Complete the missing information in the table below:
Symbol
Protons
23
34
28
15
20
Neutrons
28
45
31
16
20
Electrons
23
36
26
18
18
Net Charge
0
2-
2+
3-
2+
Atomic No.
23
34
28
15
20
Mass No.
51
79
59
31
40
The following are the results of analysis of two samples containing phosphorous and oxygen. From these results determine if the two samples are the same compound. If the compounds are different, show that the data follows the law of multiple proportions.
Mass of O
Sample A
3.322 g
Mass of Sample
Sample B
3.718 g
2.881 g
Determine percentage of P in each sample:
Sample Sample
Since the two samples do not possess the same percentage of , they are not the same (Law of Definite Proportions)
Determine ratio of P to O in each sample:
Sample
Sample
Since the ratio of to is in small whole numbers, the Law of Multiple Proportions is valid.
3. Gallium has two naturally occurring isotopes with the following masses and natural abundances:
Abundance (%)
70.9258
60.108
Ga.92470
39.892
Using the information above, sketch the mass spectrum of Gallium.
The intensity of the more abundant isotope is set to in the mass spectrum. The intensity of the other isotope can be calculated relative to the other as shown below:
4. The isotope of an unknown element, , has a mass number of 79. The most stable ion of the isotope has 36 electrons and forms a binary compound with sodium, having a formula of . Which of the following statements is (are) true? For the false statements, correct them.
a) The binary compound formed between X and fluorine will be a covalent compound. (True)
b) The isotope of X has 38 protons. (Falso; the isotope of has 34 protons)
c) The isotope of X contains 41 neutrons. (False; the isotope of contains 45 neutrons)
d) The identify of X is strontium, Sr . (False; the identity of is selenium, Se)
5. Three different samples of a solid containing mercury and oxygen were analyzed and the following data was obtained:
Mass of
Sample
Mass of
Mercury
Mass of
Oxygen
Sample A
1.0410 g
0.9641 g
0.0769 g
Sample B
1.5434 g
1.4293 g
0.1141 g
Sample C
1.2183 g
1.1283 g
0.0900 g
Are these data consistent with the hypothesis that the material is a compound?
Calculate the percentage of mercury in each sample:
Since all sample have the same percentage of one element (fixed composition), all samples are therefore the same compound.
6. Elements in the same family often form oxyanions of the same general formula. The anions are named in a similar fashion. What are the names of the oxyanions of selenium and tellurium shown below:
a) selenate
b) selenite
c) tellerate
d) tellerite
7. Write isotopic symbols in the form of X-A (e.g. C-13) for each isotope listed below:
a) The copper isotope with 34 neutrons Cu-63
b) The uranium isotope with 146 neutrons
U-238
8. Use the mass spectrum of lead, shown below, to determine the atomic mass of lead. (Estimate the values from the graph to 3 significant figures)
Calculate relative abundance of each isotope from its intensity in the mass spectrum
Atomic mass
9. The atomic mass of fluorine is 18.998 amu and its mass spectrum shows a large peak at this mass. The atomic mass of chlorine is 35.45 amu, but the mass spectrum of chlorine does not have a peak at this mass. Explain the difference.
The fluorine isotope with mass of amu is abundant by a very large amount, causing the average mass of fluorine to be close to 19 and producing a large peak in its mass spectrum. Chlorine however, has two isotopes which are not in great excess of one another. Therefore, the average mass of chlorine is not equal to one of its isoptopes and therefore no peak appears at this value in its mass spectrum.
10. Calculate the molar mass of each substance shown below:
a)
b)
11. Calculate the mass (in grams) of each of the following:
a)
b) lead atoms
Brass is a copper and zinc alloy containing zinc by mass and has a density of 8.48 . A brass fitting has a total volume of . How many copper atoms does this fitting contain? brass atoms Cu
