chapter 3 stoichiometry

Question 1

Which of the following reactions is the combination reaction between elemental aluminum and oxygen gas?
2Al(s) + 6O(g) = Al2O3(s)
Al(s) + O(s) = AlO(s)
4Al(s) + 3O2(s) = 2Al2O3(s)
Al(s) + 3O(s) = AlO3(s)
Al(s) + O2(s) = AlO2(s)

Answer 1

4Al(s) + 3O2(s) = 2Al2O3(s)

I write the product first. Then I add the subscripts based on their charges. Hint: Al always has the same charge; 3+

Question 2

Which of the following best describes what type of reaction is shown below?
CH4(g) + 2O2(g) = CO2(g) + 2H2O(l)

Answer 2

Combustion

Question 3

Which of the following best describes what type of reaction is shown below?
2Na(s) + Cl2(g) = 2NaCl(s)

Answer 3

Combination

Question 4

Which of the following best describes what type of reaction is shown below?
CaCO3(s) = CaO(s) + CO2(g)

Answer 4

Decomosition

Question 5

Predict the products of the following reaction and balance it properly.
Al(s) + Br2(l) =

Answer 5

2Al(s) + 3Br2(l) = 2AlBr3(s)

Question 6

Which of the following reactions is the combustion of
C4H10O(l)
Hint: you need to add O(g) as a reactant and then balance. It’s a combustion so you know what your products should be.

Answer 6

C4H10O(l) + 6O2(g) = 4CO2(g) + 5H2O(l)

Question 7

How many molecules are in 3 moles of CO2?
Hint: just look up Avagadro’s number if you don’t have it memorized. And don’t forget to move the decimal to keep proper scientific notation.

Answer 7

1.8 x 10 ^24

Question 8

How many atoms are in 2 moles of HNO3?

Answer 8

6.0 x 10 ^24

Question 9

How many oxygen atoms are in 1.5 moles of N2O4?

Answer 9

3.6 x 10 ^24

Question 10

There are 1.5 x 10 ^25 water molecules in a container. How many moles of water is this?

Answer 10

25

Question 11

What is the mass of 1.2 moles of NaOH?

Answer 11

48 grams

Question 12

How many moles are in a 45 gram sample of C6H12O6?

Answer 12

0.25

Question 13

What is the mass of 20 moles of NH3?

Answer 13

340 grams

Question 14

How many molecules are in a 48 grams sample of SO2?

Answer 14

4.5 x 10 ^23

Question 15

What is the mass of 1.5 x 10 ^21 water molecules?

Answer 15

0.045 grams

Question 16

Which of the following compounds is the molecular formula the same as the empirical formula?
P4O10
C6H6
C6H10O2
CH3CH2OH
H2O2

Answer 16

CH3CH2OH

Question 17

The empirical formula of a compound is CH and its molecular weight is 78 amu. Which of the following is this compound?
C5H18
C6H6
C4H14O
C4H4
C5H5

Answer 17

C6H6

The wording is cofusing on the question. The important part is; CH is the empirical formula which means that C6H6, C4H4, and C5H5 can all be reduced to CH. So… It’s one of those 3. But C6H6 is the only one that addds up to 78 amu.
C5H18 is an empirical formula but it’s not the one that’s mentioned in the question.

Question 18

What is the empirical formula of C6H12O6?

Answer 18

CH2O

Question 19

A compound is 50% sulfur by mass and 50% oxygen by mass. Which of the following could be this compound?
SO2
S2O3
SO3
SO
S2O

Answer 19

SO2

Question 20

What is the mass percent of oxygen in HNO3?

Answer 20

76%
use the p table
it’s an easy enough math problem

Question 21

What is the mass percent of titanium in TiCl2?

Answer 21

40%

Question 22

Which of the following would have the greatest mass percent iron?
FeO
FeS
Fe2O3
FeBr3
FeBr

Answer 22

FeO

Question 23

A compound is 30.4% nitrogen by mass and 69.6% oxygen by mass. Which of the following could be this compound?
NO
NO3
N2O
N2O4
N4O

Answer 23

N2O4

Question 24

If 81 grams aluminum reacts completely with 142 grams Cl2, what mass of AlCl3 is produced?
2Al + 3Cl2 = 2AlCl3
1.33 grams
3 grams
71 grams
178 grams
401 grams

Answer 24

178 grams
I really use my percentage math skills for these. Convert to moles but don’t forget to convert back to grams for the final answer.

Question 25

If 16 grams of H2 reacts with 160 grams of O2 to produce 6 moles of H2O, what is the percent yield? 2H2 + O2 = 2H2O

Answer 25

75% This one takes some thinking. The 6 moles of H2O is your actual yield. So you have to figure out what the theoretical yield would be based on the given equation. Then it's just, actual yield divided by theoretical yield.

Question 26

If 42 grams of N2 reacts with 18 grams of H2 to produce 34 grams of NH3, what is the percent yield? N2 + 3H2 = 2NH3

Answer 26

67%

Question 27

If 8 moles of C react completely with excess H2, how many moles of C2H6 are produced? 2C + 3H2 = C2H6

Answer 27

4 moles of C2H6 You can pretty much do that it your head.

Question 28

If 1.5 moles of H2 react completely with excess C, how many moles of C2H6 are produced? 2C + 3H2 = C2H6

Answer 28

0.5 moles

Question 29

How many moles of C would be required for 10 moles of H2 to react completely in the following reaction? 2C + 3H2 = C2H6 (answer in fraction form)

Answer 29

20/3

Question 30

If 12 moles of H2 react completely with 10 moles of C, what is the reagent in excess and how many moles are left over? 2C + 3H2 = C2H6

Answer 30

2 moles of C are left over

Question 31

If 37 grams of C4H10O react completely with excess O2, how many moles of CO2 are produced? C4H10O + 6O2 = 4CO2 + 5H2O

Answer 31

2 moles

Question 32

If 128 grams of O2 react completely with excess C4H10O, how many moles of H2O are produced? C4H10O + 6O2 = 4CO2 + 5H2O (answer given in fraction or decimal form)

Answer 32

(remember you're converting O2, not just O) 10/3 or 3.33333 I figure this out by calculating 4 moles of O2 is 66% of the 6 moles given in the equation. Then I calculate 66% of the 5 moles of H2O in the given equation.

Question 33

If 49 grams of H3PO4 and 60 grams of NaOH react to completion, what mass of H2O is produced? H3PO4 + 3NaOH = 3H2O + Na3PO4

Answer 33

27 grams remember to convert your answer back into grams

Question 34

If 140 grams of N2 reacts completely with 24 grams of H2, what mass of NH3 is produced? N2 + 3H2 = 2NH3

Answer 34

136 grams

Question 35

If 81 grams of Al reacts completely with 142 grams of Cl2, what mass of AlCl3 is produced? 2Al + 3Cl2 = 2AlCl3

Answer 35

178 grams (I actually got 174 but it's just from rounding or using less sig figs)

Question 36

If 16 grams of H2 reacts with 160 grams of O2 to produce 6 moles of H2O, what is the percent yield? 2H2 + O2 = 2H2O (basically, it's already telling you what your actual yield is)

Answer 36

75%

Question 37

If 42 grams of N2 reacts with 18 grams of H2 to produce 34 grams of NH3, what is the percent yield? N2 + 3H2 = 2NH3

Answer 37

67%