Are ALL salts a neutral PH?
and if they're not, how can you tell from the salt given what PH it is,
for example: Barium Nitrate.
How could i tell what PH it is?
- TimothyLv 61 decade agoFavorite Answer
No - all salts do not dissolve in water to yield a neutral pH. Ba nitrate does dissolve to give neutral solution.
If a salt contains a cation which is the conjugate acid of a weak base and an anion which is the conjugate base of a strong acid, it will dissolve to give an acidic solution. Example: NH4Cl dissolves to give NH4+ and Cl–. The Cl– ion is a spectator - a VERY weak base - it doesn't take protons from H2O or even from H3O+ to form HCl molecules. Of course, we know that is true because HCl is a strong acid and is completely dissociated in water. Therefore, Cl– is the conjugate base of a strong acid. NH4+, on the other hand, is the conjugate acid of a WEAK base, ammonia (NH3).
In water, the equilibrium NH4+ + H2O ⇌ NH3 + H3O+ is established. NH4+ gives up some protons to water and the solution is acidic.
The opposite situation can also occur. If a salt contains a cation which is the conjugate acid of a strong base and an anion which is the conjugate base of a WEAK acid, it will dissolve to give an basic solution. Example: KOAc - potassium acetate. Now its the K+ ion that is the spectator - no "KOH" is formed. But the acetate can act as a weak base:
OAc– + H2O ⇌ HOAc +OH– - and the solution is basic.
So, why is barium nitrate neutral? Because Ba(OH)2 is a strong base and nitric acid (HNO3) is a strong acid. When you dissolve Ba(NO3)2 in water, NO3^– doesn't take protons from H2O to form any HNO3 and Ba^2+ doesn't take up OH– to form any "Ba(OH)2". Except for being surrounded by water molecules, both the nitrate and barium ions remain much as as they are in the salt.
- Merlin's FelineLv 71 decade ago
Blob, salts of weak acids or weak bases are not neutral in water as they hydrolyze.As an example the salt sodium acetate is formed by reaction of acetic acid and sodium hydroxide
CH3COOH + NaOH --------> CH3COO^-1 Na+ + H2O since acetate is the conjugate base of a weak acid ( Ka of acetic acid = 1.8 X 10^-5 )it is a moderately strong base and can compete to some limited extent with O^-1 for protons. This means it can pull a proton away from water and generate hydroxide anion which will raise the pH above neutrality.
CH3COO^-1 + H2O ----> CH3COOH + OH^-1 the amount of OH^-1 produced depends upon the Ka of the weak acid..in this case, the hydrolysis constant is 10^-14 ( water's Ka)/1.8 X 10^-5 = 5.56 X 10^-10
so a solution of sodium acetate will have a pH in the 8s
for other weaker acids like HCN ( Ka = 3 X 10^-9 ) the pH of the salt
in water will be above 10 or 11.Source(s): Ph.D. Biochem BS Chem
- 1 decade ago
It depends on the concentration of the salts as my first point, but no all salts are not neutral. It depends on what the conjugate acid or base of the ions in salt are. If those are strong, then the ion is a neutral ion, as in the case of Barium(2+) and NO3-. Ba(OH) is the conjugate base of Ba2+ and it is a very strong base (Kb 10^2)
If it were... ammonium nitrate, NH4NO3, then the conjugate base of NH4+ is NH3, which is a weak base. If the conjugate is weak, the the salt ion effects the pH. NH4+ is acidic and will make the solution acidic while the Nitrate has little effect.
Just for clarification - if the conjugate is a base, then the salt ion will make the solution acidic.
You could then calculate the pH by assuming that it is a solution of just NH4+ for example (factoring in concentration and the Ka of NH4+) because NO3- is a spectator ion in the acid reaction.
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- Old Science GuyLv 71 decade ago
Salts of weak bases ---> acid pH
Salts of weak acids ---> basic pH
check the related acids and bases
in this case
barium hydroxide is soluble so not weak
HNO3 is a strong acid
pH is 7
compare that to Na2CO3
NaOH is a strong base
H2CO3 is a weak acid
pH > 7 (basic)
- _Lv 41 decade ago
What you have to look at are the two parts of the salt.
Barium first. Barium comes from a weak base (Ba(OH)2).
Now Nitrate. Nitrate comes from a strong acid (HNO3).
From this, we determine that the pH of a solution of this salt will be acidic.
weak base + strong acid = acidic
strong base + weak acid = basic
weak base + weak acid = neutral
strong base + strong acid = neutral
- kumorifoxLv 71 decade ago
No, there are acidic and basic salts.
Ba(NO3)3 is a salt made from a strong acid and a strong base (nitric acid and barium hydroxide). Such salts are usually neutral.
Salts made from a weak acid and a strong base (such as sodium acetate, CH3COONa) are basic, due to the hydrolysis of water.
Salts made from a strong acid and a weak base (such as ammonium chloride, NH4Cl) are acidic, also due to water hydrolysis.
Single salts of strong polyprotic acids (such as sodium bisulfate, NaHSO4) are acidic, due to the H atom left in the molecule.
Single basic salts of weak polyprotic acids (such as sodium bicarbonate, NaHCO3) are basic, due to the bicarbonate trying to pick up a new hydrogen and forming OH from water.
Salts made from a weak acid and a weak base can be either.