acids and alkali/redox

Question 1

what are titrations?

Answer 1

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

Question 2

what can titrations be used for?

Answer 2

• finding the conc. of a solution
• identification of unknown chemicals
• finding the purity of a substance

Question 3

how do you prepare a standard solution? (a solution of known concentration)

Answer 3

• solid first weighed accurately
• then dissolved in a beaker using distilled water
• transferred to a volumetric flask, rinsed distilled water from beaker also added to get last traces of solution
• flask carefully filled to the graduation line - if excess, solution will be too dilute
• volumetric flask is slowly inverted several times otherwise titration results will be inconsistent

Question 4

how do you titrate?

Answer 4

• add standard solution to conical flask
• add a few drops of indicator to the solution in the conical flask
• add another solution eg an acid into the burette - make sure to run excess solution to avoid any air bubbles so that air isn’t released during the titration
• record the initial burette reading
• put conical flask under burette, then run it, while swirling conical flask to mix the two solutions
• end point of titration will be when indicator changes colour - when the exact vol. of one solution has reacted with the exact vol. of another solution
• record final burette reading
• find titre by: final - initial reading
• repeat until further two titrations are concordant

Question 5

equation linking mol. concentration and volume

Answer 5

mol = concentration x volume

Question 6

what is an oxidation number?

Answer 6

the measure of the number of electrons that an atom uses to bond with atoms of another element

Question 7

what are the oxidation rules for elements?

Answer 7

the oxidation number is always 0 as in a pure element, any bonding is to atoms of the same element

Question 8

oxidation rules for compounds and ions?

Answer 8

• each atom in a compound has an oxidation number
• oxidation number sign is placed before the number

Question 9

oxidation number equation

Answer 9

sum of oxidation numbers = total charge

Question 10

oxidation number of oxygen

Answer 10

-2

Question 11

oxidation number of hydrogen

Answer 11

+1

Question 12

oxidation number of fluorine

Answer 12

-1

Question 13

oxidation no. of H in metal hydrides (NaH, CaH2)

Answer 13

-1

Question 14

oxidation no. of O in peroxides (H2O2)

Answer 14

-1

Question 15

oxidation of O when bonded to F (F2O)

Answer 15

+2

Question 16

what is the oxidation no. in ions?

Answer 16

oxidation number in an ion of an element is the same as the ionic charge

Question 17

what is redox in terms of an oxidation number?

Answer 17

• reduction is a decrease in oxidation number
• oxidation is an increase in oxidation number

Question 18

redox reactions of acids:

Answer 18

metal + acid = salt + hydrogen