1.What values of x , y and z balance the equation: x SO 2 + y H + + Cr 2 O 7 2–

Question

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

x SO2    +   y H+   +    Cr2O72– 3 SO42–  + 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, (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

Explanation / Answer

1. x SO2    +   y H+   +    Cr2O72– 3 SO42–  + z Cr3+ +   H2O

3SO2    +   2H+   +    Cr2O72– 3 SO42–  + 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

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