

Question 32

Examples of reactions of acids with metals

Answer 32

Mg(s) + 2HCL (aq) -> MgCl2 (aq) + H2 (g) 2Al(s) + 3H2SO4(aq) -> Al2(SO4)3(aq) + 3G2 (g)

Question 33

Metal carbonate + acid ->

Answer 33

Salt Water carbon dioxide Eg CaCO3 (s) + 2HCL (aq) -> CaCl2 (aq) + H2O (l) + CO2

Question 34

Test for hydrogen

Answer 34

Lighted splint ignited hydrogen with a ‘pop’

Question 35

Test for carbon dioxide

Answer 35

Turns limewater Milky or cloudy white

Question 36

What neautralisation

Answer 36

The reaction between an acid and a base In an acid-alkaline neaturalisatuon, hydrogen ions from the acid react with hydroxide ions from the alkali to form water H+ (aq) + OH- (aq) reversible H2O (l)

Question 37

Three main steps needed to make a soluble salt from a soluble base

Answer 37

Use an acid - base titration to find the exact volume of the soluble base that reacts with the acid Mix the acid and soluble base in the correct proportions producing a solution of the salt and water Warm the salt solution to evaporate the water - this will leave crystals of the salt behind

Question 38

How do you carry out a typical titration

Answer 38

Put acid in a burette Use a pipette to put a known volume of alkali into a conical flask Put a few drops of suitable indicator solution such as phenolphthalein or methyl orange into the alkali Record the burette start reading Add acid to the alkali until the colour changes - the end-point Record the burette end reading

Question 39

Mean titres

Answer 39

The tires is the volume of acid added to exactly neutralise the alkali Titre = (end reading) - (start reading) Concordant titres are identical to each other or very close together usually within 0.10cm^3

Question 40

How do you normally calculate the mean titre

Answer 40

Using your concordant results only Mean = sum of concordant titres/number