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)

+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)

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

Question 1 of 17

2. 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 2 of 17

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

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

(12+13)/2 = 12.5

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

(12x13)/100 = 1.56

Question 3 of 17

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

48 dm³

12 dm³

48 cm³

12 cm³

Question 4 of 17

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

44 g

24 g

176 g

88g

Question 5 of 17

6. 25 cm³ of sodium chloride solution has a concentration of 0.5 mol/dm³. What amount of sodium chloride does it contain?

1.25 mol

0.05 mol

12.5 mol

0.0125 mol

Question 6 of 17

7. 7.485 g of a hydrated copper(II) sulphate CuSO₄.xH₂O was heated producing 4.785g of anhydrous copper(II) sulphate. What is the formula of the hydrated salt?

CuSO₄.7H₂O

CuSO₄.4H₂O

CuSO₄.5H₂O

CuSO₄.10H₂O

Question 7 of 17

8. 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)

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

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

Question 8 of 17

9. What are the units for amount in Chemistry?

Moles

g per 100g of solvent

Grams

mol/dm³

Question 9 of 17

10. 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 10 of 17

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

Aᵣ / Mᵣ

mass / Mᵣ

amount (in moles) x Mᵣ

Mᵣ / mass

Question 11 of 17

12. 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 N₂O₅. Molecular formula is N₄O₁₀

Empirical formula is N₄O₁₀. Molecular formula is N₂O₅

Empirical formula is N₂O₅. Molecular formula is also N₂O₅

Empirical formula is NO₂.₅ Molecular formula is N₂O₅

Question 12 of 17

13. 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 allow carbon dioxide to escape

To allow some magnesium oxide smoke to escape

To stop the crucible heating up too much

Question 13 of 17

14. Calculate the relative formula mass(Mr) of calcium hydroxide (Ca(OH)₂)

38

73

58

74

Question 14 of 17

15. Use Q=mcΔT and c=4.18J/°C/g. A strip of magnesium is added to a beaker with 200cm³ of copper (II) sulfate. The temperature starts at 21.7°C and rises to a maximum of 23.1°C. What is the total heat energy change?

2.153 kJ

1944 kJ

1170 J

1247 J

Question 15 of 17

16. 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 = (actual amount of products/theoretical amount of products) x 100

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

Question 16 of 17

17. Describe how to carry out an acid-alkali titration

1) Pipette 25cm³ of alkali into a conical flask. 2) Add indicator. 3) Fill a burette with acid, record the initial volume. 4) Whilst swirling the flask, add the acid dropwise until the indicator changes colour. 5) Record the volume and calculate the volume of acid which was added. 6) Repeat until three concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.

1) Pipette 25cm³ of alkali into a conical flask. 2) Add indicator. 3) Fill a burette with acid, record the initial volume. 4) Whilst swirling the flask, add the acid dropwise until the indicator is just about to change colour. 5) Record the volume and calculate the volume of acid which was added. 6) Repeat until three concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.

1) Pipette 25cm³ of alkali into a conical flask. 2) Add indicator. 3) Fill a burette with acid, record the initial volume. 4) Whilst swirling the flask, add the acid dropwise until the indicator is just about to change colour. 5) Record the volume and calculate the volume of acid which was added. 6) Repeat until two concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.

1) Pipette 25cm³ of alkali into a conical flask. 2) Add indicator. 3) Fill a burette with acid, record the initial volume. 4) Whilst swirling the flask, add the acid dropwise until the indicator changes colour. 5) Record the volume and calculate the volume of acid which was added. 6) Repeat until two concordant results (within 0.2cm³ of each other). 7) Result is the average of all concordant results.

Question 17 of 17

Key Calculations quiz

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