I need help with my chemistry assignment

Question

Hi. I do sit-ins at my mum's university because she wanted me to excel in chemistry but I'm only in 8th grade and the lectures my professor gives are in advanced levels. I'm forced to take exams with uni students next week and I need help with my assignment asap. Thanks in advance :)





I already answered three pages but I only need help with some questions.





1. What is the mass of one mole of molecules of Bromine, Dihydrogen, Phosphorus and Oxygen?





2. Complete the following table by filling in the necessary information

Moles of Compound       Moles of Cations       Moles of Anions

1 mol KCI                      _____________      ________________

2 mol Na2SO4                _______________     ________________

0.2 mol calcium nitrate     _____________          ________________

______________             0.50 mol NH4+          0.25 mol SO4^2+




23. The atomic weight of copper is 63.546 amu. The two naturally ocurring isotopes of copper have the following masses: ^63Cu, 62.9298 amu; ^65Cu, 64.9278 amu. Calculate the percent of ^63Cu in naturally occuring copper.

Answer 1

1. Refer to the periodic table. The mass of 1 Mole of any element is the same as the atomic mass in grams. For example, the mass of 1 mole of Br would be 79.904 and the mass of 1 mole of H₂ would be 1.008 * 2 = 2.016. Try the other two by yourself!

 

2. This problem is about dissociation. Let's recall that cations are have positive charge and anions have negative charge.

 

When KCl dissociates, it forms K⁺ and Cl^-. So when 1 mole of KCl dissociates, it will produce 1 mole of cation and 1 mole of anion.

 

When Na₂SO₄ dissociates, it will produce 2Na⁺ and SO4^-2. 1 Mole of Na₂SO₄ would produce 2 moles of Na⁺ and 1 mole of SO₄. So when you have 2 moles of Na₂SO₄ you'd get 4 moles of Na⁺ and 2 moles of SO₄. Which is 4 moles of cations and 2 moles of anions. Again, give the other two a shot yourself.

 

23. The atomic weight of an element is the sum of the the mass of each isotope multiplied by the naturally occurring frequency.

 

Since there are only two naturally occurring isotopes. If one isotope occurs x of the time, then the other must occur (1 - x) of the time. 

When you put it into the equation, it becomes 63.546 = 62.9298x + (1 - x) * 64.9278. Now you just solve for x to find the percentage.