Quantitative Chemistry questions

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Quantitative Chemistry question collection

Review Quantitative Chemistry questions for Chemistry, with correct answers shown and coverage across relative formula mass; moles and reacting masses; concentration calculations.

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Question 1

What does the law of conservation of mass state for chemical reactions?
  1. Total mass of reactants equals total mass of products
  2. Mass is always lost during reactions
  3. Mass is always gained during reactions
  4. Only gases follow conservation of mass

Question 2

Why are chemical equations balanced?
  1. To show the same number of each type of atom on both sides
  2. To make reactants and products have the same formula
  3. To make all coefficients equal to 1
  4. To show that reactions are reversible

Question 3

Which is the balanced equation for forming water?
  1. \(2\mathrm{H}_{2} + \mathrm{O}_{2} \to 2\mathrm{H}_{2}\mathrm{O}\)
  2. \(\mathrm{H}_{2} + \mathrm{O}_{2} \to \mathrm{H}_{2}\mathrm{O}\)
  3. \(\mathrm{H}_{2} + \mathrm{O}_{2} \to 2\mathrm{H}_{2}\mathrm{O}\)
  4. \(2\mathrm{H}_{2} + 2\mathrm{O}_{2} \to 2\mathrm{H}_{2}\mathrm{O}\)

Question 4

How many oxygen atoms are in one formula unit of CaCO3?
  1. 3
  2. 1
  3. 2
  4. 4

Question 5

How many hydrogen atoms are in one molecule of H2SO4?
  1. 2
  2. 1
  3. 4
  4. 6

Question 6

What is the relative formula mass (Mr) of H2O? (H = 1, O = 16)?
  1. 18
  2. 16
  3. 17
  4. 20

Question 7

What is the relative formula mass (Mr) of CO2? (C = 12, O = 16)?
  1. 44
  2. 28
  3. 32
  4. 48

Question 8

If \(5\,\mathrm{g}\) of A reacts with \(7\,\mathrm{g}\) of B and all reactants are used, what mass of product forms?
  1. \(12\,\mathrm{g}\)
  2. \(2\,\mathrm{g}\)
  3. \(7\,\mathrm{g}\)
  4. \(35\,\mathrm{g}\)

Question 9

Carbon burns in oxygen to form carbon dioxide. If \(12\,\mathrm{g}\) of carbon forms \(44\,\mathrm{g}\) of CO2, what mass of oxygen reacted?
  1. \(32\,\mathrm{g}\)
  2. \(12\,\mathrm{g}\)
  3. \(44\,\mathrm{g}\)
  4. \(56\,\mathrm{g}\)

Question 10

In \(2\mathrm{Mg} + \mathrm{O}_2 \to 2\mathrm{MgO}\), what does the coefficient \(2\) before Mg mean?
  1. Two magnesium atoms or moles react
  2. Magnesium has atomic number 2
  3. Each magnesium atom has 2 neutrons
  4. Two oxygen atoms are in Mg

Question 11

What does the subscript 2 in H2 mean?
  1. There are two hydrogen atoms in each molecule
  2. There are two hydrogen molecules
  3. Hydrogen has charge +2
  4. Hydrogen has atomic number 2

Question 12

Why might mass appear to decrease in a reaction carried out in an open flask?
  1. A gaseous product can escape to the air
  2. Atoms are destroyed during the reaction
  3. Mass turns into heat and disappears completely
  4. The balance always reads lower for liquids

Question 13

Which setup best tests conservation of mass in a reaction that produces gas?
  1. A sealed container on a balance
  2. An open beaker on a windowsill
  3. A hot crucible without a lid
  4. Any container, because gas mass is ignored

Question 14

What does concentration describe?
  1. How much solute is dissolved in a given volume of solution
  2. How quickly a reaction finishes
  3. How acidic a gas is
  4. How much energy is released per reaction

Question 15

Which unit is commonly used for concentration at this level?
  1. \(\mathrm{g\,dm^{-3}}\)
  2. \(\mathrm{N}\)
  3. \(\mathrm{Pa}\)
  4. \(\mathrm{m\,s^{-1}}\)

Question 16

\(4\,\mathrm{g}\) of salt are dissolved to make \(200\,\mathrm{cm^3}\) of solution. What is the concentration in \(\mathrm{g\,dm^{-3}}\)?
  1. \(20\,\mathrm{g\,dm^{-3}}\)
  2. \(0.02\,\mathrm{g\,dm^{-3}}\)
  3. \(2\,\mathrm{g\,dm^{-3}}\)
  4. \(200\,\mathrm{g\,dm^{-3}}\)

Question 17

\(250\,\mathrm{cm^3}\) is equal to how many \(\mathrm{dm^3}\)?
  1. \(0.250\,\mathrm{dm^3}\)
  2. \(2.50\,\mathrm{dm^3}\)
  3. \(25.0\,\mathrm{dm^3}\)
  4. \(0.025\,\mathrm{dm^3}\)

Question 18

Which has the greatest relative formula mass?
  1. CaCO3
  2. H2O
  3. CO2
  4. CH4

Question 19

In \(\mathrm{N}_2 + 3\mathrm{H}_2 \to 2\mathrm{NH}_3\), how many hydrogen molecules react with one nitrogen molecule?
  1. 3
  2. 1
  3. 2
  4. 6

Question 20

If the mass of products in a closed system is \(18\,\mathrm{g}\), what must be true about the reactants?
  1. Their total mass was also \(18\,\mathrm{g}\)
  2. Their total mass was less than \(18\,\mathrm{g}\)
  3. Their total mass was more than \(18\,\mathrm{g}\)
  4. Their mass is unrelated to product mass

Question 21

In a closed system, what does conservation of mass mean for a chemical reaction?
  1. Total mass of reactants equals total mass of products
  2. Products always have lower mass than reactants
  3. Reactants always gain mass from heat
  4. Only solids obey conservation of mass

Question 22

Why can mass appear to decrease when magnesium reacts with acid in an open flask?
  1. Hydrogen gas escapes from the flask
  2. Atoms are destroyed in the reaction
  3. Magnesium has negative mass
  4. Acid evaporates into oxygen

Question 23

Which equation is correctly balanced?
  1. \(\mathrm{Mg} + 2\mathrm{HCl} \to \mathrm{MgCl}_{2} + \mathrm{H}_{2}\)
  2. \(\mathrm{Mg} + \mathrm{HCl} \to \mathrm{MgCl} + \mathrm{H}_{2}\)
  3. \(2\mathrm{Mg} + \mathrm{HCl} \to \mathrm{MgCl}_{2} + \mathrm{H}_{2}\)
  4. \(\mathrm{Mg} + 2\mathrm{HCl} \to \mathrm{MgCl} + \mathrm{H}_{2}\)

Question 24

What is the relative formula mass, Mr, of CaCO3? (Ca = \(40\), C = \(12\), O = \(16\))?
  1. \(100\)
  2. \(84\)
  3. \(88\)
  4. \(116\)

Question 25

What is the Mr of MgCl2? (Mg = \(24\), Cl = \(35.5\))?
  1. \(95\)
  2. \(71\)
  3. \(59.5\)
  4. \(119\)

Question 26

What is the percentage by mass of oxygen in MgO? (Mg = \(24\), O = \(16\))?
  1. \(40\%\)
  2. \(60\%\)
  3. \(25\%\)
  4. \(16\%\)

Question 27

What is the percentage by mass of carbon in CO2? (C = \(12\), O = \(16\))?
  1. \(27.3\%\)
  2. \(12\%\)
  3. \(44\%\)
  4. \(72.7\%\)

Question 28

Which formula is used for concentration in \(\mathrm{g\,dm^{-3}}\)?
  1. concentration = mass (\(\mathrm{g}\)) / volume (\(\mathrm{dm^3}\))
  2. concentration = volume / mass
  3. concentration = mass x volume
  4. concentration = mass - volume

Question 29

What is \(250\,\mathrm{cm^3}\) in \(\mathrm{dm^3}\)?
  1. \(0.250\,\mathrm{dm^3}\)
  2. \(2.50\,\mathrm{dm^3}\)
  3. \(25.0\,\mathrm{dm^3}\)
  4. \(0.025\,\mathrm{dm^3}\)

Question 30

How much solute is needed to make \(0.50\,\mathrm{dm^3}\) of a \(20\,\mathrm{g\,dm^{-3}}\) solution?
  1. \(10\,\mathrm{g}\)
  2. \(40\,\mathrm{g}\)
  3. \(0.04\,\mathrm{g}\)
  4. \(20\,\mathrm{g}\)

Question 31

\(5.0\,\mathrm{g}\) of salt are dissolved to make \(200\,\mathrm{cm^3}\) solution. What is the concentration in \(\mathrm{g\,dm^{-3}}\)?
  1. \(25\,\mathrm{g\,dm^{-3}}\)
  2. \(2.5\,\mathrm{g\,dm^{-3}}\)
  3. \(10\,\mathrm{g\,dm^{-3}}\)
  4. \(250\,\mathrm{g\,dm^{-3}}\)

Question 32

In calculations, a limiting reactant is the reactant that?
  1. Is completely used up first and stops further product formation
  2. Has the largest mass at the start
  3. Always appears first in the equation
  4. Is never consumed

Question 33

\(\mathrm{CaCO}_3 \to \mathrm{CaO} + \mathrm{CO}_2\). If \(25\,\mathrm{g}\) of \(\mathrm{CaCO}_3\) decomposes completely, what mass of \(\mathrm{CO}_2\) is formed? (Mr: \(\mathrm{CaCO}_3 = 100\), \(\mathrm{CO}_2 = 44\))?
  1. \(11\,\mathrm{g}\)
  2. \(4.4\,\mathrm{g}\)
  3. \(22\,\mathrm{g}\)
  4. \(44\,\mathrm{g}\)

Question 34

A reaction has a theoretical yield of \(8.0\,\mathrm{g}\) and an actual yield of \(6.0\,\mathrm{g}\). What is the percentage yield?
  1. \(75\%\)
  2. \(133\%\)
  3. \(25\%\)
  4. \(48\%\)

Question 35

Which reason can explain a percentage yield less than 100%?
  1. Not all reactant is converted into desired product
  2. Mass is created in every reaction
  3. Theoretical yield is always too low
  4. Products cannot be separated from catalysts

Question 36

What does atom economy measure?
  1. How much of the reactants end up in the desired useful product
  2. How quickly atoms move in gases
  3. How many protons are in products
  4. How concentrated a solution is

Question 37

Why do industrial chemists prefer reactions with high atom economy?
  1. They produce less waste and use raw materials more efficiently
  2. They always run at lower temperatures
  3. They never need catalysts
  4. They guarantee 100% percentage yield

Question 38

For concentrations in mol/dm3, what is the equation for moles?
  1. moles = concentration x volume (in \(\mathrm{dm^3}\))
  2. moles = concentration / volume
  3. moles = mass x volume
  4. moles = volume / concentration x 1000

Question 39

At room temperature and pressure, what volume does \(1\,\mathrm{mol}\) of gas occupy?
  1. \(24\,\mathrm{dm^3}\)
  2. \(2.4\,\mathrm{dm^3}\)
  3. \(240\,\mathrm{dm^3}\)
  4. \(12\,\mathrm{dm^3}\)

Question 40

\(0.50\,\mathrm{mol}\) of gas at RTP has what volume?
  1. \(12\,\mathrm{dm^3}\)
  2. \(24\,\mathrm{dm^3}\)
  3. \(6\,\mathrm{dm^3}\)
  4. \(48\,\mathrm{dm^3}\)

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Review Quantitative Chemistry questions for Chemistry, with correct answers shown and coverage across relative formula mass; moles and reacting masses; concentration calculations.

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