Chapter 9: Solutions, Acids, Bases and Salts

Q: I don't understand how you determine if a compound is polar or non polar. Can someone help?

A: First of all a compound must be covalent (not ionic) to exist as a polar molecule. Polarity is caused by one atom pulling on the electrons within the molecule with a much greater pull than the other atom. Since it is the protons (+ charge) that pull on the electrons (- charge), the element with the greatest number of protons has the greatest pull on the electrons.

Hydrogen only has one proton so it will always lose the "tug of war" with the other element and become partial positive while the other atom will become partial negative. Polar molecules that contain Hydrogen are always partial + at the hydrogen end of the molecule.Atoms in a compound with similar numbers of protons will be non-polar since neither has a greater pulling power on the electrons than the other. For example CO2 would be non-polar because C and O have close to the same number of protons.

While polarity also has to do with the structure of the molecule (whether it is symmetrical) we will only look at the proton number this year. It's not really that easy but for now we'll say it is. You will learn more about it in Chem Honors.So for now, greater than 4 in the difference between atomic number and the molecule is polar.

-Mr. Gilliland

Q:I do not understand how to write a equation for things ionizing and dissociating in water. can you help me and give me an example?

A: Acid ionize in water. Acids are polar molecules composed of atoms that are "pulled apart" by water (also polar) to produce ions. In all of these, a hydrogen proton is pulled from a molecule (such as HBr) while the other element  of the acid keeps hydrogen's electron and becomes an anion. HBr (g) -->  H+ (aq)  +  Br- (aq) Ionization involves changing atoms (in a covalent molecule) into ions. Dissociation involves bases which are ionic compounds consisting of cations and anions in a crystalline lattice. The unit cell is pulled apart by polar water molecules producing individual ions free to move about. Since you started with ions and end up with ions this is called dissociation. Ba(NO3)2 (s) --> Ba+2 (aq)  +  2NO3-1 (aq) Look on NetTutor for more info if you need it. -Mr. Gilliland

Q: I have a quesion that if we have a Hydrogen with polyatomic ion how could we do it with a strong acid or weak aicd and base? Eample: H2SO4.  And how do you remember strong or weak acid and bases?

A: Acids are strong in the following instances: Binary acids*: If they contain a halogen. If they don't they are weak.

Examples: HCl = strong *exception to the rule HF = weak

Ternary acids: If the oxygen outnumbers the hydrogen by 2 or more in the formula they are strong. If not they are weak.

Examples: H2SO4 = strong,   HNO2 = weak

Bases are stong if they contain metals in Group 1A or 2 A.

Examples: KOH = strong,   Cu(OH)2 = weak

Acids are strong if they ionize 100% in aqueous solution. Weak acids ionize less than 30% in aqueous solution.Bases are strong if they dissociate 100% in aqueous solution. Weak bases are not very soluble in water.-Mr. Gilliland

Q: Does anyone know the proper way to name acids and bases. If I have H2SO3 and H2SO4 what is the proper suffix for them. Also, if you just have HS do you add a hydro- to the beginning.

A: In your computer program you learned that there are two types of acids: binary and ternary. Binary acids contain only two elements (one of which is hydrogen) while ternary acids contain 3 elements (hydrogen, oxygen and another element). A ternary acid is one in which hydrogen has combined with a polyatomic ion.

Binary acids get their name by adding the prefix hydro- to the root of the element hydrogen is combined with along with the suffix -ic. You finish it with the word: acid.

HCl is hydrochloric acid, HBr is hydrobromic acid, HF is hydrofluoric acid

You cannot have HS. The correct formula for hydrogen sulfide is H2S.

As for ternary acids you usually use the root for the element that is not hydrogen or oxygen then use the suffix -ic.

You also end with the word: acid.

H2CO3 is carbonic acid, H3PO4 is phosphoric acid

Some of the ternary acids have similar formulas in which only the number of oxygen atoms differ:

HNO2 and HNO3

H2SO3 and H2SO4

For these you use the suffix -ous with the formula that has the lesser number of oxygen and -ic with the greater number of oxygen.

HNO2 is nitrous acid while HNO3 is nitric acid

H2SO3 is sulfurous acid while H2SO4 is sulfuric acid

- Mr. Gilliland