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CHAPTER 2 REGULAR HOMEWORK

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Order of questions may vary, but all answers are here. Use CTRL+F to find all the questions.

 

Question 1

In one on the compounds that contains only oxygen and nitrogen, 3.50 g of nitrogen combines with 2.00 g of oxygen. In another, 0.875 g of nitrogen combines with 1.00 g of oxygen. Show that these compounds obey the law of multiple proportions.

Select one:
 Correct

 

Explanation

 The law of multiple proportions states that when two elements combine with each other to form more than one compound, the weights of one element that combine with a fixed weight of the other are in a ratio of small whole numbers. For example, there are five distinct oxides of nitrogen, and the weights of oxygen in combination with 14 grams of nitrogen are, in increasing order, 8, 16, 24, 32, and 40 grams, or in a ratio of 1, 2, 3, 4, 5. 


In the first compound the ratio of oxygen to nitrogen is 1: 1.75

In the second compound the ratio of oxygen to nitrogen is 1: .875


The difference between those two compounds is in the amount of nitrogen in while the first has double the amount of the second making it a 2:1. (which is exactly what the answer choice b is implying).


To look at this in depth click this!

 

Question 2

Chromium forms two bromides, one that is 17.82% chromium by mass and another that is 24.55% chromium. You will show that these compounds obey the law of multiple proportions. In the first sample, what is the mass of chromium per 1 gram of bromide? (Hint, in a 100 g sample how many grams are chromium and how many grams are bromide? The chromium to bromide ratio gives the mass of chromium per 1 gram of bromide.)

Correct

 

Explanation

 In a 100g sample...

The first bromide is 17.82 g Chromium and is 82.18 g Bromine

Ratio: 1: 4.6116 in accordance to Chromium (17.82/17.82 && 82.18/17.82)

Ratio: .216:1in accordance to Bromine(17.82/82.18 && 82.18/82.18)


 

Question 3

In the second sample, what is the mass of chromium per 1 gram of bromide?

Correct

 

Explanation

 

The second bromide us 24.55 g Chromium and is 75.45 g Bromine

Ratio: 1: 3.07 in accordance to Chromium

Ratio: .325:1

 

Question 4

What is the ratio of mass of chromium in the two samples per gram of bromide? (Use the ratio of the larger mass to the smaller mass.)

Note, you must enter a number for you answer. 1:1 or 1/1 = 1. So enter 1.
5:4 or 5/4 = 1.2, 4:3 or 4/3 = 1.33, 3:2 or 3/2 = 1.5, etc.

Correct

 

Explanation

Note that this ratio is equivalent to the ratio of small whole numbers. (Divide your answer by 1 and multiple numerator and denominator by 2.)


.325 : .216
.325/.216 = 1.50

 

Question 5

Given the symbol 127I-. What is the atomic number?

Correct

 

Explanation

 The atomic number (proton number) of an element will never change, because if it did than the element itself would change.


So find iodine on a periodic table and find its atomic number.

 

Question 6

Given the symbol 127I-. What is the mass number?

Correct

 

Explanation

 Mass number is also not dependent on the number of electrons as they are simply negligible in comparison to neutrons and protons, so the mass number of this element will be equivalent to its atomic number (proton count) and its number of neutrons, which just so happens to be shown here on the top left corner (127).

 

Question 7

Given the symbol 127I-. What is the charge?

Correct

 

Explanation

 There is an extra electron in this Iodine and it has a charge of -1 which can be seen on the top right corner of elemental I.

 

Question 8

Given the symbol 127I-. What is the number of protons?

Correct

 

Explanation

 I hope you've finally figured it out by now...it's the same exact thing as it's atomic number, which you already found.. surprise surprise it's 53.

 

Question 9

Given the symbol 127I-. What is the number of electrons?

Correct

 

Explanation

 If this element was in its ground state than it would have the same number of electrons as it does protons, but since it's in an excited state as an ion and has a charge of -1, it has an additional electron making it 53 + 1, which is 54. Ya got the gist!

 

Question 10

Given the symbol 127I-. What is the number of neutrons?

Correct

 

Explanation

 Take the mass number and subtract it from the atomic number aka

take 127 - 53 = 74. 

 

Question 11

Given a mass number of 17, a charge of 2-, and 10 electrons. What is the atomic number?

Correct

 

Explanation

 A charge of 2- means there was originally only 8 electrons (8 + 2 =10) and usually in the ground state the number of electrons and protons are the same, so that means there was 8 protons, which makes 8 the atomic number as the two are synonymous.

 

Question 12

Given a mass number of 17, a charge of 2-, and 10 electrons. What is the number of protons?

Correct

 

Explanation

 Ya'll at this point if you haven't figured out that the atomic number and the number of protons is the same I DONT KNOW WHAT I CAN DO!

 

Question 13

Given a mass number of 17, a charge of 2-, and 10 electrons. What is the number of neutrons?

Correct

 

Explanation

 With a mass number of 17 and an atomic number/# of protons being 8: 17-8=9 giving us 9 neutrons.

 

Question 14

Given a mass number of 17, a charge of 2-, and 10 electrons. What is the element?

Select one:
 Correct

 

Explanation

 Protons/Atomic # will give you the element and in this case it's oxygen.

 

Question 15

Chlorine has two stable isotopes of mass 34.97 u and 36.97 u. Suppose the percent abundance of the lighter isotope were 67.22%. What would be the average atomic mass of Cl? (The actual abundance is 75.77%.) USE 4 SIG. FIG.

Correct

 

Explanation

 34.97 ( .6722) + 36.97 (.3278) = 35.62

 

Question 16

The mass spectrum of a hypothetical element shows that 75.58% of the atoms have a mass of 27.977 u, 1.522% have a mass of 28.976 u, and the remaining have a mass of 29.974 u. Calculate the average atomic mass of this element (in units of u). (Use 4 Sig. Fig. Don't round until end.)
Correct


 

Explanation

4 Sig. Fig. (Don't round until end.)


27.977(.7558) + 28.976(.01522) + 29.974( .22898)= 28.45

 

Question 17

Hypothetical element X has 3 stable isotopes. The relative peak intensities are 20.00 for 180.0 u, 100.0 for 184.0 u, and 60.00 for 186.0 u. What is the average atomic mass for X? USE THE CORRECT NUMBER OF SIG. FIG.

Correct

 

Explanation

(180*20 + 100*184 + 60*186) / (20 + 100 + 60) = 184.2

 

Question 18

Bromine occurs naturally as two isotopes, one with a mass of 78.918 u and the other with a mass of 80.916 u. Suppose the average atomic mass from the periodic table were 80.77 u. What would be the percent abundance of the lighter isotope? (Use, 4 SIG. FIG.)

FYI (not useful for solving the problem) the actual mass and % abundance are 79.904 u and 50.65%, respectively.

Correct

 

Explanation

 solve using a system of equations


80.77 = 78.918x + 80.916y

1 = x + y 


1-y =x

80.77 = 78.918(1-y) + 80.916y

y= .92693


x= .07307

y=.92693

 

Question 19

Calculate the molecular mass (in u) of phosphoric acid, H3PO4 to 4 significant figures.

Correct

 

Explanation

 Get the molar masses of each individual atom and multiply it by the subscript and add them all up.


 H-1.008 * 3 = 3.024

P- 30.97 

O-16*4 = 64


97.9

 

Question 20

Calculate the molecular mass (in u) of aniline, C6H7N to 4 significant figures.

Correct

 

Explanation

 Get the molar masses of each individual atom and multiply it by the subscript and add them all up.


C-12.0107 * 6 = 72.06

H-1.008 * 7 = 7.056

N-14* 1 = 14


93.11/93.12


 

Question 21

What charge is expected for the following elements in ionic compounds--Be, Mg, Ca, Sr, Ba, Ra, Zn, and Cd?

For positive charges write: 1 or +1, 2 or +2, etc.
For negative charges write: -1, -2, etc. DO NOT WRITE: 1-, etc.

Correct

 

Explanation

 +2 look at the charges periodic table above or linked here

 

Question 22

What charge is expected for the following elements in ionic compounds--O, S, Se, Te, and Po?

Correct

 

Explanation

  -2 look at the charges periodic table above or linked here

 

Question 23

What charge is expected for the following elements in ionic compounds--Li, Na, K, Rb, Cs, and Fr?

Correct

 

Explanation

 +1 look at the charges periodic table above or linked here

 

Question 24

What is the expected empirical formula for the ionic compound made from Li and I?

Select one:
 Correct

 

Explanation

 Lithium has a 1+ charge

Iodine has a 1- charge 

1:1

 

Question 25

What is the expected empirical formula for the ionic compound made from Cs and O?

Select one:
 Correct

 

Explanation

 Oxygen has a 2- change

Cesium has a 1+ charge

 

O=1

Cs=2

 

Question 26

What is the empirical formula for the compound made from Y3+ and Cl1-?

Select one:
 Correct

 

Explanation

 Always balance the charges to make it equal 0.


Y = 3+

Cl=1-


3+  + 3(1-) = 0


1Y

3Cl

 

Question 27

Calculate the number of moles in 12.7 g of Se. 

Correct

 

Explanation

3 Sig. Fig.


12.7 / 78.96 = .16

 

Question 28

Calculate the number of moles in 1.33x1022 NO2 molecules. 

Correct

 

Explanation

3 Sig. Fig.


1.33 * 10^22 / (6.022*10^23) = .0220

 

Question 29

Calculate the mass (in g) of 1.41 moles of H2O. 

Correct


 

Explanation

g/ (18 MM ) = 1.41mol


g = 25.38 

 

Question 30

Calculate the number of moles in 13.7 g SO3

Correct


 

Explanation

80.066 MM of SO#


13.7/80.066 = .171 mol

 

Question 31

Calculate the number of oxygen atoms in 77.8 g SO3

Correct


 

Explanation

80.066= MM of SO3


77.8 g / 80.066 g = .972 mol



.972 mol * 6.022 * 10^23 * 3 (multiply the number by 3 because there was 3 oxygen atoms on every mol of SO3)

==1.75e24