Key Calculations quiz

1. Use Q=mcΔT and c=4.18J/°C/g. 25cm³ of sulfuric acid is put into a boiling tube. The starting temperature is 21°C. A spatula of iron filings is added. After a while the temperature reaches 33°C. What is the total heat energy change?

1254 J

3383 J

2.153 kJ

2153 J

Question 1 of 17

2. 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

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

(12+13)/2 = 12.5

Question 2 of 17

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

120 g

240 g

480 g

200g

Question 3 of 17

4. 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 200g water?

0.68g

0.34g

17g

68g

Question 4 of 17

5. What is the empirical formula of a compound in which 0.48 g of carbon combines with 0.08 g of hydrogen and 0.64 g of oxygen?

CH₂O

CH₄O

C₂H₄O₂

C₄H₂O

Question 5 of 17

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

Exothermic

Depends on the temperature of the surroundings

Endothermic

Depends on the reagents

Question 6 of 17

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

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)

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)

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

Question 7 of 17

8. Name this piece of lab equipment

burette

measuring cylinder

pipette

funnel

Question 8 of 17

9. 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 NO₂.₅ Molecular formula is N₂O₅

Empirical formula is N₂O₅. Molecular formula is also N₂O₅

Empirical formula is N₂O₅. Molecular formula is N₄O₁₀

Question 9 of 17

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

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

-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)

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

Question 10 of 17

11. Calculate the relative formula mass(Mr) of hydrated copper (II) sulfate (CuSO₄.5H₂O)

249.5

180.5

127

177.5

Question 11 of 17

12. 25 cm³ of sodium chloride solution has a concentration of 0.5 mol/dm³. What amount of sodium chloride does it contain?

12.5 mol

0.0125 mol

0.05 mol

1.25 mol

Question 12 of 17

13. To determine the formula of a metal oxide by combustion, magnesium is heated in a crucible. Why is the crucible is cooled, weighed, reheated, cooled, re-weighed, and so on?

To make sure the mass is still going down so the magnesium is still reacting

To ensure all the magnesium oxide to escape

To allow any water to escape

To make sure a constant mass has been reached and there is no more magnesium left to react

Question 13 of 17

14. Complete the following expression: amount (in moles) =

mass / Mᵣ

amount (in moles) x Mᵣ

Aᵣ / Mᵣ

Mᵣ / mass

Question 14 of 17

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

8 dm³

72 cm³

72 dm³

8 cm³

Question 15 of 17

16. 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?

0.857 %

85.7 %

0.56 %

56 %

Question 16 of 17

17. What is meant by the term empirical formula?

Baby food for emperors

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

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

A method of calculating the ratios of masses in an equation

Question 17 of 17

Key Calculations quiz

Key Calculations quiz

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