Post-Lecture Assignment Chapter 7
Which of the following aqueous solutions has the lowest concentration of H+ ions?
0.10 MNH3
Which of the following aqueous solutions has the highest concentration of H+ ions?
0.10 MHNO3
Which is likely to be a better buffer, a solution of ammonia with ammonium acetate or a solution of sodium hydroxide with sodium acetate? Why?
1. A solution of ammonia with ammonium acetate is like to make the better buffer. 2. A buffer is a solution of a weak acid and its conjugate base, or a weak base and its conjugate acid. Sodium hydroxide is a strong base, and it will not make a buffer solution.
Carbonic acid reacts with water to yield bicarbonate ions and hydronium ions: H2CO3+H2O⇌HCO−3+H3O+H2CO3+H2O⇌HCO3−+H3O+ Identify the conjugate acid-base pairs.
Acid H2CO3 Conjugate base HCO3- Base H2O Conjugate acid H3O+
Bicarbonate reacts with water to produce carbonate ions and hydronium ions: HCO3−+H2O⇌CO32−+H3O+HCO3−+H2O⇌CO32−+H3O+ Identify the conjugate acid-base pairs.
Acid HCO3^- Conjugate base CO3^2- Base H2O Conjugate acid H3O^+
The active ingredient in the antacid Basaljel is a gel of solid aluminum carbonate. Write the equation for the neutralization of aluminum carbonate by stomach acid (aqueous HCl).
Al2(CO3)^3+6HCl→3H2O+3CO2+2AlCl3
Al(OH)3
Aluminum Hydroxide
Given the balanced neutralization equation from part B, how many moles of potassium hydroxide (KOH) are required to neutralize 4.5 mol of sulfuric acid (H2SO4)? Assume that the sulfuric acid completely dissociates in water.
Amount of KOH = 9.0 mol
Explain why not all compounds are containing that element acids.
An Arrhenius acid is defined as a substance whose water solution contains the hydrogen ion as the only positive ion. Not all substances that contain hydrogen are acids.
Write equations for the reaction of 1 mol of barium hydroxide with 2 mol of hydrochloric acid.
Ba(OH)2+2HCl→BaCl2+2H2O
For the following acids and bases, supply a formula to match the name or a name to match the formula. cesium hydroxide
CsOH
An acidic buffer consists of a weak acid, and the salt of that weak acid. An example is HCNwith NaCN. A basic buffer consists of a weak base, and the salt of that weak base. An example is NH3with NH4Cl. What substance would you add to NaHCO3(aq) to form a buffer solution?
H2CO3 The weak acid H2CO3 dissociates only partially, and thus an equilibrium forms between H2CO3 and HCO3−HCO3−: H2CO3(aq)+H2O(l)⇌H3O+(aq)+HCO−3(aq)H2CO3(aq)+H2O(l)⇌H3O+(aq)+HCO3−(aq) However, this equilibrium is quite reactant-favored on its own. By increasing the HCO3- concentration (through the addition of NaHCO3, we achieve a balance between the reactant and product concentrations. Thus, the equilibrium can move in either direction to counteract the addition of either acid or base.
Give the formula for the compound formed when carbon dioxide reacts with water. Is it an acid or a base?
H2CO3 Acid
The chemical potassium sulfate, commonly known as potash of sulfur, is used in fertilizers. This chemical provides both potassium and sulfur to the soil and is easily soluble in water. Potassium sulfate is formed when a strong acid like sulfuric acid (H2SO4) reacts with a strong base like potassium hydroxide. Write the complete balanced molecular equation for this neutralization reaction.
H2SO4(aq)+2KOH(aq)→K2SO4(aq)+2H2O(l)
Write equations for the reaction of 1 mol of sulfuric acid with 2 mol of potassium hydroxide.
H2SO4+2KOH→K2SO4+2H2O
hydrocyanic acid
HCN
Write the product for the result of dichlorine oxide (Cl2O) reacting with water (the product will have only 1 equivalent (atom) of chlorine in it).
HClO Dichlorine oxide reacts with water to form hypochlorous acid (HClO), which can be used as a bleach, an oxidizer, a deodorant, and a disinfectant, due to its ability to kill the cells of many microscopic pathogens, such as bacteria and viruses.
Write an equation that represents the action in water of nitrous acid as an Arrhenius acid.
HNO2(aq)+H2O(l)→H3O+(aq)+NO2−(aq)
Define the term salt.
Ionic compound
Write the product for the reaction of potassium oxide (K2O) with water.
KOH Potassium oxide reacts with water to form potassium hydroxide (KOH), which can be used to clear clogged drains due to the ability of the base to corrode clogs in its path.
Rank the following from most to least acidic.
Most acidic [H3O+]=10−2 pH=2.5 pH=4 [H3O+]=10−5 pH=9 Least acidic
Most soaps have a bitter taste. What does this hint indicate about the pH of most soaps?
Most soaps have a pH value greater than 7
Give the formula for the compound formed when sodium oxide reacts with water. Is it an acid or a base?
NaOH Base
Neutralization reactions are reactions in which an acid and a base, in an aqueous solution, react to form a salt and water. The H+ ions from the acid react with the OH− ions from the base to form H2O: H+OH−→ H2O The negative ion from the acid and the positive ion from the base react to form a salt. Such reactions are called neutralization reactions. The products water and salt are neither acidic nor basic, as indicated by their inability to change the color of litmus paper. Consider the following example of a neutralization reaction. When hydrogen bromide is neutralized by potassium hydroxide, the products are water and potassium bromide. If you were to evaporate off all the water from the solution, the residual salt formed is potassium bromide. Identify the neutralization reactions.
Neutralization reactions Ca(OH)2(aq) + H2SO4(aq)CaSO4(aq) + 2H2O HNO3(aq) + KOH(aq) KNO3 + H2O Other reactions CH4(g)+2O2(g)→CO2(g)+2H2O(g) CaCl2(aq) + 2AgNO3(aq) Ca(NO3)2(aq) + 2AgCl
Are all compounds containing that element acids?
No, not all compounds are containing that element acids.
Write an equation that represents the action in water of rubidium hydroxide as an Arrhenius base.
RbOH(aq)→Rb+(aq)+OH−(aq)
Thallium hydroxide (TlOH) is a water-soluble ionic compound. Classify TlOHas a strong acid, a weak acid, a weak base, or a strong base.
Strong Base
What is meant by a proton in acid-base chemistry?
The Brønsted-Lowry theory describes acid-base interactions in terms of proton transfer between chemical species
Describe the effect on litmus on iron or zinc of a solution that has been neutralized.
The effect of iron oxides on litmus paper there will be a suspension of iron oxide in water. Red litmus paper turns blue. This shows that iron oxide suspension is basic in nature. When an acid reacts with a base, the properties of each are neutralized
Describe the action on iron or zinc of a solution that has been neutralized.
When Iron is a component of rust the neutralization reaction produces products that are soluble and wash away.
Classify the following reactions as acidic anhydride or basic anhydride.
acidic anhydride SO3+H2OH2SO4 N2O5+H2O2HNO3 P4O10+6H2O4H3PO4 basic anhydride. K2O+H2O2KOH MgO+H2OMg(OH)2 Li2O + H2O → 2LiOH
HSO4− is the conjugate _____ of H2SO4 and the conjugate _____ of SO2−4.
base / acid
According to the Arrhenius theory, all acids have one element in common. What is that element?
hydrogen
Define the terms acid.
hydrogen ion donor
Define the terms base.
hydroxide ion donor
HNO3
nitric acid
Three varieties of Tums have calcium carbonate as the only active ingredient: Regular Tums tablets have 500 mg; Tums E-X, 750 mg; and Tums ULTRA, 1000 mg. How many regular Tums would you have to take to get the same quantity of calcium carbonate as you would get with three Tums E-X?
number of Regular Tums = 5
How many regular Tums would you have to take to get the same quantity of calcium carbonate as you would get with four Tums ULTRA tablets?
number of Regular Tums = 8
What is the pH of a solution that has a hydroxide ion concentration of 1.0×10−6 M?
pH = 8.00
To calculate pH and use it as a measure of acidity. The pH expresses the molar concentration of hydronium ions in an aqueous solution on a logarithmic scale: pH=−log[H3O+]pH=−log[H3O+] As pHpH decreases, acidity increases. As pHpH increases, acidity decreases.Acidic solution: pH<7pH<7Neutral solution: pH=7pH=7Basic solution: pH>7 What is the pHpH of an aqueous solution with [H3O+] =6×10−12 M ?
pH= 11.2
What is the pH of a solution that has a hydrogen ion concentration of 1.0×10−9 M?
pH= 9.0
What is the pOH of a solution that has a hydroxide ion concentration of a 0.01 M HCl solution?
pOH = 12
What is the pOH of a solution that has a hydroxide ion concentration of a 0.01 M KOH solution?
pOH = 2.0
The pOH is related to [OH−] just as pH is related to [H+]. What is the pOH of a solution that has a hydroxide ion concentration of 1.0×10−5 M?
pOH = 5.0
Identify each of the following substances as a strong acid, a weak acid, a strong base, a weak base, or a salt.
strong acid HCl weak acid CH3COOH strong base NaOH weak base NH4OH salt CaBr2 NH4Cl
A solution made by adding 7.00 mol of HOCN to 7.00 L of water contains 0.385 mol each of H+ ions and OCN− ions and 6.62 mol of HOCN molecules. Classify HOCN as a strong acid, weak acid, weak base, or strong base.
weak acid
