which salt gives solution with ph less than 7

[csulapredental]

which salt gives ph less than 7
NaBr
LiBr
AlCl3
KF
two of these


the book does the crossing of the H2O thing. isn't there a simpler way?

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[deehov]

I do the thing Chad did in his video were you examine each one so like
NaBr both of those are negligible so its neutral
LiBr both of those are also negligible so overall neutral
AlCl3 The Cl is negligible but the Al is considered acidic.. so entire thing is Acidic
KF The K is negligible but the F is basic so entire thing basic

its asking for pH less than 7 aka acidic so only one that was acidic was the AlCl3 hope that makes sense. the water crossing thing they do works too if u get it but i find this easier.

 

[Hard Work Pays Off]

cations= acidic
anions= basic
looking at cation: group 1 (on the periodic table) ? cross it out
group 2 ? cross it out
looking at anions: came from a strong acid? like a Cl- that would have came from HCl? cool, cross it out
the things not crossed out are what the solution is. so like NaBr, I'll cross Na because its group one and I'll cross Br, because it came from HBr, both are crossed out, so its neutral.

 

[redhotchiligochu]

On top of what Hard Work Pays Off said regarding group 1 and halogens (except F-), what works for me is having a mental relation between acids/bases and the strength of their conjugate pair.

"Acidic" salts come from weak Bronsted Lowry bases (NH4Cl <-> NH3) and "basic" salts come from weak Bronsted Lowry acids (NaC2H3O2 <-> HC2H3O2).

The question you posted is actually tricky conceptually because AlCl3 is a Lewis acid because of lack of lone pair electrons in Al, and many students like to gloss over Lewis acid-base theory....

Edit: added some stuff