Here are the answers to the worksheet problems, broken down step-by-step.
1. Arrhenius Definition
Rule: An Arrhenius
acid produces hydrogen ions ($H^+$) in water. An Arrhenius
base produces hydroxide ions ($OH^-$) in water.
* a.) $HNO_3$ breaks apart into $H^+$ and $NO_3^-$. It has Hydrogen at the start. ->
Acid
* b.) $KOH$ breaks apart into $K^+$ and $OH^-$. It has OH at the end. ->
Base
* c.) $Ca(OH)_2$ has OH groups. ->
Base
* d.) $HCl$ breaks apart into $H^+$ and $Cl^-$. ->
Acid
* e.) $NaOH$ has an OH group. ->
Base
2. Bronsted-Lowry Definition
Rule: A
Bronsted-Lowry acid is a proton ($H^+$) donor. A
base is a proton acceptor. An
amphoteric substance can act as both (it can give away an H or take one).
* a.) $NH_4^+$: It has extra Hydrogens it can give away to become $NH_3$, but it is positive so it won't accept more protons easily. ->
Acid
* b.) $H_3O^+$: This is the hydronium ion. It gives away an H to become water. ->
Acid
* c.) $H_2SO_4$: Sulfuric acid. It donates protons. ->
Acid
* d.) $H_2O$: Water can accept an H to become $H_3O^+$ OR give away an H to become $OH^-$. ->
Amphoteric
3. Conjugate Bases
Rule: To find a conjugate base, remove one $H^+$ from the acid. (Decrease H count by 1, decrease charge by 1).
* a.) $HCN$ minus $H^+$ becomes ->
$CN^-$
* b.) $HSO_4^-$ minus $H^+$ becomes ->
$SO_4^{2-}$
* c.) $HF$ minus $H^+$ becomes ->
$F^-$
* d.) $HNO_2$ minus $H^+$ becomes ->
$NO_2^-$
4. Conjugate Acids
Rule: To find a conjugate acid, add one $H^+$ to the base. (Increase H count by 1, increase charge by 1).
* a.) $NH_3$ plus $H^+$ becomes ->
$NH_4^+$
* b.) $HCO_3^-$ plus $H^+$ becomes ->
$H_2CO_3$
* c.) $HS^-$ plus $H^+$ becomes ->
$H_2S$
* d.) $Br^-$ plus $H^+$ becomes ->
$HBr$
5. Conjugate Partners
Rule: Look at the formula. If it looks like an acid (starts with H), find its base (remove H). If it looks like a base (negative charge/no H), find its acid (add H).
* a.) $SO_4^{2-}$ is a base. Add H ->
$HSO_4^-$
* b.) $HI$ is an acid. Remove H ->
$I^-$
* c.) $S^{2-}$ is a base. Add H ->
$HS^-$
* d.) $HNO_3$ is an acid. Remove H ->
$NO_3^-$
6. Identify Acid/Base in Reactions
Rule: The
Acid on the left loses an H to become its partner on the right. The
Base on the left gains an H to become its partner on the right.
a.) $CHOOH + H_2O \leftrightarrow HCOO^- + H_3O^+$
* $CHOOH$ turns into $HCOO^-$ (it lost an H). So, $CHOOH$ is the
Acid. Its partner is
$HCOO^-$.
* $H_2O$ turns into $H_3O^+$ (it gained an H). So, $H_2O$ is the
Base. Its partner is
$H_3O^+$.
b.) $H_2S + NH_3 \leftrightarrow NH_4^+ + HS^-$
* $H_2S$ turns into $HS^-$ (it lost an H). So, $H_2S$ is the
Acid. Its partner is
$HS^-$.
* $NH_3$ turns into $NH_4^+$ (it gained an H). So, $NH_3$ is the
Base. Its partner is
$NH_4^+$.
7. Lewis Acid or Base
Rule: A Lewis
Base has lone pair electrons to share (donate). A Lewis
Acid accepts electron pairs (often has an incomplete octet or empty orbitals).
* a.) $PH_3$: Phosphorus is in Group 15 and has a lone pair of electrons to share. ->
Lewis Base
* b.) $BCl_3$: Boron only has 6 valence electrons here (incomplete octet). It wants to accept electrons to fill its shell. ->
Lewis Acid
* c.) $H_2S$: Sulfur is in Group 16 and has two lone pairs of electrons to share. ->
Lewis Base
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Final Answer:
1. Classify (Arrhenius):
a.) Acid
b.) Base
c.) Base
d.) Acid
e.) Base
2. Classify (Bronsted-Lowry):
a.) Acid
b.) Acid
c.) Acid
d.) Amphoteric
3. Conjugate Bases:
a.) $CN^-$
b.) $SO_4^{2-}$
c.) $F^-$
d.) $NO_2^-$
4. Conjugate Acids:
a.) $NH_4^+$
b.) $H_2CO_3$
c.) $H_2S$
d.) $HBr$
5. Conjugate Partners:
a.) $HSO_4^-$
b.) $I^-$
c.) $HS^-$
d.) $NO_3^-$
6. Reaction Identification:
a.) Left: Acid = $CHOOH$, Base = $H_2O$. Right: Conj. Base = $HCOO^-$, Conj. Acid = $H_3O^+$
b.) Left: Acid = $H_2S$, Base = $NH_3$. Right: Conj. Base = $HS^-$, Conj. Acid = $NH_4^+$
7. Lewis Identification:
a.) Lewis Base
b.) Lewis Acid
c.) Lewis Base
Parent Tip: Review the logic above to help your child master the concept of acids and bases worksheet.
