Chapter 4 Acids and Redox

Question 1

What is an acid?

Answer 1

A substance which released hydrogen ions H+, protons, when dissolved

Question 2

What is a strong acid?

Answer 2

An acid with fully disassociates when dissolved, releases all of its hydrogens ions into solution

Question 3

What is a weak acid?

Answer 3

A substance which partially disassociates when dissolved, releasing some of its hydrogen ions into solution

Question 4

What is a base?

Answer 4

A substance which neutralises an acid to form a salt, accepts protons

Question 5

What is an alkali?

Answer 5

A substance which releases hydroxide ions OH- when dissolved, a soluble base

Question 6

What is neutralisation?

Answer 6

When an acid and base react to form a salt and neutral water

Question 7

Define a salt

Answer 7

The product of when a H+ ion is replaced a metal ion or ammonium ion

Question 8

How would name this salt: CH3CH2COONa

Answer 8

Sodium Propanoate

Question 9

What are some of the uses of titrations?

Answer 9

Calculating Concentrations
Identification of unknown substances
Verifying purity

Question 10

What are the steps for preparing a standard solution?

Answer 10

Weigh the solid in a weighing boat very accurately
Transfer the solid to a small beaker and add a minimal amount of water, only sufficient enough to allow the solid to dissolve fully. Use a glass rod to stir.
Transfer the solution to a volumetric flask using a funnel.
Rinse the weighing boat, beaker, glass rod, and finally funnel to the volumetric flask, to ensure all of the solid has been accounted for, no traces remain.
Fill the volumetric flask with distilled water. When close to the graduation line, add drop wise. The bottom of the meniscus should align with the graduation line
Place the stopper. Invert several times to mix.

Question 11

How do you calculate percentage uncertainty of a burette?

Answer 11

(Uncertainty burette/titre) x 2 x100

Question 12

What are the steps for carrying out an acid base titration for HCl and NaOH?

Answer 12

Using a pipette and pipette filler to measure and transfer 25cm3 of NaOH to a conical flask
Add a few drops of a single indicator such as phenolphthalein (purple in base, colourless acidic).
Set up a burette. Add an excess amount of HCl to the burette.
Place the conical flask on a white tile underneath the tap of the burette.
Record the value of acid in the burette. Open the tap and close when the colour in the flask changes.
Record this final value in the burette. The titre is the final volume - initial volume. This first tire is the rough titre.
Repeat the experiment, swirling the conical flask as you go. When the colour changes but reverts, add the acid drop wise.
Repeat until concordant results

Question 13

What does titre mean? What does concordant mean?

Answer 13

Titre is the volume of solution used to neutralise the other solution
Concordant titres are those which are within 0.10cm3 of each other

Question 14

Which results should be used to calculate the mean titre?

Answer 14

Only concordant values

Question 15

What are the general steps for acid base calculations?

Answer 15

For concertation: n=Cv, ratio, C=n/v
For substance: n=Cv, ratio, scale up to number of moles in standard solution, Mr=mass/n

Question 16

What are oxidation numbers?

Answer 16

A system used to show the number of electrons involved in bonding to a different element

Question 17

What can oxidation number help with?

Answer 17

Ensuring all electrons have been accounted for
Formulae and Balancing
Oxidation and Reduction of covalent compounds

Question 18

What are the main rules for oxidation numbers?

Answer 18

Elements alone (or bonded to each other) have an oxidation number of
Place the sign in front of the number
Each atom in a compound has an individual oxidation number
The sum of the oxidation numbers is equal to the charge of the compound
Use the ion charge most of the time
O is normally -2, H is usually +1

Question 19

What are some exceptions to oxidation number rules?

Answer 19

O is peroxides (oxygen bonded together to other elements) = -1
H in metal hydrides = -1
O bonded to F= +1

Question 20

How do you use Roman numerals in naming relating to oxidation numbers?

Answer 20

For elements with multiple oxidation states (transition metals, Cl, N…) use Roman numerals to show oxidation state, for when not obvious
E,g Iron(II) dichromate vs Iron(III) dichromate
FeCr2O7 vs Fe2(Cr2O7)3

Question 21

What are oxidation and reduction in terms of oxygen?

Answer 21

Oxidation is the gain of oxygen. Reduction is the loss of oxygen.

Question 22

What are oxidation and reduction in terms of electron?

Answer 22

Oxidation is the loss of electrons. Reduction is the gain of electrons.

Question 23

What are oxidation and reduction in terms of oxidation numbers?

Answer 23

Oxidation is the increase is oxidation number. Reduction is the decrease in oxidation number

Question 24

What are redox reactions? What are disproportionation reactions?

Answer 24

Redox reactions are where oxidation and reduction occur in the same reaction
Disproportion is when the same elements is both oxidised and reduced in the same reaction

Question 25

What is the oxidation number of P in H5P3O10?

Answer 25

+5 +3p -20=0
P=+5

Question 26

Which atom is negative in oxidation number?

Answer 26

The one which is more electronegative

Question 27

What would the effect of washing the pipette with water rather than solution be?

Answer 27

Measured volume more dilute, so titre needed decreases