Question

1- Ethanol (C2H6O) combusts in oxygen gas to produce carbon dioxide and water vapor. When the equation describing this reaction is correctly balanced, which of the following statements is true?

a- 4 CO2 and 4 H2O are produced

b- 3 O2 are consumed and 4 H2O are produced

c- 2 O2 are consumed and 4 H2O are produced

d- 3 O2 are consumed and 2 CO2 are produced

e- 4 O2 are consumed and 5 CO2 are produced 2- There are 1.326 x 1024 molecules in a 500.0 gram sample of the compound. What is the molar mass of the compound? 3- A sample of metal is measured to have a mass of 435.7 g. When the sample is placed in a graduated cylinder containing 500.0 mL of water, the water level in the graduated cylinder rises to 552.7 mL. Based on these measurements, what is the density of the metal sample ?

Answer 1

In balanced chemical reaction, atoms on either side of reaction are same.

Hence complete balanced combustion reaction of ethanol is:

C₂H₆O +3O₂(g) 2CO₂(g) + 3H₂O(g)

From reaction, option d is correct.

2. 1 mol of sample contains = 6.022 * 10²³ molecules

Mass of Sample = 500 g

Number of molecules = 1.326 * 10²⁴ molecules

Number of moles = 1.326 * 10²⁴ molecules/ 6.022 * 10²³ molecules = 2.20 moles

Mole = mass/ molar mass

Molar mass = mass/ mol =500 g/ 2.20mol = 227 g/mol

3. Volume of metal = 552.7- 500 = 52.7 mL

Mass of metal = 435.7 g

Density = mass/ Volume = 435.7g/ 52.7 mL = 8.27 g/mL