WCH11 June 2022

SECTION B

Answer ALL the questions. Write your answers in the spaces provided.

19.​​ The element iron forms two chlorides: iron (II) chloride, FeCl2, and iron (III) chloride, FeCl3.

(a) A known mass of iron powder is added to 200cm3​​ of a hot solution of iron (III) chloride with a concentration of 0.500moldm−3. When the reaction is complete, the solution only contains iron (II) chloride. The unreacted iron is filtered, dried and weighed.​​ 

Initial mass of iron powder = 6.17g​​ 

Final mass of iron powder = 3.38g

(i) Calculate the number of moles of iron that react.​​ 

(2)

ANSWER

Step 1: Calculating Reacted mass of Iron

Reacted mass of iron=initial mass of iron powder-Final mass of iron powder

=6.17-3.38g

=2.79 g

Step 2: calculating moles by ratio method

1 mole of Fe=56g

x mole of Fe=2.79g

x mole of Fe=2.7956

x mole of Fe=0.05 mol

(ii) Calculate the number of moles of iron (III) chloride that react.​​ 

(2)

ANSWER

Method 1: Number of Moles by using formula

moles=c×v

=(2001000)×0.5

=0.1 mol

Method 2: calculating moles by ratio method

0.5 mole of iron IIIchloride=1000 cm3

x mole of ron IIIchloride=200 cm3

x mole of iron IIIchloride=2001000×0.5

x mole of iron IIIchloride=0.1 moles

(iii) Use your answers to (a) (i) and (a) (ii) to write the ionic equation for the reaction of iron with iron (III) chloride. Include state symbols. You must show your working.

​​ (3)

ANSWER

Step 1: Writing the equation

Fe+FeCl3→FeCl2

Step 2: In the question it is mentioned to use answer of a (i) and (ii), therefore

Fe+FeCl3→FeCl2

Therefore, rewriting the equation with state symbols

Fes+2FeCl3aq→3FeCl2aq

Step 3: making ionic equation

Fe​​ (s) + 2Fe3+​​ + 6Cl-→3Fe2+​​ + 6Cl-

For ionic equation, solid remains the same and aqueous is ionized and we cancel the thing which appear on both sides of the equation

Fe​​ (s) + 2Fe3+​​ +​​ 6Cl-→3Fe2+​​ +​​ 6Cl-

Fe​​ (s) + 2Fe3+-→3Fe2+

(b) The concentration of the solution obtained in (a) is increased by heating it gently to remove some of the water. The solution is allowed to cool and pale green crystals of a hydrated iron (II) chloride, FeCl2·xH2O, form.​​ 

Analysis shows that these crystals contain 28.1% by mass of iron.​​ 

Calculate the number of moles of water of crystallization, x, per mole of hydrated iron(II) chloride.​​ 

(4)

ANSWER

Step 1: ​​ calculating moles of iron by using formula

moles of Fe=massMr

=28.156

=0.5038 moles

Step 2: Mass of Chlorine

moles of chlorine=massMr

mass=0.5038 moles×2×35.5

mass of chlorine=35.574 g

Step 3: mass of water

mass of water=100-35.574+28.1

=36.146 gram

Step 4: Moles of water

moles of water=36.14618

=2.008 moles

Step 5: finding value of X

Moles of FeCl2: Moles of water

0.50358mol : 2.008 mol

Dividing by smaller number

0.50358mol0.50358mol:​​ 2.008mol2.008mol

1:4

Therefore, value of X is 4.