Experiment 5

Topic : Volumetric – stochiometry

Purpose : to determine the exact concentration of monobasic acid, HX

Question : you are provided with a monobasic acid, HX, with a concentration in the range of 0.5 mol dm-3 to 1.0 mol dm -3. You are required to plan and carry out an experiment to determine the exact concentration of the HX solution provided.

Materials

KA 1 is a solution containing an unknown acid, HX with a concentration varying from 0.5 mol dm -3 to 1.0 mol dm -3

KA2 is a solution containing sodium carbonate, NA2CO3 with a concentration of 1.0 mol dm-3

Phenolphthalein as indicator

Apparatus

Weighing bottle, volumetric flask 500 ml or 500 cm3, electric balance, filter funnel, wash bottles, droppers, beaker, retort stand, burette, pipette, sucker, conical flasks, white tiles, distilled water and a spatula.

Theory

The equation of neatralisation as following:

H+¿+OH−¿→H 2O ¿¿

To find the mass,m needed for the base , we have

No of moles = MV1000

mMr

= MV1000

m= MV1000

×Mr

Where m= mass needed

M=concentration of the base

V=volume of the base

Mr=Relative molecular mass

The concentration of the monobasic acid can be found through the formula below :

MAV A

M BV B

= xy

Where M A=¿concentration of the monobasic acid

MB=concentration of the base

V A=¿volume of the monobasic acid from titration

V B=volume of the base

x=number of moles of the monobasic acid

y=number of moles of the base

Introduction

Preparation of a standard solution of sodium hydroxide, NaOH is done by dissolving pure sodium metals in water, H2O. In the process, small sparks are seen as the reaction takes place. The Na+ ions react with OH- ions to form sodium hydroxide solution which used in second part of the experiment. Sodium hydroxide solution can be prepared by dissolving sodium hydroxide pellets with certain amount of water to get suitable molarity.

Procedure:

Part 1: preparing a standard solution of 1.0 mol dm-3 sodium hydroxide, NaOH.

1. A electronic balance and weighing bottle are used to weigh 10 g of sodium hydroxide powder using a spatula.

2. The solid are carefully tipped into a beaker containing distilled water.3. Any solids remaining in the weighing bottle is washed into the beaker into the beaker with a wash

bottle.4. After dissolving the solid, the final solution is carefully transferred into the volumetric flask using a

glass rod and a filter funnel.5. About reaching the volume needed, stop at 1 or 2 cm from the line. By using a dropper or a wash

bottle, carefully filling it until the mark. 6. The flask is then shaken to mix the solution thoroughly. 7. The solution prepared is a standard solution of 1.0 mol dm -3 or 1.0M.

Part 2: Titration of 1.0 mol dm-3 sodium hydroxide, NaOH, with an unknown acid, HX with a concentration between 0.5 mol dm-3 to 1.0 mol dm-3

Pipette 25cm3 of KA1 into the titration flask. Titre the solution with KA2.

Repeat titration as many times as you think it is necessarily to achieve accurate results.

Results:

Titration Rough AccurateFirst Second Third

Final reading / cm3

25.00 24.90 24.80

Intitial reading/ cm3

0.00 0.00 0.00

Volume of KA2/ cm3

25.00 24.70 24.80

i) 25cm3 of KA 1 required __24.75__cm3 of KA 2 for a complete reaction.

ii) Average titre value = 24.70+24.80

2=24.75cm2

Calculation:

HX (aq )+NaOH (aq )→Nax (aq )+H 2O(l)

MAV A

M BV B

= xy

MAV A

M BV B

= 11

M A= ( 11 )(MBV BV A

)

=1(25.0)24.75

=1.010 Mol dm-3

Conclusion:

The exact concentration of a monobasic acid , HX is 1.

Precaution

1. Sodium in metal form is highly reactive. Wearing protective gears and precautionary steps are taken to minimize accidents during the process of cutting Sodium (natrium , Na) solids.

2.Handle sodium metal with gloves. Sodium is reactive when come in contact with water.