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WJEC CHEMISTRY UNIT 1 > 1.7 Simple equilibria and acid-base reactions > Flashcards

1.7 Simple equilibria and acid-base reactions Flashcards

2
Q

What are reversible reactions?

A

A reaction that can go in either direction depending on the conditions

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3
Q

What is the symbol of reversible reactions?

A

⇌

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4
Q

Give an example of a reversible reaction.

A

H2O (l) ⇌ H2O (s)

(water ⇌ ice)

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5
Q

What is the test for water?

A

When the copper (II) sulfate is heated, the water of crystallisation is given off as steam, leaving a white powder called anhydrous copper (II) sulfate.

When water is added to the white powder, the powder gets hot and turns blue.

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6
Q

What is the Haber process?

A

The formation of ammonia from nitrogen and hydrogen.

N2 (g) + 3H2 (g) ⇌ 2NH3 (g)

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7
Q

What are the two types of equilibrium?

A

Static equilibrium
Dynamic equilibrium

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8
Q

Define dynamic equilibrium.

A

When the forward and reverse reactions occur at the same rate.

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9
Q

Give an example of dynamic equilibrium.

A

Dissolving an ionic compound in water.

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10
Q

What are the features of an equilibrium?

A
  1. There is a closed system
  2. It is dynamic at a molecular level
  3. The forward and reverse reactions occur at the same rate
  4. Macroscopic properties remain constant
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11
Q

What is the position of equilibrium?

A

The proportion of products to reactants in an equilibrium mixture.

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12
Q

What is Le Chatelier’s principle?

A

If a system at equilibrium is subjected to a change then the position of equilibrium will shift to minimise that change.

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13
Q

What is the effect of increased concentration on the position of equilibrium?

A

If the concentration of a reactant is increased, the position of equilibrium moves to the right and more products are formed.

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14
Q

What is the effect of increased pressure on the position of equilibrium?

A

Increasing the pressure moves the position of equilibrium to whichever side of the equation has fewer gas molecules.

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15
Q

What is the effect of increased temperature on the position of equilibrium?

A

An increased temperature moves the position of equilibrium in the endothermic direction.

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16
Q

What is the effect of catalysts on the position of equilibrium?

A

A catalyst speeds up a chemical reaction by lowering the activation energy of the reaction.

A catalyst will increase the rate of the forward and backward reaction to the same extent.

A catalyst does not affect the position of equilibrium, but equilibrium is reached faster.

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17
Q

How do you find the equilibrium constant?

A

Kc = (C)^c (D)^d / (A)^a (B)^b

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18
Q

What is an acid?

A

A proton donor (H+)

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19
Q

What is a base?

A

A proton acceptor (H+)

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20
Q

List some common acids.

A

Hydrochloric acid (HCl)
Sulfuric acid (H2SO4)
Nitric acid (HNO3)
Ethanoic acid (CH3COOH)

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21
Q

Give the equation for hydrochloric acid dissociating.

A

HCl (g) ————> H+ (aq) + Cl-(aq)

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22
Q

What is an alkali?

A

A base that dissolves in water.

The ion common to all alkalis is the hydroxide ion, OH-

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23
Q

Write the equation for the dissociation of an alkali (sodium hydroxide).

A

NaOH (s) ——-> Na+ (aq) + OH- (aq)

24
Q

What is a strong acid?

A

One that fully dissociates in aqueous solution.

25
Q

What is a weak acid?

A

One that partially dissociates in aqueous solution.

26
What does a concentrated acid consist of?
A large quantity of acid and a small quantity of water.
27
What is a diluted acid consist of?
A dilute acid contains a large quantity of water.
28
How do you calculate the pH from H+ concentration?
pH = -lg(H+)
29
What is the simplest way to measure pH?
Using universal indicator. More accurate measurements can be made by using pH meters.
30
Give me the correlation between H+ ion conc and pH.
The higher the H+ ion concentration, the lower the pH and the stronger the acid.
31
What is a salt?
The compound that forms when a metal ion replaces the hydrogen ion in an acid.
32
What are the salts of HCl?
chlorides
33
What are the salts of H2SO4?
sulfates
34
What are the salts of HNO3?
nitrates
35
Write an ionic equation for neutralisation.
H+ (aq) + OH-(aq) ----> H2O(l)
36
Write a general equation for neutralisation.
acid + base ----> salt + water acid + alkali ----> salt + water acid + carbonate ----> salt + water + carbon dioxide
37
In what other way can a salt be made?
A salt can also be made by reacting a metal with an acid in a similar way to neutralising a base with an acid.
38
What is an acid-base titration?
A type of volumetric analysis where the volume of one solution (an acid) that reacts exactly with a known volume of another solution (base)
39
How can you find the precise point of neutralisation?
Using an indicator.
40
What is a standard solution?
A standard solution is one for which the concentration is accurately known
41
How is a standard solution prepared?
Using a primary standard. (a reagent which can be weighed easily and which is so pure that its weight is truly representative of the no. of moles of substance contained)
42
What does a feature of a primary standard include?
1. High purity 2. Stability 3. Low hygroscopicity (minimise wight changes due to humidity) 4. High molar mass (to minimise weighing errors)
43
Give examples of primary standards.
Potassium hydrogen phthalate Sodium carbonate
44
How is a standard solution prepared?
1. Calculate the mass of the solid required and accurately weigh this amount into a weighing bottle. 2. Transfer all of the solid into a beaker. Add water ans stir until all the solid dissolves 3. Pour all the solution carefully through a funnel into a volumetric flask, washing all the solution off the beaker and the glass rod. Add water until just below the graduation mark 4. Add water drop by drop until the graduation mark is reached and mix the solution thoroughly.
45
What equipment and chemicals do titrations involve?
1. A burette containing one solution (acid) 2. A conical flask containing the other solution (e.g. base) 3. A pipette to accurately transfer the solution into conical flask 4. indicator to show when the reaction is completed.
46
What are the two common indicators used in titrations?
Phenolphthalein and Methyl Orange
47
Tell me the colour change in phenolphthalein?
Colourless in acid, pink in alkaline
48
Tell me the colour change in methyl orange.
Red in acid, yellow in alkaline.
49
Describe the method for a titration.
1. Pour acid into a burette using a funnel, making sure that the jet is filled. Remove the funnel and read the burette 2. Use a pipette to add a measured volume of the base into a conical flask 3. Add a few drops of indicator to the solution in the flask 4. Run the acid from the burette into the solution in the conical flask, swirling the flask 5. Stop when the indicator just changes colour (end-point) 6. Read the burette again and subtract to find the volume of acid used. This is known as a titre. 7. Repeat titration, making sure that the acid is added drop by drop near the end point, until there are at least two concordant readings (within 0.2 of each other). Then calculate a mean titre.
50
How many indicators are used in a double titration?
2
51
When does phenolphthalein change colour?
at around pH 9
52
When does methyl orange change colour
at around pH 4
53
What does the first stage of the titration relate to?
(the change in colour of the phenolphthalein) concentration of the hydroxide and the carbonate
54
What does the second stage of the titration relate to?
(methyl orange) relates to the concentration of carbonate only.
55
What happens during a back titration?
In back titration a known excess of one reagent A reacts with an unknown amount of reagent B. At the end of the reaction, the amount of reagent A that remains is found by titration. A simple calculation gives the amount of reagent A that has been used and the amount of reagent B

WJEC CHEMISTRY UNIT 1 (7 decks)

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