Question

1.What values of x,  y and z balance the equation:

x SO₂    +   y H⁺   +    Cr₂O₇^2– → 3 SO₄^2–  + z Cr³⁺ +   H₂O ?

2.What is the stoichiometric ratio of solid phosphorus (P) to chlorine gas (Cl₂) required to give phosphorus trichloride (PCl₃)?

3.What is the mass fraction of carbon in aniline C₆H₅NH₂ expressed as a percentage?

4.

Arrange the following in order of increasing amount of substance:

(i)            24 g of sodium metal
(ii)           40 g of carbon dioxide
(iii)          4 g of hydrogen gas

5.What volume of 0.220 M NaOH(aq) should be used to prepare 303 mL of 2.02 x 10^–3 M NaOH(aq) ?

6.

Gold hydroxide Au(OH)₃ is prepared for electroplating gold by the following reaction

2 KAuCl₄(aq) + 3 Na₂CO₃(aq) + 3 H₂O(l) → 2 Au(OH)₃(s) + 6 NaCl(aq) + 2 KCl(aq) + 3 CO₂(g)

The following amounts are mixed KAuCl₄ = 2.3 mol, Na₂CO₃ = 7.0 mol and H₂O = 10 L.
What is the limiting reagent, and what amount of gold hydroxide is formed if the reaction is ‘stoichiometric’? (M (H₂O) = 18 g mol^–1, ρ(H₂O) = 1.0 kg L^–1)

Select one:

a. Na₂CO₃ , 1.57 mol

b. KAuCl₄ , 4.6 mol

c. KAuCl₄ , 2.3 mol

d. H₂O , 6.9 mol

e. KAuCl₄ , 6.9 mol

7.

What are the chemical formulae for the following acids: nitric acid, acetic acid, hydrochloric acid, sulfuric acid?

Select one:

a. H₂NO₃, CH₃COOH, HClO₂, H₂SO₃

b. HNO₂, CH₃COOH, HCl, HSO₃

c. HNO₃, CH₃CH₂OH, HCl, H₂SO₃

d. HNO₂, CH₃CH₂OH, HClO, H₂SO₄

e. HNO₃, CH₃COOH, HCl, H₂SO₄

Answer 1

1. x SO₂    +   y H⁺   +    Cr₂O₇^2– → 3 SO₄^2–  + z Cr³⁺ +   H₂O

3SO₂    +   2H⁺   +    Cr₂O₇^2– → 3 SO₄^2–  + 2 Cr³⁺ +   H₂O

2.P + 3Cl2 -----> 2PCl3

P : Cl2 = 1:3

3. mass fraction of carbon = mass of carbon*100/molar mass of aniline

                                         = 6*12*100/93 = 77.42%

4.   4 g of hydrogen gas< 24 g of sodium metal <40 g of carbon dioxide

5.initial molarity of NaOH M1 = 0.22M

initial volume of NaOH V1

final molarity of NaOH M2 = 2.02*10^-2 M

final volume of NaOH V2 = 303ml

M1V1 = M2V2

V1 = M2v2/M1

    = 2.02*10^-3*303/0.22

   = 2.78ml >>>> answer

2 KAuCl₄(aq) + 3 Na₂CO₃(aq) + 3 H₂O(l) → 2 Au(OH)₃(s) + 6 NaCl(aq) + 2 KCl(aq) + 3 CO₂(g)

2 moles of KAuCl₄ react with 3 moles of Na2CO3

2.3 moles of KAuCl₄ react with = 3*2.3/2 = 3.45 moles of Na2CO3

limiting reagent is KAuCl₄

7. e. HNO₃, CH₃COOH, HCl, H₂SO₄