Acids and Bases Flashcards

1
Q

Define bronsted-Lowry acid

Give an example

A

Proton donor

HA + H2O → H3O+ + A-

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2
Q

Define bronsted-Lowry base

Give an example

A

Proton acceptor

B + H2O → BH+ + OH-

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3
Q

Define strong acid

A

Completely dissociates

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4
Q

Define weak acid

A

Slighty dissociates

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5
Q

Define strong base

A

Completely ionises

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6
Q

Define weak base

A

Slightly ionises

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7
Q

What happens during acid base equilibria?

A

Protons are transferred from acid to base

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8
Q

Does water fully dissociate or slightly?

A

Slightly dissociates

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9
Q

Where is kw derived from?

A

Kc x [H2O]

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10
Q

Ionic product of water

Unit

A

Kw = [H+] [OH-]

mol2 dm-6

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11
Q

Does the value of Kw change as the temp changes?

A

Yes, it varies w/ temp

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12
Q

What is the value of Kw at 298k?

A

1.00 x 10-14 mol2 dm-6

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13
Q

Why is a solution w/ pH 6 still considered neutral?

A

[H+] = [OH-]

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14
Q

Equation for pH

A

pH = -log [H+]

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15
Q

pH to conc equation

A

[H+] = 10-pH

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16
Q

Give the expression of Ka

Unit

A

Ka = [H+] [A-] / [HA]

Ka = [H+]2 / [HA]

mol dm-3

17
Q

When is Ka used?

18
Q

How do you work out Ka from pKa?

A

Ka = 10-pKa

19
Q

How do you work out pKa from Ka?

A

pKa = -log (Ka)

20
Q

Would you expect strong acids to have higher or lower pKa value than weak acids?

21
Q

What is the vertical line in a pH curve?

A

Equivalence point - neutral

22
Q

How do you work out which indicator to use?

A

The one that changes colour over narrow pH range that lies on vertical part of pH curve

23
Q

Methyl orange

Colour change

pH range

A
  • Red to yellow
  • 3.1 - 4.4
24
Q

Phenolphthalein

Colour change

pH range

A
  • Colourless to pink
  • 8.3 - 10
25
Which indicator do you use for Strong acid/strong base titration
* **Either indicator** * **Rapid pH change over range** of **both** indicator
26
Which indicator do you use for Strong acid/weak base titration
**Methyl orange**
27
Which indicator do you use for Weak acid/strong base titration
**Phenolphthalein**
28
Which indicator do you use for Weak acid/weak base titration
* **Neither** bc **no sharp pH change** * Use **pH meter**
29
Define buffer
Sol that **resists changes** in **pH** when **small amounts** of **acid/base** are **added** or when **diluted**
30
What is an acidic buffer?
* **pH less than 7** * Mixing **weak acid** w/ **salt** * **Weak acid slightly dissociates, salt fully dissociates**
31
What happens when you add acid to an acidic buffer?
* **H+ conc inc** * **Equil shifts** to **left** * **Oppose inc** in H+ * **pH doesn't change**
32
What happens when you add base to an acidic buffer?
* **OH- conc inc** * **OH- reacts** w/ **H+** to form **water**, **removing H+** from solution * **Equil shifts** to **right** bc **acid dissociates** to **form H+** * **pH doesn't change**
33
What is a basic buffer?
* **pH greater than 7** * Mixing **weak base** w/ **salt** * **eg. ammonia + ammonium chloride** * **Salt fully dissociates** * **Weak base reacts** w/ **water** * **NH3 + H2O ⇔ NH4+ + OH-**
34
What happens when you add base to a basic buffer?
* **OH- conc inc** * Sol = **more basic** * **OH- reacts** w/ **NH4+** → **NH3 + H2O** * **Equil shifts** to **left** to **remove OH-**
35
What happens when you add acid to a basic buffer?
* **H+ conc inc** * Sol = **more acidic** * **H+ reacts** w/ **OH-** → **H2O** * **Equil shifts** to **right to replace** in **OH-** * **H+ reacts** w/ **NH3** → **NH4+**
36
What are buffers used for?
* **Shampoo** (pH 5.5) - hair becomes **rougher** if exposed to **alkaline** * **Biological washing powder** - keep pH right level for **enzymes** to work **efficiently**