# Chemistry practice Test 1

Q. 1
Calculate the molarity (M), when 580g of NaCl is added to 2L of water.
• a. 5 M
• b. 3 M
• c. 2.5 M
• d. 80 M
• e. 10 M
• Answer: A

• Explaination: Explanation: Molarity (M) = (moles of solute/litres of solution)
Molecular weight of NaCl = 23+35= 58 g/mol
Moles of NaCl = 580/58 = 10 mol
Therefore, Molarity (M) = 10 mol/2 L= 5 M
Q. 2
Which of the following gas is the most easily liquefied?
 Gas O2 N2 NH3 CH4 Van der Waals constant (a) 1.3 1.39 4.17 2.21
• a. O2
• b. N2
• c. NH3
• d. CH4
• e. Can’t be predicted using this value
• Answer: C

• Explaination: Explanation: A gas with the greater ‘a’ value will liquefy easily. Here NH3 has greater ‘a’ value than the other gases. Therefore, it will liquefy easily.
Q. 3
The coordination number of the Na+ in Rock salt is
• a. 4
• b. 3
• c. 6
• d. 8
• e. 2
• Answer: C

• Explaination: Explanation: In Rock salt the coordination number of Na+ is six. Because each Na+ is surrounded by six Cl- ions and each Cl- is surrounded by six Na+ ions.
Q. 4
Choose the property, which depends only on, the amount of solute in a solution.
• a. Osmotic pressure
• b. Temperature
• c. Heat capacity
• d. Melting point
• e. None of the above
• Answer: A

• Explaination: Explanation: Properties that depend only on the amount of the solute not on their identity are known as colligative properties. In the above four, osmotic pressure alone depends on the amount of the solute and the rest of properties are independent of amount of solute.
Q. 5
Choose the strongest acid from the following.
• a. HClO4
• b. HClO3
• c. HClO2
• d. HOCl
• e. None of the above
• Answer: A

• Explaination: Explanation: HClO4 is the strongest acid than the rest of the acids. The acidity is due to the presence of the more electronegative oxygen. The acid with ore oxygen is the strongest acid and it has the highest electro negativity. It can easily pull the electrons from the central atom and induces the central atom to draw the electrons from the hydrogenated oxygen. This weakens the O-H bond and H+ ion leaves the molecule easily.
Q. 6
Which of the following represents a spontaneous reaction if T = +10 k?
• a. ΔH = +10, ΔS = -30
• b. ΔH = +10, ΔS = +30
• c. ΔH = -10, ΔS = +30
• d. ΔH = -10, ΔS = -30
• e. Both B and D
• Answer: E

• Explaination: Explanation: If the value of enthalpy is negative and the entropy is positive then the reaction is always spontaneous (ΔH = -10, ΔS = +30). If both enthalpy and entropy are negative (ΔH = -10, ΔS = -30), and T