CE Chemistry Review Chapter 2 KEY
1. Why is MgO the symbol for magnesium oxide rather than MGO? Each element starts with a
capital letter, but if there are 2 letters in the symbol the 2nd letter is lower case.
2. What is the meaning of the 2 in H2SO4? There are 2 hydrogen atoms in every molecule of
H2SO4
3. Find the molecular weight of CaCl2 in u or amu. Ca= 40.078, Cl = 35.4527 therefore
1(40.078) + 2(35.4527) = 110.9834u
4. Using whole numbers, find the molecular weight of Al(OH)3. Al= 27 O = 3(16) H= 3(1)
27 + 48 + 3 = 78u
5. Describe and compare the mass, charge and location of protons, neutrons, and electrons.
Particle
Relative Mass Charge Location
Proton
1
+1
Nucleus
Neutron
1
0
Nucleus
Electron 1/1839
-1
Outside of nucleus
6. How many electrons are in a neutral atom of calcium-41, ( 41𝐶𝑎)? 20 electrons
7. What charge do atoms have and why? (explain) atoms have no charge because they have the
same number of protons as electrons, therefore the positive charges cancel out the negative
charges.
8. How are isotopes the same? Isotopes have the same number of protons and electrons. How
are isotopes different? Isotopes have different numbers of neutrons.
9. How is Thorium-232 different from Thorium-230? Thorium-232 has 142 neutrons, Thorium230 has 140 neutrons
10. How many protons are in the nucleus of 25𝑀𝑔 atom? 12
11. How many neutrons are in the nucleus of 25𝑀𝑔 atom? 13
12. What is the mass number of 25𝑀𝑔? 25
13. Naturally occurring copper (Cu) has 2 isotopes, Cu-63 and Cu-65. Use the periodic table and
determine which isotope is present in the larger percentage. Cu-63 has a larger percent
abundance compared to Cu-65 because the average atomic mass is 63.546 which is closer to 63
than 65.
14. What mass of aluminum (Al) in grams contains the same number of atoms as 83.80 g of Kr?
26.981538 g (this is the atomic mass)
15. One Avogadro’s number of silver (Ag) atoms would weigh? 107.8682 g (remember that the
atomic mass = 1 mole = 6.02x1023 atoms)
16. How many atoms are contained in a sample of Fluorine (F) that weighs 18.999 g? 6.022x1023
atoms
17. Which has the largest mass? I multiplied the atomic mass by the number of moles
5.0 moles Li = 34.705g, 3.1 mole H2O = 55.847g,
2.0 moles C2H4 = 56.10632g, or
2.5 moles NH3 = 42.5764g
2.0 moles of C2H4
18. How many boron (B) atoms are contained in 10.2g sample of boron?
10.2 𝑔 𝐵
1 𝑚𝑜𝑙𝑒 𝐵
∙ 10.811𝑔 𝐵 ∙
6.02×1023 𝑎𝑡𝑜𝑚𝑠 𝐵
1 𝑚𝑜𝑙𝑒 𝐵
= 5.68x1023 atoms B
19. How many moles of hydrogen atoms are in 1 mole of H2O? 2 mol H atoms
20. How many hydrogen atoms are in 1.00 moles CH4?
1.00𝑚𝑜𝑙 𝐶𝐻4
∙
4 𝑚𝑜𝑙 𝐻
1.00 𝑚𝑜𝑙 𝐶𝐻4
∙
6.022×1023 𝑎𝑡𝑜𝑚𝑠 𝐻
1 𝑚𝑜𝑙 𝐻
= 2.41 x 1024 atoms H
21. Calculate the weight percentage of hydrogen in methane, CH4? C= 12.0107 H=1.00794
4(1.00794)
× 100 = 𝟐𝟓. 𝟏%
12.0107 + 4(1.00794)
22. What is the percent weight of hydrogen in urea, CN2H4O?
C = 12.0107 N= 14.00674 H = 1.00794 O = 15.9994
4(1.00794)
× 100 = 𝟔. 𝟕% 𝒉𝒚𝒅𝒓𝒐𝒈𝒆𝒏
12.0107 + 2(14.00674) + 4(1.00794) + 15.9994
23. How many carbon atoms are contained in 5.50g of propane, C3H8 ?
5.50𝑔 𝐶3 𝐻8
1 𝑚𝑜𝑙 𝐶 𝐻
3 𝑚𝑜𝑙 𝐶
∙ 44.09562𝑔3 𝐶 8𝐻 ∙ 1 𝑚𝑜𝑙 𝐶
3 𝐻8
3 8
∙
6.022×1023 𝑎𝑡𝑜𝑚𝑠 𝐶
1 𝑚𝑜𝑙 𝐶
= 2.25x1023 atoms C
24. How many grams of calcium is contained in 17.9g of Ca(OH)2?
17.9𝑔𝐶𝑎(𝑂𝐻)2
∙
1 𝑚𝑜𝑙 𝐶𝑎(𝑂𝐻)2
74.09𝑔𝐶𝑎(𝑂𝐻)2
∙
1 𝑚𝑜𝑙 𝐶𝑎
1 𝑚𝑜𝑙 𝐶𝑎(𝑂𝐻)2
∙
40.078 𝑔 𝐶𝑎
1 𝑚𝑜𝑙 𝐶𝑎
= 9.68g Ca
25. The weight percentage of phosphorus (P) in H3PO4 is?
30.973761
× 100 = 𝟑𝟏. 𝟔% 𝒑𝒉𝒐𝒔𝒑𝒉𝒐𝒓𝒖𝒔
3(1.00794) + 30.973761 + 4(15.9998)
26. How many neutrons are in an atom that has a mass number of 55 and contains 25 protons?30n
27. Determine the number of electrons and protons in element Mo. 42 protons and 42 electrons
28. Write the formula of a compound consisting of 1 sodium atom, 1 nitrogen atom and 3 oxygen
atoms. NaNO3
29.
How many electrons are found in an antimony (Sb) atom? 51
30.
What is the molar mass of Ca3(PO4)2? 310.17g/mol
31. Th-230 is one form of thorium. How many protons, neutrons and electrons does one atom of
this isotope consists of? 90 protons, 90 electrons, 140 neutrons
32. What is the mass of oxygen found in 1.000 mole of H2C2O4?
1.000𝑚𝑜𝑙 𝐻2 𝐶2 𝑂4
∙
4 𝑚𝑜𝑙 𝑂
1𝑚𝑜𝑙 𝐻2 𝐶2 𝑂4
∙
15.9994𝑔 𝑂
1 𝑚𝑜𝑙 𝑂
= 63.9976g O = 64.00g O
33. A new element consists of 2 isotopes, 31𝑋 (𝑚𝑎𝑠𝑠 = 30.964 𝑢)𝑐𝑜𝑚𝑝𝑟𝑖𝑠𝑒𝑠 25.357% of the total.
The 2nd isotope, 29𝑋 (𝑚𝑎𝑠𝑠 = 29.012 𝑢)𝑎𝑐𝑐𝑜𝑢𝑛𝑡𝑠 𝑓𝑜𝑟 𝑡ℎ𝑒 𝑟𝑒𝑠𝑡. What will be the average atomic
mass for the new element?
100-25.357=74.643% 29𝑋 30.964(.25357) + 29.012(.74643) = 29.50696864 amu
=29.507amu