Precipitation reaction between sodium hydroxide and sulphate heptahydrate PDF

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This is a lab report investigating yield percentages and comparing them to molar calculations. This lab report is to standard in grade 11 chemistry classes and includes charts and tables where needed. Note that this experiment was designed by the student as well. ...

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The Precipitate created when Iron (II) Sulphate Heptahydrate Reacts with Sodium Hydroxide Solution SCH3U 25th April, 2017 Purpose: The purpose of this lab is to investigate the actual and theoretical yield precipitate when iron (II) sulphate heptahydrate is mixed with equal volumes of sodium hydroxide solution. This will be achieved by mixing 10mL of each solution together in a beaker for three minutes and then filtering the mixture using filter paper. The filter paper will be left overnight to dry and then the mass of the filter paper will be determined. The final mass of the filter paper will be compared to the initial mass of the filter paper to define the mass of precipitate. It is predicted through stoichiometry that this reaction should produce 0.2247g of Fe(OH)₂ as a precipitate, therefore the results of this lab should show the filter paper gaining a mass of 0.2247g after the solution is filtered. [3] In the chemical reaction of FeSO₄(aq) + 2NaOH( aq) → Fe(OH)₂(s) + Na₂SO₄(aq), the two metals switch places (iron and sodium), making this reaction a double displacement chemical reaction. When the new substances are filtered, the sodium sulphate created is in an aqueous form, and the iron (II) hydroxide created is in a solid form, acting as the precipitate. Materials: 250mL beaker 2x 50mL beaker funnel 250mL Erlenmeyer flask glass stirring rod tweezers wash bottle

3x filter paper paper towel electronic balance 30mL iron (II) sulphate heptahydrate 30mL sodium hydroxide solution tap water

Procedure: 1) Put on safety goggles. 2) Determine the mass of a piece of filter paper and record it. Fold the filter paper and put it in the funnel and wet it with water in the wash bottle. 3) Pour 10mL of iron (II) sulphate heptahydrate into a 50mL beaker, and 10mL of sodium hydroxide solution into another 50mL beaker. 4) Combine the iron (II) sulphate heptahydrate and the sodium hydroxide solution in the 250mL beaker and set the timer for 3 minutes. Stir with the glass stirring rod often. 5) Put the funnel with the filter paper on the Erlenmeyer flask, and then begin to filter the solution, making sure to stir each portion before filtering. 6) Once the solution is done filtering, pull the filter paper out of the funnel and rest on a paper towel. Label the area beside the filter paper “1”. Leave overnight. 7) Repeat steps 2-6 two more times, but on the 2nd time label the area beside the filter paper “2”, and the third time “3”. 8) After leaving overnight, use the electronic balance to determine the mass of the filter paper and record it.

9) Dispose of the solution and filter paper in the blue inorganic waste bin, and put the paper towel in the garbage. Observations: Table 1: The Mass of the Filter Paper Before the FIltration of the New Substance and After the Filtration of the New Substance in Grams (for calculations, refer to appendix A) Mass of Filter Paper (g) Time of Weighing

Trial 1

Trial 2

Trial 3

Average

Before

0.362

0.381

0.363

0.369

After

0.642

0.741

0.727

0.702

Table 2: The Mass of Precipitate (Fe(OH)₂) Produced per Trial (for calculations, refer to appendix A)

Mass of Fe(OH) (g)

Trial 1

Trial 2

Trial 3

Average

0.280

0.360

0.364

0.335

Trials

Figure 1: The Percent Yield Precipitate Produced from each Trial

Discussion: The purpose of this lab was to investigate the actual yield and theoretical yield precipitate of iron hydroxide liberated when iron (II) sulphate is mixed with equal volumes of sodium hydroxide. This was achieved by mixing 10mL of each solution together to create the precipitate, then filtering the mixture using filter paper and leaving the filters overnight to dry. It was predicted that this double displacement reaction would produce 0.2247g of precipitate using stoichiometry to calculate. The actual average mass produced from this reaction (refer to table 2) was 0.335g, and in all three trials the mass of precipitate produced was more than the theoretical mass, resulting in the percent yield of this experiment having a higher value than 100%. Table one demonstrates the initial mass of the filter paper and the final mass of the filter paper. In each trial there is an increase of mass of the filter paper, representing the mass of the precipitate on the filter paper. The average initial mass of the filter paper is 0.369g, and the average final mass is 0.702g. Table 2 presents the mass of the precipitate created, the average amount being 0.335g. The data on table 1 and table 2 proves that mixing iron (II) sulphate and sodium hydroxide is a double displacement chemical reaction because of the increase of mass seen on the filter paper after the solution was filtrated. Figure 1 displays the percentage yield, the actual mass of the precipitate is divided by the theoretical mass of the precipitate. This figure shows that each trial made more than 100% of the predicted mass of Fe(OH)₂, proving the prediction of this lab to be incorrect. The predicted amount of liberated precipitate for the reaction was 0.2247g, and all the trials went above this number by at least 0.0563g. [3] The new substances created from this experiment were iron hydroxide and sodium sulphate. [1] Sodium sulphate was present as a liquid because the sulphate is linked to 7 water molecules, because even though sodium sulphate is a solid in room temperature, the water molecules attached to the sodium sulphate make the sodium sulphate an aqueous solution, since water is a polar covalent and is attracted to the negative charge in the sulphate and the positive charge in the sodium. The iron (II) hydroxide in the final product presents itself as a solid. This is because the hydroxide is not linked to any water molecules, and [2] at room temperature iron (II) hydroxide is a solid. The information collected from this lab proves that FeSO₄(aq) + 2NaOH( aq) → Fe(OH)₂(s) + Na₂SO₄(aq) is a double displacement chemical reaction, and it proves that this reaction produces iron (II) hydroxide as a precipitate, however this lab also proves the prediction of this lab to incorrect because the actual mass was considerably larger than the theoretical mass by 48.9% (refer to appendix A for calculations). The percent error of this lab is 11%. This error could have been induced by the oxygen in the room oxidizing the products or reactants, the filter paper could have collected excess debris overnight from the environment, or some fibre from the paper towel the filter paper was resting on could have attached to the filter paper. This lab would produce more definitive results if it was isolated from potential sources that could add mass to it, including oxygen. The precipitate created, iron (II) hydroxide was a dark green. Iron (II) hydroxide is sometimes called green rust because it will turn in green if exposed to the smallest amount of oxygen, and in this lab the oxygen was present in the hydroxide.

Appendix A Formulas: Finding the limiting reactant in FeSO₄(aq) + 2NaOH(aq) → Fe(OH)₂(s) + Na₂SO₄(aq): moles of reactant x ratio of Fe(OH)₂ / ratio of reactant = moles of Fe(OH)₂ produced Find grams of Fe(OH)₂ using NaOH because it is limiting reactant: moles Fe(OH)₂ x molar mass Fe(OH)₂ / 1 mol = mass of Fe(OH)₂ produced Finding the % yield: % yield = (actual mass/theoretical mass) x 100% Finding the average % yield of results: (percent yield trial 1 + percent yield trial 2 + percent yield trial 3) /3 = average percent yield Finding the mass of precipitate produced each trial: Mass of filter paper and precipitate of trial - mass of filter paper of trial = mass of precipitate Percent error: % error = (experimental value - accepted value / accepted value) x 100% Finding the amount of moles in the reactants: 0.5m/L / 1000 = moles in 10mL of reactants

Appendix B

Works Cited US National Library of Medicine. (n.d.). Iron(II) sulfate. Retrieved May 03, 2017, from https://pubchem.ncbi.nlm.nih.gov/compound/ferrous_sulfate#section=Top [1] Wikidot. (2008, January 10). Chemistry. Retrieved May 03, 2017, from http://fearschemistry.wikidot.com/sodium-sulfate US National Library of Medicine. SODIUM HYDROXIDE. Retrieved May 03, 2017, from https://pubchem.ncbi.nlm.nih.gov/compound/sodium_hydroxide#section=Top [2] Substance:Iron(II) hydroxide. Retrieved May 03, 2017, from http://www.rsc.org/learn-chemistry/wiki/Substance:Iron(II)_hydroxide [3] Quora (2017, February 15). Sodium Hydroxide solution added to Ferrous Sulphate Solution. Retrived May 03, 2017, from https://www.quora.com/What-happens-when-Sodium-hydroxide-solution-is-added-to-Ferrous-Su lphate-solution-Write-with-observation-and-balanced-chemical-equation

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