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CHEMISTRY > Chemical changes.4 > Flashcards

Chemical changes.4 Flashcards

1
Q

Method for investigating inks

A

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

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2
Q

Properties of acids

A

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

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3
Q

What are the alkali properties

A

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

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4
Q

What’s the pH scale

A

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

From 0-14

Neutral = 7

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5
Q

What are indicators

A

Substances that have different colours, depending on their pH

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6
Q

What colour does litmus go in acid

A

Red

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7
Q

Litmus turns in alkaline

A

Blue

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8
Q

What colour does phenolphthalein go in acid

A

Colourless

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9
Q

What colour does phenolphthalein go in alkaline

A

Pink

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10
Q

Methyl orange in acid

A

Red

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11
Q

Methyl orange in alkaline

A

Yellow

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12
Q

Red litmus in acid

A

Red

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13
Q

Red litmus in alkaline

A

Blue

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14
Q

Blue litmus in acid

A

Red

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15
Q

Blue litmus in alkaline

A

Blue

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16
Q

For a given volume a concentrated solution :

A

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

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17
Q

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

A

Dissolving more solute in it

Evaporating some of the water

18
Q

Strong acids

A

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
Q

Weak acids

A

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
Q

At a given concentration of acid:

A

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
Q

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

A

10

22
Q

An alkali is a

A

Soluble base

23
Q

What does a soluble bass mean

A

One tht will dissolve in water

24
Q

A base is

A

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

25
Q

What are examples of bases

A

Metal oxides and metal hydroxides

26
Q

In general base + acid ->

A

Salt + water

27
Q

Examples of reactions of acids with bases

A

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

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

28
Q

When does a salt form

A

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

29
Q

What is the first name of a salt

A

The metal in the base

30
Q

What’s the second part of naming a salt

A

From the acid used

31
Q

Metals + acid ->

A

Salt + hydrogen

32
Q

Examples of reactions of acids with metals

A

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

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

33
Q

Metal carbonate + acid ->

A

Salt
Water carbon dioxide

Eg

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

34
Q

Test for hydrogen

A

Lighted splint ignited hydrogen with a ‘pop’

35
Q

Test for carbon dioxide

A

Turns limewater Milky or cloudy white

36
Q

What neautralisation

A

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
Q

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

A

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
Q

How do you carry out a typical titration

A

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
Q

Mean titres

A

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
Q

How do you normally calculate the mean titre

A

Using your concordant results only

Mean = sum of concordant titres/number

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