Name: __________________________________ Chemistry Problem Set 1 Section 1: Stoichiometry, Basic Titrations and Quantitative Analysis 1.

Suppose that 10.0-mL of 3.0 M KOH

(aq)

is transferred to a 250.0-mL volumetric flask and diluted to the mark. It was found that 38.5-mL of this diluted solution was needed to reach the stoichiometric point (also called equivalence point) in a titration of 10.0- mL of a Phosphoric acid solution. Note that Phosphoric acid has 3 acidic protons and therefore is a triprotic acid. (a) Calculate the molarity of H

3

PO

4

in the solution. (b) What mass of H

3

PO

4

is in the initial sample? (Atkins and Jones F92) 2.

A forensic laboratory is analyzing a mixture of the two solids Calcium Chloride Dihydrate (CaCl

2

·2H

2

O) and anhydrous (without any waters of hydration) Potassium Chloride (KCl). The mixture is heated to drive the waters of hydration off the Calcium Chloride dihydrate to form a mix of CaCl

2

and KCl anhydrous. A sample of the mixture weighed 2.543 g before heating and 2.312 g after heating. Assuming only water left the mixture, what is the percent by mass of each compound in the original mixture? (Atkins and Jones F92) 3.

Thiosulfate ions (S

2

O

3 2-

) can be made to "disproportio nate" in acidic solution upon the addition of HCl to give solid sulfur (S) and hydrogen sulfite ion (HSO

3 -

). The following net ionic equation is given for this "disproportiona tion"reaction:

2 S

2

O

3 2- (aq)

+ 2 H

3

O

+ (aq)

→

2 HSO

3 - (aq)

+ 2 H

2

O

(l)

+ 2 S

(s)

(a) A "disproportionation" reaction is a type of redox (oxidation-reduction) reaction. Which reactant species is oxidized and which is reduced? (b) If 10.1-mL of 55.0% HSO

3 - (aq)

by mass is obtained in the reaction, what mass of S

2

O

3 2- (aq)

was present initially, assuming tthe reaction went to completion. The density of the HSO

3 - (aq)

is 1.45 g/mL. (Atkins and Jones F92) 4.

A mixture of 10.325 g of Iron(II) Oxide and 5.734 g of Aluminum metal is placed in a crucible and heated in a high-temperature oven, where a reduction of the oxide takes place, forming elemental liquid Iron and solid Aluminum oxide from solid Iron(II) oxide and elemental liquid Aluminum. (a) Write the balanced reaction for this redox process. (b) What is the limiting reactant? (c) Determine the maximum amount of iron (in moles of Fe) that can be produced. (d) Calculate the mass of excess reactant remaining in the crucible. (Atkins and Jones F100) 5.

A folk medicine used in the Anhui province of China to treat acute dysentery is cha-tiao-qi, a preparation of the leaves of

Acer ginnala