Volumetric analysis

Question 1

types of errors

Answer 1

random/ intermediate errors
systematic/ determinate errors

Question 2

systematic error

Answer 2

Errors that can be avoided and is usually due to the person making the measurement

ex) instrumental errors, personal errors

Question 3

howcan random error be reduced?

Answer 3

Repeating the measurements
Using the accurate apparatus/ devices
Use different instruments to make the same measurement

Question 4

how to caculate absolute error?

Answer 4

true value- measured value

Question 5

how to calculate relative error?

Answer 5

True value - Measured value
True value

Question 6

what is accuracy?

Answer 6

Accuracy refers to the degree to which an experimental value varies with the true or accepted value ie. it refers to how close the measured value is to the true value.

Question 7

what is precision?

Answer 7

The precision of results refers to how close several values are to each other ie. the closer the measured values, the greater the degree of precision.

Question 8

what is standard deviation?

Answer 8

The standard deviation of a series of measured values gives a measure of the precision among the values.

Question 9

relationship between standard deviation and measured values

Answer 9

Whenever the standard deviation is large, the measured values are scattered wildly from the mean.
Whenever the standard deviation is small, the measured values are close together and close to the mean.

Question 10

how is volumetric analysis carried out?

Answer 10

This method of analysis is carried out by determining the volume of a solution of accurately known concentration which reacts with a measured volume of a solution of an unknown concentration.

Question 11

what is the standard solution/ titrant?

Answer 11

the solution of accurately known concentration

Question 12

what is the primary standard?

Answer 12

primary standard is a pure, stable, and soluble substance that can be used to calibrate other standards and determine the concentration of other substances.

Question 13

properties of primary standard

Answer 13

Must have a very high purity (99.98%)
Must be stable in air (composition does not change when exposed to air)
Must be easy to obtain and purify at a temperature below 110-120 degrees Celsius.
Must have a high relative molecular mass (RMM) in order to minimize the errors associated with weighings.
Must be easily soluble in water

Question 14

why is NaOH not a good primary standard?

Answer 14

its RMM is low (40) and it cannot be made and stored as it reacts readily with the CO2 from the atmosphere to create Na2CO3 (contaminated and impure)

Question 15

what is secondary standard?

Answer 15

any substance that is prepared for a specific analysis and is usually standardized with a primary standard before it is used.

Question 16

properties of secondary standard

Answer 16

Must be simple and easily expressed by an equation

Must take plume quickly

The reaction must have some noticeable change in a physical or chemical property close to the equivalence point.

Question 17

end point in a titration

Answer 17

The end point in a titration is the volume at which a signal is noticed which means the completion of the reaction in the titration.

Question 18

equivalence point of a titration

Answer 18

The equivalence point is the volume at which the number of moles of the standard reagent is equal to the number of moles of the substance being analyzed with respect to the equation for the reaction ie. the equivalence point is the point at which the reagent is in excess.
* This is more accurate.

Question 19

what is the purpose of a back titration?

Answer 19

back titration is used to determine the percentage of a substance in a sample. This titration involves 2 steps:
A weighed amount of the sample is added to an excess amount of a reagent.
After reaction, the amount of the excess reagent is determined by titration with another solution.

Question 20

steps in calculating back titration

Answer 20

1. write the equation for the reaction between the sample and the excess reagent
2. calculate the number of moles of excess reagent added to the acid
3. Using the titration results, calculate the number of moles of the excess reagent which remains.
4. Calculate the amount of excess reagent which reacted with the sample.
5. calculate the amount of the active substance in the sample
6. convert number of moles to grams then calculate the percentage of the active ingredient

Question 21

how to obtain equivalence point in titration?

Answer 21

monitoring changes in the other physical properties which change during the reaction

Question 22

thermometric titration

Answer 22

The end point is obtained by measuring temperature changes. One reagent is added to a fixed volume of the other reagent.

This procedure is continued until the temperature begins to drop ie. There is an initial increase in temperature followed by a decrease in temperature.

The end point is obtained by plotting a graph of temperature against volume of reagent added.

Question 23

conductometric titration

Answer 23

A fixed amount of 1 reagent is measured and placed in a beaker.
The electrode of the conductivity Metre is placed in the solution.
Small amounts of the reagent in the burette is added. The mixture is stirred and the conductivity is measured.

The reagent from the burette is added until the conductivity begins to increase.

The end point is obtained by plotting a graph of conductivity against volume of reagent added.

Question 24

potentiometric titration

Answer 24

The potential difference is monitored as small amounts of 1 reagent is added to a fixed volume using a voltmeter.

During this titration, 2 electrodes are needed:

The end point is obtained by plotting a graph of potential difference against volume of reagent added.

Question 25

electrodes needed for potentiometric titration

Answer 25

Reference electrode- has an electrode potential which does not change the reagent being added.

Indicator electrode- develops a potential difference according to the concentration of the substances being analyzed.