CHEM 14BL Study Guide - Final Guide: Reaction Rate Constant, Thiocyanate, Sodium Hydroxide

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whiteraccoon303

25 Aug 2015

School

UCLA

Department

Chemistry and Biochemistry

Course

CHEM 14BL

Professor

Henary Maher

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Document Summary

Titrations/buffer chemistry: suppose that 15. 0 ml of 0. 15 m nh3 (aq) is titrated with 0. 10 m hcl (aq). Answer the following questions for a titration of a weak monoprotic acid (ha) with a strong base (oh-). A buffer solution of volume 100. 0 ml is 0. 100 m ch3cooh (aq) and 0. 100 m nach3co2 (aq). You have mixed 35. 00ml of 0. 15 m potassium acetate with 10. 50 ml of 0. 50 m hydrochloric acid. (ka = 1. 8x10-5). The following table summarizes the solubility of the amino acid dl-alanine in water. The following situations describe students, who did not follow the lab procedure for the aspirin lab. For each situation, determine whether the % recrystallized yield would be higher or lower in comparison to the lab procedure. Situation #1: a student obtained 0. 2542 g of crude aspirin. Instead of adding a minimum amount of hot ethanol to dissolve crude aspirin initially, the student added an excess amount of hot ethanol to dissolve the crude aspirin.

Related Questions

1. Rank the following 0.100 M solutions in terms of increasing pH:

HCl(aq), H₂O(l), NaOH(aq) < NaF, (aq), and H₂CO₃.

2. The pH of a solution at the phenolphthalein end point is 9.0. For which type of titration could you use phenolphthalein as an indicator?

Select one:

a. Titrations of strong acids only.

b. Titration of all strong and most weak acids.

c. Titrations of weak bases only.

d. Titrations of weak acids only.

e. All titrations of strong or weak acids or bases.

3. 4.199 g of NaF(s) are dissolved in water and poured quantitatively into a 50.00 mL volumetric flask which is filled to the line with DI water and mixed well. 20.00 mL of this solution is pipetted into a 100 mL volumetric flask which is filled with DI water and mixed well. 25.00 mL of this solution is pipetted into a 100 mL volumetric flask which is filled with DI water and mixed. What is the [NaF] in this final solution?

Select one:

a. 0.2000 M

b. 0.1000 M

c. 0.04000 M

d. 0.2500 M

e. 1.000x10^-4 M

plumelephant645

160 g of a 0.80% sodium hydroxide solution.

The following question involves the reaction of sodium hydroxide and succinic acid. Succinic acid is diprotic: the acid (H₂C₄H₄O₄) reacts with two of its hydrogens to give C₄H₄O₄^2-. The balanced âmolecularâ equation for the reaction has coefficients of 2 for NaOH and 1 for succinic acid:

2 NaOH (aq) + H₂C₄H₄O₄ (aq) --> Na₂C₄H₄O₄ (aq) + 2 H₂O (l)

A student weighs 1.700 g of succinic acid and dissolves it in water in a 250.0 mL volumetric flask. A 25.00 mL sample of this solution is withdrawn and placed in a 125 mL Erlenmeyer flask, to which 5 drops of the acid-base indicator phenolphthalein is added. This solution is titrated with a sodium hydroxide solution of unknown molarity in a buret.

a) How many moles of succinic acid were weighed and dissolved in the volumetric flask?

0.0572 M

b) How many moles of succinic acid were placed in the Erlenmeyer flask?

1.43 x 10^-3 mol

c) If the unknown sodium hydroxide solution was known to be approximately 0.20 M, at approximately what buret volume would you expect the end point of the titration? Show the calculation, including the use of the appropriate coefficients, as a 2 significant figure estimate:

14.30 mL NaOH

d) If the measured volume at the end point was 13.32 mL of sodium hydroxide added, calculate the actual molarity of the sodium hydroxide solution.

0.214 M NaOH

You are going to standardize a 0.80% solution of sodium hydroxide solution for which the molarity is approximately 0.20 M. You will have dry succinic acid, a 250 mL volumetric flask, a 25.00 mL pipet, a 50.00 mL buret, a phenolphthalein indicator solution, and other standard laboratory equipment. For each titration you will withdraw a 25.00 mL sample of the succinic acid solution with a volumetric pipet. Therefore, you will deliver exactly one-tenth of your initial mass of succinic acid (to four significant figures) in each titration. In deciding the amount of succinic acid to weigh, assume that you will be using approximately 15 mL of the sodium hydroxide of approximate 0.20 M concentration for each titration, and you need enough succinic acid for ten titrations. Show how to calculate the mass of succinic acid you will need to weigh.

Equipment Materials

50.00 ml buret, 250.ml volumetric flask, 1.00 ml volumetric pipet 10.0 mL volumetric pipet, 25.00 mL volumetric pipet, pipettor, 250 mL Erlenmeyer flask, 10.0 mL graduated cylinder, several beakers, several watchglasses, unkown bleach solution, 10% potassium iodide solution, 2M hydrochloric acid solution, 0.150 M sodium thiosulfate solution, 1% starch solution.

Background information regarding this experiment is as follows:

An aqueous solution of sodium hypochlorite (NaOCI) is a clear, slightly yellow liquid, and is commonly known as bleach. Aside from its uses as a bleaching agent, sodium hypochlorite solutions are also used as sterlizing agents and in water treatment. Industrial uses include agricultural, food handling, paper production, and textile production. Sodium hypochlorite is also added to waste water to reduce odors.

The concentration of sodium hypochlorite in bleach solutions can be determined by titration. Therefore, we must use a two-step method to titrate sodium hypochlorite. In the first step, sodium hypochlortie, hydrochloric acid, iodide ion, and starch are combined to form a starch-triiodide complex. In this step there are 3 reactions that take place:

The result of these 3 reactions is that when sodium hypochlorite is present the starch-triiodide complex is produced.

In the second step the starch-triiodide product is titrated by sodium thiosulfate to form a colorless solution of iodide, dithionate.

I do not know how to answer the following on the data sheet: (? means I do not know how to answer)

Table 1:

Mass of 1.00 ml of unknown (by tare): 10.552 g

Density of bleach: (g/ml) : 1.055 g/ml

Volume of diluted bleach used in each titration: 10.00

Concentration of sodium thiosulfate: ? (M)

Titration Data:

Initial buret reading (ml): trial1: 0.000 ml Trial 2: 0.00 ml Trial 3: 0.000ml

Final buret reading (ml): trial 1: 13.50ml Trial 2: 13.30ml Trial 3: 13.40ml

Volume delivered(ml: trial 1: ? Trial 2: ? trial 3:?

Calculations: (show clearly)

For trial 1,2,3 ???

1.Moles of Na₂S₂O₃ in titration: ??? trial 1,2,3

2.Moles of NaOCl: ???trial 1, 2,3

3.Average moles of diluted NaOCl: (one answer) ?

4.Average moles of undiluted NaOCl: (one answer.. mol) ?

5.Standard Deviation: (one answer) (mol)

6.Average mass of NaOCl in 25.00mL of undiluted bleach: ? (g)

7.mass of 25.00 mL of undiluted bleach: ? (g)

8. Mass % of NaOCL from experiment: ? (%)

9.Actual mass % of NaOCL (from prof; student does not make an entry):? (%)

More questions all need to be answered please:

1. Calculate the volume of the reagent thiosulafte solution which would be required if you titrated a 25ml sample of the original commercial bleach instead of 25ml of the diluted solution.

2. Why would we choose a graduated cylinder to measure the HCl and KI solutions instead of a volumetric pipette? When would we use a volumetric pippette?

3. You calculated the mass percent of sodium hypochlorite in the bleach( dilute and undiluted). Now calculate the molarity of the sodium hypochlorite in the diulte and undiluted solution/

4. Use oxidation states to show that equations (2) and (4) in the introduction are redox reactions and that equation 1 is not a redox reaction. :

-(1) NaOCl(aq) + HCl(aq) yields HOCl(aq)+NaCl(aq)

-(2) HOCL (aq) + HCl(aq) + 3I(aq) yields I3(aq) + 2CL(aq) + H₂O(l)

-(4) (I₃) (Starch) + 2S₂O₃ yields 3I + S₄O₆ + starch

5. combine equation 1-3 to show the overall reaction for the products of the starch-triiodide complex.

-(1) NaOCl(aq) + HCl(aq) yields HOCl(aq)+NaCl(aq)

-(2) HOCL (aq) + HCl(aq) + 3I(aq) yields I3(aq) + 2CL(aq) + H₂O(l)

-(3) I₃ + Starch yields (I₃) (Starch)

6. What standard was used in this experiment?

7. Describe the naming of NaClO and HClO. What are the names of the following compounds? NaClO₂ , NaClO_3, NaClO₄ , HClO₂, HClO₃, HClO₄

8 Submit a one paged (typed double spaced) report that discusses the following topics:

a. the goals or objectives of the experiment

b.your results as they relate to the goals and objectives

c. the quality of your results.

CHEM 14BL Study Guide - Final Guide: Reaction Rate Constant, Thiocyanate, Sodium Hydroxide

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