Unit 5: Applying Chemical Reactions Chem Com Test 4/20/09

1. What are the three key elements plant need from their environment?

Nitrogen Phosphorus Potassium

2. Why do farmers add nitrogen fertilizers to the soil if nitrogen is the most abundant element in the atmosphere?

N 2 gas is unreactive and plants cannot utilize it.

3. What percent of nitrogen makes up a lawn fertilizer labeled ?

10% Nitrogen by weight. The numbers 10 – 5 – 5 show the percentage of Nitrogen – Phosphorus – Potassium respectively.

4. What percent of potassium makes up a crop fertilizer labeled 30 – ?

15% Potassium

What percent of potassium makes up a crop fertilizer labeled 30 – ? 15% Potassium

What is the role of denitrifying bacteria in the environment?

Denitrifying bacteria breakdown ammonia, nitrites and nitrates from animal waste and dead organic matter and release nitrogen gas back into the atmosphere.

List three key substances containing nitrogen that are biologically essential for human physiology.

1.Protein synthesis (amino acids) 2.DNA/RNA synthesis 3.ATP production (provides energy for essential biological processes)

What role do legumes play in the nitrogen cycle?

Legumes are the only plants that contribute to the fixation of N 2 to usable forms of NH 3 and NH 4 +

What is unique about the roots of legumes?

Their root nodules contain bacteria that CAN convert atmospheric nitrogen to ammonia and ammonium ions.

What is the characteristic of an atom to attract atoms based upon the architecture of its nucleus?

Electronegativity

Describe the general trend of electronegativity among the elements on the periodic table?

Elements increase in electronegativity as you move up a column or to the right in the periodic table. These values have been determined and have to be looked up when positions on the periodic table make it difficult to predict.

What is the most electronegative of all elements?

F - fluorine

Refer to a periodic table. Arrange the following elements from least electronegative to most electronegative? Na, Cu, Mg, O, Br, Ne

Refer to a periodic table. Arrange the following elements from least electronegative to most electronegative? Ne, Na, Mg, Cu, Br, O,

In the previous question, why was Ne placed least electronegative when it is farthest to the right?

Ne, Na, Mg, Cu, Br, O, In the previous question, why was Ne placed least electronegative when it is farthest to the right? Neon is a Noble Gas and therefore has a full set of valence electrons so it will not attract anymore.

Which of the following is most electro- negative?

Transition metals are not very predictable so the electronegativities have been determined empirically. Refer to the number to determine electronegativity. The higher the number the more electronegative.

What is meant by the oxidation state of an element in a compound?

What is meant by the oxidation state of an element in a covalent compound? Oxidation state (or number) is determined by the number of electrons associated with an atom’s nucleus in a covalent bond. It will be the “apparent” charge on the atom.

What is the oxidation state of nitrogen in NH 4 +1 ? Use your rules to assign oxidation states to elements in covalent compounds. Total charge = +1 overall charge on NH 4 OX#+1 NH4H4

What is the oxidation state of nitrogen in NH 4 +1 ? Use your rules to assign oxidation states to elements in covalent compounds. H almost always has a +1 charge. Total charge = +1 overall charge on NH 4 OX#+1 NH4H4

What is the oxidation state of nitrogen in NH 4 +1 ? Multiply the oxidation number for the element by the number of atoms in the compound Total charge +4 = +1 overall charge on NH 4 OX#+1 NH4H4

What is the oxidation state of nitrogen in NH 4 +1 ? Determine the amount of charge necessary to give the overall charge of the specie, in this case +1 Total charge +4 = +1 overall charge on NH 4 SO = +1 You need to add a total of -3 to the species. OX#+1 NH4H4

What is the oxidation state of nitrogen in NH 4 +1 ? Figure out the total negative charge must be distributed over the remaining atoms. Total charge -3+4 = +1 overall charge on NH 4 OX#-3+1 There is only one N so it must carry the entire -3 charge NH4H4

What is the oxidation state of N in lithium nitride, Li 3 N ? Hint: Li is a group 1 metal.

What is the oxidation state of N in lithium nitride, Li 3 N? Hint: Li is a group 1 metal. 1.Li, group 1 metal has a +1 charge. 2.Multiply +1 by the 3 Li atoms for an overall contribution from Li of +3 3.To get an overall charge of 0 you will have to -3 from Since there is only one N atom it must carry a -3 charge. Total charge +3-3 = 0 overall charge OX#+1-3 Li 3 N

In binary compounds, why do metals usually have a positive oxidation state and nonmetals usually have a negative oxidation state?

Nonmetals are MORE electronegative so they attract electrons while the less electronegative metals readily donate electrons.

What is the name of the industrial process for manufacturing ammonia gas from atmospheric nitrogen?

Haber-Bosch Process

Write the chemical reaction for the Haber- Bosch Process.

N 2 + H 2 NH 3

What does the double arrow mean in the equation? N 2 + H 2 NH 3

What does the double arrow mean in the equation? N 2 + H 2 NH 3 The reaction is reversible.

How is hydrogen supplied in concentrated enough amounts to efficiently drive this reaction? N 2 + H 2 NH 3

How is hydrogen supplied in concentrated enough amounts to efficiently drive this reaction? N 2 + H 2 NH 3 Methane (CH 4 ) is reacted with steam to produce hydrogen gas and carbon monoxide. CH 4 + H 2 O (g) CO + H 2

How is hydrogen supplied in concentrated enough amounts to efficiently drive this reaction? N 2 + H 2 NH 3 Methane (CH 4 ) is reacted with steam to produce hydrogen gas and carbon monoxide. CH 4 + H 2 O (g) CO + H 2

What is the difference between chemical activity and electronegativity?

Chemical activity describes how readily an element will give up it’s electrons (oxidize). Electronegativity describes how strongly an element will attract electrons (reduction).

Which elements are most active?

Elements in Groups 1 and 2. In general Metals are more active than non-metals.

What will happen if silver is placed in a solution of copper nitrate?

Silver is less active than copper. Copper ions will remain in solution and silver will not ionize. So NOTHING happens.

What will happen if copper is placed in a solution of silver nitrate?

Copper is more active than silver so it will oxidize (Cu  Cu e - ) The Ag+ ions in solution will absorb the electrons and convert to Ag.

What is an electrolytic cell?

A combination of two half cells connected by a conducting wire and a salt bridge: oxidation occurs in one cell creating a flow of electrons to the other, less active electrode. Electric current is generated.

What process occurs at the electrode containing the most active element? Hint: If it is most active it will be the one losing electrons

What process occurs at the electrode containing the most active element? Hint: If it is most active it will be the one losing electrons Oxidation is Loss

What is the name for the electrode where oxidation occurs?

Anode

When the metal atom gives up an electron (like the zinc at the right) what happens to the atom?

The less active metal receives electrons a process called ________.

The less active metal receives electrons a process called reduction.

The less electrode where reduction occurs is called the ______________.

The less electrode where reduction occurs is called the cathode. Remember “Red Cat”

The less electrode where reduction occurs is called the cathode. Remember “Red Cat”