✅ 5. Required Practical: Neutralisation - Acid-Alkali Titration (C4)

Question 1

What is an Independant Variable

Answer 1

An Independant Variable is the variable that is altered during a scientific experiment.

Question 2

What is a Dependant Variable

Answer 2

A dependant Variable is the variable being tested or measured during a scientific experiment.

Question 3

What is a Control Variable

Answer 3

A Control Variable is the variable that is kept the same during a scientific experiement.

Question 4

What are Tritations and Why do you do them?

Answer 4

Titrations are a very accurate way of measuring the concentration of acids and alkalis.

In a titration, we measure the volume of an acid (or alkali), measured in a burette, needed to exactly neutralise an alkali (or acid) which has been carefully measured into a conical flask with a pipette and filler.

We use an indicator (either Phenolphtalein or Methyl Orange) to judge the exact volume required to do this.

Question 5

What colour does phenolphthalein go when the solution is Acid and Alkalai

Answer 5

For Acid, the solution is Colourless

For Alkali, the solution is Pink

Question 6

What colour does Methyl Orange go when the solution is Acid and Alkalai

Answer 6

For Acid, the solution is Red

For Alkalai, the solution is Yellow

(When both are equal, it is Orange)

Question 7

What is the Aim of this Practical

Answer 7

You are going to find the concentration of a solution of alkali using a solution of acid in a technique called a Titration. You will pipette 25.0 cm3 of alkali into a conical flask and, using a burette, find the volume of acid needed to neutralise the alkali solution.

Question 8

Health and Safety Measures

Answer 8

• The acid and alkalai are irritants
• Be careful not to allow solution to enter the pipette filler
• You will need eye protection
• You could choose to wear safety gloves
• If you smash your concial flask, clean up the solution, and dispose of the glass

Question 9

Method for Neutralisation (Acid-Alkali Titration) RP

Answer 9

1. Use a clean, dry pipette and pipette filler to measure exactly 25.0cm^3 of sodium hydroxide solution in a conical flask.
2. Place the flask on a white tile
3. Add three or four drops of phenolphthalein / methyl orange indicator to the flask
4. Prepare and fill the burette with dialute acid and record the initial volume in the results tables.
5. Titrate the acid with the sodium hydroxide solution swirling the flask on addition.
6. Once the indicator changes colour, record you final reading.
7. Once you have completed your rough titration, you then move onto doing you accurate ones, until you get two concordant results. To do this:
   - Rinse out the conical flask woth water
   - Re-fill ghe burette with acid and record the start reading
   - Add another 25cm^3 of sodium hydroxide solution from the pipette into the conical flask and add 4 drops of indicator
   - Add acid from the burette to the conical flask until you are close to the point where it changes colour, and the. Start adding the acid drop by drop to get a more accurate ejd point; as you approach the end point, rinse down the insides of the flask with deionised water from a wash bottle
   - Record the final reading
8. When you have done enough titrations, rinse out all the glassware with water. To rinse the burette, pour water from a beaker through the burette. For the pipette, use a pipette filler to fill and drain the pipette with water.

Question 10

How to lay out the Results Table

Answer 10

________________________________________________
| | Rough | Exp 1 | Exp2 | Exp 3 |
|————————|————–|————–|————|————-|
| Final vol/cm^3 | | | | |
|————————|————–|————–|————|————-|
| Initial vol/cm^3 | | | | |
|————————|————–|————–|————|————-|
| Titre/cm^3 | | | | |
|————————|————–|————–|————|————-|
| Concordants | - | | | |
———————————————————————————-

(Then from this table, you will need to work out the average titre/cm^3 (not including the Rough one)

Question 11

How will you calculate the mol/dm^3 (concentration) of HCl for Titration when the equation is NaOH + HCl → NaCl + H2O (starting with 0.1 mol)

(When NaOH volume is 25cm^3
And the Average Titre is 24.95cm^3)

Answer 11

n(alkali) = cV = 0.1 mol/ dm3 x (25.0/1000) dm3 = 0.0025 mol mol

ratio from equation = 1:1

n(acid) = cV = 0.0025 mol

c(acid) = n/V = 0.0025 mol ÷ (24.95/cm^3 /1000) dm^3 = 0.10 mol/ dm^3

Question 12

How will you calculate the mol/dm^3 (concentration) for Titration when the equation is 2NaOH + H2SO4 → Na2SO4 + 2H2O (starting with 0.1 mol)

(When NaOH volume is 25cm^3
And the Average Titre is 24.95cm^3)

Answer 12

n(alkali) = cV = 0.1 mol/ dm^3 x (25.0/1000) dm3 = 0.0025 mol

mol ratio from equation = 2:1

n(acid) = cV = 1/2 x 0.0025 mol

c(acid) = n/V = 0.00125 mol ÷ (24.95 /cm^3 /1000) dm^3 = 0.050mol/dm^3

Question 13

Example Question: 25.0 cm3 of 0.200 mol/dm^3 barium hydroxide solution reacted with 22.8 cm^3 of hydrochloric acid. Calculate the concentration of the hydrochloric acid in mol/dm3.

Equation: Ba(OH)2(aq) + 2 HCl(aq) → BaCl2(aq) + 2 H2O(l)

Answer 13

Firstly, you will find the moles of barium hydroxide, and then apply it to the mole ratio to find the number of Hydrochloric Acids. After this you will do the Moles/Volume to get Concentration of the Hydrochloric Acid in dm^3.

n(BaOH) = cV = 0.200 x (25/1000) = 5x10^-3 mols
Mole Ratio = 1:2
n(HCl) = 5x10^-3 x 2 = 0.01
C(HCl) = Mols/Vols = 0.01 / (22.8/1000) = 0.439dm^3

Question 14

What is the equation for amount of moles, and concentration in g/dm^3

Answer 14

Amount in moles = ( Concentration (mol/dm^3) x Volume (cm^3) ) / 1000

Concentration in g/dm^3 = Concentration in mol/dm^3 x Molar Mass

Question 15

What do you do in this Practical/What is the aim?

Answer 15

You are going to find the concentration of a solution of sodium hydroxide solution using a solution of 0.10 mol/dm^3 of Hydrochloric Acid

Question 16

What Equipment is needed for this Practical?

Answer 16

• 50cm^3 burette plus stand and burette holder
• 2 x 250xm^3 beaker
• 250cm^3 conical flask
• 25.0cm^3 bulb pipette plus pipette filler
• White Tile
• Funnel
• Phenolphthalein Indicator / Methyl Orange Indicator
• 0.1mol/dm^3 hydrochloric acid
• Sodium Hydroxide of unknown concentration
• Wash bottle of distilled water

Question 17

What is repeatability and reproducability?

Answer 17

Repeatability is is the closeness of the agreement between the results of successive measurements of the same measure, when carried out under the same conditions of measurement.

Reproducability means that a result obtained by an experiment or observational study should be achieved again with a high degree of agreement when the study is replicated with the same methodology by different researchers.