Question
The structure of a molecule of a compound is shown.
What is the formula of this compound?
A. \(C_{3}H_{7}O\) B. \(C_{3}H_{8}O\) C. \(C_{8}H_{3}O\) D. \(C_{8}HO_{3}\)
▶️Answer/Explanation
Ans:
B
There are 3C, 8H and 1 O atoms. Hence, formula = \(C_{3}H_{8}O\) .
Question
Which statements about lime are correct?
1 Lime is made by heating calcium carbonate (limestone).
2 Lime is used to desulfurize flue gases.
3 Lime is used to treat alkaline soil.
4 The chemical name for lime is calcium oxide.
A. 1 and 3 B. 1, 2 and 4 C. 1 and 4 only D. 2, 3 and 4
▶️Answer/Explanation
Ans:
B
Lime or calcium oxide(CaO) is produced by heating calcium carbonate, a naturally occurring mineral, in a process called calcination.
It is added to acidic soils to neutralize acidity and make the soil more favorable for plant growth.
Lime is also used in flue gas desulfurization (FGD) systems to remove sulfur dioxide emissions from power plants and industrial facilities.
Question
Methane burns in oxygen to produce carbon dioxide and water.
What is the balanced equation for this reaction?
A \(CH_4 + 2O_2 \rightarrow 2CO_2 + 2H_2O\)
B \(CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O\)
C \(CH_4 + 2O_2 \rightarrow CO_2 + H_2O\)
D \(CH_4 + O_2 \rightarrow CO_2 + 2H_2O\)
▶️Answer/Explanation
Ans: B
\(CH_4 + O_2 \rightarrow CO_2 + H_2O\)
To balance H atoms, place 2 in front of \(H_2O\)
To balance O atoms, place 1 in front of \(O_2\)
\(CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O\)
Question
What is the balanced chemical equation for the reaction between calcium and water?
A \(Ca + H_2O \rightarrow CaOH + H_2\)
B \(Ca + H_2O \rightarrow Ca(OH)_2 + H_2\)
C \(Ca + 2H_2O \rightarrow CaOH + H_2\)
D \(Ca + 2H_2O \rightarrow Ca(OH)_2 + H_2\)
▶️Answer/Explanation
Ans: D
Ca reacts with water to form calcium hydroxide and hydrogen gas.
\(Ca + H_2O \rightarrow Ca(OH)_2 + H_2\)
To balance H atoms, place 2 in front of \(H_2\)
\(Ca + 2H_2O \rightarrow Ca(OH)_2 + H_2\)
Question
The formula of sodium chlorate(V) is \(NaClO_3\).
What is the relative formula mass of sodium chlorate(V), \(NaClO_3\)?
A 52.0 B 74.5 C 106.5 D 223.5
▶️Answer/Explanation
Ans: C
The relative formula mass of a molecule is the sum of the atomic masses of all the atoms in its chemical formula. It is also known as the molecular mass or molecular weight.
The relative formula mass of sodium chlorate(V), \(NaClO_3\) = 23+35.5+3*16 = 106.5