Magdalena 1

Irene Magdalena

Mr Owen

Chemistry HL

20 September 2012

Limiting Reagent Lab Report

Data Collection and Processing Total DCP Mark __/6Aspect 1 – Recording Raw Data

Aspect 2 – Processing Raw Data

Aspect 3 – Presenting Processed Data

Raw DataData collected

independentlyData primarily numbericalQualitative data collected

Table organizationDescriptive titlesColumn/Row same as

graphIV on leftSpecific termsTable not split over pageCells contain one valueTable arranged verticallyTable has grid lines

Table NumbersUnits/Uncertainties in

headingAll values in column have

same dec placesUses sig figsMean appropriate sig figs% or relative uncertainty 2

sig figs

Suitable processedAll raw data processedExample calculationsData processed correctlySig figs correct

GeneralAll processed data suitably

presentedLogical clear progressionFinal result correct n of sig

figsUncertainty are errors

correct and appropriateGraphsAppropriate style of graphTitles on graph and axisCorrect Units on axisUncertainty shown on axisScales shown on axisScales appropriateGraphs large enough SI units usedLine of best fit (if

appropiate)

Criterion Mark /2 Criterion Mark /2 Criterion Mark /2

Raw Data:

Reactant Compounds Amount Measured (g) Possible error (g)

Pb (NO3)2 1.01 ± 0.01

KI 0.801 ± 0.01

Magdalena 2

Product Compounds Amount measured (g) Possible error (g)

PbI2 1.10 ± 0.01

KNO3 3.71 ± 0.01

Processing Data:

Balanced Chemical Equation:

Pb (NO3)2 (aq) + 2 KI(s) PbI2 (s) + 2 KNO3 (aq)

Reactants

Pb (NO3)2:

- Mass used: 1.01 ± 0.01 g

- Mr : 207.2 + 124.02 = 331.22 g 1 mol of Pb (NO3)2

- n = (1.01/331.22) = 3.049 x 10-3 mols

KI:

- Mass used: 0.801 ± 0.01 g

- Mr : 39.1 + 126.9 = 166.01 g 1 mol of KI

- n = (0.801/166.01) = 4.825 x 10-3 mols

Since there are 2KI: (4.825 x 10-3)/2 = 2.413 x 10-3 mols

To determine which one is the limiting reagent:

2.413 x 10-3 > 3.049 x 10-3

KI > Pb (NO3)2

∴ The limiting reagent is KI since the value calculated for KI is smaller than Pb (NO3)2

Magdalena 3

Products:

PbI2

- Mr : 4.61 x 102 g 1 mol of PbI2

- Actual yield: 1.10 ± 0.01 g

- Theoretical yield: (4.16 x 102) x (2.413 x 10-3) = 1.112 g

- Percentage yield: ((1.10) / (1.112)) x 100 = 98.92%

KNO3

- Mr : 1.0111 x 102 g 1 mol

- Actual yield: 3.71 ± 0.01 g

- Theoretical yield: (1.0111 x 102) x (4.825 x 10-3) = 4.879 x 10-1 g

- Percentage yield: ((3.710) / (4.879 x 10-1)) x 100 = 760.47%

Table:

Balanced Chemical Equation:

Pb (NO3)2 (aq) + 2 KI(s) PbI2 (s) + 2 KNO3 (aq)

Reactant Product

Compound Name Pb (NO3)2 KI PbI2 2 KNO3

Mass (g) 1.01 ± 0.01 0.801 ± 0.01

Theoretical yield (g) 1.112 4.879 x 10-1

Actual yield (g) 1.10 ± 0.01 3.71 ± 0.01

Percentage yield (g) 98.92% 760.47%

Magdalena 4

Conclusion:

We know currently that PbI2 only has a percentage of 98.92% and that is less from

100%. There are reasons to why this happened. After we poured the PbI2 into the filter paper,

there might be some of the compound left inside and however much water we use to try and

rinse it out and into the filter paper, some might be too small for us to see. Another

possibility, although highly unlikely, is that since the substance is too small, it flows out from

the filter paper along with the water. Not only that, there might be instrumental error

involving the scale since the scale won’t give us a proper reading and keeps on changing its

numbers. The wind around us might have blown out some of the powder when we weren’t

aware of it. All these possibilities that I have stated might be the reason to why we didn’t

achieve 100%, although we were close enough in terms of numbers since if we were to round

up, we would get at least 99%.

We may have gotten a more or less accurate reading for PbI2 but that doesn’t seem to

be the case for KNO3 since we found out that our calculations exceed 100% greatly with a

total of 760.47%. I’m not entirely sure how we came into terms with this number but it could

have been the water that was evaporating. My group had the most water amongst the other

group in the flask. While the water is evaporating, we ran out of time and had to leave the

flask in the hands of the lab helper. We came back later to find that our flask is wide open

and not closed with a stopper. There might be a possibility that the water molecules inside the

air and other unknown substances entered the flask. We reheated the flask, as it wasn’t heated

when we re-entered the lab. After all the aqueous solution has been evaporated, we find that

our flask had certain green and yellow elements stuck to the bottom of the flask. It could be

due to our ignorance that we didn’t provide a stopper or it could have been a miscalculation

someplace but we highly doubt the latter is the case.

Magdalena 5

We did what we were told by the instructions to the best of our ability. There are

however, errors in our ways. We didn’t get an accurate reading while evaporating the

aqueous solution in the flask since the numbers kept changing. There might also be an error

while we were trying to dry the lead (II) iodide in the filter paper using tissue; we might have

dabbed a little too much, causing some of the compound to fasten on the tissue and thus there

isn’t an accurate reading when we calculated it.

The scale, as mentioned several times before, might have issues inside it. We tried

hard to get an accurate reading but try as we might, the numbers displayed on the screen

didn’t seem to stop and kept on changing in values no matter what. We concluded that

although the numbers kept on changing, it didn’t really go over 0.01 g so we made that our

uncertainty.

The experiment was not the biggest success but like all experiments, we learn through

trial and error. If given the right tools and more time, we could have gotten a much better

result than the ones we have now.