11th grade chemical reactions, acids and bases

Question 1

H₂ + Br₂ → 2HBr. Bond energies (kJ/mol): H–H 436, Br–Br 193, H–Br 366. Calculate the energy change, in kJ/mol.

Answer kJ/mol

Question 2

A student's yield is low because some crystals were left stuck to the filter paper. How could they improve it?

• A. use less of each reactant
• B. throw away the first crystals
• C. rinse the filter paper with a little cold solvent to recover more product
• D. weigh the product while it is still wet

Question 3

What is the mass of 4 mol of methane (CH₄, Mr = 16), in g?

Answer g

Question 4

How many atoms in total are in 2 mol of H₂O? (Avogadro constant = 6.02 × 10²³ per mol) Give your answer as a number × 10²³ (to 2 decimal places).

Answer 

Question 5

What volume does 0.5 g of hydrogen (H₂, Mr = 2) occupy at RTP, in dm³? (1 mol of gas = 24 dm³)

Answer dm³

Question 6

What mass of sodium hydroxide (NaOH, Mr = 40) is needed to make 250 cm³ of 0.2 mol/dm³ solution, in g? Give 2 decimal places.

Answer g

Question 7

How many carbon atoms are in 3 mol? The Avogadro constant is 6.02 × 10²³ per mol. Give your answer as a number × 10²³ (to 2 decimal places).

Answer 

Question 8

CaCO₃ → CaO + CO₂. What mass of carbon dioxide is released when 100 g of calcium carbonate decomposes? (Mr: CaCO₃ = 100, CO₂ = 44)

Answer g

Question 9

Atom economy: which statement is NOT true?

• A. Selling or using by-products makes a process less wasteful.
• B. Green chemistry aims to use reactions with high atom economy.
• C. Atom economy is the same as percentage yield.
• D. Reactions with only one product have 100 % atom economy.

Question 10

CaCO₃ → CaO + CO₂. The useful product is calcium oxide (Mr 56). Relative masses of reactants: CaCO₃ = 100. What is the atom economy? Give 1 decimal place.

Answer %

Question 11

What volume does 0.1 mol of methane gas occupy at room temperature and pressure, in dm³? (1 mol of any gas occupies 24 dm³ at RTP)

Answer dm³

Question 12

In a reaction, 1800 kJ is needed to break bonds and 2200 kJ is released when new bonds form. Is the reaction exothermic or endothermic?

• A. exothermic
• B. endothermic

Question 13

In an exothermic reaction, how do the energies of bonds broken and bonds made compare?

• A. no bonds are made
• B. breaking bonds releases more energy
• C. they are always equal
• D. more energy is released making bonds than is taken in breaking bonds

Question 14

A reaction could make 20 g of product in theory, but 15 g was actually collected. What is the percentage yield?

Answer %

Question 15

0.05 mol of hydrochloric acid is in 100 cm³ of solution. What is the concentration, in mol/dm³?

Answer mol/dm³

Question 16

CaCO₃ → CaO + CO₂ (Mr: CaCO₃ = 100, CaO = 56). 25 g of calcium carbonate was heated and 10.5 g of calcium oxide was collected. What is the percentage yield? Give 1 decimal place.

Answer %