Stoiciometry

Question 1

State the formulae of these molecules
carbon dioxide
water
ammonia
methane
Sodium chloride
Sodium oxide

Answer 1

CO2
H2O
NH3
CH4
NaCl
Na2O

Question 2

Figure out the formula for copper(2) oxide
Cu2+
O2-

Answer 2

CuO
The charges cancel each other out

Question 3

Find the formula of pottasium oxide
K+
O2-

Answer 3

K+ and O2-
two K+ are needed to cancel out the charge on O2-
so
K2O

Question 4

Write the chemical and symbol equation of magnesium and oxygen
bonus –> add state symbols

Answer 4

Magnesium + oxygen –> Magnesium oxide
2Mg(s) + O2(g) –> 2MgO(s)

Question 5

Determine how many atoms of each element are in
Al2O3
H2SO4

Answer 5

Al2O3–> Al= 2 O=3
H2SO4–> H=2 S=1 O=4

Question 6

Write the word and symbol equation between hydrogen and oxygen

Answer 6

hydrogen + oxygen –> water
H2+ O2 –> H2O

Question 7

Define Relative molecular mass (Mr)

Answer 7

The sum of the relative atomic masses of every atom in a molecule

Question 8

Define relative atomic mass (Ar)

Answer 8

The average mass of naturally occurring atoms of an element. (on a scale where the 12C atom has exactly 12 units)

Question 9

Work out the Mr of CO2
Ar of C = 12
Ar of O = 12

Answer 9

= Ar of C + (Ar of O x 2)
= 12+ (16 * 2)
=44

Question 10

Work out the Mr of H2SO4
Ar of H = 1
Ar of S= 32
Ar of O= 16

Answer 10

= (Ar of H * 2) + Ar of S + (Ar of O 4)
= (12) + 32 + (16*4)
= 98

Question 11

How do you figure out the number of mols with only mass and Mr?

Answer 11

Divide mass (g) by Mr

Question 12

Calculate the number of moles of silicone in 56g of silicon. (Ar of Si = 28)

Answer 12

moles of silicon= mass in g/mass of one mole (in g)
56g/28g = 2 mol

Question 13

Calculate the mass of 0.5 mol of methane CH4
(Ar of C= 12 and H = 1)

Answer 13

one mol of CH4= 12 + (4*1) = 16
mass in g=amount in moles * mass of one mol (g)
0.5 mol * 16g = 8g

Question 14

Calculate the number of moles of iron atoms in 56g of iron. (Ar of Iron = 26)

Answer 14

moles of iron= mass in g/ mass of one mole (g)
56/26 = 2M