Chemistry practical notes

In titration, where does the acid go and where does the alkali go

The acid is pipetted into the conical flask and the alkali is in the burette

What is the sources of errors in titration

1. the type of apparatus used in the experiment

2. not repeating the experiment

3. impurities present that may react with the solution in the conical flask

How to explain the impurities present answer

1. since the impurities present in the acid reacts with the alkali, the volume of alkali needed for neutralisation will be higher than expected. this will lead to…

Explain why conical flasks are used inside of a beaker

the sloping sides of a conical flask prevents loss of reactant due to splashing during swirling which would lead to inaccurate titration results

explain why during titration it is not necessary to dry the conical flask before adding the alkali or acid

the water present will not change the number of moms of reactant added into the conical flask. hence the titration value will not be affected

explain why the conical flask is not rinsed with the solution that it contains

rinsing the conical flask with the solution will cause the volume of reactant to be higher than 25.0 cm. the volume of acid or alkali recorded will then be higher than expected

explain why it is necessary to sometimes dilute a solution before titration

the original solution is too concentrated, and will require more than xxx of the alkali during titration, this is not practical as the burette has to be refilled during the titration and willl result in greater percentage error

how many decimal places does the reading need to be recorded to in titration table?

always 2dp!!!

what is the initial burette reading/cm3 in the titration table

0.00

how much can the two titration ticked results be differed by at the very most

± 0.20

if the question asks for a suitable graph without stating which variable is the x axis and y axis, what should you do

put the dependent variable on the y axis (dependent variable is the one being measured eg time taken, or temperature rise, it is also the result of the experiment)

put the independent variable on the x axis, this is the factor that is changed

what is the dependent variable and what is the indepedent variable in the speed of reaction experience where concentration of solution is changed and time is taken

concentration is independent variable

time is the dependent variable

if the question asks you to plot temperature rise against time taken, which is the y axis and which is the x axis

temperature rise is the y axis and time taken is the x axis

what is measuring the mass of solid using an electronics weighing balance used for (gravimetry)

to determine the empirical formula

to determine the yield of the salt

determine the x, water of cryslisation of hydrated salt

determine the mass of product formed during decomposition reaction

how to conduct gravimetry

1. weigh a clean dry empty boiling tube/crucible'

2. place x g of solid in the boiling tube and record the total mass

3. heat the boiling tube and its content gently for one minute and then strongly for about five minutes

4. allow the boiling tube and its contents to cool

5. reweigh the boiling tube and its contents

6. repeat heating, cooling and reweighing until the mass is constant

what are some sources of error during gravimetry

in determining the empirical formula, not all the of the metal may have reacted with oxygen, and there was a loss of the oxide during heating

in determining the yield of the salt, not all the salt crystallised, and there is a loss of salt due to the sputtering of salt during evaporation of the salt solution to dryness and the salt is not completely dry before weighing

what are some sources of error in chemistry experiments

1. the apparatus (degree of accuracy)

2. the materials used (eg stability of chemicals if it decomposes at room temperature and pressure or reacts with the moisture and the oxygen in the air)

3. purpose of experiment (eg if the time taken is the dependent variable, human reaction time in starting and stopping the stop watch is inconsistent hence affecting the accuracy of the experiment)

4. salt prep (solids may not be completely dry, some solids lost during filtration, sputtering of the solids)

5. measuring temperature change involving large pieces of a solid reagent (large piece does not allow for fast reaction, more heat loss to the surroundings due to slow reaction)