Key Calculations quiz

1. 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

To stop the escape of magnesium oxide smoke

To keep the magnesium warm

Question 1 of 17

2. 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 also N₂O₅

Empirical formula is N₂O₅. Molecular formula is N₄O₁₀

Empirical formula is NO₂.₅ Molecular formula is N₂O₅

Empirical formula is N₄O₁₀. Molecular formula is N₂O₅

Question 2 of 17

3. 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

1944 kJ

355 J

Question 3 of 17

4. Complete the following expression: Mᵣ =

amount (in moles) /mass

mass x amount (in moles)

mass² / amount (in moles)

mass / amount (in moles)

Question 4 of 17

5. State the units of molar enthalpy change.

kJ/⁰C

mol/⁰C

J/⁰C/mol

kJ/mol

Question 5 of 17

6. What is meant by the term molecular formula?

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

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

Question 6 of 17

7. What are the units for amount in Chemistry?

g per 100g of solvent

Moles

mol/dm³

Grams

Question 7 of 17

8. State the expression for calculating molar concentration

Molar concentration = volume (in dm³) / Amount (in moles)

Molar concentration = Amount (in moles) x volume (in cm³)

Molar concentration = Amount (in moles)/volume (in cm³)

Molar concentration = Amount (in moles)/volume (in dm³)

Question 8 of 17

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

88g

44 g

176 g

24 g

Question 9 of 17

10. Calculate the relative formula mass(Mr) of aluminium oxide (Al₂O₃)

43

86

129

102

Question 10 of 17

11. State the steps for calculating empirical 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) 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

Question 11 of 17

12. 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 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)

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

Question 12 of 17

13. 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

17g

0.68g

Question 13 of 17

14. State the expression for calculating % yield.

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

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

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

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

Question 14 of 17

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

8 cm³

72 cm³

72 dm³

8 dm³

Question 15 of 17

16. 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 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.

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.

Question 16 of 17

17. A sample of bromine contained the two isotopes in the following proportions: bromine-79 = 50.7% and bromine-81 = 49.3%. Calculate the relative atomic mass of bromine

(81 + 79)/2 = 80

((79x50.7)+(81x49.3))/100 = 79.99

(81x79)/100 = 63.99

((81x50.7)+(79x49.3))/100 = 80.01

Question 17 of 17

Key Calculations quiz

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