Module 2, Atoms And Moles

Question 1

Isoelectronic

Answer 1

When ions of different elements have same number of electrons

Question 2

Relative atomic mass

Answer 2

Average weighted mass of all isotopes of an element

Question 3

How to calculate Ar of element

Answer 3

Ar= (% of isotope X x isotopic mass of X) + (% of isotope Y x isotopic mass of Y) / 100 . The more information/isotopes of element the more brackets.

Question 4

Naturally occurring potassium consists of k-39 and k-41. Calculate percentage of each isotope present if Ar is 39.1

Answer 4

1. 39.1=(X x 39)+(100-X)x41)/100. 2. Then x100. 3. 3910=39x+4100-41x. 4. -4100. 5. -190=39x-41x. 6. -190=-2x. 7. 95=x. K-39=95%. K-41=5%

Question 5

The relative atomic mass of neon is 20.18. It consists of 3 isotopes, Ne-20, Ne-21, Ne-22. It contains 90.5% Ne-20. Find percentage composition by mass of the other 2 isotopes in neon.

Answer 5

1. 20.18=(90.5 x 20)+(21 x X)+(22x(9.5-X))/100. 2. 20.18=1810+21X+209-22X/100. 3. X100. 4. 2018= 1810+21X+209-22X. 5. -209. 6. 1809=1810+21X-22X. 7. -1=-X. Ne-21=8.5%. Ne-22=1%

Question 6

What do the peaks represent in mass spectrometry

Answer 6

Different isotopes

Question 7

What is avogadro’s constant

Answer 7

6.022x10^23

Question 8

What is the equation for number of particles

Answer 8

N(moles) x Na(avogadro’s constant)

Question 9

How many atoms are there in 3 moles of water molecules

Answer 9

H2O= 3 atoms. 3x3x6.022x10^23=5.4198x10^24

Question 10

What is the equation for number of moles

Answer 10

Mass(g)/mr

Question 11

Calculate number of moles of c atoms and o atoms in 11g of carbon dioxide.

Answer 11

11/44=0.25 number of moles. CO2. C=0.25. O=0.5

Question 12

Empirical formula definition

Answer 12

Simplest whole number of ratio. Of atoms/ions of an element in a compound.

Question 13

Aluminium bromide is formed from 0.51g of aluminium and 4.49g of bromine. Calculate aluminium bromides empirical formula.

Answer 13

Calc moles. Ar 0.51/27=0.0189. Br 4.49/80=0.0561. Divide by smallest /0.0189. 1:2.97. 1:3. AlBr3

Question 14

Work out molecular formula of NH2, given empirical and Mr= 32

Answer 14

N has 14 Mr and H has Mr of 1= NH2=16. 16x2=32. X ratio by 2. =N2H4

Question 15

Find simplest whole number ratio for, 1:1.33

Answer 15

X3 so that 1.33 becomes 3.99 which round to 4 so ratio becomes 3:4