chemistry

What is the mass percentage of carbon (C) in methane (CH4)? (The molar mass of carbon is approximately 12 g/mol.)
A. 25%
B. 12%
C. 75%
D. 50%

Correct Option: Answer is D
The molar mass of methane (CH4) is calculated by adding the atomic masses of carbon (approximately 12 g/mol) and hydrogen (approximately 1 g/mol). Therefore, the molar mass of CH4 is 12 g/mol + 4 x 1 g/mol = 16 g/mol. The mass percentage of carbon in CH4 is given by (mass of carbon / total mass) x 100% = (12 g / 16 g) x 100% = 75%.

What type of reaction is involved in the formation of alkanols from alkenes?
A. Elimination reaction
B. Redox reaction
C. Substitution reaction
D. Addition reaction

Correct Option: Answer is D
Alkanols can be formed from alkenes through an addition reaction. In this reaction, the carbon-carbon double bond of the alkene is broken, and a hydroxyl group (-OH) is added to one of the carbon atoms, resulting in the formation of an alcohol.

What is the common name for ethanoic acid?
A. Acetic acid
B. Butyric acid
C. Propionic acid
D. Formic acid

Correct Option: Answer is A
Ethanoic acid is commonly known as acetic acid. It is the main component of vinegar and is used in various industrial processes.

Which separation technique is used to separate different pigments in a mixture based on their affinity for a stationary phase and a mobile phase?
A. Chromatography
B. Filtration
C. Decantation
D. Distillation

Correct Option: Answer is A
Chromatography is a separation technique used to separate and analyze components of a mixture based on their differential partitioning between a stationary phase (e.g., paper or a column) and a mobile phase (e.g., solvent). Different components move at different rates, leading to separation.

What is the empirical formula of a compound containing 40.00% carbon, 6.67% hydrogen, and 53.33% oxygen by mass?
A. C4H8O4
B. CH2O
C. C2H4O2
D. C3H6O3

Correct Option: Answer is B
The empirical formula of the compound is B. CH2O. Here’s how we can determine it:

Assume 100 grams of the compound: This makes calculations easier as percentages translate directly to grams.
Convert percentages to grams:
Carbon: 40.00% * 100 g = 40.00 g
Hydrogen: 6.67% * 100 g = 6.67 g
Oxygen: 53.33% * 100 g = 53.33 g
Convert grams to moles by dividing by their respective atomic weights:
Carbon: 40.00 g / 12.011 g/mol = 3.33 mol
Hydrogen: 6.67 g / 1.008 g/mol = 6.63 mol
Oxygen: 53.33 g / 15.999 g/mol = 3.33 mol
Find the smallest whole-number ratio of the moles: All three elements have the same mole value of 3.33, so the ratio is 1:1:1.
Write the empirical formula based on the mole ratio: CH2O
Therefore, the empirical formula of the compound is CH2O

What is the main source of carbon monoxide (CO) in urban areas?
A. Volcanic eruptions
B. Vehicle emissions
C. Forest fires
D. Industrial processes

Correct Option: Answer is B
The main source of carbon monoxide (CO) in urban areas is vehicle emissions, especially from incomplete combustion of gasoline and diesel in engines.

Which of the following is a primary constituent of crude oil?
A. Pentane
B. Ethanol
C. Heptane
D. Methane

Correct Option: Answer is A

Which group does calcium belong to in the periodic table?
A. Alkaline earth metals
B. Halogens
C. Alkali metals
D. Noble gases

Correct Option: Answer is A
Calcium belongs to the alkaline earth metals group in the periodic table. It is located in Group 2 and has two valence electrons.

What is the principal ore of iron, from which iron is extracted?
A. Calcite
B. Bauxite
C. Magnetite
D. Hematite

Correct Option: Answer is D
Hematite (Fe2O3) is the principal ore of iron and is widely mined for the extraction of iron metal.

What is the chemical formula of rust, which is formed on the surface of iron in the presence of oxygen and moisture?
A. Fe3O4
B. FeO
C. Fe(OH)3
D. Fe2O3

Correct Option: Answer is D
Rust is a reddish-brown compound that forms on the surface of iron in the presence of oxygen and moisture. Its chemical formula is Fe22O3