Chapter 4 Practice Questions

A 4.36 g sample of an unknown alkali metal hydroxide is dissolved in 100 mL of water. An acid-base indicator is added, and the resulting solution is titrated with 2.50 M HCl (aq) solution. The indicator changes color, signaling that the equivalence point has been reached, after 17.0 mL of the hydrochloric acid solution has been added. a. What is the molar mass of the metal hydroxide? b. What is the identity of the alkali metal cation?

103g Rb+

Oxidation number of P in PF3 and S in SO2

3+ 4+

You are presented with a white solid and told that due to carless labeling it is not clear if the substance is barium chloride, lead chloride or zinc chloride. When you transfer the solid to a beaker and add water the solid dissolves to give a clear solution. Next a Na2SO4 (aq) solution is added and a white precipitate forms. What is the identity of the unknown white solid?

BaCl2

Redox or metathesis? Decomposition

Can be either

Redox or metathesis? Synthesis

Can be either

Write balanced molecular and net ionic equation for the following reaction and identify the gas formed: Solid magnesium carbonate reacts with aqueous solution of perchloric acid

MgCO3 (s) + 2HClO4 (aq) = Mg(ClO4)2 (aq) + H2O(l) + CO2(g) MgCO3(s) + 2H+ (aq) = H2O(l) + CO2(g) + Mg2+ (aq)

A solution of 100.0 mL of 0.200 M KOH is mixed with a solution of 200.0 mL of 0.150 M NiSO4 a. Write the balanced equation b, What precipitate forms? c. What is the limiting reactant d. How many grams of this precipitate forms? e. What is the concentration of each ion that remains in the solution?

NiSO4 (aq) + 2KOH (aq) = K2SO4(aq) + Ni(OH)2 (s) b. Ni(OH)2 (s) c. KOH d. .93 g Ni(OH)2 e. SO4 = 1M K2 = .0667M Ni = .0667M

Peroxide ion

O2 2- oxidation number -1 only peroxide ion if with metal, SO2 (not peroxide) -2 oxidation number

3Fe(NO3)2(aq) + 2Al(s) = 3Fe(s) + 2Al(NO3)3(aq)

Oxidized 2Al to 2Al3+ Reduced 3Fe2+ to 3Fe

What is oxidized what is reduced? PbS(s) + 4H2O2(aq) = PbSO4(s) + 4H2O(l)

Oxidized S2- to SO4 Reduced H2O2 to H20 peroxide

Separate samples of a solution of an unknown salt are treated with dilute solutions of HBr, H2SO4 and NaOH. A precipitate forms in all three cases. Which cations could be present in the unknown salt: K+, Pb2+, Ba2+

Pb2+

The labels have fallen off three bottles containing powdered samples of metals: zinc, lead and platinum. You have three solutions: 1 M sodium nitrate, 1 M nitric acid, 1 M nickel nitrate. Identify the metals using the solutions.

Platinum will not be oxidized by any of the solutions Lead will be oxidized by HNO3 Zinc will be oxidized by NiNO3 or HNO3

Which section on the periodic table is the most difficult to oxidize

The nonmetals - noble gases, halogens, chalcogens, N, P and C

Disproportionation

The oxidation and reduction of the same element in a redox reaction 2H2O2 = 2H2O + O2

You want to analyze a silver nitrate solution. a. You could add HCl (aq) to the solution to precipitate out AgCl(s). What volume of a 0.150 M HCl (aq) solution is needed to precipitate the silver ions from 15.0 mL of a 0.200 M AgNO3 solution? b. You could add solid KCl to the solution to precipitate out AgCl (s). What mass of KCl is needed to precipitate the silver ions from 15.0 mL of 0.200 M AgNO3 solution?

Volume = .02 L HCl Mass = .224 g KCl

Is H2SO4 a strong, weak or Non-electrolyte?

Weak

The metal cadmium tends to form Cd2+ ions. The following observations are made: (i) When a strip of zinc metal is placed in CdCl2(aq), cadmium metal is deposited on the strip. (ii) When a strip of cadmium metal is placed in Ni(NO3)2 (aq), nickel metal is deposited on the strip. a. Write net ionic equations for both b. Which elements more closely define the position of cadmium in the activity series c.What experiments would you need to perform to locate more precisely the position of cadmium in the activity series.

Zn(s) + Cd2+(aq) = Zn2+ (aq) + Cd(s) Cd (s) + Ni2+ (aq) = Cd2+(aq) + Ni (s) b. Chromium, Iron and Cobalt c. Add a strip of Fe to CdCl2 if Cd2+ deposits on the Fe strip cadmium is less reactive than Fe (lower in the activity series) and will oxidize iron. If deposited, conduct the same test with cobalt. If Cd2+ deposits on cobalt, it is less reactive(lower)/if not more reactive(higher) If strip does not initially work with Fe, it is more reactive than Fe. Try the same test with chromium

When calculating concentration of each ion that remains in a limiting reactant problem, don't forget to

add the amount of the non-limiting reactant that is left over

Redox or metathesis? Double displacement

always metathesis

Redox or metathesis? Combustion

always redox

Redox or metathesis? Single displacement

always redox

Why do electrolytes conduct electricity?

because ions are moving through the solution and they are charged

Methanol is a base true or false

false a nonelectrolyte, molecular compound base between Group 1 or 2 and OH group

A mixture of 45.0 mL of 0.272 M NaCl and 65.0 mL of 0.0247 M (NH4)2CO3. Indicate concentration of each ion or molecule and assume volumes are additive.

find moles for each add together volumes find M for moles/total volume 0.111M Na+ and Cl- .0292 M NH4+ .0146 m CO3 2-

Is the concentration of a solution an intensive or extensive property?

intensive the ratio of solute to total amount of solution is the same regardless of how much solution is present 1 M of HCl/same ratio regardless of solution amount present

Copper metal is added to a solution of silver nitrate. Ag1+ start depositing on the copper metal. Is silver more or less reactive than copper?

less (lower on the activity table) so it will oxidize copper

Neutralization reactions between acids and metal hydroxides are

metathesis reactions or exchange reactions water and salt produced

Relationship between moles, molar mass and mass of substance

moles = mass/molar mass

Does adding a non-electrolyte to a solution with an electrolyte change the conductivity of the solution?

no

Do weak acids dissociate completely?

no, they will be a mixture of molecules and ions in an aqueous solution

Do weak bases dissociate completely?

no, they will be a mixture of molecules and ions in an aqueous solution

What kind of reaction is the water splitting reaction? H2O = H2 + 1/2O2

redox

How do the sulfide ion and the cabonate ion react with acids?

they form gases carbonate with an acid forms water and carbon dioxide (H2CO3 is not stable)

Is NH3 a strong, weak or Non-electrolyte?

weak