Chemical changes.4 Flashcards Preview

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Flashcards in Chemical changes.4 Deck (40):
1

Method for investigating inks

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

2

Properties of acids

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

3

What are the alkali properties

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

4

What’s the pH scale

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

From 0-14

Neutral = 7

5

What are indicators

Substances that have different colours, depending on their pH

6

What colour does litmus go in acid

Red

7

Litmus turns in alkaline

Blue

8

What colour does phenolphthalein go in acid

Colourless

9

What colour does phenolphthalein go in alkaline

Pink

10

Methyl orange in acid

Red

11

Methyl orange in alkaline

Yellow

12

Red litmus in acid

Red

13

Red litmus in alkaline

Blue

14

Blue litmus in acid

Red

15

Blue litmus in alkaline

Blue

16

For a given volume a concentrated solution :

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

17

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

Dissolving more solute in it

Evaporating some of the water

18

Strong acids

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)

19

Weak acids

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)

20

At a given concentration of acid:

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

A strong acid has a lower pH than a weaknacid

21

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

10

22

An alkali is a

Soluble base

23

What does a soluble bass mean

One tht will dissolve in water

24

A base is

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

25

What are examples of bases

Metal oxides and metal hydroxides

26

In general base + acid ->

Salt + water

27

Examples of reactions of acids with bases

NaOH(aq) + HCL(aq) -> NaCL(aq) + H2O (l)

CuO(s) + 2HNO3 (aq) -> Cu(NO3)2 (aq) + H2o (l)

28

When does a salt form

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

29

What is the first name of a salt

The metal in the base

30

What’s the second part of naming a salt

From the acid used

31

Metals + acid ->

Salt + hydrogen

32

Examples of reactions of acids with metals

Mg(s) + 2HCL (aq) -> MgCl2 (aq) + H2 (g)


2Al(s) + 3H2SO4(aq) -> Al2(SO4)3(aq) + 3G2 (g)

33

Metal carbonate + acid ->

Salt
Water carbon dioxide

Eg

CaCO3 (s) + 2HCL (aq) -> CaCl2 (aq) + H2O (l) + CO2

34

Test for hydrogen

Lighted splint ignited hydrogen with a ‘pop’

35

Test for carbon dioxide

Turns limewater Milky or cloudy white

36

What neautralisation

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)

37

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

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

38

How do you carry out a typical titration

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

39

Mean titres

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

40

How do you normally calculate the mean titre

Using your concordant results only

Mean = sum of concordant titres/number