Practice Problems Week 7

1. Find the oxidation number of chromium in each of the following compounds:

(a) _{}

(b) _{}

(c) _{}

2. For each of the following equations, (a) complete and balance the equation; (b) determine if the reaction is redox or not; (c) for redox, write the oxidation and reduction half reactions and (d) indicate the element that is reduced, the element that is oxidized, the reducing agent and the oxidizing agent.

(i) sodium carbonate
+ iron(III) nitrate -> **sodium nitrate + iron(III) carbonate**

(a) _{}

**(b) ****It is not redox (all atoms retain their formal charges)**

(ii) aluminum + nitric
acid (hydrogen nitrate) -> **aluminum nitrate +
hydrogen gas**

(a) _{}

(b) **It is redox because Al and H are changing charge states**

(c) **Oxidation: _{}, reduction: _{}**

(d) **Oxidizing agent: nitric
acid; reducing agent: aluminum**

(iii) aluminum +
bromine -> **aluminum bromide**

(a) _{}

(b) **It is redox because Al and Br change charge states**

(c) **Oxidation: _{}, reduction: _{}**

(d) **Oxidizing agent: bromine;
reducing agent: aluminum**

3. Given the equation: _{}

(a) How many moles of
SO_{2} are produced from 6.68 moles of O_{2}?

_{}

(b) How many grams of
FeS_{2} are required to react with 0.750 moles O_{2}?

_{}

(c) How many grams of
SO_{2} can be prepared from 25.0 grams of O_{2}?

_{}

(d) If 31.8 grams of
SO_{2} were isolated in problem 3(c) above, what is the percent yield
of SO_{2}?

_{}

4. Given the reaction: _{}

(a) What is the limiting reactant?

**To determine which
reactant is limiting, we need to see if** _{}** is greater or less than _{}:**

_{}

**So _{} is clearly greater
than _{} and so hydrogen is in
excess.**

(b) What is the
theoretical yield of ammonia (NH_{3}) when 15.0 grams of N_{2} is mixed with 5.00 grams of H_{2}?

_{}

5. Given the reaction: _{}

(a) What is the
theoretical yield when 20.0 grams of Mg are mixed with 10.0 grams of N_{2}?

_{}

**So is less than and so N _{2} is in excess and there isn't enough Mg. So Mg will go away first. We must
calculate the theoretical yield based on Mg.**

_{}

**(b) **What is the
limiting reactant? **Magnesium, because it goes
away first, stopping the reaction.**