Key Calculations quiz

1. Name this piece of lab equipment

measuring cylinder

gas syringe

pipette

burette

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

(12+13)/2 = 12.5

(12x13)/100 = 1.56

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

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

Question 2 of 17

3. Assuming bond energies in kJ/mol: H-C 412, C-C 348, O-H 463, C-O 360, C=C 612. Calculate the molar enthalpy change for the reaction: ethanol → ethene + water

+45 kJ/mol (Some workings as follows. Breaking bonds 3231 kJ/mol. Making bonds 3186kJ/mol. Breaking - making = 3231-3186 = +45 kJ/mol)

+96 kJ/mol (Some workings as follows. Breaking bonds 1583 kJ/mol. Making bonds 1487/mol. Breaking - making = 1583-1487 = +96 kJ/mol)

-45 kJ/mol (Some workings as follows. Breaking bonds 3231 kJ/mol. Making bonds 3186kJ/mol. Making - breaking = 3186-3231 = -45 kJ/mol)

-45 kJ/mol (Some workings as follows. Breaking bonds 1583 kJ/mol. Making bonds 1487/mol. Making - breaking = 1487-1583 = -96 kJ/mol)

Question 3 of 17

4. What is meant by the term molecular formula?

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 method of calculating the ratios of masses in an equation

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

Question 4 of 17

5. What volume does 0.5 moles of ethene gas occupy (at rtp)

12 cm³

12 dm³

48 cm³

48 dm³

Question 5 of 17

6. State the steps for calculating empirical formula

1) mass/Aᵣ. 2) divide by the largest. 3) Give the ratio has a whole number. 4) State final empirial formula

1) Aᵣ/mass. 2) divide by the smallest. 3) Give the ratio has a whole number. 4) State final empirial formula

1) mass/Aᵣ. 2) divide by the smallest. 3) Give the ratio has a whole number. 4) State final empirial formula

1) Aᵣ/mass. 2) divide by the largest. 3) Give the ratio has a whole number. 4) State final empirial formula

Question 6 of 17

7. Complete the following expression: Mᵣ =

mass x amount (in moles)

mass / amount (in moles)

amount (in moles) /mass

mass² / amount (in moles)

Question 7 of 17

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

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 is 10 g of a substance)

A mole is a small burrowing mammal

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)

Question 8 of 17

9. 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?

355 kJ/mol

1944 kJ

1944 J

355 J

Question 9 of 17

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

240 g

120 g

480 g

200g

Question 10 of 17

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

160

70

140

80

Question 11 of 17

12. A beaker of 2 dm³ of ammonium nitrate solution contains 1 mol of ammonium nitrate. What is the concentration of the solution?

2 mol/dm³

0.0005 mol/dm³

0.5 dm³/mol

0.5 mol/dm³

Question 12 of 17

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

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

-369 kJ/mol (Amount = 0.78/23 = 0.034 mol. Answer = 12540/1000/0.034 = 369 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 13 of 17

14. State the expression for calculating % yield.

% yield = (theroretical amount of products/actual amount of products)

% yield = (actual amount of products/theoretical amount of products)

% yield = (actual amount of products/theoretical amount of products) x 100

% yield = (theroretical amount of products/actual amount of products) x 100

Question 14 of 17

15. 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 carbon dioxide to escape

To allow oxygen in so the magnesium fully reacts

To allow some magnesium oxide smoke to escape

To stop the crucible heating up too much

Question 15 of 17

16. 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

0.17g

0.68g

17g

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 NO₂.₅ Molecular formula is N₂O₅

Empirical formula is N₂O₅. Molecular formula is N₄O₁₀

Empirical formula is N₂O₅. Molecular formula is also N₂O₅

Question 17 of 17

Key Calculations quiz

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