Chem Lab Report Oxalic Acid

Chem lab report Design Aim: To  To determine determine the moles of water water of crystallization in oxalic acid. Hypothesis: If NaOH is added to Hydrated Oxalic acid, then the hydrogen hydrogen ions from the acid will react with hydroxide ions from NaOH to produce water. The rest forms a colorless salt. In this experiment, the moles of water of crystallization is calculated using titration. An indicator is used to show when the titration has ended. Since two moles of NaOH react with one mole of oxalic acid, we can nd out the moles of oxalic acid used, then using the mass of the crystals ta!en, nd the mass of water present in the crystals which will gi"e the molecules of water of crystallization in oxalic acid.

Variables: •

•

Independent # o $olume of NaOH used% since &'cm() of NaOH is ta!en for all trials *ependent# o $olume of oxalic acid solution used%the "olume of oxalic acid solution used would

depend on the "olume of NaOH ta!en for titration.

•

+ontrolled "ariales# NaOH ta!en ta!en for titration o  The "olume of NaOH should e !ept constant for each trials. o -ass of oxalic acid crystals%the mass should e controlled at the eginning of the experiment and should e ta!en in small amount/.'g0  Temperature%since e%since it a1ects the reaction, reaction, it o  Temperatur should e maintained.

Materials and equipment: o o o o o

2urette '3ml0 4ipette /3ml0 NaOH Oxalic acid crystals 2alance

o o o

o

4henolphthalein +onical 5as! $olumetric 5as! &'3ml0 4ipette ller

Environmental care:  the solutions can e drained down the sin!. Safety: • •

wear eye protection use pipette ller

rocedure: /. 6eigh out accurately /.' g of oxalic crystals using a digital alance chec! for zero error efore weighing the crystals0. &. 4ut the crystals in the "olumetric 5as! using a funnel. -a!e sure that the crystals don7t fall out. ). 4our water into the "olumetric 5as! and ll it up to the 250 c m mar!. 3

8. +lose the opening of the 5as! and sha!e sha!e the solution efore pouring it into the urette using a funnel. 3

'. 4ipette of 3./ solution into a conical 5as!. 25.0 c m

−3

mold m

 sodium hydroxide

9. Add two to three drops of phenolphthalein into the conical 5as!. :. 4our the oxalic acid slowly into the conical 5as!. -a!e sure you swirl continuou c ontinuously sly.. ;. Add oxalic acid until the indicator loses its color. <. =ecord the reading of the urette and repeat the experiment.

DC !able": ra# data of volume of o$alic acid used

$olume of oxalic acid used (± 0.12 ml ) Oser"ation#

 Trial  Trial  Trial  Trial  Trial  Trial  Trial  Trial  Trial  Trial / & ) 8 ' &/.' &).3 /:.9 /;.< &8.' Since one molecule of oxalic acid, when diluted in water, gi"es & hydrogen ions. (COOH ) . x H  O → 2 H − 2

1

2

 These & ions neutralize neutralize with

one hydroxide ions from NaOH. + 1( aq )

 NaOH (aq ) → N a

+ O H −

1( aq )

−¿( aq) ↔ H  O + ¿( aq) +2 OH ¿ 2

¿ 2 H 

 The indicator lost lost its color at the end of the reaction.

!able %: data processing for average volume of acid used -easure d "olume> m?

-ean> m?

4recision Accuracy =ange> Standa @rror>m  m? rd ? error de"iati on

&8.' &:.< &).8 &'.98 8.' &8.< &:.' !able &: calculation

/.<9

4rocessing

3.3'

uncertainty + (COOH ) . x H  O→Na C  O + y H  O

2 NaOH 

2

2

2

2

4

2

3./<

-oles of NaOH# 25 × 0.1 1000

=2.5 × 10−

3

-oles of oxalic acid used to titrate NaOH# −3 2.5 × 10

2

=1.25 × 10−

3

-oles of oxalic acid present in &'3 c m #

%uncertainty =

3

( 1.25 × 10−

3

× 250 )

25.64

  0.12 25.64

× 100=± 0.46

Bncertainty in "olumetric 5as!

=0.012

¿ ± 0.12

-ass of one mole of oxalic acid# →

1.5 0.012

%uncertainty = 6.66

=125

0.1 1.5

× 100 =6.66

+0.46 =7.12

→ 125 ± 8.90

-ass of water of crystallizationC /&' D <3 C )' (± 8.90) Numer of molecules of water present in one mole# 35 18

=1.9 ≈ 2 molecules

 Therefore  Therefore oxalic oxalic acid + (COOH )

2 NaOH 

2

(COOH ) .2 H  O

.2 H 2 O→Na2 C 2 O 4

2

2

+ 4 H  O 2

CE Conclusion and evaluation

 There are are & molecules of water water of crystallization crystallization in one mole of oxalic acid. The calculated result is close to the actual "alue.  The "olumes of the acid are found found to e precise precise and accurate which might reduce random errors.  de"iation#

2

−1.9 2

× 100 =5

Howe"er there might e some errors in the experiment to account for the de"iationE 4arallax errors

@nd point

Bsing contaminated solutions

6hen lling the "olumetric 5as! with water, ma!e sure the lower meniscus is parallel with the line of &'3 cm() +olor changes of indicators are not instant and therefore more acid is used often. Since using tap water which contains impurities, it might a1ect the readings. Also, when the pipette is not rinsed with distilled water in etween the trials, the

Amount of phenolphthalein used

existing oxalic acid may react with NaOH and gi"e di1erent reading.  The amount of indicator indicator used can cause the end point to shift.

Impro"ements# Bse pure water

4arallax error

=andom errors 4ipette use

+hec! the purity of water y oiling at /33 degree degree +elsius, and use fractional distillation to get pure water. A"oid seeing the readings from an angle. -a!e sure that the urette>pipette are straight when recording "alue =epeat the experiment for more accuracy 6ash after e"ery trial.