Chapter 8 chemistry note

·         The term acid means sour. Acids are substances that produce H+ ions when they dissolve in water. Their formulas start with H and the suffixes are –ic or –ous. An acid can donate a proton. The chemical that remains after the proton is donated is a base.

Formula	Name	Strong?
HCl	hydrochloric acid	yes
HBr	hydrobromic acid	yes
HI	hydroiodic acid	yes
HF	hydrofluoric acid	no
HNO3	nitric acid	yes
H2SO4	sulfuric acid	yes
H3PO4	phosphoric acid	no
CH3COOH	acetic acid	no

·         Bases are ionic compounds that dissociate into a metal ion and hydroxide ions (OH-) when they dissolve in water. Their formulas end with OH and that last word in the formula is hydroxide.

Formula	Name	Strong?
NaOH	sodium hydroxide	yes
LiOH	lithium hydroxide	yes
KOH	potassium hydroxide	yes
Mg(OH)2	magnesium hydroxide	no
Ca(OH)2	calcium hydroxide	no
Al(OH)3	Aluminum hydroxide	no

·         When a base accepts a proton, it becomes an acid because it now has a proton that it can donate. And when an acid donates a proton it becomes a base, because it now has room to accept a proton.

original acid	conjugate base
HNO3	NO3-
H2O	OH-
H3O+	H2O
H2SO4	HSO4-
HBr	Br -
HCO3-	CO32-

original base	conjugate acid
OH-	H2O
H2O	H3O+
HCO3-	H2CO3
SO42-	HSO4-
ClO4-	HClO4

·         When an acid gives up its proton, what remains is called the conjugate base of that acid. When a base accepts a proton, the resulting chemical is called the conjugate acid of that original base. HF and F^- are a conjugate acid-base pair. H₂O and H₃O⁺ are a conjugate pair, where H₃O⁺ is the acid and H₂O is the base.

equation

H2SO4 + H2O HSO4- + H3O+

HCl + OH- Cl- + H2O

HCl + NH3 Cl- + NH4+

NH3 + H2O NH4+ + OH-

·         The strength of an acid or a base in water is determined by its ability to donate or accept protons.

·         Strong acids are examples of strong electrolytes because they donate protons so easily that their disassociation in water in virtually complete. Weak acids don’t donate as many protons.

·         Most acids are weak acids, which mean that they are also weak electrolytes. They disassociate slightly in water, which means that only a small percentage of the dissolved molecules donate H+ to H ₂O.

·         Citric acid is a weak acid found in fruits and fruit juices such as lemons, oranges, and grapefruit.

·         Vinegar contains another weak acid known as lactic acid.

·         As strong electrolytes, the Arrhenius bases are strong bases that disassociate virtually completely in water. Because these strong bases are ionic compounds, they disassociate in water to give an aqueous solution of a metal ion and hydroxide ion. Strong bases accept protons readily.

·         Weak bases are weak electrolytes that are poor acceptors of protons and produce very few ions in solution. A typical weak base, ammonia, NH₃, is used in cleaning products. In an aqueous solution of NH₃, only a few molecules accept protons to form ammonium hydroxide.

·         Water acts as an acid or a base. It is a base when one water molecule donates an H+ to another water molecule.

·         When acid mixes with H2O it ALWAYS makes H3O and the H comes off of the front of the acid formula.

·         When writing formulas for acids- check the polyatomic table, as many acids come from this, and the H can be added to it and the numbers switched if need be.

·         When asked to write the formula and name of the conjugate base for an acid, take out the H and add –ide.

o   HF = F-, fluoride ion

o   H₂O = OH-, hydroxide ion

o   H₂CO₃ = HCO₃, bicarbonate ion

·         Every time a H+ is transferred between two water molecules, the products are one H₃O and one OH-. Experiments have determined that, in pure water, the concentrations of H3O+ and OH- at 25C are each 1.0 X 10^-7 M.

·         Square brackets around the symbols indicate their concentrations in moles per liter (M). [H3O+] = [OH-] = 1.0 X 10^-7 M.

·         When we multiply these concentrations, we obtain the ion-product constant of water, K_w, which is 1.0 X 10^-14. The concentration units are omitted in the K_w value.

·         The K_w value of 1.0 X 10^-14 is important because it applies to any aqueous solution: all aqueous solutions have H3O+ and OH-.

·         No matter the amount of acid and base, it always equals 1 X 10^-14

·         Any aqueous solution that’s an acid, base, or neutral, the product is equal to K_w.

·         On the pH scale, a number between 0 and 14 represents the H₃O+ concentration for most solutions.

·         A neutral solution has a pH of 7.0      [H₃O+] = 1 X 10^-7

·          An acidic solution has a pH < 7.0       [H₃O+] > 1 X 10^-7

·         A basic solution has a pH > 7.0            [H₃O+] < 1 X 10^-7

·         pH  = -log[H₃O+]

·         The negative powers of 10 in the molar concentrations are converted to positive numbers. For example 1 X 10^-3 has a pH of 3.

·         Because the pH is a log scale, a change of one pH unit corresponds to a ten-fold change in [H3O+]. For example, a solution with a pH of 2 has a [H3O+] 10 times higher than a solution with a pH of 3 and 100 times higher that a solution with a pH of 4.

·         As the pH decreases as the [H₃O+] increases.

·         Typical reactions of acids and bases include the reactions of acids with metals, bases, and carbonate or bicarbonate ions.

·         Acids react with certain metals to produce hydrogen gas (H₂) and a salt, which is an ionic compound that does not contain H+ or OH-.

·         Neutralization is a reaction between an acid and a base to produce a salt and water. In the reaction, the H+ of an acid that can be strong or weak and the OH- of a strong base combine to form water as one product. The salt that is usually soluble is the cation from the base and the anion from the acid.

·         ****Watch for polyatomics!!!************************When the elements combine don’t forget to switch their number according to the periodic table***************************

·         In a neutralization reaction, one H+ always combines with one OH-.

·         Writing the balanced equation for the reaction of HCl

o   Al:

§  Write the reactants and products: when a metal reacts with an acid, the products are H₂ gas and a salt.

Al + HCl à H₂ + salt

§  Determine the formula of the salt: when Al dissolves, it forms Al^3+, which is balanced by 3 Cl- from HCl.

Al + HCl à H₂ + AlCl₃

§  Balance the equation

2Al + 6HCl à 3H₂ + 2AlCl₃

·         When a carbonate (CO­₃)  reacts with an acid, the products are CO₂, H₂O, and a salt (GAS + WATER + SALT)

o   K­₂CO₃ + HCL à CO₂ + H₂O + KCl

o   *****Whenever you see CO₃ in a balancing problem, automatically take out CO₂ and H₂O first, then figure out the rest.

·         When H­ is combined with (OH) it makes water (H₂O)

·         Titration is used to find the molarity of a solution in which we neutralize an acid sample with a known amount of base.

·         A buffer is a solution that maintains pH by neutralizing added acid or base. For example, blood contains buffers that maintain a constant pH of 7.4.

·         Buffers consist of nearly equal concentrations of a weak acid and it’s conjugate base or a weak base and it’s conjugate acid.

·         To indicate whether a solution is acidic, basic, or neutral (calculating the pH):

o    Of a solution [H₃O+] : –log (place the scientific notation problem here) = <7 is acidic, >7 is basic, =7 is neutral

o   Of a solution [OH-]: first divide the solution problem into (10^-14), then use the –log formula to complete it

§  [OH-] = 8.0 X 10^-3 M

·         (10^-14)/(8.0 X 10^-3) = 1.25 X 10^-12; -log (1.25 X 10^-12) = 11.9

·         If the pH is given, the [H₃O+] is 1 X 10^pH