Determine Acidity of Water

 EXPERIMENT NO. 02

OBJECT: To determine the acidity of a given sample of water using N/50 Sodium Hydroxide (NaOH) solution and Methyl Orange and Phenolphthalein as indicators.

 

OBSERVATION TABLE:

Titration between given water sample and N/100 sodium hydroxide solution and methyl orange and phenolphthalein as indicators.

S. No.	Volume of sample (X) (mL)	Burette reading (mL)			Concordant reading (mL)
		Initial	Methyl Orange end point (Y)	Phenolphthalein end point (Z)	Y	Z
1.	20	0.0	5.8	13.6	5.8	13.6

 

 

 

 

 

 

CALCULATION:

Volume of given water sample (X) = 20 mL

Volume of NaOH used up to methyl orange end point = Y mL Volume of NaOH used up to phenolphthalein end point = Z mL

 

1.  Acidity up to Methyl orange endpoint:

According to the law of equivalence:

N1V1 of Sample	= N2V2 of NaOH
N1 × 20	= N/50 × 5.8
N1	= 5.8/1000

 

Acidity up to the Methyl orange end point (in terms of CaCO₃ equivalent):

 

= Normality x Equivalent Weight of CaCO₃

= (5.8/1000) x 50 g/L

= (5.8/1000) × 50 × 1000 mg/L or

ppm strong or mineral acidity = 290 ppm

 

2.  Acidity up to Phenolphthalein endpoint:

According to the law of equivalence:

 

N1V1 of Sample	= N2V2 of NaOH
N1 × 20	= N/50 × 13.6
N1	= 13.6/1000

 

Acidity up to the Phenolphthalein (in terms of CaCO₃ equivalent):

 

                    = Normality x Equivalent Weight of CaCO₃                                                                                                   = (13.6/1000) x 50 g/L                                                                                                                      = (13.6/1000) × 50 × 1000 mg/L  or ppm        

                    Total acidity = 680ppm

Now,

Weak acid acidity = Total acidity - Mineral acid acidity

 

 

RESULT: Acidity of given water sample:

Total acidity =680 ppm

Strong acid acidity = 290 ppm

Weak acid acidity=390 ppm