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OCR Chemistry > Chapter 4 - Acids and Redox > Flashcards

Chapter 4 - Acids and Redox Flashcards

Acids, bases and neutralisation, Acid-base titration and Redox.

1
Q

What is an acid?

A

When dissolved in water, it will release hydrogen ions as protons into the solution.

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2
Q

What is a strong acid?

A

Releases all of its hydrogen atoms into solution.

It completely dissociates in aqueous solution.

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3
Q

What is a weak acid?

A

Releases a small proportion of its available hydrogen atoms into solution.
It partially dissociates in aqueous solution.

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4
Q

What is a base?

A

A base neutralises an acid to form a salt.

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5
Q

What is an alkali?

A

A base that dissolves in water releasing hydroxide ions into the solution.

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6
Q

What is the word equation for the neutralisation of acids with metal oxides/hydroxides?

A

Metal oxide/hydroxide + acid -> salt + water

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7
Q

What is the word equation for the neutralisation of acids with alkalis?

A

Acid + alkali -> salt + water

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8
Q

What is the word equation for the neutralisation of acids with carbonates?

A

Carbonate + acid -> salt + water + carbon dioxide

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9
Q

What is a titration?

A

A technique used to accurately measure the volume of one solution that reacts exactly with another solution.

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10
Q

What are the uses of titrations?

A

Finding the concentration of a solution.
Identification of unknown chemicals.
Finding the purity of a substance.

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11
Q

What are concordant results?

A

Within 0.10 cm^3 of each other.

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12
Q

When can a mean titre be worked out?

A

When two or more concordant results are obtained.

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13
Q

When is the oxidation number zero?

A

For elements on their own or bonded to atoms of the same element.

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14
Q

What is the common oxidation number of oxygen?

A

-2

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15
Q

What is the common oxidation number of hydrogen when bonded to non-metals and metal

A

+1 non metal

-1 with metal

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16
Q

What is the common oxidation number of fluorine?

A

always -1

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17
Q

What is the common oxidation number of Na+ or K+?

A

+1 as they group 1

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18
Q

What is the common oxidation number of Mg2+ or Ca2+

A

+2 as they are group 2

19
Q

What is the common oxidation number of other halides?

A

usually -1, but +ve with oxygen

20
Q

In what special case, can hydrogen have an oxidation number of -1?

A

When in metal hydrides (when hydrogen bonded to a metal)

i.e. NaH or CaH(2)

21
Q

In what special case, can oxygen have an oxidation number of -1?

A

In peroxides.

i.e. H(2)O(2)

22
Q

In what special case, can oxygen have an oxidation number of +2?

A

When bonded to fluorine as fluorine rule dictate that its oxidation number is always -1
i.e. F(2)O

23
Q

What do roman numerals mean in the use of iron(II) or iron(III)?

A

Iron(II) represents Fe2+ with oxidation number +2.

Iron(III) represents Fe3+ with oxidation number +3.

24
Q

What is oxidation?

A

The loss of electrons

25
Q

What is reduction?

A

The gain of electrons.

26
Q

What is oxidation in terms of oxidation number?

A

An increase in oxidation number

27
Q

What is reduction in terms of oxidation number?

A

A decrease in oxidation number

28
Q

What is the word equation for the reaction of a metal with acid?

A

Metal + acid -> salt + hydrogen

29
Q

How do you make a standard solution?

A

1) The solid is first weighed acurately using a balance.
2) Then transfer solid from weighing boat to beaker. (Wash any solid left behind into the beaker using deionised water).
3) Dissolve your solid fully using deionised water. Stir to ensure the solid is dissolved fully.
4) Transfer solution to a volumetric flask. Use a funnel to avoid spillage and rinse the beaker, glass rod and funnel into the flask to ensure most of the solution is transferred.
5) Use more deionised water to fill to the graduation mark. (Be careful not to go above this line, or else it will be too diluted! Use a pipette to fill to the line when you get near. Make sure the base of the meniscus touches the mark)
6) Add a stopper. Then invert the flask a few times. To ensure the solution is thoroughly mixed and ready to use.

30
Q

Write down the methods to carry out a titration experiment

A
  1. Using a pipette, measure the volume of a solution
  2. Add the solution into a conical flask and add an indicator to it
  3. Add the other solution into a burette and record the volume to the nearest 0.05cm^3
  4. Slowly add the solution in the burette into the conical flask
  5. Swirl the mixture continuously until the endpoint is reached
  6. Record the final burette reading to nearest
  7. 05cm^3 to obtain titre
    7) run a quick trial
  8. Repeat until concordant results are obtained - agreeing to within 0.10cm^3
31
Q

what is the colour of methyl orange in an acid, base and at the endpoint?

A

Acid - red
Base - yellow
End point - orange

32
Q

What is a salt

A

A compound that is formed when H+ of an ion is replaced by a metal ion or positive ion - ammonium ion, NH4+

33
Q

What does a dot formula indicate?

A

The amount of water present in a crystalline structure

34
Q

Which base is used to treat acid indigestion

A

magnesium hydroxide

35
Q

What does anhydrous crystals mean

A

crystalline structure that contains no water molecules

36
Q

How are ammonium salts formed?

A

When acid reacts with aqueous ammonia

37
Q

What are hydrated crystals

A

a crystalline structure containing water molecules

38
Q

what is a redox reaction?

A

A reaction in which both oxidation and reduction takes place

39
Q

what is the oxidation number of a metal?

A

0, because the element is on its own

40
Q

Explain the effect on the titre of the following error.

1) The pipette has an air bubble inside.
2) The burette readings are taken from the top, rather than the bottom, of the meniscus.

A

1) Titre would be less as less solution has been added than the correct pipette volume.
2) No effect as volume is measured by difference between two readings.

41
Q

How can we remove any air bubble inside a burette prior to the titration experiment?

A

Ensure to run an excess solution out through the tap to remove any air bubbles.

42
Q

what’s nitride oxidation state

A

N^(3-)

43
Q

What is an oxidation-reduction reaction: explain?

A

it is the transfer of electrons between atoms

OCR Chemistry (28 decks)

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