<p>Please help me with acids and bases because I'm still not grasping the whole concept. can someone explain the reasoning behind the questions below:
1) Which of the following reagents could not be added together to make a buffer solution?
a) NaOH(aq) and CH3COOH(aq)
b) NaCH3COO and CH3COOH
c) NaOH and NaCH3 (answer)
d) NH4Cl and NH3</p>
<p>2) Which salt does not form an acidic solution in water?
a) MgCl2
b) Na2CO3 (answer)
c) FeCl3
d) NH4NO3</p>
<p>1) A buffer consists of a weak acid and its salt or a weak base and its salt.
a. Adding a strong base to a weak acid always creates a buffered solution because the OH ions from NaOH reacts with the acetic acid to form water and acetate ions. So, there is the weak acid (acetic acid) and its conjugate base (acetate) required for a buffer solution.
b. This solution already has the weak acid, acetic acid, and it's conjugate base, acetate, from the salt (which dissociates) and is thus a buffer solution
c. These are both salts (what is NaCH3?!) and the OH- will probably not react with the CH3- (because they are both negative ions i guess) to create a conjugate so it can't be a buffer.
d. This solution already has the weak base, NH3, and it's conjugate acid, NH4+ and is therefore a buffer solution. :) I hope that helps~</p>
<p>2.</p>
<p>you can think of a salt as a product of neutralization reaction.
so, MgCl2 is produced by Mg(OH)2 and HCl
as HCl is a strong acid, but Mg(OH)2 is not, the salt should be acidic</p>
<p>and for Na2CO3, NaOH is a strong base, but H2CO3 is not a strong acid, so the salt is basic.</p>
<ol>
<li>The acidity or basic-ness of a salt solution depends on its component ions~
Remember! The stronger the acid or base, the weaker it's conjugate base or acid. The weaker the acid of base, the stronger it's conjugate base or acid.
a.MgCl2 makes Mg ions and Cl ions. Mg ion is the conjugate acid of a weak base, Mg(OH)2 and is therefore a kind of strong acid. THe Cl ion is the conjugate base of a really strong acid, HCl and because of this, it is weak and is often considered neutral (neither acidic nor basic). Therefore the Mg ion makes the solution acidic.
b. Na2CO3 makes Na ions and CO3 2- ions. The Na ion is the conjugate acid of a really strong base, NaOH, and because of this, it is weak and is also considered neither acidic nor basic. The carbonate ion, on the other hand, is the conjugate base of a weak acid and is therefore kind of strong. The solution, as determined by the carbonate ion, is basic.
c. FeCl3 makes Fe ions and Cl ions. As mentioned earlier, the Cl ion is considered neutral and does not contribute to the acidity/basic-ness of the solution. The Fe ions are the conjugate acid of a weak base, Fe(OH)(H2O)6 2+ (i think,it's a complex ion anyways) and is therefore kind of strong. The solution is acidic.
d.NH4NO3 makes NH4+ and NO3- ions. NH4+ is the kind of strong conjugate acid of a weak base, NH3. NO3- is the conjugate base of a really strong acid, HNO3 and is therefore really really weak (it is also considered neutral). The solution is acidic.
~It's important to memorize the strong bases and acids :D</li>
</ol>
<p>Thank you guys so much.</p>
<p>What about this one?</p>
<p>OH + ? = (CrO4)-2 + H
why is the answer (Cr2O7)-2 and not Cr3+</p>
<p>And this one?
Which of the following does not react with a dilute H2SO4 solution?
a) NaNO3 (answer)
b) Na2S
c) Na3PO4
d)Na2CO3
e) NaOH</p>
<p>1st one is Cr2O7 2- and not Cr3+ b/c OH- --> H is oxidizing so the Cr needs to reduce (gain electrons).</p>
<p>THe charge in CrO4 2- for Cr is 6+ therefore the charge of Cr on the reactant side must be greater then 6. the charge in Cr2O7 2- for Cr is 7+ so therefore this is ur answer..</p>
<p>the 2nd one is a b/c H2SO4 + NaNO3 --> HNO3 + NaSO4 and both of the products are completely soluble and everything will break up.</p>