ch6 mole

Question 1

Mr Cu = 64
Mr O = 16

how many oxygen atoms has same Mr as Cu?

Answer 1

4

Question 2

define Ar

Answer 2

average of mass of one atom of element compared to 1/12 of mass of C-12 atom

Question 3

neon has 3 isotopes
90.92% Ne-20
0.26% Ne-21
8.82% Ne-22

calculating relative atomic mass of atoms with multiple isotopes

Answer 3

(90.92/100) x 20
+
(0.25/100) x 21
+
(8.82/100) x 22

Question 4

for emp formula calculation of Iron (34.5%), Chloride

steps

Answer 4

Step1: Fe Cl
Step2: 34.5% v 65.5%
Step3: 34.5/56 v 65.5/35.5
Step4: 0.61607 v 1.8450
Step5: 0.61607/0.61607 v 1.8450/0.61607
Step6 (round nearest whole no.): 1 v 3

Fe:Cl
1:3

Fe (Cl2) 3

56 is Mr of iron, 35.5 is Mr of Cl

ignore Cl2 being diatomic for calculations

Question 5

percentage purity of 6g carbon burnt in air -> 15g co2

Answer 5

eqn: c (s) + o2 (g) -> co2 (g)
Step1: find mole of product, 15/44
Step2: molar ratio, c mole = 15/44
Step3: C actual mass = 15/44x12 = 4.09
Step4: actual mass/pure mass
(4.09/6)*100

44 is mole of co2

Question 6

when to find limiting reactant?

Answer 6

2 substances as reactants
sufficient info given (i.e. volume, conc.) of 2 substance

Question 7

a 20g copper screw dissolved in water, form 100cm^3 of Cu2+ ions

25cm^3 of solution found to have 0.2mol of Cu2+

how many moles of Cu2+ in screw?

Answer 7

100/25 * 0.2
= 0.8 mol

Question 8

relative formula mass

Answer 8

Mr

Question 9

avogardo constant

Answer 9

6.02x10^23

Question 10

ratio by mass vs ratio by moles

Answer 10

mass
- given values i.e. 97.8% iron, 0.12% carbon

ratio is 0.12 : 97.8

moles
- emp formula

Question 11

kJ/mol to kJ/g

Answer 11

divide by Mr