Which method is most suitable for separating a mixture of sand and salt?
A. Filtration
B. Distillation
C. Decantation
D. Crystallization
Answer: A) Filtration
Explanation:
The mixture of sand and salt is separated by dissolving the salt in water, filtering to remove the sand, and then evaporating the water to retrieve the salt.
If 4.4 g of carbon dioxide is produced by burning 1 g of carbon in oxygen, calculate the mass of oxygen that reacted. (C = 12, O = 16)
A. 3.0 g
B. 3.2 g
C. 2.4 g
D. 1.6 g
Answer: B) 3.2 g
Explanation:
The reaction is \( C + O_2 \rightarrow CO_2 \).
From the molar mass: \( 12 + 32 = 44 \, g/mol \).
Mass of oxygen: \( \frac{32}{44} \times 4.4 = 3.2 \, g \).
Which gas law explains why a balloon expands when heated?
A. Charles' Law
B. Boyle's Law
C. Dalton's Law
D. Graham's Law
Answer: A) Charles' Law
Explanation:
Charles' Law states that the volume of a gas is directly proportional to its temperature at constant pressure, causing the balloon to expand when heated.
Who proposed the nuclear model of the atom?
A. Dalton
B. Thomson
C. Rutherford
D. Bohr
Answer: C) Rutherford
Explanation:
Ernest Rutherford proposed the nuclear model of the atom after his gold foil experiment, showing that atoms have a dense nucleus.
Which of the following increases across a period in the periodic table?
A. Atomic radius
B. Electronegativity
C. Metallic character
D. Ionization energy
Answer: B) Electronegativity
Explanation:
Electronegativity increases across a period due to an increase in nuclear charge, attracting electrons more strongly.
Which of the following is an example of a covalent compound?
A. NaCl
B. MgO
C. H2O
D. KBr
Answer: C) H2O
Explanation:
H2O is a covalent compound because it involves the sharing of electrons between hydrogen and oxygen atoms.
What is the shape of a methane (CH4) molecule?
A. Linear
B. Tetrahedral
C. Trigonal planar
D. Bent
Answer: B) Tetrahedral
Explanation:
Methane has a tetrahedral shape due to the arrangement of four bonding pairs of electrons around the central carbon atom.
What particle is emitted during the conversion of a neutron to a proton in a nucleus?
A. Alpha particle
B. Beta particle
C. Gamma ray
D. Positron
Answer: B) Beta particle
Explanation:
A beta particle is emitted when a neutron decays into a proton and an electron.
A gas occupies 200 cm³ at 27°C. What volume will it occupy at 127°C, if the pressure remains constant?
A. 260 cm³
B. 267 cm³
C. 273 cm³
D. 300 cm³
Answer: B) 267 cm³
Explanation:
Using Charles' Law:
\( \frac{V_1}{T_1} = \frac{V_2}{T_2} \)
\( \frac{200}{27 + 273} = \frac{V_2}{127 + 273} \)
\( V_2 = 267 \, cm^3 \).
How many moles of oxygen are in 4.4 g of CO2? (C = 12, O = 16)
A. 0.1
B. 0.2
C. 0.3
D. 0.4
Answer: B) 0.2
Explanation:
Molar mass of CO2: \( 12 + (16 \times 2) = 44 \, g/mol \).
Moles of CO2: \( \frac{4.4}{44} = 0.1 \).
Each CO2 molecule has 2 moles of oxygen, so \( 0.1 \times 2 = 0.2 \, \text{moles of oxygen} \).