Limiting Reagent LABORATORY task.

xxxxxxxxx.

TITLE PAGE

Title of the Laboratory Assignment: Limiting Reagent

Name: xxxxxxxxxxxxx

Course and Section Number: xxxxxxxxxxxxxxx

Instructor: xxxxxxxxxx

Lab Partner(s): xxxxxxxxxx

LABORATORY REPORT

I. Introduction/Purpose of Experiment

1. To Obtain firsthand knowledge on experience with the limiting reagent problem together with learning how to use filtration to isolate a solid product.

2. To account the importance of drying a sample in a quest to obtain an accurate weight of a product that ascertains the experimentally measured percent yield.

II. Materials

Reagents- 0.5M Calcium Chloride (CaCl2), 0.5M Sodium Carbonate (Na2CO3)

Apparatus- Test tube, Test tube rags,10ml measuring cylinder, labeling stickers,50ML beakers, Stopwatch, Vortex- Mixer, Filter papers, plastic-funnel, ring stand, watch glass, heating plate, electronic weighing balance, teat pipettes, wash bottle, De-Ionized water.

III. Procedure

1). Six clean test tubes were labeled as A1, A2, A3, B1, B2 and B3 to hold the reaction mixtures. Into each of the test tubes, 4 ml of Calcium Chloride were added.The initial and final volumes were recorded taking note of the molarity on the reagent bottle.

2).To the test tubes, corresponding approximate amounts of Sodium Carbonate solution were added as indicated. A1 and B1 (1mL to each), A2 and B2 (4 ml to each), A3 and B3 (6 ml to each). Initial and final volumes were precisely recorded. The molarity from the reagent bottles was also noted

3). Each of the test-tubes was placed in a Vortex mixer and allowed to mix for up to 30 minutes then left to settle undisturbed for a remarkable duration of up to an hour. The test tubes were put on two different rags as per their individual letters.

4).Filtration apparatus were set up for the corresponding labeled precipitates ensuring no precipitate remained in the test tubes to effect proper filtration process. The filtrates were well kept for further use in the experiment.

5). Each filter paper with the precipitate was put on a watch glass and left to dry on a hot plate after that the filter papers plus the contents weighed and results recorded

6).The actual yield for each trial was calculated and a balanced chemical equation written thereby identifying the precipitate. Calculation, the theoretical yield of each of the trials, helped determine the percentage, the limiting and reagent in excess.

7).Of the filtrates A1, A2, and A3, each was poured out into two identical test tubes and 1ml of CaCl2 added to both. The precipitates were allowed to settle for an hour and observations drawn in the lab notebook as Data & Results Summary Table – Part III, bringing to account the observable physical properties. This was a test of dissolved ions

8). Without any disturbance, the test tubes on rack B that had been left to settle for an hour were keenly scrutinized and observations drawn in the lab notebook. The physical properties of the precipitate were also accounted for.

IV. Data and Results

CaCl2 (aq) + Na2CO3 (aq) →CaCO3(s) + 2NaCl (aq)

Ex, Table- Determining the mass of dry solid, (CaCO3).

Amount in grams	A1	A2	A3
Filter paper weight with dry solid(g)	0.9878	1.4750	1.1107
Filter paper weight without solid(g)	0.9240	0.9219	0.9308
Amount of solid (g)	0.0638	0.5531	0.1799

Ex, Table I and II.-Analysis of the six trials

CaCl2 (aq) + Na2CO3 (aq) →CaCO3(s) + 2NaCl (aq)

Trial	A1	A2	A3	B1	B2	B3
Volume of CaCl2 (ml)	3.9	3.9	4.1	3.9	4.1	3.9
Volume of Na2CO3 (ml)	0.9	3.9	6.0	1.0	4.0	6.0
Theoretical mass of precipitate(g)	0.045	0.195	0.205	0.050	0.20	0.195
Limiting Reagent	Na2CO3	None	CaCl2	Na2CO3	Na2CO3	CaCl2
Reagent in Excess	CaCl2	None	Na2CO3	CaCl2	CaCl2	Na2CO3
Actual mass of precipitate	0.0638	0.5531	0.1799	N/A	N/A	N/A
Percentage yield (%)	141.78	283.64	87.76	N/A	N/A	N/A

CaCl2 (aq) + Na2CO3 (aq) →CaCO3(s) + 2NaCl (aq)

Ex, Table III.-Supernatant test

Trial	A1	A2	A3
Predicted reagent in excess	CaCl2	㆒㆒	Na2CO3
Observation after adding CaCl2 (aq)	Clear liquid. No reaction.	Clear thick liquid. No reaction.	Clear liquid. No reaction.
Observation after adding Na2CO3(aq)	White Precipitate Thicker white precipitate.	Clear thick liquid. No reaction.	White precipitate. Thicker white precipitate.

V. Calculations

i).The number of Moles of each of the reactants used were calculated as; Volume in ml x (1L/1000ML) x Molarity.

For Instance; 4ml of 0.5M CaCl2 and 6ml 0f O.5M Na2CO3 were used at some point of the experiment. Calculating the number of moles in each case, the above formula applies.

CaCl2- 4ml x 1L/1000ml x 0.5m/1000ml=0.002 moles

Na2CO3- 6ml x 1L/1000ml x 0.5m/1000ml=0.003 moles

ii).Mass of the precipitate solid=Mass of dry solid and filter paper-mass of the plain unused filter paper. i.e. If the mass of filter paper and dry solid was 1.1107 and that of plain filter paper was 0.9308, the mass of precipitate is given by; (1.1107-0.9308)g =0.1799g

iii).Given the chemical equation; CaCl2 (aq) + Na2CO3 (aq) →CaCO3(s) + 2NaCl (aq)

The limiting and reagent in excess plus the theoretical yield of precipitate was determined as; (Volume of reagent X the molarity X mole ratio with the precipitate X Relative molecular mass of precipitate.)The reagent with the minimal mass is the limiting reagent whereas the one with more mass is in excess. For the case of the experiment basing that 4ml of 0.5M CaCl2 and 6ml 0f O.5M Na2CO3 we reacted;

4ml x (1L/1000ml) x (0.5mol CaCl2 /1000ml) x (1mol CaCO3/1mol CaCl2 ) x (100g CaCO3/1mol CaCO3) = 0.0002g CaCO3

6ml x (1L/1000ml) x (0.5 mol Na2CO3/1000ml) x (1mol CaCO3/1mol Na2CO3 ) x (100g CaCO3/1mol CaCO3) = 0.0003g CaCO3

The limiting reagent is CaCl2, and the one in excess is Na2CO3. 0.0002g is the theoretical mass of precipitate

iv). Percentage yield is equivalent to (actual yield/theoretical yield) x 100.For example; given the theoretical mass of a sample as 0.205g and actual mass as 0.1799g, percentage yield is calculated using the above formula.

Percentage yield → (0.1799g/0.205g) x 100=87.76%

VI. Discussion

The laboratory experiment conducted was a good example of double replacement/Precipitation reaction that involved the mixing of two aqueous ionic compounds in producing a precipitate. The precipitate formed was easily predicted by the use of solubility concept due to cations switching lanes when an excess solution was added. The theory behind precipitation was achieved because one of the products was insoluble and thus brought forth the desired purpose of the experiment

The limiting reagent (the substance that was totally depleted when the chemical reaction was complete) could not be deduced at a glance unless otherwise a well balanced chemical equation written. Calculations were conducted basing on the used volumes and concentrations that helped determine the ultimate answer of the unknown limiting reagent, excess reagent and eventually the theoretical mass of the said precipitate.

The supernatant solution obtained after the filtration process came to a halt further brought to account and clarified the ions present in solution from the initial chemical reaction. At points where there was no remarkable change, it indicated that ions of a similar kind were being added. The precipitation in the variant test tubes was a clear indication that ions of a different kind were introduced hence reacted

Gross contamination was the main attributed reason as to why erroneous results in percentage yield of the precipitate were encountered. Thorough rinsing of the reaction apparatus and sufficient drying would have rather brought quite accurate results.

VII. Conclusion.

The prime purpose of the laboratory session was to obtain firsthand knowledge of experience with the limiting reagent problem together with learning how to use filtration to isolate a solid product. The prior knowledge gained from solubility was vital in primarily predicting the precipitate before a step was further taken in ascertaining the limiting and excess reagent and also the theoretical yield of the precipitate, backed the formula, (Volume of reagent X the molarity X mole ratio with the precipitate X Relative molecular mass of precipitate.)

The actual mass of solid precipitate dried out, together with the theoretical mass postulated aided in the calculation of percentage yield of precipitate as desired .i.e. (actual yield/theoretical yield) x 100.

8