MDCAT ECAT Chemistry MCQs with Answers – All Units – Page 13

Question 241 Liquids

Why does water have an unusually high enthalpy of vaporisation for a molecule of its size?

Correct answer A. Strong hydrogen bonds must be broken to separate the molecules

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Question 242 Fundamental Concepts of Chemistry

How many moles are present in 49 g of sulphuric acid, H₂SO₄ (H = 1, S = 32, O = 16)?

Correct answer A. 0.50 mol

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Question 243 Fundamental Concepts of Chemistry

How many sodium ions are present in 5.85 g of sodium chloride (Na = 23, Cl = 35.5)?

Correct answer D. 6.02 × 10²²

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Question 244 Fundamental Concepts of Chemistry

In the decomposition 2KClO₃ → 2KCl + 3O₂, how many moles of oxygen are produced from 4 mol of KClO₃?

Correct answer B. 6 mol

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Question 245 Fundamental Concepts of Chemistry

What mass of KClO₃ must be decomposed to give 9.6 g of oxygen (2KClO₃ → 2KCl + 3O₂; K = 39, Cl = 35.5, O = 16)?

Correct answer D. 24.5 g

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Question 246 Fundamental Concepts of Chemistry

10 g of H₂ is mixed with 64 g of O₂ and reacted (2H₂ + O₂ → 2H₂O). Which reactant is limiting and what mass of water forms?

Correct answer B. O₂ is limiting; 72 g of water

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Question 247 Fundamental Concepts of Chemistry

The theoretical yield of a product is 25 g and the percentage yield is 80%. What is the actual yield?

Correct answer A. 20 g

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Question 248 Fundamental Concepts of Chemistry

What is the mass of 3.01 × 10²³ atoms of magnesium (Mg = 24)?

Correct answer D. 12 g

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Question 249 Fundamental Concepts of Chemistry

Which sample contains the same number of molecules as 16 g of O₂ (H = 1, C = 12, N = 14, O = 16)?

Correct answer A. 22 g of CO₂

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Question 250 Fundamental Concepts of Chemistry

The atomic mass of an element expressed in grams is called one ____

Correct answer C. gram atom

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Question 251 Fundamental Concepts of Chemistry

The mole is defined as the amount of substance containing as many particles as there are atoms in exactly 12 g of which isotope?

Correct answer B. Carbon-12

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Question 252 Fundamental Concepts of Chemistry

How many moles of ions are produced when 1 mol of Ca₃(PO₄)₂ is completely broken into its ions?

Correct answer D. 5 mol

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Question 253 Fundamental Concepts of Chemistry

Stoichiometric calculations based on a balanced equation assume that ____

Correct answer D. reactants are completely converted into products with no side reactions

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Question 254 Fundamental Concepts of Chemistry

In a limiting reactant problem, the amount of product formed should be calculated from ____

Correct answer D. the reactant that gives the smaller amount of product

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Question 255 Fundamental Concepts of Chemistry

The mass of one mole of formula units of an ionic compound such as NaCl, expressed in grams, is called its ____

Correct answer A. gram formula mass

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Question 256 Fundamental Concepts of Chemistry

How many moles of chloride ions are present in 0.20 mol of aluminium chloride, AlCl₃?

Correct answer B. 0.60 mol

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Question 257 Atomic Structure

Unlike that of cathode rays, the e/m value of positive rays ____

Correct answer C. depends on the gas present in the discharge tube

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Question 258 Atomic Structure

Which scientist gave the name proton to the lightest positive particle obtained from hydrogen?

Correct answer D. Ernest Rutherford

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Question 259 Atomic Structure

If the wavelength of a photon is doubled, what happens to its energy?

Correct answer C. It is halved

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Question 260 Atomic Structure

Light of wavelength 663 nm has photons of energy 3.0 × 10⁻¹⁹ J. About how many such photons carry a total energy of 1.0 J?

Correct answer D. 3.3 × 10¹⁸

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