Key Calculations quiz

1. Name this piece of lab equipment

burette

pipette

gas syringe

measuring cylinder

Question 1 of 17

2. Calculate the relative formula mass(Mr) of a molecule of bromine (Br₂)

160

140

70

80

Question 2 of 17

3. What volume does 3 moles of carbon dioxide gas occupy (at rtp)?

72 dm³

72 cm³

8 cm³

8 dm³

Question 3 of 17

4. To determine the formula of a metal oxide by combustion, magnesium is heated in a crucible. Why is a lid lifted from time to time?

To allow oxygen in so the magnesium fully reacts

To stop the crucible heating up too much

To allow carbon dioxide to escape

To allow some magnesium oxide smoke to escape

Question 4 of 17

5. In a chemical reaction, the overall molar enthalpy is -87 kJ/mol. Is this reaction exothermic or endothermic?

Exothermic

Endothermic

Depends on the temperature of the surroundings

Depends on the reagents

Question 5 of 17

6. What is the meaning of the word mole in Chemistry?

Moles are the units for amount of substance. (1 mole is 10 g of a substance)

Moles are the units for amount of substance. 1 mole of an element is its atomic number in grams (e.g. 1 mole of magnesium is 12 g)

A mole is a small burrowing mammal

Moles are the units for amount of substance. 1 mole of a substance is its relative formula mass in grams (e.g. 1 mole of magnesium is 24 g)

Question 6 of 17

7. In a combustion calorimetry experiment, 0.78g of ethanol (C₂H₅OH) produced 12,540 J of heat energy. Calculate the molar enthalpy change.

-369 kJ/mol (Amount = 0.78/23 = 0.034 mol. Answer = 12540/1000/0.034 = 369 kJ/mol)

-738 kJ/mol (Amount = 0.78/46 = 0.017 mol. Answer = 12540/1000/0.017 = 738 kJ/mol)

-425 kJ/mol (Amount = 23/0.78 = 29.5 mol. Answer = 12540/29.5 = 425 kJ/mol)

-213 kJ/mol (Amount = 46/0.78 = 59.0 mol. Answer = 12540/59.0 = 213 kJ/mol)

Question 7 of 17

8. What is meant by the term molecular formula?

A method of calculating the ratios of masses in an equation

A chemical formula that shows the actual numbers of the different types of atoms in a molecule

A method of calculating the mass needed to make a certain yield in an equation

A chemical formula that shows the simplest ratio of the numbers of atoms in a compound

Question 8 of 17

9. A beaker of 1.5 mol/dm³ calcium chloride solution contains 0.3 mol of calcium chloride. What is the volume of the solution?

0.45 dm³

0.002 dm³

4.5 dm³

0.2 dm³

Question 9 of 17

10. Complete the following expression: mass =

Aᵣ / Mᵣ

Mᵣ / amount (in moles)

amount (in moles) x Mᵣ

amount (in moles) / Mᵣ

Question 10 of 17

11. What mass of calcium bromide will fully react with 71g of chlorine?

200g

120 g

240 g

480 g

Question 11 of 17

12. What is the empirical formula of an alcohol with the analysis; 52.2% C, 13.0% H and 34.8% O?

CH₆O

C₂H₆O₂

C₂H₆O

C₂H₃O

Question 12 of 17

13. A sample of carbon contained 98.90% carbon-12 and 1.10% carbon-13. Calculate the relative atomic mass of carbon

(12x13)/100 = 1.56

((13x98.90)+(12x1.10))/100 = 12.99

(12+13)/2 = 12.5

((12x98.90)+(13x1.10))/100 = 12.01

Question 13 of 17

14. In the thermal decomposition of calcium carbonate, we might expect 50g of calcium carbonate to produce 28g of calcium oxide. If instead only 24g of calcium oxide is produced, what is the percentage yield?

85.7 %

0.56 %

56 %

0.857 %

Question 14 of 17

15. A graph shows the solubility of sodium chloride in water at 50°C is 34g/100g. At that temperature, what mass of sodium chloride will dissolve in 50g water?

68g

0.68g

0.17g

17g

Question 15 of 17

16. Use Q=mcΔT and c=4.18J/°C/g. A spatula of sodium fluoride is put into a boiling tube with 25cm³ of water. The temperature drops from 22.0°C to 18.6°C. What is the total heat energy change?

1944 J

355 kJ/mol

355 J

1944 kJ

Question 16 of 17

17. An oxide of nitrogen contains 26% nitrogen and 74% oxygen and has a relative molecular mass of 108. Find the empirical and molecular formulae for the oxide.

Empirical formula is N₄O₁₀. Molecular formula is N₂O₅

Empirical formula is N₂O₅. Molecular formula is N₄O₁₀

Empirical formula is N₂O₅. Molecular formula is also N₂O₅

Empirical formula is NO₂.₅ Molecular formula is N₂O₅

Question 17 of 17

Key Calculations quiz

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