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CHAPTER 3 BASIC HOMEWORK I

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Look at Chapter 3 Basic I Homework (New) for the updated questions!

 

Question 1

What is the mass of 1 mol of CH3NH2 in g?

Help: Molar mass

Correct

 

Explanation

 1 mol = x g / MM CH3NH2


MM of CH3NH2 = 12 + 5(1.008) + 14 = 31


1mol= x g / 31 MM


x= 31 g

 

Question 2

What is the percent composition by mass of oxygen in carbon dioxide?

Help: Percent composition by mass

Correct

 

Explanation

 carbon dioxide = CO2


C= 12 MM

O =16 MM * 2 = 32


32/ (32+12) = .7272 * 100 = 72.72%

 

Question 3

What is the percent composition by mass of carbon in lithium carbonate, Li2CO3?

Correct

 

Explanation

 Li2CO3


Li-6.941(2)=13.882

C-12

O-16(3)=48


12/ (13.882 +12 +48) = 16.22

 

Question 4

What is the mass of 41 molecules of nitrogen dioxide, NO2, in g? USE 3 SIG. FIG.

Help: Conversion Factor

Correct

 

Explanation

 (14 +16(2)) MM NO2


41/(6.022*10^23) = 6.81e-23 mol = X g/ 46 MM

X= 3.1326e-21


 

Question 5

What is the mass of 3.66 mol NaCl in grams? 

Correct

 

Explanation

 3.66 mol = X g/ MM of NaCl

MM of NaCl = 58.4428


3.66 mol = X g/ 58.4428 MM


X = 213.9

 

Question 6

What is the mass in grams of 0.13 mol sodium phosphate, Na3PO4 ?

Correct

 

Explanation

0 .13 mol = X g/ MM of Na3PO4 


MM of Na3PO4 = 163.94


0.13 mol = X g/ 163.94 MM 


X = 21.3122

 

Question 7

How many moles is 390.0 g calcium carbonate, CaCO3 ? 

Correct

 

Explanation

 390 g/ MM of CaCO3 = X moles


MM of CaCO3 = 100.0869


390/ 100.0869 = 3.9


X = 3.9 moles

 

Question 8

How many moles is 126 g lithium carbonate, Li2CO3 ?

Correct

 

Explanation

 126 g Li2CO3/ 73.891 MM


1.7 moles Li2CO3

 

Question 9

What is the empirical formula for acetone, C2H4O2? (Keep elements in same order for your answer) 

Remember to use correct symbols for elements--C for carbon (NOT c), etc.

 

Explanation

The empirical formula indicates the simplest whole number ratio of atoms in a substance. 

The molecular formula indicates the number of atoms of each element in a molecule of the substance. 

Ex:

Molecular formula: H2O2; empirical formula: HO
Molecular formulas: C2H4, C5H10; empirical formula: CH2
Molecular formula: CH4; empirical formula: CH4

C2H4O2 / 2

CH2O

 

Question 10

A substance contains 5.00 g C and 1.70 g H. What is the empirical formula? (Answer starts with C and H is last.) 

 

Explanation

 5 g C

5 g / 12 MM = .4167 mol C

1.70 g H / 1.008 MM = 1.686 mol H

1.686 mol H / .4167 = 4.05  about 4

CH4

 

Question 11

What is the empirical formula of a compound which is 82.64 % C by mass and 17.36 % H. (Answer starts with C and H is last.)

 

Explanation

 Use a 100g sample...

82.64 g C / 12 MM  = 6.89

17.63 g H/ 1.008 MM = 17.49


17.49 / 6.89 = 2.5 (not a whole number) multiply it by 2 to make it a whole number

CH2.5

goes to 

C2H5

 

Question 12

Balance the following chemical reaction using smallest whole numbers: 

C3H8(g) + O2(g) --> CO2(g)+ H2O(g) 

What is the number of CO2 molecules in the balanced equation?

Correct

 

Explanation

 WHOOT BALANCING

Left side v Right Side

Left 

  • 3 mols C
  • 8 mols H
  • 2 mols O
Right

  • 1 mol C
  • 3 mol O
  • 2 mol H
Lets start by balancing the H...

simply add a 4 coefficient in front of the H2O on the right

C3H8(g) + O2(g) --> CO2(g)+ 4H2O(g) 

Next the Cs...

add a 3 coefficient in front of the CO2 on the right 

C3H8(g) + O2(g) --> 3CO2(g)+ 4H2O(g) 


Next the Os...

add a 5 coefficient in front of the O2 on the left 

C3H8(g) + 5O2(g) --> 3CO2(g)+ 4H2O(g) 


Now lets recheck to make sure

3 C: L and R

8 H: L and R

10 O: L and R


 

Question 13

What is the number of H2O molecules in the balanced equation?

Correct

 

Explanation

Look Above

 

Question 14

What is the number of O2 molecules in the balanced equation?

Correct

 

 

 

Question 15

Balance the following chemical reaction using smallest whole numbers: 

CuO(s) +NH3(g) --> Cu(s) + N2(g) + H2O(g) 

Hint, balance the elements in the following order--nitrogen, hydrogen, oxygen, and copper.

What is the number of Cu atoms in the balanced equation?

Correct

 

Explanation

 Balancing equations heck friggin yeah...


Basically all you need to do is get the same amount of stuff on both sides

On the reactants side aka the left side we have:

1 mol of Cu

1 mol of O

1 mol of N

3 mols of H


On the products side aka the right side we have:

1 mol of Cu

1 mol of O

2 mols of  N

2 mols of H


... so were going to balance out the N first

and put a coefficient of 2 in front NH3 (on the reactant side) so we can have 2 mols of N on both sides

  • when we do this we double the mols of H on the left
...next we balance the H

and were going to put a 3 in front of the H2O on the right side so we can have 6 mols of H on both sides
-- next we balance the O
we have three mols on the right so were going to put a 3 coefficient on the left side in front of the CuO to balance the Os
..and finally we balance the Cu
and all we have to do is put a 3 coefficient in front of the Cu on the right side and there we have it
 

Question 16

What is the number of nitrogen molecules in the balanced equation? (Refer to the previous question)

Correct

 

 

Nitrogen molecules refer to N2 (btw)

 

Question 17

What is the number of water molecules in the balanced equation? (Refer to previous questions)

Correct

 

 Look at solutions of questions 15