Key Calculations quiz

1. 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. Making - breaking = 3186-3231 = -45 kJ/mol)

+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 1583 kJ/mol. Making bonds 1487/mol. Making - breaking = 1487-1583 = -96 kJ/mol)

Question 1 of 17

2. State the expression for calculating % yield.

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

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

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

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

Question 2 of 17

3. 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)

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

Question 3 of 17

4. 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) 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

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

Question 4 of 17

5. 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

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

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

Question 5 of 17

6. Name this piece of lab equipment

burette

gas syringe

measuring cylinder

pipette

Question 6 of 17

7. What is the equation linking moles, Mᵣ and mass

moles = mass x Mᵣ

moles = mass / Mᵣ

Mᵣ = mass x moles

mass = moles / Mᵣ

Question 7 of 17

8. Calculate the relative formula mass(Mr) of carbon dioxide (CO₂)

88

44

22

38

Question 8 of 17

9. To determine the formula of a metal oxide by combustion, magnesium is heated in a crucible. Why is a lid used?

To stop carbon dioxide escaping

To stop the escape of magnesium oxide smoke

To keep the magnesium warm

To stop the escape of magnesium

Question 9 of 17

10. 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

1944 kJ

355 kJ/mol

355 J

Question 10 of 17

11. A sample of hydrogen chloride gas has a volume of 48 dm³. What amount of hydrogen chloride is this?

48 moles

2 moles

1 mole

24 moles

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?

0.0005 mol/dm³

2 mol/dm³

0.5 dm³/mol

0.5 mol/dm³

Question 12 of 17

13. What is meant by the term molecular formula?

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 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

Question 13 of 17

14. What are the units for amount in Chemistry?

mol/dm³

g per 100g of solvent

Moles

Grams

Question 14 of 17

15. A compound that contained 24.24% Carbon. 4.04% Hydrogen and 71.72% Chlorine and has a relative molecular mass of 99. Calculate the empirical formula and the molecular formula.

Empirical formula is C₂H₄Cl₂. Molecular formula is CH₂Cl

Empirical formula is CH₂Cl. Molecular formula is CH₂Cl

Empirical formula is CH₂Cl. Molecular formula is C₂H₄Cl₂

Empirical formula is C₂H₄Cl₂. Molecular formula is C₂H₄Cl₂

Question 15 of 17

16. What mass of carbon dioxide is produced when 24g of carbon undergoes completely combustion?

44 g

24 g

176 g

88g

Question 16 of 17

17. 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?

17g

0.68g

68g

0.17g

Question 17 of 17

Key Calculations quiz

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