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Chemistry > (1) Acids and Bases > Flashcards

(1) Acids and Bases Flashcards

1
Q

Write the products of the following reactions:

Acid + Metal –>

Acid + Metal Oxide –>

Acid + Metal Hydroxide –>

Acid + Metal Carbonate –>

A

Acid + Metal –> Salt + Hydrogen

Acid + Metal Oxide –> Salt + Water

Acid + Metal Hydroxide –> Salt + Water

Acid + Metal Carbonate –> Salt + CO2 + Water

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2
Q

Write the formula, ions and charges of the following acids:

Hydrochloric

Sulfuric

Nitric

Phosphoric

Ethanoic

A

Hydrochloric - HCl (Cl-)

Sulfuric - H2SO4 (SO4 2-)

Nitric - HNO3 (NO3 -)

Phosphoric - H3PO4 (PO4 3-)

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3
Q

What is a Bronsted-Lowry Acid?

A

An ACID is a proton donor (H+).

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4
Q

What are Monoprotic and Diprotic Acids?

A

Monoprotic acid - releases ONE H+ ion

Diprotic acid - releases TWO H+ ions

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5
Q

What is a Bronsted-Lowry Base?

A

A BASE is a proton acceptor

OH-, NO3-, NH3-

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6
Q

HNO3 + H2SO4 –> H2NO3+ + HSO4-

Which is base and which is acid?

A

H2SO4 is an acid as it loses an H+

HNO3 is a base as it gains an H+

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7
Q

Define Amphoteric.

A

A substance that can act as both an acid and a base.

e.g. water

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8
Q

What are the formulas to find pH and [H+]?

A

pH = -Log10[H+]

[H+] = 10-pH

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9
Q

Key points about pH scale?

A
  • smaller pH = greater [H+]

- A difference of 1 on the pH scale means a 10x difference in [H+]

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10
Q

Define a Strong Acid and give examples.

A

A STRONG acid FULLY DISSOCIATES

  • HCl, H2SO4, HNO3, H3PO4
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11
Q

What do you have to make sure to do when the acid in the question is diatomic?

A
  • make sure you times the concentration of [H+] by 2
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12
Q

Define a Weak Acid.

A

A WEAK acid only PARTIALLY DISSOCIATES

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13
Q

How can you find the pH of a Weak Acid?

A

Ka = [H+][A-]

       [HA]

Which can be written as …

Ka = ___[H+]2 __
[HA]

Rearrange to find [H+] ….

SQUARE ROOT of Ka x [Weak Acid]

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14
Q

What is the formula for pKa?

A

pKa = -Log10Ka

Ka = 10-pKa

The stronger the acid = lower the pKa value.

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15
Q

Define a Buffer.

A

A BUFFER = weak acid and salt.

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16
Q

Define an Acidic Buffer.

A

An ACIDIC BUFFER is made of a weak acid and a soluble salt of that acid. It maintains a pH below 7.

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17
Q

How will adding acid [H+] to a buffer will affect equilibrium. Use this equation for reference

HA H+ + A-

A
  • when acid [H+] is added, the H+ will combine will A- to form HA
  • acid will INCREASE
  • salt will DECREASE
  • EQUILIBRIUM SHIFTS TO LEFT
18
Q

How will adding base [OH-] to a buffer will affect equilibrium. Use this equation for reference

HA H+ + A-

A
  • when base is added [OH-], the OH- will combine with H+ to form H2O
  • acid will DECREASE
  • Salt will INCREASE
  • EQUILIBRIUM SHIFTS TO RIGHT
19
Q

Define a Basic Buffer.

A

A BASIC BUFFER is made of a weak BASE and a soluble salt of that BASE. It maintains a pH above 7.

weak base- NH3

20
Q

How can the pH of an Acidic Buffer be calculated?

A

Ka = [H+][ A-]

       [HA]

rearrange for [H+]

[H+] = Ka x [ HA]

          [A-]
21
Q

When is an ICE Box required?

A
  • when you have volume and concentration in the question
  • minus by limiting

ICE when acid and base = use moles that didn’t cancel out and divide by TOTAL volume to get conc [H+]

ICE when buffer = substitute numbers in ka equation

22
Q

What happens if moles of the Salt and and moles of the Weak Acid are the same?

23
Q

What is Kw?

A

Kw = [H+][-OH]

value of 1x10-14mol2dm-6 at 298K

24
Q

Rearrange equation of Kw for PURE WATER.

A

Pure water [H+] = square root of Kw

25
Q

Define a Strong Base.

A

Strong bases fully dissociate to release -OH ions.

e.g - NaOH , KOH

26
Q

Rearrange Kw to find [H+] FOR STRONG BASE.

A
  • [H+] = Ka / OH-
27
Q

How will pH change with increased temperature? Use this equation to help:

H2O(l) —> H+(aq) + -OH(aq) ∆H = +57.3 kJmol-1

A
  • Equilibrium shifts to the right in the endothermic direction to oppose the temp rise
  • H+ increases
  • so pH decreases
28
Q

Outline the method for a Titration.

A

(1) Fill a burette with the acid of known concentration.
(2) Accurately measure out 25cm3 of the alkali standard solution using a pipette and transfer to a conical flask.
(3) Add a few drops of a suitable indicator to the alkali.
(4) Slowly add the acid from the burette into the conical flask, swirling constantly. As soon as the indicator changes colour the solution has turned neutral so stop adding the acid. Record the volume of acid which has been added.
(5) Repeat the process until you get two results which are within 0.1cm3 of each other. The mean of these two results are then used to calculate an average titre.

29
Q

Outline the method for a pH titration.

A

(1) Measure the pH of the acid solution and record.
(2) Add 1cm3 of the base solution
(3) Stir the mixture
(4) Measure the pH and record.
(5) Repeat the process until the base is in excess.
(6) Add base in smaller increments near the end point

30
Q

How is a pH Meter calibrated?

A

To calibrate pH meter you place the pH meter in a solution of known pH and then adjust the meter accordingly.

31
Q

Key points about pH titration curves?

A
  • There are sections which are almost horizontal, meaning adding base has a very small effect on pH.
  • The starting point of the curve depends on the strength of the acid. strong acid starts ~pH 1.0, a weak acid starts ~pH 3.0
  • The end point of the curve depends on the strength of the base. A strong base ends ~pH 13.0, a weak base ends ~pH 9.0
32
Q

What is the equivalence point?

A
  • when exactly enough acid has been added to neutralise the base
  • indicates what the average titre would be.
33
Q

How can as Acid-Base pH titration calculation be performed?

A
  • balance equation
  • calculate moles by using concentration and volume
  • read average titre from the titration curve and work out concentration
34
Q

Define End Point.

A

The exact volume of acid or base which needs to be added to cause an indicator to change colour.

35
Q

What is the link between vertical section of pH curve and suitable indicator?

A

A SUITABLE INDIATOR CHANGES COLOUR SOMEWHERE ON THE VERTICAL SECTION OF A pH TITRATION CURVE.

36
Q

What is a suitable indicator for a reaction between a Strong Acid and Strong Base?

A

Both phenolphthalein and methyl orange are suitable indicators as they both change colour during the vertical section of the titration curve.

37
Q

What is a suitable indicator for a reaction between a Weak Acid and a Strong Base?

A

Methyl orange is not suitable as this would change colour before the mixture has neutralised.

Phenolphthalein would work.

38
Q

What is a suitable indicator for a reaction between a Strong Acid and a Weak Base?

A

Phenolphthalein is not suitable as this would change colour after the mixture has neutralised.

Methyl orange would work.

39
Q

What is a suitable indicator for a reaction between a Weak Acid and a Weak Base?

A

Neither indicator would be suitable here.

Methyl orange would change colour before the equivalence point, and phenolphthalein would change colour after it.

40
Q

Define the Half-Neutralisation Point.

A

The point at which enough base has been added to neutralise exactly half of the acid.

Chemistry (29 decks)

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