Researching Chemistry 1 - Stochiometry, Gravimetric and Volumetric Analysis

Question 1

What is a stochiometric equation, and what does it tell you?

Answer 1

A balanced chemical equation, and it tells you the mole ratios

Question 2

A quantitative reaction is one that ___ ___ according to the ___ ___.

Answer 2

reacts completely, mole ratios

Question 3

If you want to find the exact quantity of a substance present in a compound, you can carry out a ___ reaction, and use the ___ of the reaction to determine the mass.

Answer 3

quantitative, stochiometry

Question 4

Some common units for concentration are: ___, ___ by ___, ___ by ___, and ___.

Answer 4

PPM, % by volume, % by mass, and mol/L

Question 5

Two methods commonly used in quantitative analysis are ___ and ___ analysis.

Answer 5

Gravimetric, volumetric

Question 6

What is gravimetric analysis?

Answer 6

A process used to determine the mass of an element or compound present in a substance, by changing that substance to one of known chemical composition

Question 7

What is ‘weighing accurately approximately’?

Answer 7

Measuring out a rough mass of something, but knowing it’s mass to three d.p. (eg ‘measure 2.5g acc. approx.’ - and you then measure 2.476)

Question 8

What does the tare function do on a scale?

Answer 8

Sets it to zero

Question 9

Once the product has been __, it can be ___ and ___.

Answer 9

Isolated / collected, purified, weighed

Question 10

What is heating to a constant mass?

Answer 10

A process of repeated heating and cooling cycles, until the substances mass remains constant.
>The heating drives off moisture and the cooling is done in a dessicator to prevent any moisture from being absorbed

Question 11

Once the mass of the substance has been determined, the number of ___ can be calculated using the formula: ___.

Answer 11

moles, n = m/GFM

Question 12

The formula of the compound you started with can also be ___, using the difference in mass to find the number of ___ of ___.

Answer 12

Determined, moles, water
>Example question: ‘Find n’
BaCl2 n.H2O

Question 13

The conversion of one substance to another of known chemical composition can be done through ___ or ___ reactions.

Answer 13

Precipitation or volatilisation
>The precipitate should be washed, dried to a constant mass, and weighed.
>In volatilisation, the substance is heated to remove volatile substances and weighed

Question 14

A volumetric analysis procedure is called a ___.
>A ___ ___ is used to determine the ___ of the other reactant.

Answer 14

Titration,
standard solution, concentration

Question 15

One solution is measured, ___ (using a ___) into a ___ flask.
The other solution is dispensed from a ___ until a ___ ___ change appears.

Answer 15

Accurately (using a pipette), conical flask
Burette, permanent colour change

Question 16

A ‘___’ titration is usually carried out first, followed by ___ more ___ titrations, until ___ results are achieved.
Concordant values are within __cm3 of each other.

Answer 16

‘rough’, several, accurate, concordant,
0.1

Question 17

What is a standard solution?
What can they be directly prepared from?

Answer 17

A solution of accurately known concentration.
A primary standard.

Question 18

Solutions which are not primary standards require standardisation before they are used. What does standardisation mean?

Answer 18

determining the concentration of the unknown solute in the solution (the concentration of the solution), by titrating it with a standard solution

Question 19

How do you prepare a standard solution?
1.
2.
3.
4.

Answer 19

1. Accurately weigh/measure (with 3dp balance/pipette) the primary standard.
2. Dissolve the primary standard in deionized water.
3. Transfer quantitatively (‘with rinsings’) to a standard flask
4. Make it up to the graduation mark with deionised water. Stopper and invert to create a uniform solution.

Question 20

List the five properties of a primary standard.

Answer 20

Available in a high purity.
stable as a solid
soluble in water
high GFM
not hydroscopic

Question 21

Properties of a primary standard:
~Avaliable in a ___ ___.
~Stable as a ___.
~ Soluble in ___.
~Has high enough ___ to reduce ___ ___ when rounding.
~Not h___.

Answer 21

high purity
solid
water
GFM, percentage errors.
Not Hydroscopic (doesnt absorb water)

Question 22

Give three examples of primary standards.

Answer 22

Sodium Carbonate
Hydrated Oxalic Acid
silver nitrate

Question 23

Why is NaOH not a primary standard?

Answer 23

Low GFM
Hydroscopic (Absorbs moisture)

Question 24

What is the difference between the end-point and the equivalence point of a titration?

Answer 24

End-point: Colour change is visible
Equivalence point: Reaction is just complete (not usually visible)

Question 25

What are the four types of volumetric analysis that you should know? >They are titrations.

Answer 25

Acid-base titrations. REDOX titrations. Complexometric titrations. Back titrations.

Question 26

1/4 Acid-base titrations use an acid or ___ of ___ ___ to find the ___ of the unknown (the other one). A pH ___ is used to detect ___.

Answer 26

acid or base of known concentration, concentration, pH indicator, neutralisation

Question 27

2/4 In a REDOX titration, an ___ agent reacts with a ___ ___. Again, (as in all titrations), the ___ of one solution that neutralises/has an effect on the other solution is ___, and used in ___.

Answer 27

oxidising agent, reduction agent, volume, recorded (using burette + indicator), calculations

Question 28

3/4 Complexometric titrations are based on reactions in which ___ ___ are formed. ___ is an important complexometric reagent because it reacts in a _ : _ ratio to form ___ ____. The concentration of ___ ___ in solution can then be calculated (using ___ of the complexometric reagent).

Answer 28

metal complexes EDTA, 1:1, metal complexes, metal ions, moles

Question 29

4/4 Back titrations are used to find the number of ___ of a substance, by reacting it with an ___ volume of reactant, of known ___. You can then calculate the number of moles of the ___ ___ that is left, by doing a ___. This allows you to find the number of ___ of excess reactant, that reacted with the ___ ___, and therefore the number of moles of the substance.

Answer 29

moles, excess, concentration excess reactant, titration moles, unknown substance

Question 30

When are back titrations useful?

Answer 30

When trying to determine the quantity of a substance in a solid, that does not dissolve in water. >So, you use another chemical in excess and find how much of your substance there is by looking at how much of the excess was used

Question 31

Percentage yield can be calculated by the equation...

Answer 31

actual yield / theoretical yield X 100

Question 32

What four things reduce percentage yields?

Answer 32

transfer errors purification position of equilibrium side reactions

Question 33

What is a back titration?

Answer 33

It is when a substance is not titrated itself but instead a compound is reacted with the substance and then the remaining compound is titrated to see how much did not react ie how much was left over.