11th grade chemical reactions, acids and bases

Question 1

A sample contains 1.204 × 10²⁴ molecules. How many moles is this? (Avogadro constant = 6.02 × 10²³ per mol)

Answer mol

Question 2

0.1 mol of hydrochloric acid is in 500 cm³ of solution. What is the concentration, in mol/dm³?

Answer mol/dm³

Question 3

In a reaction, 550 kJ is needed to break bonds and 250 kJ is released when new bonds form. Is the reaction exothermic or endothermic?

• A. exothermic
• B. endothermic

Question 4

N₂ + 3H₂ → 2NH₃. Bond energies (kJ/mol): N≡N 945, H–H 436, N–H 391. Calculate the energy change, in kJ/mol.

Answer kJ/mol

Question 5

How many moles of sodium hydroxide are in 25 cm³ of a 1.5 mol/dm³ solution?

Answer mol

Question 6

A reaction produced 240 cm³ of carbon dioxide at RTP. How many moles of gas is this? (1 mol occupies 24 dm³ = 24 000 cm³)

Answer mol

Question 7

Why is breaking bonds endothermic?

• A. Breaking bonds releases heat
• B. Atoms repel each other
• C. Energy must be supplied to overcome the attraction holding atoms together
• D. Bonds contain no energy

Question 8

What is the mass of 0.1 mol of magnesium oxide (MgO, Mr = 40), in g?

Answer g

Question 9

How many atoms in total are in 0.5 mol of CH₄? (Avogadro constant = 6.02 × 10²³ per mol) Give your answer as a number × 10²³ (to 2 decimal places).

Answer 

Question 10

Which is NOT a reason why the percentage yield is less than 100 %?

• A. some product is lost when it is separated
• B. some reactants form unexpected side products
• C. the reaction is reversible and does not go to completion
• D. atoms are destroyed during the reaction

Question 11

A reaction could make 25 g of product in theory, but 22.5 g was actually collected. What is the percentage yield?

Answer %

Question 12

What volume does 4 g of hydrogen (H₂, Mr = 2) occupy at RTP, in dm³? (1 mol of gas = 24 dm³)

Answer dm³

Question 13

CaCO₃ → CaO + CO₂ (Mr: CaCO₃ = 100, CaO = 56). 10 g of calcium carbonate was heated and 4.76 g of calcium oxide was collected. What is the percentage yield? Give 1 decimal place.

Answer %

Question 14

What does a 100 % atom economy mean?

• A. The reaction is very fast
• B. All the atoms in the reactants end up in the desired product
• C. No energy is needed
• D. The yield is always 100 %

Question 15

Atom economy: which statement is NOT true?

• A. Thermal decomposition of calcium carbonate has 100 % atom economy for calcium oxide.
• B. Reactions with only one product have 100 % atom economy.
• C. Atom economy is calculated from the balanced equation.
• D. Selling or using by-products makes a process less wasteful.

Question 16

How many moles are in 22 g of carbon dioxide (CO₂, Mr = 44)?

Answer mol