İHSAN DOĞRAMACI FOUNDATION
BİLKENT ERZURUM LABORATORY SCHOOL
2011-2012 Academic Year
2nd Semester
9th Grade Chemistry
LAB REPORT 2
Name: İrem Gaye Kars
Topic: Testing acids and bases using litmus paper
Purpose of the Experiment: To learn how to use litmus paper to calculate the pH of the
acids and bases.
Hypothesis: In my opinion, pH degrees of each substance will vary.
Introduction: In chemistry, pH is a measure of the acidity or basicity of an aqueous
solution by discriminate the colors. In the picture below, you can see how it is decided.
Another way to test acids and bases is using titration. An acid-base titration is the
determination of the concentration of an acid or base by exactly neutralizing the acid/base
with an acid or base of known concentration. Titration is a procedure used in chemistry in
order to determine the molarity of an acid or a base. A chemical reaction is set up between a
known volume of a solution of unknown concentration and a known volume of a solution
with a known concentration. The relative acidity (basicity) of an aqueous solution can be
determined using the relative acid (base) equivalents.
Here there are some examples of titration calculations.
Example 1: 25 cm3 of vinegar were neutralized by 20 cm3 of 1 M sodium hydroxide solution.
What is the concentration of the ethanoic acid in the vinegar?
Step 1  calculate the number of moles of sodium hydroxide used.
1000 cm3 of 1 M solution contains 1 mole so 20 cm3 contains
20
100
𝑥 1 mole or 0.02 mole.
Step 2  from the equation; find the molar ratio of acid to alkali.
CH3COOH (aq) + NaOH (aq)  CH3COONa (aq) + H2O (l)
1 mole
1 mole
The ratio is 1 mole of acid to 1 mole of alkali.
Step 3  work out the number of moles of acid neutralized.
1 mole of alkali neutralizes 1 mole of acid so
0.02 mole of alkali neutralizes 0.02 mole of acid.
Step 4  calculate the concentration of the acid. (25 cm3 = 0.025 dm3)
𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 =
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑙𝑒𝑠
𝑣𝑜𝑙𝑢𝑚𝑒 𝑖𝑛 dm3
=
0.02
0.025
= 0.8 mol/dm3
So the concentration of ethanoic acid in the vinegar is 0.8 mole
Example 2: Step 1  calculate the number of moles of sodium carbonate used.
100 𝑐𝑚3 of 1 M solution contains 1 mole so
25
25𝑐𝑚3 contains 1000 * 1 mole or 0,025
Step 2  from the equation; find the molar ratio of acid to alkali.
2HCI(aq) + 𝑁𝑎2 𝐶𝑂3(aq) → 2NaCl(aq)+𝐻2 O(l) + C𝑂2(g)
Step 3  work out the number of moles of acid neutralised.
1 mole of alkali neutralizes 2 mole acid so
0,025 mole of alkali neutralizes 2*0,025 moles of acid
0,05 moles of acid were neutralized.
Step 4  calculate the concentration of the acid.
𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 =
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑙𝑒𝑠
𝑣𝑜𝑙𝑢𝑚𝑒 𝑖𝑛 dm3
=
0.05
0.0278
=1,8 mol/𝑑𝑚3
So the concentration of the hydrochloric acid is 1,8 M.
Example 3: Step 1  calculate the number of moles of acid neutralized.
1000 𝑐𝑚3 of the sulphuric acid contains 2 moles so ,
12𝑐𝑚3 contains
12
1000
*2 moles or 0,0024 mole.
Step 2  from the equation; find the molar ratio of acid to alkali.
𝑯𝟐 𝑺𝑶𝟒 (aq)+ 2N𝑯𝟑 (aq) → (𝑵𝑯𝟒 )2 𝑺𝑶𝟒 (aq)
Step 3  work out the number of moles of acid neutralised.
1 mole of acid is neutralized by 2 moles of alkali so ,
0,0024 mole of acid is neutralized by 0,0048 mole of alkali
Step 4  calculate the concentration of the acid.
𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 =
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑙𝑒𝑠
𝑣𝑜𝑙𝑢𝑚𝑒 𝑖𝑛 dm3
=
0.0048
0.01
= 0,48 𝑑𝑚3
So the concentration of ammonia in the cleaner is 0,48 mol/𝑑𝑚3
Experimental Setup: Before start to the experiment, area of experiment, equipments and
safety should be controlled. Experimenter student must wear lab coat, gloves and glasses to be
protected from some possible dangers. Also, be sure that lab safety rules are being acted.
List of Equipment:
 30 cm3 of tap water
 30 cm3 of lemon juice
 30 cm3 of apple vinegar
 30 cm3 of lemon vinegar
 Bicarbonate of soda dissolved 30 cm3 of water
 Na2O3
 H2SO4
 HCl
 NaOH
 NH3
 10 beakers
 Litmus paper (orange)
Procedure to Follow:

Firstly, prepare the apparatus needed during the experiment.

Then fill the beakers with the aquatic solutions.

To indicate acids and bases, sink a piece of litmus paper into the aquatic solutions.

Wait for drying.

By looking at the color change, decide the pH number of the solution.

Compare the color with the pH chart (shown in the introduction part.)

Record the results.

Determine the acids and bases, and compare.
Data Result:
pH degree of:
30 cm3 of tap water is between 7 and 8. It is nearly neutral.
30 cm3 of lemon juice is 2. It is strong acid.
30 cm3 of apple vinegar is between 3 and 4. It is acid that weaker that lemon juice.
30 cm3 of lemon vinegar is 1. It is stronger acid than lemon juice.
Bicarbonate of soda dissolved 30 cm3 of water is between 9 and 10. It is weak base.
Na2O3 is 12. It is stronger base than bicarbonate of soda.
H2SO4 is between 0 and 1. It is a little bit stronger acid than lemon vinegar.
HCl is 1. It is as strong acid as H2SO4.
NH3 is 13. It is strong base.
NaOH is 14. It is the strongest base ever calculated in this experiment.
Conclusion and Evaluation:
As a result of experiment, it is proved that every different aquatic solution has
different pH number that depends on its acidic and basicity qualities. Because of some
unexpected conditions, results cannot be the real ones but they are absolutely closer.
Therefore, experiment is successful.