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1. In a reaction between copper metal and an aqueous iron (III) chloride, Fe3+(aq) is reduced to Fe2+(aq), while Cu(s) is oxidized to Cu2+(aq). Determine the mass of Cu(s) required to react with 18.3 ml of 1.88 M FeCl3(aq).

2. What is the mass, in grams, of Vitamin C, which contains 0.768 grams of carbon? (Vitamin C, C6H8O6.)

3. The color change from pink/violet to colorless is caused by:

a.

change from MnO4- to Mn2+
b.

change from Fe2+ to Fe3+
c.

change from H+ to H2O
d.

addition of indicator
4. When MnO4- reacts to form Mn2+ the manganese in MnO4- is:

  1. reduced as its oxidation number decreases
    b.

    oxidized as its oxidation number decreases
    c.

    oxidized as its oxidation number increases
    d.

    reduced as its oxidation number increases
  2. 5. What is the difference between the endpoint and equivalence point in a titration?
  3. a.

    the endpoint is when the pH is exactly 7
    b.

    the equivalence point is when the pH is exactly 7
    c.

    the endpoint and the equivalence point are the same thing
    d.

    none of these answers is correct

What is the mass, in grams, of Vitamin C, which contains 0.768 grams of carbon? (Vitamin C, C6H8O6.)

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Jean Keeling
Jean KeelingLv2
1 Jan 2019

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Related questions

Need answers to all the three please.

INTRODUCTION

Many transition metal cations can have more than one possible charge (Worksheet 1). Differently charged species of the same element can have different chemical and physical properties. Knowing the charge can allow separation of the different ions based on their properties. For example, Cu2+ is blue and stable in solution, while Cu+ is colorless and reacts with oxygen. Hemoglobin contains iron as Fe2+, but it is inactive at binding oxygen when the iron gets oxidized to Fe3+. There are many similar situations in which it is important to always properly indicate charges of ions.

This laboratory experiment uses the difference in chemical properties of Fe2+, iron(II), and Fe3+, iron(III), to quantify the amount of each present in a solution of unknown concentrations of each. You will first determine the amount of iron(II) in your sample by titrating with a reagent that does not react with iron(III). You will then titrate a second sample after converting all the iron(III) to iron(II) in order to determine the total iron present. The percent composition of Fe2+ in the unknown mixture will be calculated.

BACKGROUND

The concentrations of both iron(II) and iron(III) ions in a solution can be determined by titration with potassium permanganate. The reaction is an oxidation-reduction reaction, or redox, for short. A brief introduction to oxidation-reduction reactions is given in the background of the “Acids and Bases” experiment. The permanganate ion effectively oxidizes iron(II) to iron(III) in an acidic solution while being reduced to manganese(II) ion. The balanced net ionic reaction is:

5 Fe2+(aq) + MnO4–(aq) + 8 H+(aq) → 5 Fe3+(aq) + Mn2+(aq) + 4 H2O(l)

Iron(III) is not oxidized by the permanganate ion, and thus does not react. Thus in order to determine the concentration of iron(III) ions, they must first be reduced to iron(II) ions. Zinc metal is used as the reducing agent, also under acidic conditions.

Zn(s) + 2 Fe3+(aq) → 2 Fe2+(aq) + Zn2+(aq) (reduction of the Fe3+)

Zn(s) + 2 H+(aq) → Zn2+(aq) + H2(g) (a side reaction that oxidizes excess Zn)

The Zn2+ formed does not interfere with the subsequent titration because Zn2+ is not oxidized by permanganate. Notice that converting all the iron(III) to iron(II) means that the total iron concentration ([Fe2+] + [Fe3+]) is titrated, not just the iron(II) originally present.

Techniques

This is a lab will utilize several of the techniques introduced in the experiment “Laboratory Techniques and Measurements,” the procedures for which are given in Appendix B. Poor laboratory technique and misuse of the glassware will result in poor data results, which will affect the grade you receive on the laboratory report. In order to use your time efficiently in lab, review how to properly:

rinse glassware prepare a standard solution use a volumetric pipette

weigh by difference set up and use a burette use a graduated cylinder

heat samples on a hot plate

Analysis of Iron by Oxidation-Reduction Titration

This lab uses the common quantitative technique of titration. The only difference between the titration you will be doing in this lab and that done in the Molar Mass of a Known Acid lab is the type of reaction used: this lab will use a redox reaction in place of the acid-base reaction performed in the previous experiment.

In order to determine the concentrations of iron(II) and iron(III) ions in a solution containing both ions, two portions of the same sample must be titrated separately. This first titration will determine only the iron(II) concentration. A second sample will be treated with zinc metal in order to reduce the iron(III) to iron(II). The resulting solution will be titrated with potassium permanganate. The result of this titration will give the total iron concentration in the sample. The difference between the first and second titration is the equal to the iron(III) concentration.

In this titration, potassium permanganate serves as its own indicator. The intense purple color of the permanganate solution becomes colorless when the permanganate is reduced to manganese(II). Thus, as iron(II) is oxidized with the addition of the permanganate solution from the burette it will impart a purple color that will fade. However, once there is no iron(II) left in solution a faint purple color will remain, marking the endpoint of the titration. This color can be slightly altered by the presence of iron(III), which is yellow in solution. Remember that iron(III) is generated by the reaction between iron(II) with permanganate, increasing the yellow appearance of the solution and which can interfere with the detection of the endpoint. Phosphoric acid is added to help minimize this effect.

pre lab questions:

1.Which of the following is a physical property?

A) ozone reacts with silver to give silver oxide

B) platinum metal does not react with hydrochloric acid

C) the density of lead

E) Sulfur burns in oxygen to form sulfur trioxide

2. Which of the following is a chemical property of gold?

A) is malleable

B) does not react with hydrochloric acid

C) is a good conductor of heat

D) is a good conductor of electricity

3) Which of the following is a physical change?

a) the freezing of water to form ice

B) the inability of gold react with water

C) the burning of paper

D) the sodium metal vigorously with water

E) the reaction of zinc with hydrochloric acid

4. Which one of the following would be classified as a heterogenous mixture?

A) copper nitrate solution

B) mix of table salt and black pepper

C) Salt water

D)brass

E) a sugar solution

5. Which of the following is a chemical change?

A) the boiling of water to form steam

B) crushing of lump of sulfur into yellow powder

C) the reaction of chlorine gas and sodium to form salt

E) hammering zinc into a thin film

6) An extensive property is

A) independent of the quantity of matter observed

B) difficult to measure

C) always strongly dependent on the external conditions

D) dependent on the quantity of matter observed

E) is a unique value regardless of the measurement conditions

7) Which of the following defines or expresses the concepts of accuracy?

A) average of the data

B) differences between the accepted answer and the average value of the data

C) deviation of the average

D) the closest value to the expected answer

E) reproducibility of a measurement

8) Hydrates are:

A) orgainc compounds that contain oxygen together with usual carbon and hydrogen

B) readily soluble in water and release energy

C) concentrated solutions of salts in water

D) moistyre sensitive hygroscopic inorganic salts

E) compounds in which each formula unit has one or more water molecules associated with it

9) Which of the following is the correct defintion of isomer?

A) Isomers are molecules with the same empirical formula but have different isotopes

B) Isomers are molecules that have the same molecular formula but contain different istotopes.

C) Isomers are molecules that have the same molecular formula but different arrangement of atoms in space

D) Isomers are molecules that have the same arrangements of atoms in space but different empirical and molecular formulas

E) Isomes are molecules that have the same empirical formula but different arrangements of atoms in space

10) Most water-soluble compounds of Group 1A or 2A elements are:

A) nonelectrolytes

B) weak electrolyes

C) weak acid

D) strong electrolytes

E) strong acids

11) to precipitate Cd2+(aq) from solution one could add:

A) KI(Aq)

B) NaCl(aq)

C) H2S(aq)

D)HNO3(aq)

E) HCl(aq)

12) Select a statement that best describe the oxidation process

A) in the oxidation process all elements experience an increase in oxidation state

B) in the oxidation process all elements change oxidation state

C) in the oxidation process some elements change their oxidation state

D) in the oxidation process some elements experience oxidation state increase

E) In the oxidation process only oxygen increases its oxidation state.

13. A disproportionation reaction is one in which:

A) the dame substance is oxidized and reduced

B) the equation is not balanced

C) both reactants are reduced

D) water must be added

C) more of one substance reacts than another

14) The energy of molecules of a gas:

A) is the same for all molecules at constant temperture

B) is dependent on concentration

C) increases with an increase in pressure

D) is distributed over a wide rande at constant temperature

E) increase with a decrease in temperture

15. The volume correction term in the van der Waals equation is present because:

A) molecules occupy volume

B) molecules attract each other

C) barometers are inaccurate

D) molecules repel each other

E) molecules are diatomic

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