Posted by **JAKE** on Monday, February 25, 2008 at 9:26pm.

I need some help with my science homework. Well it is not really my homework it is my study guide but the actual test is the same as the study guide almost. They just switch around the words and stuff around to mess with your mind. These were just the only 7 problems I need help with out of all 100 problems in the study guide.

3.

The rows in the periodic table indicate the number of _______________ or energy levels

A) points

B) nucleus

C) particles

D) electron orbitals

4.

Columns indicate the number of _________________ in the outer shell.

A) quarks

B) neutrons

C) protons

D) electrons

25.

Calculate the number of moles in 34 grams of copper (Cu).

A) 0.54 moles Cu

B) 63.5 moles Cu

C) 34 moles Cu

D) 54 moles Cu

26.

Convert 22 grams of copper to atoms of copper (Cu). Hint: Remember Avogadro

A) 2.09 X 1023

B) 3.5 X 1023

C) 1.09 X 1023

D) 6.5 X 1023

27.

Calculate the number of g that are in 39.0 mol of CaO.

A) 2190 g or 2.19 x 103 g

B) 56g

C) 16 g or 1.6 x 103 g

D) 5190 g or 5.19 x 103 g

28.

Calculate the number of mol that are in 0.608 g of SiO2.

A) 0.0535 mol or 5.35 x 10-2 mol

B) 60.804 mol

C) 0.0608 mol or 6.08 x 10-2 mol

D) 0.0101 mol or 1.01 x 10-2 mol

- science -
**Christiaan**, Monday, February 25, 2008 at 9:43pm
3)D

4)D

25)A

When we look in the periodic table of elements, we find that copper has an atomic weight of 63,5 g/mol

=> 34g/(63,5g/mol) = 0,54 mol

26)A

Using the previous exercise as an example, we are able to calculate the number of mol in 22 grams of copper

=> 22g/(63.5g/mol) = 0.346 mol

We know that Avogrado's number indicates the number of particles (i.e. atoms or molecules) per mol and this number equals 6.023*10^23.

So 0.346 mol*6.023*10^23particles/mol = 2.09*10^23 particles

27)A

We find in the periodic table that the atomic weights of Calcium and Oxygen are resp. 40 and 16 g/mol. So the molecular weight of CaO equals 40+16 g/mol = 56 g/mol

=> 39.0 mol * 56 g/mol = 2190 g

28) D

We find in the periodic table that the atomic weights of Silicon and Oxygen are resp. 28 and 16 g/mol. So the molecular weight of SiO2 equals 28+(2*16) g/mol = 60 g/mol

=> 0.608g/(60g/mol)= 0.0101 mol

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