More Pretest Questions

 

1.         Given:   1 molecule of nitrogen gas reacts with 3 molecules of hydrogen gas to produce 2 molecules of nitrogen trihydride gas.

 

 

Oval: NWrite a chemical equation for the above, and then draw what it represents using:

 

for each N atom, and

 

 

Oval: H
 


for each H atom.

 

 

 

2.                  One polyatomic that we have not studied is thiocyanate, SCN-1. Now that you know its name and charge, what is the formula of calcium thiocyanate?

 

3.                  What is the charge of Zn in ZnSO4?

 

4.                  What is the charge of the NO2 ion in Al(NO2)3?

 

5.                  Translate into a word equation:

 

Cl2(g) + 2 NaBr(aq) 2 NaCl(aq) + Br2(l)

 

6.                  Balance:

 

a.       P4O10 + H2OH3PO4

b.      Cu + HNO3 Cu(NO3)2 + NO + H2O

 

Solutions:

 


1.                  N2(g)+ 3 H2(g)  2NH3(g)                                       

 

 

 

 

 

 

 

 

Note that nitrogen and hydrogen gas consist of diatomic molecules. Also note that each hydrogen can only be attached to one atom in NH3.

 

2.                  Ca+2 needs two SCN-1 in order to end up with a total charge of 0. The correct formula is Ca(SCN)2.

 

3.                  Since sulfate is –2, then x + (-2) = 0, so x = 2. Zn is +2. Interestingly, although Zn is technically a transition metal, its charge is always +2. So chemists don’t bother using the Roman numeral for zinc. Only two other transition metals are that inflexible: silver, which is always +1; and cadmium, which is always +2.

 

4.                  Since Al’s charge is known to be +3, then 3 + 3x = 0. x= -1, which is nitrite’s charge. Nitrite has the same charge as nitrate, NO3-1.

 

5.                  One mole of chlorine gas reacts with 2 moles of aqueous sodium bromide to produce 2 moles of aqueous sodium chloride and 1 mole of liquid bromine.

 

P4O10 + 6 H2O 4 H3PO4

6.                  3 Cu +  8 HNO3 3 Cu(NO3)2 + 2 NO + 4 H2O