1.         Here’s the fast way, as shown in class. But from # 2 onwards; I’ll only show it, step by step using proportions instead of the ratio.

 

a.         3 moles of NH3­­

or

a.         equation shows:            5 O2     4NH3, so

 

                       

 

                        4x = 15

                        x = 3.75 moles of O2

 

 

b.

 

3 moles of O2

 

 

Or

                       

 

                        x = 12/5 = 2.4 moles of NO

                        2.4 moles of NO (14 +16 g/mole) =72 g

 

 

c.                   2.8 g NO= 0.0933 moles NO

0.0933 moles NO

 

 

or         2.8 g NO /(14 +16 g/mole) =0.0933 moles NO

 

                        x = 0.14 moles of water

 

d.                  90 g H2O = 5 moles H2O

 

5 moles H2O = = 4.166 moles O2

 

4.166 moles O2

 

or         90 g H2O / (18 g/mole) = 5.0 moles H2O

 

                        x = 25/6 = 4.2 moles O2

 

                        4.2 moles O2(32 g/mole) = 133 g         

 

2.         a.         answer = 8 moles  

 

            b.         H2 + Cu2S à 2 Cu + H2S

 

                        1g H2/(2g/mole) = 0.5 mole H2

 

                        From ratio, twice as many moles of Cu will be produced:

                        0.5 (2) = 1.0 moles = 63.5 g

 

 

 

 

3.         a. Given:                       C6H14         +    9.5 O2 à         6 CO2   +   7 H2O   +   3500 kJ

 

a.         How much heat in kJ will be released if only 0.34 moles of C6H14 react?(treat kJ like moles)

 

            b.         How many moles of CO2 will escape if 4.5 moles of oxygen react?

 

Answer            Since kJ are part of the equation, you can treat them like moles.

 

0.34 moles of C6H14  

 

                       

 

            b.        

 

            x = 2.84 moles CO2

 

 

4.                     16 KClO3        + 3 P4S3 à 6 P2O5 + 16 KCl + 9 SO2

 

            a.         How many grams of sulfur dioxide escape each time 0.0010 moles of KClO3 react?

0.0010 moles of KClO3   = 0.0005625 moles SO2

 

           

            0.0005625 moles SO2*(64 g/mole) = 0.036 g SO2

 

           

            b.         4.4 g of P4S3 = 0.02 moles of P4S3.

            Then apply the ratio and you will obtain 0.06 moles of SO2.

 

 

 

c.         12.2 g KClO3/ (39+ 35.3 + 48 g/mole) = 0.10 moles of KClO3           

 

Apply the ratio:             = 0.10 moles of KCl  

 

Then convert to grams: 0.10 (39+35.5) = 7.5 g KCl

 

5.         a.         equation reveals that 4 KNO3 react with 7 moles of C, so

                        Apply the ratio and you will get 3.5 moles of C

                        3.5 moles of C = 3.5 * 12 = 42 g of C

 

 

b.         1010 g KNO3= 10 moles KNO3

from the equation we get the ratio,( remember we are comparing KNO3 to both CO and CO2

 

;           x = 30/4 = 7.5 moles of CO and 7.5 moles of CO2.

 

            7.5 moles of CO2.= 330 g of CO2.

 

7.5 moles of CO2.= 210 g of CO

 

Total = 330 + 210 = 540 g.

 

c.                   4.4 g = 0.10 moles of  CO2.

 

From the ratio, 0.10/3 = 0.033 moles of S                   

 

                                   

 

6.         The question was: Vodka is 40% alcohol by volume. Alcohol's density is 0.7893g/mL. What's the minimum mass of H2CrO4 and HCl needed to destroy the alcohol in 2.0 L of vodka?

 

3 C2H6O + 4 H2CrO4 + 12 HCl àC2H4O2 + 4 CrCl­3 + 13 H2O

 

Vodka is 40%alcohol, so:         0.40 ( 2.0 L) = 0.80 L of alcohol = 800 mL

 

Apply the ratio from the equation:

= 54.88 moles of HCl

 

= 54.88 moles HCl (36.5g/mole) = 2003 g HCl

 

If they had asked for H2CrO4.

 

Repeat the procedure. Start with . Apply the ratio of 4/3

 

  18.3 moles of H2CrO4

 

 18.3 moles H2CrO4 ([2 + 52+64]g /mole) = 2159 g H2CrO4.